Improved Preparation of (3β,5α,14α)-3-Hydroxy-14-methylcholest-7-en-15-one. Synthesis of Ergostenone and 20a-(Hydroxymethyl)pregnenone Analogues

Reexamination of the synthesis of (3β,5α,14α)-3-hydroxy-14-methylcholest-7-en-15-one has led to an improved, large-scale preparation of this ketone. Noteworthy is the controlled outcome of a solvent effect observed during the pinacol-type rearrangement of vinyl epoxide 18 and the use of the ethoxyethyl ether protecting group at the C3 alcohol during alkylation. Preparative-scale routes to ergostenone derivatives 3 and 4 and pregnenone analogue 5 are described.