Studies on the regioselectivity of the Baeyer-Villiger reaction of 3-keto steroids: Conformational effects determine the migration aptitude

A detailed study of the Baeyer-Villiger reaction of 3-ketosteroids has been performed by using m-chloroperoxybenzoic and trifluoroperoxyacetic acids as oxidants. The process was fully regiospecific for 3-keto-5α-steroids with the employ of both peracids, and only partially regioselective for 3-keto-5β-steroids by using trifluoroperoxyacetic acid. Interestingly, the reaction resulted completely unselective for 3-keto-5β-steroids by using m-chloroperoxybenzoic acid. Theoretical studies were performed to explain the regiochemistry of this process, which is suggested to be controlled by conformational effects in the transition state of the Criegee rearrangement.

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