Cyanosilylation at pregnane side-chains. Selective synthesis and crystal structure of 20(R)-silylated cyanohydrins.

Trimethylsilylcyanide addition to different carbonyl moieties, i.e. saturated ketones, an enone and an aldehyde, at the steroid side-chain, was studied in the presence of a convenient catalyst. Depending on the nature of the carbonyl group, different outcomes were noticed. Saturated 20-keto pregnanes yielded epimerically pure silylated cyanohydrins, being the absolute configuration unambiguously established by X-ray crystallographic analysis.