The chemistry of triterpenes and related compounds. Part XLV. The acid-catalysed rearrangements of the 5α,6α-diols and 5,6-epoxides of some 4,4-dimethylsteroids

Abstract

A number of 5,6-diols and -epoxides in the 4,4-dimethyl-chlolestane and -androstane series have been prepared and their reactions under acidic conditions studied. Different products are obtained from the diols and the epoxides and, as expected, the type of oxygen function at C-3 influences the nature of the products formed.

Dehydration of the 5α,6α-diol system with an acetate or hydroxyl group at C-3 gives 6-ketones of both the 5α and 5β series and also, with the 4,4-dimethyl-cholestane compounds, 4a-ketones of the A-homo-B-nor series (1).

In the case of the 5α,6α-epoxides the 3β-hydroxy-group participates in the rearrangement leading to methyl migration from C-4 to C-5 and eventually to the 6α-hydroxy-4,5-dimethyl-3-oxo derivatives (2). Such participation is obviated when a keto-group is present at C-3, and these 5α,6α-epoxides undergo a rearrangement involving the migration of the C(1)–C(10) bond with the formation of the spirans (3).

With the corresponding 5β,6β-epoxides cis C-10 methyl group migration predominates. [graphic omitted]