Catalytic Asymmetric Addition of Polyfunctional Dialkylzincs to .beta.-Stannylated and .beta.-Silylated Unsaturated Aldehydes
摘要:
The addition of functionalized dialkylzincs to readily available beta-stannylated or beta-silylated unsaturated aldehydes in the presence of a catalytic amount of (1R,2R)-1,2-bis(trifluorosulfonamido)cyclohexane (8 mol%) provides chiral allylic alcohols in good yields (60-90%) and excellent enantioselectivity (usually in the range of 85-95% ee). The synthetic utility of these allylic alcohols as chiral building blacks is demonstrated. The gamma-stannylated allylic alcohols were submitted to a Stille coupling leading to polyfunctional allylic alcohols and gamma-alkoxy enones. A treatment with CuCN in N-methylpyrrolidone at 130 degrees C provided chiral unsaturated gamma-hydroxy nitriles. Finally, the desilylation of the gamma-silylated alcohols gave chiral allylic alcohols having a terminal double bond. The catalytic asymmetric addition was found to show an important inverse temperature dependance. A mechanism for this addition is proposed.
Nucleophilic addition of dialkylzincs to aldehydes in hydrocarbon solvents is markedly accelerated by the presence of a catalytic amount of a β-dialkylamino alcohol. Use of certain sterically constrained chiral amino alcohols such as 3-exo-(dimethylamino)isoborneol or 1-t-butyl-2-piperidinoethanol effects highly enantioselective catalysis giving secondary alcohols in up to 99% ee. Dimethyl-, diethyl-
aldehyde or nitroalkene in place of the propargylic iodide affords the C-7 and C-6 functionalized prostaglandins, respectively. This new protocol constitutes the simplest three-component method for the synthesis of various natural and unnatural prostaglandins.
A hydroxy-1-alkyne is reacted with a tin hydride compound, and the obtained (E,Z)-hydroxyvinylstannanes are separated to give the (E)-substance which is further converted to a vinylcopper complex shown by
followed by the conjugate addition reaction with an &agr;, &bgr;-unsaturated cyclopentenone, and the deprotecting reaction is subsequently carried out to prepare a prostaglandin or an intermediate of prostaglandins easily, efficiently and industrially favorably.
A Highly Efficient Synthesis of Prostaglandin ω-Chain Precursors
作者:Yasunori Kitano、Takashi Matsumoto、Sentaro Okamoto、Toshiyuki Shimazaki、Yuichi Kobayashi、Fumie Sato
DOI:10.1246/cl.1987.1523
日期:1987.8.5
γ-tributylstannyl allylic alcohols by the Sharpless asymmetric epoxidation proceeds with synthetically satisfactory rate differences for the two enantiomers, thus providing a highly efficient method for the synthesis of prostaglandin ω-chain.
Simple Preparation of the Optically Active γ-Hydroxy Vinylstannanes Using Lipase-Catalyzed Hydrolysis
作者:Toshiyuki Itoh、Tadataka Ohta
DOI:10.1246/cl.1991.217
日期:1991.2
An efficient optical resolution of γ-hydroxy vinylstannanes was achieved by the lipase-catalyzed enantioselective hydrolysis of the corresponding racemic acetates using lipase PS(Pseudomonas sp.).