An efficient, stereospecific synthesis of 25-hydroxy-7,8-dihydroergosterol, starting from the aldehyde 3 (7 steps, 30% overall) was developed. Key steps are the stereospecific displacement of an allylic carbamate by Li 2Cu 3 (CH 3γ 5 and the stereoselective reduction of a propargylic ketone by a chiral aluminum complex.