Synthesis of 18-substituted steroids. Part III. Reactions of 18-substituted pregnan-20-ones
Abstract
An 18-acetoxy-substituent inhibits some of the usual reactions of the pregnan-20-one side chain, and causes preferential formation of the Δ17(20)-rather than the usual Δ20(21)-enol acetate with isopropenyl acetate. 20,20′-Anhydro-dimers can arise from an 18-hydroxypregnan-20-one in the 18 → 20-hemiacetal form. The formation and cleavage of 17β,18-cyclo-17α-pregnan-20-ones is described.