Competing pathway involved in allylic acetoxylation of androst-5-en-17-one, and oxidation of allylic alcohols with chromium oxides

Abstract

Allylic acetoxylation of androst-5-en-17-one ( 1 ) with bromine and silver acetate gave 6α- and 6β-acetoxyandrost-4-en-17-ones [ 4 (3%) and 5 (12%)] and 5α-bromo-6β-acetoxy steroid 8 (4%) along with the expected product 4β-acetoxy derivative 2 (45%). Treatment of 5α,6β-bromide 12 , an intermediate of the acetoxylation reaction, with silver acetate also produced the acetates 2, 4, 5, and 8 in relative yields similar to those above. These results indicate that the 6-acetates 4 and 5 are produced through a competing pathway involving formation of a bridged carbonium ion 13 followed by attack of an acetate anion. Oxidation of the axial allylic alcohol, 5-en-4β-ol 3, with Jones reagent yielded no trace of the previously reported androst-5-ene-4,17-dione ( 18 ) but instead gave a 1:4 mixture of 5β,6β-epoxy-4-one 16 and 4β,5β-epoxy-6-one 17 in high yield. In contrast, a 1:4 mixture of androst-4-ene-6,17-dione ( 10 ) and compound 18 was obtained upon treatment with chromium trioxide in pyridine. Similar results were also found with the oxidation of another axial allylic alcohol, 4-en-6β-ol 7 .