4,5-erythro/5,6-threo-Stereoselectivity in vinylogous Mukaiyama aldol addition of a silyloxypyrrole to a threose derivative:stereochemical rationalization and relevance to (+)-castanospermine synthesis

摘要

Vinylogous Mukaiyama aldol addition of N-p-methoxybenzyl-4-methoxy-2-trimethylsilyloxypyrrole 7 to bis-MOM threose 6 using SnCl4 as promoter gave the 4,5-erythro/5,6-threo adduct 8,with the correct absolute configurations for the castano-spermine framework as determined by a single-crystal X-ray structure.A transition-state model is presented to rationalize the stereoselectivity.