Yasumitsu Tamura

A synthetic approach to discorhabdin alkaloids: Hypervalent iodine oxidation of p-substituted phenol derivatives to azacarbocyclic spirodienones

Abstract Hypervalent iodine oxidation of O -silylated p -substituted phenols by phenyliodosyl bis (trifluoroacetate) (PIFA) in 2,2,2-trifluoroethanol gave azacarbocyclic spirodienones inn good yields.

An efficient conversion of keto groups into dihydroxyacetone groups: oxidation of ethynylcarbinol intermediates by using hypervalent iodine reagent

Abstract A short and efficient synthesis of dihydroxyacetone groups from keto groups involving the oxidation of ethynylcarbinol intermediates with [bis(trifluoroacetoxy) iodo] benzene (PIFA), is described.

Syntheses and some properties of N-unsubstituted sulfilimines

Abstract A variety of S-aminosulfonium mesitylenesulfonates, R1R2S+NH2·X−, were prepared in high yields by the reaction of sulfides with O-mesitylenesulfonylhydroxylamine (MSH). The thermal stability of the derived sulfilimines was examined. Reaction of allyl sulfides with MSH afforded directly the salts of allylamines in good yields, presumably via [2,3]-sigmatropic rearrangement of unisolable allylsulfilimines followed by SN bond cleavage. The reactions of disulfides and thioketone with MSH are also described.

Asymmetric synthesis of anthracyclinones using chiral acetal: synthesis of a new chiral AB-synthon, ()-2-bromo-6-ethynyl-6-hydroxy-5, 6, 7, 8-tetrahydro-1, 4-naphthoquinone, and its application for ()-7-deoxydaunomycinone

Abstract A synthesis of a new chiral AB-synthon ( 4 ) for preparing the optically active anthracyclinones was attained through a stereospecific nucleophilic addition of trimethylsilylethynylmagnesium chloride to the chiral 2-tetralone-1-acetal ( 2 ). Synthesis of ( )-7- deoxydaunomycinone ( 1c ) was achieved by a regiospecific cycloaddition of 4 to 4-acetoxy-8-methoxyhomophthalic anhydride ( 5 ).

The chemistry of O-silylated ketene acetal; Pummerer rearrangement of sulfoxides into α-siloxysulfides

Abstract Treatment of sulfoxides with ketene silyl acetal in anhydrous acetonitrile in the presence of a catalytic amount of zinc iodide causes a Pummerer rearrangement to give α-siloxysulfides under extremely mild conditions.

Structure of securinine

Abstract The structure (XXVII) proposed for securinine is confirmed by synthetic structural proof of the key degradation products, lactam-carbinol B (XXIII) and quinolizidine B (XX).

Ketene methyl trialkylsilyl acetals as effective silylating agents for alcohols, carboxylic acids, mercaptans, and amides

Abstract Silyl-proton exchange reactions with ketene methyl trialkylsilyl acetals proceeded rapidly and quantitatively under mild conditions. The preparative silylation of alcohols, carboxylic acids, mercaptans, and amides is described.

O-silylated ketene acetal chemistry; β-(alkoxycarbonyl)methyl O-silyl enolates, useful synthons for α-substituted-β-(alkoxycarbonyl)methylalkanones☆

Abstract Conjugate addition of O-silylated ketene acetals 2 to α,β-unsaturated carbonyl compounds 1 in acetonitrile gave quantitative yields of the corresponding β-(alkoxycarbonyl)methyl O-silyl enolates 4 . Site specific electrophilic substitutions of 4 yielded the corresponding α-substituted β-(alkoxycarbonyl)-methylalkanones 5 , 7 , and 8 .

The chemistry of O-silylated ketene acetals: an efficientstereocontrolled synthesis of N-benzoyl L-daunosamine

Abstract N-Benzoyl L-daunosamine was synthesized with high stereoselectivity utilizing a 1,3-addition of ketene silyl acetal ( 3a ) to the chiral nitrone,(Z)-[(4R)- trans -2,2,5-trimethyl-1,3-dioxolan-4-yl]methylene[(1S)-1-phenylethyl]amine N-oxide ( 4c ) accompanied by a silyl group-transfer in acetonitrile under mild conditions.

Novel efficient synthesis of 1-ethoxyvinyl esters using ruthenium catalysts and their use in acylation of amines and alcohols : synthesis of hydrophilic 3'-N-acylated oxaunomycin derivatives

A novel and efficient synthesis of 1-ethoxyvinyl esters 3a–i from carboxylic acids 4a–i and ethoxyacetylene 5 by using a catalytic amount of ruthenium complex [{RuCl2(p-cymene)}2]6f has been developed. These reagents reacted smoothly with amines and alcohols to give the corresponding N- and O-acylated compounds in excellent yields. This acylation method has been applied to the synthesis of hydrophilic 3′-N-acylated oxaunomycin derivatives 13a, b.