Abstract
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 asymmetric epoxidation, followed by the azide displacement of the tosyl group gave the epoxy azide 12. The asymmetric dihydroxylation of 12 with (DHQ) 2 -PHAL gave the triol 13 in good diastereoselectivity. Alcohol protection, followed by reductive double cyclization of the resulting 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 dihydroxylation of 12 provided a stereoselective preparation of 4
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