Asymmetric Synthesis using Enantiomerically Defined alpha-Oxystannanes

点击翻译按钮获取中文摘要

The purpose of this work is to develop the new method for asymmetric synthesis using enantiomerically defined alpha-oxystannanes. A summary of the research results is as follow :(1) A new practical method for asymmetric synthesis of alpha-hydroxystannanesThe TiCl_4-promoted reaction of (4S,6S) - (4,6-dimethyl-1,3-dioxan-2-yl) tributylstannane with Grignard reagents is shown to sfford, after oxidation followed by base treatment, the (S) -alpha-hydroxystannanes in >95-20% ee.(2) Asymmetric [2,3] -Wittig rearrangementThe [2,3] -Wittig rearrangement of enantiomerically-defined alpha- (allyloxy) stannanes, prepared from (S) -1-tributylstannyl-1-propanol, with butyllithium is shown to proceed with essentially complete inversion of configuration at the Li-bearing migrating terminus.(3) Asymmetric [1,2] -Wittig rearrangementThe [1,2] -Wittig rearrangements of enantio-defined alpha-benzyloxypropyllithium and its (R) -alpha-methylbenzyloxy analogs, generated from the enantio-enriched stannanes via Sn/Li exchange, are shown to proceed predominantly with inversion of configuration at the Li-bearing terminus and retention of configuration at the migrating center, and exhibit a significant level of mutual enantiomer recognition in the radical recombination process.(4) Asymmetric carbolithiative cyclizationThe carbolithiative cyclization of enantiomerically-defined alpha-(homoallyloxy)stannane, with butyllithium is shown to proceed with complete retention of configuration at the Li-bearing center.