Abnormal Beckmann rearrangement of steroidal α-chlorocyclobutanone oximes: the fragmentation–substitution reaction

α,α-Dichlorocyclobutanones of various substitution patterns, readily available by the thermal cycloaddition of dichloroketene to steroid olefins, were selectively dehalogenated and further transformed to α-chlorocyclobutanone oximes. In contrast to the Beckmann rearrangement of the α-unsubstituted oximes, α-chlorocyclobutanone oximes, on treatment with thionyl chloride in benzene, gave normal and abnormal reaction products. In all reactions studied, the Beckmann fragmentation–substitution was the major process. The rearrangement of α-chlorocyclobutanone oximes is the key step of the novel method for geminal functionalization of carbonyl carbon atom in ketones and regioselective vicinal functionalization of unsymmetrical olefins. The regiochemistry observed in the rearrangements is supported by semiempirical calculations (AM1).