On Cardioactive Steroids. XVI. Stereoselective β‐Glycosylation of Digitoxose: The Synthesis of Digitoxin

Two methods for stereoselective β‐glycosylation of digitoxose were developed. The first achieved stereocontrol by a 1,3‐participation of a N ‐methylurethane group under acid catalysis. The second utilized mercuric‐ion catalyzed cleavage of thioglycosides and a 1,3‐participation of a p ‐methoxybenzoyl group in a neutral medium. The first highly stereoselective and quite efficient synthesis of digitoxin ( C7 ) was achieved by a combination of these methods. The furyl‐substituted precursor IV of digitoxigenin ( Scheme 1 ) was used as aglycone, and the furan group was converted to the unsaturated lactone of digitoxin by our known oxidation procedure ( m ‐chloroperbenzoic acid/NaBH 4 ) after the assembly of the carbohydrate portion of the molecule and its deblocking was completed.