Geminal acylation of -heterosubstituted cyclohexanones and their ketals

Geminal acylation of derivatives of cyclohexanone with Br, Cl, F, and OCH 3 in the 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 BF 3 ·Et 2 O-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.