An enantio- and stereoselective construction of the atisane scaffold via organocatalytic intramolecular Michael reaction and Diels-Alder reaction is described. The organocatalytic intramolecular Michael reaction has been found to stereoselectively generate a trans-stereodiad comprising an all-carbon quaternary and a tertiary stereogenic centers. Use of the chiral secondary amine bearing thiourea with benzoic acid as additive is the key to obtaining the desired product with excellent ee in synthetically acceptable yield. The prepared chiral building block has been successfully converted to the compound including the atisane scaffold via the highly stereoselective intramolecular Diels-Alder reaction.

© 2017 Elsevier LtdA synthetic pathway to the C-ring fragment of cotylenin A which emerged from our retrosynthetic analysis of cotylenin A is described. The catalytic asymmetric intramolecular cyclopropanation (CAIMCP) of the α-diazo-β-keto ester bearing 2,4,6-trimethylphenyl group as the ester part has been found to afford the crystalline product with high ee, which allowed to establish the approach to the C-ring fragment which required ten-pot operations. The developed approach would be beneficial to a large scale synthesis of the C-ring fragment for the total synthesis of cotylenin A.

© 2017 American Chemical Society. The asymmetric Mukaiyama-Michael reaction of cyclic α-alkylidene β-oxo phosphates and phosphine oxides that proceeds in a highly enantioselective manner is described. It is possible to carry out these reactions using a catalytic amount of a bisoxazoline-Cu(II) complex without decreasing the enantioselectivity, and one of the products has been successfully used for the first enantioselective synthesis of (R)-homosarkomycin.

A New chiral C-2 symmetric NHC ligand with two binaphthyl units has been synthesized. The new NHC ligand features two seven-membered rings that link the imidazolylidene with the binaphthyl units. X-Ray crystallographic analysis of the new NHC-AuCl complex indicates that the Au-Cl bond is located between the phenyl groups of the binaphthyl units and suggests that this arrangement could induce enantioselectivity in reactions. Indeed, catalytic asymmetric ene-yne cyclization of 2b in the presence of a catalytic amount (5 mol%) of cationic complex of 13 quantitatively afforded the cyclized product with 78% ee.

New chiral C-2 symmetric N-heterocyclic carbene (NHC) ligands with a binaphthyl backbone have been synthesized. X-ray crystallographic analysis of the new NHC-AuCI complex revealed that the phenyl groups of the binaphthyl backbone sterically regulated the direction of the nitrogen substituents of the imidazolylidene which would induce enantioselectivity in reactions. The new cationic NHC-Au(I) complexes efficiently catalyzed the cyclization of a 1,6-ene-yne and the intermediate of the cyclization was trapped by MeOH to afford the final product in high yields with up to 44% ee. (C) 2016 Elsevier Ltd. All rights reserved.

Catalytic asymmetric Mukaiyama-Michael reactions of cyclic alpha-alkylidene beta-oxo imides are described. The rationally designed cyclic alpha-alkylidene beta-oxo imides show high enantioselectivity in the Mukaiyama-Michael reaction using a bisoxazoline/Cu(OTf)(2) catalyst. The enantioselectivity can be well explained by the chelate model comprising an intramolecular hydrogen bond, wherein the cyclic alpha-alkylidene beta-oxo imide coordinates with Cu(II) through the two imide carbonyls. (C) 2015 Elsevier Ltd. All rights reserved.

A highly stereoselective intramolecular Diels Alder (IMDA) reaction for the construction of the AB ring moiety of bruceantin is described. The product of the IMDA reaction comprises a trans-AB ring junction and stereotetrad including an all carbon quaternary stereogenic center, wherein three stereogenic centers correspond to those of bruceantin. Functional groups embedded in the product are suitable for a variety of transformations. Hence, this IMDA product could be a useful intermediate for the enantioselective total synthesis of not only bruceantin, but also other bioactive compounds. (C) 2015 Elsevier Ltd. All rights reserved.

In this paper, the first total synthesis of (+)-bucidarasins A and C is described. The chiral starting material was successfully obtained via reduction using a CBS catalyst and selective mono-TBS ether formation of trans-2-benzyloxymethy1-2-methylcyclohexane-1,3-diol, which was crucial to the successful enantioselective total synthesis of (+)-bucidarasins A and C. A synthetic approach towards (+)-bucidarasin C, based on the Barton-McCombie protocol, using V-70 as a radical promoter at low temperature to remove the C6-hydroxy moiety is also described.

Highly enantioselective catalytic Friedel-Crafts reactions of cyclic alpha-alkylidene beta-oxo imides with indole, pyrrole, and furan derivatives at relatively low temperatures are described. The X-ray crystallographic analysis of the product revealed that the sense of enantioselectivity of the Friedel-Crafts reactions could be well explained by the proposed chelate model. The model was stabilized by an intramolecular hydrogen bond, wherein the cyclic alpha-alkylidene beta-oxo imide coordinates with Cu(II) through the two imide carbonyls. (C) 2015 Elsevier Ltd. All rights reserved.

The formal enantioselective total synthesis of nemorosone, garsubellin A, clusianone, and hyperforin is described. The catalytic asymmetric intramolecular cyclopropanation (CAIMCP) of an a-diazo ketone, a common synthetic intermediate for the above four polycyclic polyprenylated acylphloroglucinols previously reported by us, exhibited low enantioselectivity. However, CAIMCP of the corresponding alpha-diazo beta-keto sulfone afforded the desired product in 79% yield with 84% ee. Investigation of the CAIMCP of the alpha-diazo beta-keto sulfone demonstrated the formation of a rearrangement product in the presence of molecular sieves 4 angstrom, whereas, in the presence of H2O, the byproduct derived from ring-opening of the desired cyclopropane was observed. X-ray crystallographic analysis suggested that the above two products are derived from the same chiral intermediate. The product derived from ring-opening of the cyclopropane was successfully transformed to the respective synthetic intermediates for the total syntheses of nemorosone, garsubellin A, clusianone, and hyperforin, which had previously been reported by us.

The preparation of a new C-2-symmetrical chiral tridentate N-heterocyclic carbene (NHC) ligand coordinated Cr(III) complex is described. The new NHC ligand was prepared as its AgBr complex, which was stable but smoothly underwent carbene exchange reaction with CrCl2 to afford the new NHC ligand coordinated Cr(III) complex. The X-ray crystallographic analysis of the Cr(III) complex revealed its distorted octahedral form. The Cr(III) complex mediated reaction of allylbromide with benzaldehyde did not afford products under the catalytic conditions reported by us. (C) 2015 Elsevier Ltd. All rights reserved.

Highly enantioselective catalytic asymmetric [2+2] cycloadditions of cyclic alpha-alkylidene beta-oxo imides with ynamides are described. The high reactivity of the cyclic alpha-alkylidene beta-oxo imide allows the [2+2] cycloadditions of a hindered substrate with unreactive ynamides at low temperature. The X-ray crystallographic analysis of the product suggests that the enantioselectivity of the [2+2] cycloaddition can be well explained by the chelate model comprising the intramolecular hydrogen bond, wherein the cyclic alpha-alkylidene beta-oxo imide coordinates with CuII through the two imide carbonyls. The imide group in the product can be transformed to amide, nitrile, and ester groups; moreover, it is removable.

:The formal enantioselective total synthesis of nemorosone, garsubellin A, clusianone, and hyperforin is described. The catalytic asymmetric intramolecular cyclopropanation (CAIMCP) of an α-diazo ketone, a common synthetic intermediate for the above four polycyclic polyprenylated acylphloroglucinols previously reported by us, exhibited low enantioselectivity. However, CAIMCP of the corresponding α-diazo β-keto sulfone afforded the desired product in 79% yield with 84% ee. Investigation of the CAIMCP of the α-diazo β-keto sulfone demonstrated the formation of a rearrangement product in the presence of molecular sieves 4 Å, whereas, in the presence of H2O, the byproduct derived from ring-opening of the desired cyclopropane was observed. X-ray crystallographic analysis suggested that the above two products are derived from the same chiral intermediate. The product derived from ring-opening of the cyclopropane was successfully transformed to the respective synthetic intermediates for the total syntheses of nemorosone, garsubellin A, clusianone, and hyperforin, which had previously been reported by us.

:Highly enantioselective catalytic asymmetric [2+2] cycloadditions of cyclic α-alkylidene β-oxo imides with ynamides are described. The high reactivity of the cyclic α-alkylidene β-oxo imide allows the [2+2] cycloadditions of a hindered substrate with unreactive ynamides at low temperature. The X-ray crystallographic analysis of the product suggests that the enantioselectivity of the [2+2] cycloaddition can be well explained by the chelate model comprising the intramolecular hydrogen bond, wherein the cyclic α-alkylidene β-oxo imide coordinates with Cu(II) through the two imide carbonyls. The imide group in the product can be transformed to amide, nitrile, and ester groups; moreover, it is removable.

:A formal total synthesis of (-)-taxol by a convergent approach utilizing Pd-catalyzed intramolecular alkenylation is described. Formation of the eight-membered carbocyclic ring has been a problem in the convergent total synthesis of taxol but it was solved by the Pd-catalyzed intramolecular alkenylation of a methyl ketone affording the cyclized product in excellent yield (97 %), indicating the high efficiency of the Pd-catalyzed intramolecular alkenylation. Rearrangement of the epoxy benzyl ether through a 1,5-hydride shift, generating the C3 stereogenic center and subsequently forming the C1-C2 benzylidene, was discovered and utilized in the preparation of a substrate for the Pd-catalyzed reaction.

This paper describes a novel synthetic approach to 11,12-dimethoxy-8,9-dihydro-1H-indolo [7a,1-a] isoquinoline-2,6-dione, which is a key synthetic intermediate to some erythrinan alkaloids. This concise approach features an oxidative dearomatization-spirocyclization sequence mediated by phenyliodine (III) bis(trifluoroacetate) (PIFA) that efficiently forms the tetracyclic spiroamine scaffold. An unusual solvent effect in the oxidative dearomatization-spirocyclization sequence is also described.

A formal total synthesis of (-)-taxol by a convergent approach utilizing Pd-catalyzed intramolecular alkenylation is described. Formation of the eight-membered carbocyclic ring has been a problem in the convergent total synthesis of taxol but it was solved by the Pd-catalyzed intramolecular alkenylation of a methyl ketone affording the cyclized product in excellent yield (97 %), indicating the high efficiency of the Pd-catalyzed intramolecular alkenylation. Rearrangement of the epoxy benzyl ether through a 1,5-hydride shift, generating the C3 stereogenic center and subsequently forming the C1-C2 benzylidene, was discovered and utilized in the preparation of a substrate for the Pd-catalyzed reaction.

Au(I)-catalyzed oxidative cyclizations that successfully convert 1,5-ene-ynes and a 1,6-ene-yne to the corresponding cycloalkanone-fused cyclopropanes are described. This Au(I)-catalyzed oxidative cyclization can be effectively applied to various substrates and is an alternative to the previously used intramolecular cyclopropanation that required potentially explosive diazo compound. (C) 2014 Elsevier Ltd. All rights reserved.

The highly stereoselective total synthesis of (-)-bucidarasin A, which also elucidated the absolute structure of its natural form, is described. The total synthesis features effective use of the original chiral building block prepared by us and a series of highly stereoselective reactions, i.e., hydroxy-directed hydrogenation, [4 + 2] cycloaddition of a sterically hindered dienophile, reduction of ketones, formation of the C9 side-chain diene, and formation of the THF moiety bearing two acetyloxy groups.

The preparation of chiral building blocks, suitable for use in the enantioselective total synthesis of kauranoids and ent-kauranoids, is reported herein. The pig liver esterase-catalyzed asymmetric hydrolysis of dimethyl 3,3-dimethyl-2-methylenecyclohexane-1,2-dicarboxylate, a malonate-type prochiral diester, afforded the corresponding half-ester in 96% yield and with 99% enantiomeric excess. The absolute configuration of the half-ester was determined by X-ray crystallographic analysis of its derivative and its enantiodivergent transformations are also described herein. (C) 2014 Elsevier Ltd. All rights reserved.

The first enantioselective total synthesis of (-)-scabronine D comprising a unique bridged hemiacetal is described. The total synthesis is successfully accomplished using an enantiopure intermediate prepared in the total synthesis of (-)-scabronines G and A, and (-)-episcabronine A. Because the advanced intermediate was found to be sensitive to basic reaction conditions, the C14 keto and C11 hydroxy groups had to be co-protected as methyl acetal. In addition, both the C15 hydroxy and C17 carboxyl groups were too reactive to be chemically discriminated; hence, the carboxyl group once formed was protected as a tert-butyl ester for ensuring successful transformations.

Direct reductive amination (DRA) using triethylsilane (TESH) and catalytic bismuth(III) chloride (BiCl3) is described for the first time. The use of TESH and BiCl3 provides easy handling, low cost, non-toxicity, and a mild Lewis acid activity, thereby meeting the demand for green and sustainable chemistry. The developed DRA is highly chemoselective and applicable to less-basic amines. The experimental results of this study revealed that the developed DRA could be catalyzed by BiCl3, which was gradually reduced to Bi(0) or bismuth with a low valency by TESH, but TESCl, Bi(0), and Bi(0) with TESCl catalyzed the DRA to some extent. (C) 2014 Elsevier Ltd. All rights reserved.

A stereoselective construction of the ABC-ring system of fusidane triterpenes via intermolecular/transannular Michael reaction cascade is described. The substrate, a ten-membered carbocyclic ketone, has been successfully prepared by the Cr-mediated intramolecular alkenylation of the corresponding acyclic compound. The array of functionalities in the product stereoselectively obtained by the cascade reaction is useful for further structural modifications directed toward the total synthesis of fusidane and other triterpenes, and designed molecules intended for studying structure-activity relationships. (C) 2014 Elsevier Ltd. All rights reserved.

A Pd-catalyzed method for the preparation of imidazolinium salts from the corresponding thioureas that could then be used for the synthesis of imidazolium and amidinium salts is described. This method has great potential because all the required reagents are readily available and thioureas are safely converted to their corresponding precursors of NHCs under mild conditions. (C) 2014 Elsevier Ltd. All rights reserved.

:A Personal Account describing the enantioselective total syntheses of cyathane diterpenoids achieved in the Nakada group. A convergent approach to the cyathane scaffold, the [5-6-7] tricyclic carbon skeleton commonly found in cyathane diterpenoids, has been developed using the catalytic asymmetric intramolecular cyclopropanation (CAIMCP) and baker's yeast reduction. This approach has been successfully applied for the enantioselective total syntheses of (+)-allocyathin B2 , (-)-erinacine B, and (-)-erinacine E. The total synthesis of (-)-erinacine E has been achieved via the acyl group migratory intramolecular aldol reaction, which prevents the retro-aldol reaction and allows the construction of the strained structure. The highly efficient and stereoselective total syntheses of (-)-scabronines G, A, D, and (-)-episcabronine A have been achieved via the oxidative dearomatization/inverse electron demand Diels-Alder reaction cascade. Cascade reactions comprising three and five consecutive reactions were employed for the highly efficient total syntheses of (-)-scabronine A and (-)-episcabronine A, respectively.

A highly stereoselective Michael reduction/intramolecular Michael reaction cascade is described. The cascade is initiated by the regioselective Michael reduction of an alpha-methylidene ester with L-Selectride. This is followed by the highly stereoselective intramolecular Michael reaction which efficiently constructs a six-membered carbocyclic ring with formation of the trans-stereodiad, composed of an all-carbon quaternary center and a tertiary stereogenic center. The stereoselectivity is perfectly controlled by the choice of alkene geometry in the Michael acceptor. (C) 2013 Elsevier Ltd. All rights reserved.

The preparation of imidazolinium salts, which can be used as precursors of pincer-type N-heterocyclic carbene ligands, is described. The formation of imidazolinium salts under standard conditions is difficult, but they have been successfully synthesized by reaction of the corresponding diamines and trimethyl orthofoimate in 1,1,1,3,3,3-hexafluoroisopropanol. The synthesis of new chiral C-2 symmetric imidazolinium salts is also described.

The total synthesis of clusianone was accomplished through the stereoselective construction of a bicyclo[3.3.1]nonane derivative via a three-step sequence, which has been utilized for the total syntheses of nemorosone, garsubellin A, and hyperforin: intramolecular cyclopropanation, formation of a geminal dimethyl group, and regioselective ring opening of cyclopropane. Further elaboration, including chemo- and stereoselective hydrogenation to generate the C7 stereogenic center and cross-metathesis to construct prenyl groups in the side-chains, was employed to complete the total synthesis of clusianone.

The enantioselective total synthesis of (+)-ophiobolin A is described. This total synthesis features the construction of the spiro CD ring of (+)-ophiobolin A through a stereoselective intramolecular Hosomi-Sakurai cyclization reaction, the joining of the A ring to the CD ring by using a reaction reported by Utimoto, and the construction of the ophiobolin eight-membered carbocyclic ring through ring-closing metathesis (RCM), which was performed for the first time in this study. This successful RCM reaction required the use of a substrate that contained either a benzyloxy or a methoxymethoxy group at the C5 position and either an isopropenyl group or its hydroxylated form at the C6 position. Copyright © 2013 WILEY-VCH Verlag GmbH &amp
Co. KGaA, Weinheim.

Total synthesis of (±)-hyperforin is described. This total synthesis features an approach via a bicyclo[ 3.3.1]nonane derivative prepared by a three-step sequence: intramolecular cyclopropanation, construction of the C8 all-carbon quaternary stereogenic center, and subsequent regioselective ring opening of cyclopropane. Further steps to obtain (±)-hyperforin include chemo- and stereoselective hydrogenation to generate the C7 stereogenic center, formation of the C9 isopropyl ketone using an organocerium reagent, and cross-metathesis at high temperatures to construct trisubstituted alkenes in side-chains. © 2013 Elsevier Ltd. All rights reserved.

The pig liver esterase (PLE)-catalyzed kinetic resolution of half-esters derived from prochiral diesters is described. Generally, the PLE-catalyzed enantioselective hydrolysis of prochiral diesters affords the corresponding half-esters in high yield, because further hydrolysis of the half-esters does not typically occur. However, we found that some half-esters undergo PLE-catalyzed hydrolysis when they are gradually added to a PLE suspension in a potassium phosphate buffer at pH 8.0 via a syringe pump, leading to the kinetic resolution of the half-esters. (c) 2013 Elsevier Ltd. All rights reserved.

Two short preparations of the taxol A-ring fragment are described: one via organocatalyzed alpha-aminoxylation and the other via Sharpless asymmetric dihydroxylation (SAD). The former approach affords the A-ring fragment in 10 steps, and the latter approach involves eight steps to afford the new A-ring fragment in 91% ee, which is made enantiomerically pure through recrystallization. The new A-ring fragment bearing a bromoalkene is confirmed to be useful to form the carbocyclic eight-membered ring of a taxol model compound by palladium-catalyzed intramolecular alkenylation. The preparation of the new A-ring fragment will be beneficial for the total synthesis of taxol as well as other natural products (C) 2013 Elsevier Ltd. All rights reserved.

The preparation of imides via the palladium-catalyzed coupling reaction of organostannanes is described. The palladium-catalyzed coupling reaction of aryl-, heteroaryl-, and alkenyl(tributyl)stannanes with methyl N-[methoxy(methylthio)methylene]carbamate in the presence of Cu(I) thiophene-2-carboxylate (CuTC) affords imino ethers, which are converted to the corresponding imides in high yield through acid hydrolysis.

The stereoselective total synthesis of garsubellin A is described. The total synthesis was achieved through the stereoselective construction of a bicyclo[3.3.1] nonane derivative via a three-step sequence: intramolecular cyclopropanation, formation of a germinal dimethyl group, and regioselective ring opening of cyclopropane. To complete the total synthesis of garsubellin A, chemo-and stereoselective hydrogenation to generate the C8 stereogenic center is followed by the formation of the fused tetrahydrofuran ring by a regioselective epoxide-opening reaction with C3 ketone, and finally cross metathesis to construct two prenyl groups. The Journal of Antibiotics (2013) 66, 141-145; doi: 10.1038/ja.2012.125; published online 6 February 2013

The enantioselective total synthesis of (+)-colletoic acid, a potent naturally occurring 11 beta-hydroxysteroid dehydrogenase type 1 (11 beta-HSD1) inhibitor, is described. This total synthesis features a highly enantioselective catalytic asymmetric intramolecular cyclopropanation of an alpha-diazo-beta-keto diphenylphosphine oxide and five highly stereoselective reactions (cyclopropane opening, Diels-Alder reaction, iodolactonization, alkene formation, and reduction of alpha,beta-unsaturated carboxylic acid).

Highly enantioselective catalytic asymmetric reactions of rationally designed α-alkylidene β-keto imides are described. The [4 + 2] cycloadditions and Hosomi-Sakurai reactions of α-alkylidene β-keto imides proceed with high enantioselectivity and yield. The [4 + 2] cycloadditions of the imides with various dienes afford products bearing an all-carbon quaternary stereogenic center at the ring junction. α-Alkylidene β-keto imides should be useful for the enantioselective total synthesis of natural products and other catalytic asymmetric applications. © 2013 American Chemical Society.

:The total synthesis of clusianone was accomplished through the stereoselective construction of a bicyclo[3.3.1]nonane derivative via a three-step sequence, which has been utilized for the total syntheses of nemorosone, garsubellin A, and hyperforin: intramolecular cyclopropanation, formation of a geminal dimethyl group, and regioselective ring opening of cyclopropane. Further elaboration, including chemo- and stereoselective hydrogenation to generate the C7 stereogenic center and cross-metathesis to construct prenyl groups in the side-chains, was employed to complete the total synthesis ofclusianone.

:Making scab(ronine)s: The total synthesis of (-)-scabronine G features a highly stereoselective oxidative dearomatization/intramolecular inverse-electron-demand Diels-Alder reaction cascade, and the first total synthesis of (-)-scabronine A comprises a highly stereoselective oxa-Michael/protonation/acetalization cascade. The first total synthesis of (-)-episcabronine A includes another highly stereoselective cascade.

:The enantioselective total synthesis of (+)-ophiobolin A is described. This total synthesis features the construction of the spiro CD ring of (+)-ophiobolin A through a stereoselective intramolecular Hosomi-Sakurai cyclization reaction, the joining of the A ring to the CD ring by using a reaction reported by Utimoto, and the construction of the ophiobolin eight-membered carbocyclic ring through ring-closing metathesis (RCM), which was performed for the first time in this study. This successful RCM reaction required the use of a substrate that contained either a benzyloxy or a methoxymethoxy group at the C5 position and either an isopropenyl group or its hydroxylated form at the C6 position.

:The enantioselective total synthesis of (+)-colletoic acid, a potent naturally occurring 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) inhibitor, is described. This total synthesis features a highly enantioselective catalytic asymmetric intramolecular cyclopropanation of an α-diazo-β-keto diphenylphosphine oxide and five highly stereoselective reactions (cyclopropane opening, Diels-Alder reaction, iodolactonization, alkene formation, and reduction of α,β-unsaturated carboxylic acid).

:The stereoselective total synthesis of garsubellin A is described. The total synthesis was achieved through the stereoselective construction of a bicyclo[3.3.1]nonane derivative via a three-step sequence: intramolecular cyclopropanation, formation of a germinal dimethyl group, and regioselective ring opening of cyclopropane. To complete the total synthesis of garsubellin A, chemo- and stereoselective hydrogenation to generate the C8 stereogenic center is followed by the formation of the fused tetrahydrofuran ring by a regioselective epoxide-opening reaction with C3 ketone, and finally cross metathesis to construct two prenyl groups.

:Highly enantioselective catalytic asymmetric reactions of rationally designed α-alkylidene β-keto imides are described. The [4 + 2] cycloadditions and Hosomi-Sakurai reactions of α-alkylidene β-keto imides proceed with high enantioselectivity and yield. The [4 + 2] cycloadditions of the imides with various dienes afford products bearing an all-carbon quaternary stereogenic center at the ring junction. α-Alkylidene β-keto imides should be useful for the enantioselective total synthesis of natural products and other catalytic asymmetric applications.

Although C-H oxidation of hydrocarbons is generally difficult, allylic C-H oxidation is relatively simple and predictable, even on a preparative scale, because active species generated at the allylic position are stabilized by the double bond. Therefore, allylic oxidation has been employed in natural product synthesis, and a variety of reagents and conditions for allylic oxidation have been reported. However, reagents and conditions suitable for natural product synthesis are limited in terms of efficiency and chemo-, regio-, and stereoselectivity, owing to the structural and characteristic diversity of natural products. This review addresses allylic oxidations, highlighting reagents and conditions that meet the requirements for natural product synthesis. 1 Introduction 2 Selenium Reagents 2.1 Selenium Dioxide 2.2 Diphenyldiselenide-Iodoxybenzene 3 Chromium(VI) Reagents 3.1 Chromic Acid and Chromate Ester 3.2 Chromium Trioxide-3,5-Dimethylpyrazole (CrO 3·3,5-DMP) 3.3 PCC and PDC 4 Transition-Metal Reagents 5 Others 6 Conclusion. © Georg Thieme Verlag Stuttgart New York.

The preparation of imides via the palladium-catalyzed coupling reaction as a one-carbon elongation reaction is described. The palladium-catalyzed coupling reaction of aryl-, alkyl-, and alkenylborons with N-[methoxy(methylthio)methylene]carbamate in the presence of Cu(I) thiophene-2-carboxylate (CuTC) affords imino ethers that are converted to the corresponding imides by acidic hydrolysis in high yield. The imino ethers are also useful for preparing the corresponding ester without using carbon monoxide.

In this report, we describe an iron(III) complex containing a carbazole-based tridentate ligand that catalyzes highly enantioselective asymmetric epoxidation of (E)-alkenes at room temperature. The non-heme iron(III) complex has a five-coordinated trigonal-bipyramidal structure, and its two-electron oxidized state has the similar electronic structure as that of iron porphyrins.

The palladium-catalyzed reductive cleavage of alkyl aryl sulfides to afford the corresponding arenes in high yield, which is both accelerated and exhibits increased functional group selectivity in the presence of TMSCI, is described. This ligand-free reaction features mild conditions, easy operation, use of readily available reagents, and high functional group selectivity. (c) 2012 Elsevier Ltd. All rights reserved.

The highly stereoselective total synthesis of nemorosone via a new approach to the bic-yclo[3.3.1]nonane-2,4,9-trione core which features intramolecular cyclopropanation of an alpha-diazo ketone, stereoselective alkylation at the C8 position, and regioselective ring-opening of cyclopropane is described. The total synthesis of nemorosone includes chemo- and stereoselective hydrogenation directed by the internal alkene.

The asymmetric and highly stereoselective synthesis of compound 1, which corresponds exactly to the DEF-ring moiety of (-)-FR182877, and the biological activities of its derivatives are described. All derivatives of 1 showed no activity in the tubulin polymerization assay, but one derivative was shown to have the ability to induce mitotic arrest by interfering with microtubule dynamics, and the cellular effects are similar to those of paclitaxel.

Herein we describe the preparation of novel chiral bisoxazoline ligands with various substituents at the bisoxazoline linkage, for use in the catalytic asymmetric intramolecular cyclopropanation (CAIMCP) of alpha-diazo-beta-keto phenyl-5-hexenyl sulfone to afford a simple, but useful, bicyclo[3.1.0]hexane derivative. The enantioselectivity of the CAIMCP of alpha-diazo-beta-keto phenyl-5-hexenyl sulfone was improved and a product with 84% ee was obtained using 30 mol % of the catalyst, which was prepared in situ by CuOTf and the new bisoxazoline ligand with two 3,5-di-tert-butylbenzyl groups at the bisoxazoline linkage. The product was obtained in enantiomerically pure form by a single crystallization, enabling its use as a chiral building block. (C) 2012 Elsevier Ltd. All rights reserved.

This manuscript describes studies on the construction of the cis-decaline core of (+)-bucidarasin C. The transannular Diels-Alder (TADA) reaction of a macrocyclic lactone successfully afforded the desired cis-decaline derivative in a stereoselective manner. On the other hand, the stereoselective transannular cascade Michael (TACM) reaction of the parent macrocyclic lactone afforded the diastereomeric cis-decaline derivative as the major product. (C) 2012 Elsevier Ltd. All rights reserved.

:The preparation of imides via the palladium-catalyzed coupling reaction as a one-carbon elongation reaction is described. The palladium-catalyzed coupling reaction of aryl-, alkyl-, and alkenylborons with N-[methoxy(methylthio)methylene]carbamate in the presence of Cu(I) thiophene-2-carboxylate (CuTC) affords imino ethers that are converted to the corresponding imides by acidic hydrolysis in high yield. The imino ethers are also useful for preparing the corresponding ester without using carbon monoxide.

:In this report, we describe an iron(III) complex containing a carbazole-based tridentate ligand that catalyzes highly enantioselective asymmetric epoxidation of (E)-alkenes at room temperature. The non-heme iron(III) complex has a five-coordinated trigonal-bipyramidal structure, and its two-electron oxidized state has the similar electronic structure as that of iron porphyrins.

:The highly stereoselective total synthesis of nemorosone via a new approach to the bicyclo[3.3.1]nonane-2,4,9-trione core which features intramolecular cyclopropanation of an α-diazo ketone, stereoselective alkylation at the C8 position, and regioselective ring-opening of cyclopropane is described. The total synthesis of nemorosone includes chemo- and stereoselective hydrogenation directed by the internal alkene.

:The asymmetric and highly stereoselective synthesis of compound 1, which corresponds exactly to the DEF-ring moiety of (-)-FR182877, and the biological activities of its derivatives are described. All derivatives of 1 showed no activity in the tubulin polymerization assay, but one derivative was shown to have the ability to induce mitotic arrest by interfering with microtubule dynamics, and the cellular effects are similar to those of paclitaxel.

Synthesis of medium-sized carbocyclic ketones via the intramolecular B-alkyl Liebeskind-Srogl coupling reaction is described. The sequence of hydroboration of omega-alkenyl thiol ester with 9-BBN and the Liebeskind-Srogl reaction results in the formation of medium-sized carbocyclic ketones with good yield. (C) 2011 Elsevier Ltd. All rights reserved.

An enantioselective total synthesis of (-)-FR182877 is described. This total synthesis features 1) the one-pot stereoselective tandem IMDA-IMHDA reaction which affords the tetracyclic compound including the ABCD ring system of (-)-FR182877 with the correct new seven stereogenic centers, 2) the palladium-mediated 7-exo-trig intramolecular Heck reaction for the construction of the highly strained seven-membered F-ring, and 3) the iridium-mediated isomerization of the allylic alcohol to the alpha-methyl ketone followed by epimerization and the stereoselective reduction to furnish all the stereogenic centers of (-)-FR182877.

An enantioselective total synthesis of (−)-FR182877 is described. This total synthesis features 1) the one-pot stereoselective tandem IMDA-IMHDA reaction which affords the tetracyclic compound including the ABCD ring system of (−)-FR182877 with the correct new seven stereogenic centers, 2) the palladium-mediated 7-exo-trig intramolecular Heck reaction for the construction of the highly strained seven-membered F-ring, and 3) the iridium-mediated isomerization of the allylic alcohol to the α-methyl ketone followed by epimerization and the stereoselective reduction to furnish all the stereogenic centers of (−)-FR182877.

Enantioselective divergent approaches to (-)-platencin and (-)-platensimycin have been developed. A rationally designed chiral synthetic intermediate, possessing a useful alpha,beta-unsaturated sulfone functionality, which served as a masked ketone as well as a good Michael acceptor, was successfully prepared via the highly enantioselective catalytic asymmetric intramolecular cyclopropanation (CAIMCP) developed in our laboratory. (C) 2010 Elsevier Ltd. All rights reserved.

This Letter describes an enantioselective approach to (-)-platencin. A uniquely functionalized chiral intermediate, which was prepared via the highly enantioselective catalytic asymmetric intramolecular cyclopropanation (CAIMCP) that we have developed, was successfully transformed to Nicolaou's intermediate in his total synthesis of (-)-platencin. (C) 2010 Elsevier Ltd. All rights reserved.

This Letter describes synthetic studies of nemorosone via enantioselective intramolecular cyclopropanation. For the total synthesis of nemorosone, three potential intermediates were evaluated through the efficiency of three sequential reactions, namely, their intramolecular cyclopropanation, dimethylation of the resultant cycloproparies, and ring-opening reaction of the alkylated cyclopropanes. As a result, alpha-diazomethyl ketone 10c was found to be the most suitable. The enantroselective intramolecular cyclopropanation to construct the bicyclo[3 3 1]nonane core and preparation of the compound with all the correct stereogenic centers of nemorosone are also described. (C) 2010 Elsevier Ltd All rights reserved.

:MK8383, isolated from Phoma sp. T2526 in 1993, exhibits potent antibiotic activities against a variety of phytopathogens and has been considered a promising fungicide against Botrytis cinerea. Unfortunately, MK8383 is a photosensitive compound and it undergoes irreversible decomposition. Although much effort has been devoted to improving the photostability of MK8383 by chemical modification of its structure by a research group organized by Meiji Seika Kaishya, Ltd. and Mitsubishi Chemical Corporation, a photostable MK8383 derivative has never been prepared. We have found that a C13-14 double bond of MK8383 and (+)-phomopsidin is responsible for the photosensitivity, and herein, we report the synthesis of NH006, an MK8383 derivative with a saturated C13-14 double bond and (S) configuration at C14, based on the asymmetric total synthesis of MK8383. NH006 exhibits good photostability and potent antifungal activity against B. cinerea.

MK8383, isolated from Phoma sp. T2526 in 1993, exhibits potent antibiotic activities against a variety of phytopathogens and has been considered a promising fungicide against Botrytis cinerea. Unfortunately, MK8383 is a photosensitive compound and it undergoes irreversible decomposition. Although much effort has been devoted to improving the photostability of MK8383 by chemical modification of its structure by a research group organized by Meiji Seika Kaishya, Ltd. and Mitsubishi Chemical Corporation, a photostable MK8383 derivative has never been prepared. We have found that a C13-14 double bond of MK8383 and (+)-phomopsidin is responsible for the photosensitivity, and herein, we report the synthesis of NH006, an MK8383 derivative with a saturated C13-14 double bond and (S) configuration at C14, based on the asymmetric total synthesis of MK8383. NH006 exhibits good photostability and potent antifungal activity against B. cinerea.

Nozaki-Hiyama reactions are powerful Cr-II-mediated C-C bond-forming reactions conducted under mild conditions that show excellent compatibility with various functional groups. Therefore, Nozaki-Hiyama reactions have been utilized for many total syntheses of complex natural products, but at least two equivalents of Cr-II salt are required to complete the reaction because Cr-II salt is a one-electron donor. In 1996, however, the quantity of Cr-II salts required was successfully reduced by a catalytic redox system reported by Furstner and Shi. Since the report by Furstner, the catalytic asymmetric Nozaki-Hiyama reactions have attracted attention because they would allow control over enantioselectivity, thereby further enhancing the versatility of Nozaki-Hiyama reactions. In this review, we describe the development of a tridentate bis(oxazolinyl)carbazole ligand for the catalytic asymmetric Nozaki-Hiyama allylation, methallylation, propargylation, and allenylation. Also described are their successful applications to the highly stereoselective construction of the side chain of calcitriol lactone, as well as structure elucidation and the enantioselective first total synthesis of the potent 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, FR901512 and FR901516. (C) 2008 The Japan Chemical Journal Forum and Wiley Periodicals, Inc.

Construction of the ABCD ring system of (-)-FR182877 via the highly diastereoselective intramolecular Diels-Alder (I MDA) reaction is described. The IMDA reaction of the oj-unsaturated aldehyde generated in situ from the corresponding acetal successfully provided the desired product 14 possessing the AB ring system as the single diastereomer. The CD ring system was constructed by the subsequent IMHDA reaction and the additional experiment suggested that the diastereoselectivity of the IMHDA reaction could be related to the EIZ geometry of alkene 17, which was generated in situ from 16. (c) 2007 Elsevier Ltd. All rights reserved.

Construction of the ABCD ring system of (-)-FRI 82877 via the intramolecular Diels-Alder (IMDA) reaction and the highly diastereoselective intramolecular hetero-Diels-Alder (IMHDA) reaction is described. The IMHDA reactions of the substrates incorporating the oxabutadiene with the E- or Z-alkene were examined, revealing that the sole product was obtained from both substrates and the E-alkene geometry was found to be crucial to obtaining the desired product. (c) 2007 Elsevier Ltd. All rights reserved.

Construction of the taxane skeleton via the stereoselective conjugate addition of cyanide and the intramolecular B-alkyl Suzuki-Miyaura coupling reaction is described. A conjugate addition of cyanide to enone 17 proceeded diastereoselectively to provide the desired 18 incorporating the correct C3 stereogenic center in the taxol C-ring. The intramolecular B-alkyl Suzuki-Miyaura coupling reaction of 22, which was derived from 18, successfully furnished the taxol B-ring in 81% yield. (C) 2007 Elsevier Ltd. All rights reserved.

A new synthetic approach to the bicyclo[3.3.1]nonane system, a common structure in a number of polyisoprenylated phloroglucinol derivatives (phloroglucins), has been developed. The key step in our approach is a 'one-pot' procedure of two successive reactions, the intramolecular cyclopropanation reaction which affords the tricyclo[4.4.0.0(5.7)]dec-2-ene derivative and its methoxy group directed regioselective ring-opening reaction mediated by ZnCl2, producing the desired bicyclo[3.3.1]nonane as the sole product. (c) 2007 Elsevier Ltd. All rights reserved.

A new preparation of the tridentate bis-oxazoline carbazole ligand 1 is described. This method features direct formation of the amide, which is a precursor of the ligand 1, via the Pd-catalyzed amidation and following BF3 center dot OEt2 mediated oxazoline formation. This method required only 2 steps from the aryl iodide to form the bis-oxazoline ligand; hence, it would be generally used for preparing other bis-oxazoline ligands.

This manuscript describes studies on the catalytic asymmetric intramolecular cyclopropanation (IMCP) of 2-diazo-3-oxo-6-heptenoic acid esters. The enantioselectivity depends on the bulkiness of the ester moiety, and the 2,6-di-tert-butyl-4-methylphenyl ester of 2-diazo-3-oxo-6-heptenoic acid provided the product with 78% ee, suggesting that the catalytic asymmetric IMCP of alpha-diazo-beta-keto esters could be a key reaction for the en anti oselective synthesis of natural products as well as artificial molecules.

A new access to the bicyclo[3.3.1]nonane system, which is a common structure in a number of polyisoprenylated phloroglucinol derivatives (phloroglucins), has been developed via the Lewis acid promoted regioselective ring-opening reaction of the cyclopropane, a tricyclo[4.4.0.0(5,7)]dec-2-ene derivative. (c) 2006 Elsevier Ltd. All rights reserved.

Asymmetric synthesis of the spirocyclic CID-ring moiety of (+)-ophiobolin A is described. Fragment A, which was prepared via pig liver esterase (PLE)-mediated kinetic resolution, and fragment B, which was prepared via diastereoselective allylation and subsequent kinetic iodolactonization, were coupled to afford the allylsilane 2, which was successfully cyclized to the desired spirocyclic CD-ring moiety la in the presence of a Lewis acid.

The structure-diastereoselectivity relationships in the IMDA reactions of the terminally activated (EEE)-nona-1,6,8-trienes have been studied. It is found that the configuration of the C3 position bearing the protected hydroxyl group is crucial to the diastereoselectivity, and the magnitude of the ratio depends on the relative configuration of the C3-C5 positions. The results obtained in this study including the new successful IMDA reactions would be useful for the stereoselective synthesis of natural products containing a bicyclo[4.3.0]non-2-ene carbon skeleton. (c) 2006 Elsevier Ltd. All rights reserved.

Highly enantioselective reduction of five-, six-, seven-, and eight-membered prochiral 1,3-cycloalkanediones possessing a methyl group and a protected hydroxymethyl group at their C2 position with baker's yeast or CBS catalyst and a new efficient and general method for preparing the 1,3-cycloalkanediones have been developed. These baker's yeast mediated reductions were found to produce corresponding ketols with high optical purity (> 99% ee) and high yield. All of the prepared ketols and their derivatives, chiral building blocks, have been fully characterized, and their absolute configurations have been determined. These compounds would be useful for the convergent synthesis of complex natural products.

Silicon-tethered intramolecular nucleophilic additions of a hydroxymethyl unit to ketones in beta-hydroxyketones have been developed. The product obtained by this protocol was successfully converted to chiral A-ring moieties of Taxol(TM). Also developed was a promising silicon-tethered intramolecular alpha-alkylation reaction of the cyclic hydroxyketone. (C) 2004 Elsevier Ltd. All rights reserved.

Synthetic studies on the seven- and eight-membered rings by the intramolecular Nozaki-Hiyama reaction of the allylic phosphates are described. The yield greatly depends on the structure of substrate; however, some complex substrates afforded desired products in high to excellent yield. (C) 2004 Elsevier Ltd. All rights reserved.

Construction of eight-membered carbocyclic rings via the intramolecular B-alkyl Suzuki-Miyaura cross-coupling reaction has been studied. This protocol proved its potency through the formation of the eight-membered ring possessing a quaternary carbon on its ring in high yield, affording promise of a new access to the eight-membered ring of Taxol.

Silicon-tethered intramolecular nucleophilic additions of a hydroxymethyl unit to ketones in beta-hydroxyketones have been developed. The product obtained by this protocol was successfully converted to chiral A-ring moieties of Taxol(TM). Also developed was a promising silicon-tethered intramolecular alpha-alkylation reaction of the cyclic hydroxyketone. (C) 2004 Elsevier Ltd. All rights reserved.

Synthetic studies on the seven- and eight-membered rings by the intramolecular Nozaki-Hiyama reaction of the allylic phosphates are described. The yield greatly depends on the structure of substrate; however, some complex substrates afforded desired products in high to excellent yield. (C) 2004 Elsevier Ltd. All rights reserved.

Construction of eight-membered carbocyclic rings via the intramolecular B-alkyl Suzuki-Miyaura cross-coupling reaction has been studied. This protocol proved its potency through the formation of the eight-membered ring possessing a quaternary carbon on its ring in high yield, affording promise of a new access to the eight-membered ring of Taxol.

Catalytic asymmetric Nozaki-Hiyama propargylation with ligand 1c proceeds with good to excellent enantioselectivity. Tuning of ligand 1 dramatically changes the enantioselectivity, and we propose models A and B to explain the change and outcome of the enantioselectivity.

Catalytic asymmetric Nozaki-Hiyama propargylation with ligand 1c proceeds with good to excellent enantioselectivity. Tuning of ligand 1 dramatically changes the enantioselectivity, and we propose models A and B to explain the change and outcome of the enantioselectivity.

The first total synthesis of (+)-phomopsidin has been achieved via a diastereoselective transannular Diels-Alder (TADA) reaction. Key steps in the synthesis include diastereoselective ynone reduction with (-)-alpha-pinene and 9-BBN, macrocyclization by E-selective intramolecular Horner-Wadsworth-Emmons (HWE) reaction, as well as carbometalation under Wipf's conditions, followed by HWE reaction at low temperature to selectively construct the (E)-1-methylpropenyl and (1E,2E)-4-carboxy-1,3-butadienyl substituents.

The first total synthesis of (+)-phomopsidin has been achieved via a diastereoselective transannular Diels-Alder (TADA) reaction. Key steps in the synthesis include diastereoselective ynone reduction with (-)-alpha-pinene and 9-BBN, macrocyclization by E-selective intramolecular Horner-Wadsworth-Emmons (HWE) reaction, as well as carbometalation under Wipf's conditions, followed by HWE reaction at low temperature to selectively construct the (E)-1-methylpropenyl and (1E,2E)-4-carboxy-1,3-butadienyl substituents.

The manuscript describes our studies on a newly designed tridentate ligand. The new ligand 1 was successfully synthesized, and it was found that the asymmetric catalysis of Nozaki-Hiyama allylation with ligand 1 affords the product with good enantioselectivity in high yield.