Geminal acylation of α-heterosubstituted cyclohexanones and their ketals

Geminal acylation of derivatives of cyclohexanone with Br, Cl, F, and OCH3 in the α position, and of their corresponding dimethyl ketals, could not be accomplished to a significant extent following published procedures. The transformation was accomplished in two steps. The initial BF3·Et2O-mediated reaction with 1,2-bis(trimethylsilyloxy)cyclobutene gave a cyclobutanone product as a mixture of diastereomers. Only with 2-chlorocyclohexanone did this occur with good diastereoselectivity. Then, pinacol rearrangement of the diastereomeric mixture mediated by Amberlyst-15 in benzene provided the heterosubstituted spirocyclic diketone.