Synthesis of 20-oxo steroids

Article abstract of DOI:10.1002/recl.19921111102

The synthesis is described of a series of eighteen 16-dehydro-20-isocyano-20-sulfonylpregnanes (5 and 8-14) by C-20 alkylation of 17-androstanes 1-3.The geminal isocyano and sulfonyl groups at C-20 (compounds 5, 8-14) are removed by acid hydrolysis to provide a new entry into 20-oxo steroids (6, 15-19).The C-20 alkylation also includes halomethylation and alkoxymethylation to form 21-halo- and 21-alkoxy-16-dehydro-20-oxopregnanes, respectively.As an attractive alternative to acid hydrolysis, the isocyano group is first oxidized with Pb(OAc)4 to an isocyanato group prior to hydrolysis (of the geminal isocyanato and sulfonyl groups) to the same 20-oxo steroids.The latter conversion is carried out under non-acidic conditions at room temperature in a slurry of alumina in dichloromethane.