Highly efficient Lewis acid catalyzed, one step conversions of 16α,17α-epoxy-3β-hydroxypregn-5-en-20-one to d-homosteroid and Δ13-steroids

Conversion of 16α,17α-epoxy-3β-hydroxypregn-5-en-20-one (1a) to 16β-chloro-3β,17α-dihydroxy-17β-methyl-17a-homoandrost-5-en-17a-one (3) in very high yields (95%), in one step by treatment with 3 equiv. of anhyd. AlCl3, has been achieved; use of two equiv. of AlCl3 affords mixture of d-homosteroid 3 (70%) and chlorohydrin 4 (27%). On the other hand, treatment of 1a with excess of acetic anhydride and anhydrous ZnCl2 at room temperature leads to reversal of the direction of epoxide ring opening with concomitant methyl migration, leading to 3β,16α-diacetoxy-17-methyl-17α-pregna-5,13-diene-20-one (6) in high yield (92 %). The conversions are a remarkable improvement over related routes in terms of both yield and selectivity.