치환된 Silylpropargylic Alcohol의 Ortho Ester Claisen 재배열반응의 입체 선택성에 관한 연구

Abstract

The ortho ester Claisen rearrangement has been very useful synthetic methodology in organic synthesis. The ortho ester Claisen rearrangement of the propargylic alcohols has been very effective method for producing the corresponding allene esters of biologically significant. Particularly the rearrangement involving a β-substituted vinyl participant is a potentially powerful reaction because a diastereomeric allene product may be generated. However, only one example yielding 1,3-disubstituted allenes by ortho ester Claisen rearrangement has been examined using substituted secondary propynyl alcohols by Heathcocks group. His group was able to obtain high stereoselectivity (80-90% of the syn selectivity) of the rearrangement of the propynyl alcohol bearing a bulky alkyl group at C-1 position. The results are noteworthy due to the fact that the diastereoselectivity of the ortho ester Claisen rearrangement is generally moderate or poor because the mixture of E and Z of the vinyl moiety of the intermediate ketene acetal may be generated. 2c,4 The ortho ester Claisen rearrangement of substituted silylpropargylic alcohols might be an efficient route to obtain the stereo-defined substituted silylallenes which has been very useful intermediates in organic synthesis. Therefore, the study on the rearrangement of the 1-alkyl-3-silylpropynol 2 leading to the 1,3-disubstituted silylallenes 3 is reported in this paper.