A Concise Synthesis of Castanospermine by the Use of a Transannular Cyclization

摘要

A nine-step synthesis of (+)-eastanospermine has beenaccomplished in 22% overall yield from methyl a-o-gluco-pyranoside. The key transformations involve a zinc-mediatedfragmentation of benzyl-protected methyl 6-iodoglucopyra-noside, ring-closing olefin metathesis, and strain-releasetransannular cyclization to afford the indolizidine skeletonof the natural product.