A new synthesis of a steroid side chain via stereocontrolled protonation: synthesis of (–)-desmosterol
Abstract
Protonation of the lactone enolate (9), obtained from the 20-cyano-steroid (3) and (R)-benzyl 2,3-epoxypropyl ether (6), with saturated aqueous sodium sulphate proceeds in a highly steroselective manner from the less hindered side to give the (20R)-lactone (10) which can be converted into the (20R)-steroid, desmosterol (17).