Boron trifluoride catalyzed lead tetraacetate oxidation of 30-acetoxy-2O-oxo-oa-pregnane and of pregnenolone acetate was employed to obtain the corresponding 21-acetoxy derivatives. Reaction of 3β,21-diacetoxy-20-oxo-5a-pregnane (1) with the anion prepared from diethyl cyanomethylphosphonate and subsequent treatment with hydrochloric acid afforded the corresponding nitrile (2) and derived imino lactone hydrochloride (3a). Acid hydrolysis of the imino lactone gave 3β-acetoxy-5<x-cardenolide (4b). Analogous transformation of ketone 6 provided 3β-acetoxy-A6-cardenolide (10b). The two-step reaction sequence from readily available a-hydroxy ketones provides a potentially useful route to imino lactones and butenolides.
ASJC Scopus subject areas
- Organic Chemistry