Selective reactions using N-(tert-butoxycarbonyl)-2-(tert-butyldimethylsiloxy)pyrrole: concise asymmetric syntheses of (+)-1-deoxy-8-epi-castanospermine and its enantiomer

Advantage being taken of the versatility of the siloxydiene TBSOP in asymmetric synthesis, (6S,7R,8S,8aR)-6,7,8-trihydroxyindolizidine 11 has been assembled from the L-threose derivative 1 in six or eight steps in 22-30% overall yield. Pivotal to the success of this total synthesis venture is the ready availability of unsaturated lactam 2 with complete stereocontrol. As a corollary, the synthesis of the known indolizidine enantiomer ent-11 confirms the feasibility of the procedure. The structure of compound 5 has been determined by X-ray crystallography.