A synthesis of C-23 and C-24 diastereomers of 5α-dinosterane

Stereoselective routes for the preparation of C-23 and C-24 diastereomers of the C₃₀ biological marker, 5α-dinosterane (1), involved the alkylation of (20S)-20-(iodomethyl)-4α-methyl-5α-pregnane (7) with either a saturated ester, methyl 3,4-dimethylpentanoate (9), followed by reduction to give principally the erythro-diastereomers or the alkylation of 7 with an α,β-unsaturated ester, methyl 3,4-dimethylpentenoate (12), followed by reduction to give principally the threo-diastereomers.