秋山 隆彦

Three-component synthesis of homoallylic amines starting from aldehyde, amine, and allyltributylstannane were realized by means of tin(II) chloride dihydrate in water in the presence of SDS.

anti And syn stereoselectivity on the HBF4-catalyzed Mannich-type reaction of ketene silyl acetal derived from cc-oxy esters with aldimines were investigated. Whereas use of ketene silyl acetal derived from aryl ester in aqueous 2-propanol gave anti beta -amino-alpha -siloxy ester with excellent stereoselectivity, use of ketene silyl acetal derived from methyl ester in water in the presence of sodium dodecyl sulfate gave the syn isomer preferentially. (C) 2001 Elsevier Science Ltd. All rights reserved.

BF3. OEt2-mediated [3+2] cycloaddition of allyltriisopropylsilane to N-sulfonyl aldimine afforded silyl substituted pyrrolidines in good yields. Excellent cis selectivity was observed with aromatic aldimines. (C) 2001 Elsevier Science Ltd. All rights reserved.

On treatment of aldimines derived from aromatic aldehydes and aniline with allylsilane in the presence of Lewis acid, [4+2] cycloannulation took place smoothly to afford tetrahydroquinoline derivatives in moderate to good yields.

Allyltriethylgermane reacts with aldimines in preference to aldehydes by means of BF3. OEt2 and AcOH to afford homoallylic amines in high yields; three component syntheses of homoallytic amines starting from aldehyde, aniline and allylgermane were successfully achieved.

Three-component aza Diels-Alder reaction, starting from aldehyde, aniline, and Danishefsky's diene, took place smoothly under the influence of HBF4 in aqueous media to afford dihydro-4-pyridone derivatives in high yields. (C) 1999 Elsevier Science Ltd. All rights reserved.

Reported herein are that catalytic amount of conventional Lewis acids activated aldimines in preference to aldehydes, and addition of water to BF3. OEt2 accelerated the Mannich-type reaction significantly to afford p-amino carbonyl compounds in high yields.

HBF4 catalyzed Mannich-type reactions of aldehydes, amines, and silyl enolates took place smoothly in water in the presence of a surfactant to afford beta-amino carbonyl compounds in high yields.

Scandium(III) triflate-catalyzed allylation of carbonyl compounds with tetraallylgermane proceeded readily in aqueous nitromethane to afford homoallyl alcohols in excellent to good yields. The presence of H2O is indispensable for the allylation of aldehydes to proceed smoothly. Aldehydes were allylated highly chemoselectively in the presence of ketone moieties. (C) 1999 Elsevier Science Ltd. All rights reserved.

Bronsted acid-catalyzed cyclization of chiral N-tosyl-3-silyl-4-pentenamine proceeded smoothly by way of a P-silyl carbocation intermediate to furnish 2,3,5-trisubstituted pyrrolidines in enantiomerically pure form. (C) 1999 Elsevier Science Ltd. All rights reserved.

HBF4 catalyzed Mannich-type reaction took place smoothly in aqueous media to afford β-amino carbonyl compounds in high yields. One-pot synthesis of β-amino carbonyl compounds from aldehyde and amine also worked well.

Acid promoted cyclization of bishomoallylic alcohols bearing allylsilanes proceeded smoothly by way of beta-silyl carbocation intermediate to furnish tetrahydrofurans highly stereoselectively.

ZrCl4-mediated annulation of allyldiisopropylphenylsilane with alpha,beta-unsaturated diesters and subsequent oxidative cleavage of the carbon-silicon bond furnished cyclopentanols highly stereoselectively. (C) 1998 Elsevier Science Ltd. All rights reserved.

ZrCl4-Promoted [3+2] cycloaddition of allyldiisopropylphenylsilane to alpha,beta-unsaturated ketones proceeds smoothly to afford silyl-substituted cyclopentanes highly stereoselectively. Oxidative cleavage of the carbon-silicon bond leads to stereoselective formation of cyclopentanols.

Investigated is a three-component synthesis of homoallylamines by scandium(III) triflate catalyzed allylation of imines, generated in situ from aldehyde and amine, with allyltriethylgermane. Imines were allylated exclusively in the presence of aldehydes.

Scandium(III) triflate-catalyzed allylation of carbonyl compounds with tetraallylgermane proceeded readily in aqueous nitromethane to afford homoallyl alcohols in excellent to good yields. The presence of H2O is indispensable for the allylation of aldehydes to proceed smoothly. Aldehydes were allylated exclusively in the presence of ketone moieties. (C) 1997, Elsevier Science Ltd.

Tin(IV) chloride mediated [3 + 2] cycloaddition of allylgermanes to α-dicarbonyl compounds proceeds highly stereoselectively to give tetrahydrofurans in good yields.

Reported herein are two novel modes of reactions that were mediated by the proper choice of Lewis acid. Thus, by the influence of SnCl4, allyl-t-butyldimethylsilane reacted with aldehyde in 2:1 stoichiometry to afford a ketone derivative. In contrast, use of BF3 . OEt2 led to the formation of a 1,3-dioxane derivative, which is a 1:2 adduct.

Zirconium(IV) chloride mediated [2+2] cycloaddition of allylsilanes, which possess bulky substituents on silicon atom, to alpha-siloxyaldehydes proceeded stereoselectively in toluene to afford oxetane derivatives in good yields.

It is highly important to find a novel chiral building unit for the synthesis of enantiopure natural products of biological interest and also for developing novel asymmetric reactions. L-Quebrachitol (1L-(-)-2-O-methyl-chiro-inositol) is a naturally occurring optically active cyclitol obtained from an exudate of the rubber tree. By developing novel method for the selective demethylation of methyl ether in the presence of cyclohexylidene acetal in L-quebrachitol moieties, total syntheses of myo- inositol 1-phosphate, (+)-conduritol B, and cyclophellitol were achieved. It was found that chiral cyclitols derived from L-quebrachitol were excellent chiral auxiliaries. For instance, diastereoselective reduction and addition to α-keto ester attached to chiral cyclitol derivatives took place highly stereoselectively. Diels-Alder reactions and [3+2] cycloaddition of nitrile oxide to acryloyl ester derived from the chiral cyclitol also proceeded with high diastereoselectivity.

The TiCl4 or SnCl4 mediated Diels-Alder reaction of cyclopentadiene and chiral acryloyl ester derived from chiral cyclitols proceeded with excellent diastereoselectivity in Et(2)O via re-face attack of the acrylates. In contrast, interesting changeover of the diastereofacial selectivity was observed by use of toluene or hexane as a solvent to afford the cycloadducts derived from si-face attack of the acrylates.

Titanium(IV) chloride mediated [2+2] cycloaddition of allylsilanes, which possess bulky substituents at the silicon, to alpha-keto esters underwent highly stereoselectively in toluene to afford oxetane derivatives in excellent yields.

Tin (IV) chloride mediated [3+2] cycloadditions of allylsilanes with optically active alpha-keto esters derived from L-quebrachitol afforded tetrahydrofuran derivatives via 1,2-silyl migration with high level of diastereoselectivity. Removal of the chiral auxiliary gave silyl-substituted tetrahydrofurans of excellent optical purity.

Tin (IV) chloride promoted aldol reactions of silyl enol ether and ketene silyl acetal with alpha-keto esters derived from L-quebrachitol afforded the corresponding aldol-type adduct, alpha-hydroxy acid derivatives, in good yields with excellent diastereomeric excesses.

SnCl4 promoted [3+2] cycloaddition reactions of allylsilane to alpha-keto esters afforded tri- and tetrasubstituted tetrahydrofurans with excellent stereoselectivity via 1,2-silyl migration in good yields.

Methyl, benzyl, methoxymethyl, methylthiomethyl, methoxyethoxymethyl, and beta-(trimethylsilyl)ethoxymethyl esters could be cleaved readily under mild conditions on treatment with AlCl3-N,N-dimethylaniline in CH2Cl2 to give parent carboxylic acids in high yields.

Reduction of an alpha-keto ester derived from chiral cyclitol, readily available from L-quebrachitol, with K-Selectride proceeded via re-face attack of the ketone with high diastereoselectivity to obtain the alpha-hydroxy ester in 92% de. On the other hand, reduction of the alpha-keto ester with K-Selectride in the presence of 18-Crown-6 took place via si-face attack of the ketone to furnish the corresponding alpha-hydroxy ester in 92% de. Thus both enantiomers of mandelic acid were obtained in optically pure form.

The methyl ether of cyclitols with vicinal hydroxyl group was cleaved chemoselectively in preference to both cis- and trans-cyclohexylidene moieties by AlCl3-n-Bu4NI to afford parent alcohols in good yields. (-)-Conduritol F was prepared from L-quebrachitol, an optically active cyclitol from the serum of rubber trees, in five steps by use of the demethylation reaction. The first chiral synthesis of (+)-conduritol B and the total synthesis of cyclophellitol, a novel beta-glucosidase inhibitor, are described.

Enzyme-catalyzed regio- and enantioselective esterification of racemic 1,2:5,6-di-Ocyclohexylidene- and 1,2:3,4-di-O-cyclohexylidene-myo-inositol, which are key intermediates for syntheses of various naturally occurring myo-inositol phosphate derivatives, proceeded exclusively in organic solvent to give optically pure materials and selectively protected products in gram scale. Hydrolysis of mono-O-acetates of the corresponding racemic materials catalyzed by the same enzymes yielded complementary products. The present study provides a new and efficient method for obtaining optically pure myo-inositol derivatives. © 1993.

An acryloyl ester derived from (1L)-3-t-butyldiphenylsilyl-1,2:5,6-di-O-cyclohexylidene-chiro-inositol underwent 1,3-dipolar cycloaddition with nitrile oxide to give DELTA2-isoxazolines of high diastereomeric excess (up to 90% de).

A combination system of trimethylsilyl chloride, anisole, and a catalytic amount of tin(II) chloride cleaved p-methoxybenzyl ethers selectively in the presence of benzyl ethers under mild conditions to afford parent alcohols in high yields.

The nucleophilic addition of organometallics to alpha-keto esters derived from (1L)-1,2:5,6-di-O-cyclohexylidene-3-t-butyldimethylsilyl-chiro-inositol afforded the corresponding alpha-hydroxy esters of high diastereomeric excess (up to 98% de). Grignard reagents attacked from re-face, while organolithium reagents preferred si-face attack.