Abstract
Efficient routes for the preparation of selected C-23 and C-24 diastereomers of the C 30 biological markers 4α-methyl-5α-stigmastane (1) and 5α-dinosterane (2) involved the alkylation of 20-(iodomethyl)-4α-methyl-5α-pregnane with either saturated or α,β-unsaturated esters. The alkylation of (20S)-20-(iodomethyl)-4α-methyl-5α-pregnane with methyl (3R)-3-ethyl-4-methylpentanoate furnished methyl (20R,23ζ,24S)-4α-methyl-5α-stigmastane-23-carboxylate, and a subsequent decarbomethoxylation provided (20R,24R)-1. The alkylation of (20S)-20-(iodomethyl)-4α-methyl-5α-pregnane with methyl (3S)-3,4-dimethylpentanoate led to methyl (20R,23ζ,24R)-4α,24-dimethyl-5α-cholestane-23-carboxylate, and reduction of this mixture provided principally (20R,23S,24R)-5α-dinosteran-29-ol. The further reduction of the mesylate of this isomer secured (20R,23S,24R)-5α-dinosterane
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