Stereoselective Cyclopropylmethylation Reactions of Homoallylstannanes with Carbon Electrophiles
摘要:
The reactions of homoallylstannanes with acetals, aldehydes, and acyl chlorides in the presence of a Lewis acid proceeded smoothly to give the corresponding cyclopropylmethylated products. The reactions of E-3-pentenylstannane with aldehydes were stereoselective and gave the erythro products predominantly. A mechanism involving antiperiplanar attack is suggested. The stereoselectivity of the Z isomer was, however, not high. (C) 2000 Elsevier Science Ltd. All rights reserved.
Evaluation of the Relative Magnitude of the<b><i>β</i></b>-Effect of Silicon and the<b><i>γ</i></b>-Effect of Tin by Intermolecular Competition
作者:Masanobu Sugawara、Jun-ichi Yoshida
DOI:10.1246/bcsj.73.1253
日期:2000.5
The relative magnitude of the β-effect of silicon and the γ-effect of tin was evaluated by intermolecular competition. An acetal was allowed to react with a 1 : 1 mixture of an allylsilane and a homoallylstannane in the presence of TMSOTf (trimethylsilyl trifluoromethanesulfonate); the former was found to be more reactive than does the latter, indicating that the β-silyl group activates the carbon-carbon double bond more effectively than the γ-stannyl group. This is consistent with the results of molecular-orbital calculations which indicate that the HOMO level of the allylsilane is higher than that of the homoallylstannane. The intermolecular competition between a homoallylstannane and a terminal alkene toward electrophilic reactions with an acetal have revealed that the former is more reactive than the latter. This result indicates that the stannyl group at the γ-position definitely activates the carbon-carbon double bond toward electrophiles.
Reactions of homoallylstannanes with carbon electrophiles: stereoselective cyclopropylmethylation based on the γ-effect of tin
作者:Masanobu Sugawara、Jun-ichi Yoshida
DOI:10.1039/a900228f
日期:——
Homoallylstannanes reacted with carbon electrophiles such as acetals, acid chlorides and aldehydes in the presence of Lewis acids to give the cyclopropylmethylated products with high stereoselectivities.
Stereoselective Cyclopropylmethylation Reactions of Homoallylstannanes with Carbon Electrophiles
作者:Masanobu Sugawara、Jun-ichi Yoshida
DOI:10.1016/s0040-4020(00)00389-6
日期:2000.6
The reactions of homoallylstannanes with acetals, aldehydes, and acyl chlorides in the presence of a Lewis acid proceeded smoothly to give the corresponding cyclopropylmethylated products. The reactions of E-3-pentenylstannane with aldehydes were stereoselective and gave the erythro products predominantly. A mechanism involving antiperiplanar attack is suggested. The stereoselectivity of the Z isomer was, however, not high. (C) 2000 Elsevier Science Ltd. All rights reserved.