A CONCISE, ENANTIOSELECTIVE SYNTHESIS OF CASTANOSPERMINE

A stereoselective synthesis of the polyhydroxy indolizidine alkaloids castanospermine (1) and 6,7-diepicastanospermine (4) has been achieved starting from the readily available alcohol 8. Subsequent Sharpless a symmetric epoxidation, followed by the azide displacement of the tosyl group gave the epoxy azide 12. The asymmetric dihydroxylation of 12 w ith (DHQ)2-PHAL gave the triol 13 in good diastereoselectivity. Alcoho l protection, followed by reductive double cyclization of the resultin g epoxy azide 17 gave 5-indolizidinone 18, which was then uneventfully converted to 1. On the other hand, the use of (DHQD)2-PHAL in the dih ydroxylation of 12 provided a stereoselective preparation of 4.