Synthesis and isomerization of 19-hydroxy-5β,19-cyclosteroids

Abstract Synthesis of 19(R/S)-hydroxy-5β,19-cycloandrostane-3,17-dione by reductive cyclization of the steroid 4-en-3-one 19-aldehyde with zinc in aqueous acetic acid is reported. On either acid or base treatment the R-isomer is converted to the S-isomer through an intermediate 3-hydroxy-3,5-cyclosteroid.