Abstract
An efficient synthetic method of bufa-20, 22-dienolides from 20-ketopregnanes has been developed. The method involves the following reaction sequence : (1) 21-methoxy-methylenation, (2) 2-methoxydihydropyrane formation by reaction with excess dimethylsulfonium methylid, (3) transformation to buf-20 (22)-enolide structure, (4) dehydrogenation to bufa-20, 22-dienolide. Application of this attractive device to readily available 3β-acetoxy-5β-pregn-14-en-20-one established a new route to resibufogenin and bufalin.
