Yasumitsu Tamura
Osaka University
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Featured researches published by Yasumitsu Tamura.
Tetrahedron Letters | 1989
Yasuyuki Kita; Takayuki Yakura; Hirofumi Tohma; Kazumi Kikuchi; Yasumitsu Tamura
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.
Tetrahedron Letters | 1985
Yasumitsu Tamura; Takayuki Yakura; Jun-ichi Haruta; Yasuyuki Kita
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.
Tetrahedron | 1975
Yasumitsu Tamura; H. Matsushima; J. Minamikawa; M. Ikeda; Kunihiro Sumoto
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 SN bond cleavage. The reactions of disulfides and thioketone with MSH are also described.
Tetrahedron Letters | 1987
Yasumitsu Tamura; Hirokazu Annoura; Hirofumi Yamamoto; Hiroshi Kondo; Yasuyuki Kita; Hiromichi Fujioka
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 ).
Tetrahedron Letters | 1984
Yasuyuki Kita; Hitoshi Yasuda; Osamu Tamura; Fumio Itoh; Yasumitsu Tamura
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.
Tetrahedron | 1963
S. Saito; Keishi Kotera; N. Shigematsu; A. Ide; N. Sugimoto; Zen-ichi Horii; Miyoji Hanaoka; Yasuhiko Yamawaki; Yasumitsu Tamura
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).
Tetrahedron Letters | 1979
Yasuyuki Kita; Jun-ichi Haruta; J. Segawa; Yasumitsu Tamura
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.
Tetrahedron Letters | 1980
Yasuyuki Kita; J. Segawa; Jun-ichi Haruta; Takashi Fujii; Yasumitsu Tamura
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 .
Tetrahedron Letters | 1987
Yasuyuki Kita; Fumio Itoh; Osamu Tamura; Ya Yuan Ke; Yasumitsu Tamura
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.
Journal of The Chemical Society-perkin Transactions 1 | 1993
Yasuyuki Kita; Hiroshi Maeda; Kana Omori; Takayuki Okuno; Yasumitsu Tamura
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.