D-Homo-steroids. Part IV. Acetolysis of D-homo-5α-androstan-17aβ-yl tosylate: a novel rearrangement involving the steroid backbone

Abstract

Buffered acetolysis of the title compound (5) gave the corresponding 17aβ-yl acetate (6), along with olefinic products, but unbuffered acetolysis additionally gave D-homo-5α,13α-androstan-17aα-yl acetate (10), with inversion at C-13. The inversion reaction appears to proceed through a series of carbocation and olefinic intermediates, derived from the 14(13 → 17a)abeo skeleton (7) by migration of unsaturation involving the steroid backbone. When the acetolysis was performed in acetic [²H]acid, the 13α-product contained up to 17 deuterium atoms.

Photoisomerisation of D-homo-5α-androstan-17a-one (15) gave the 17a-ketone (12) of the 13α-series in low yield.