A novel route to geminal dibromocyclobutanes: Syntheses of 2-substituted cyclobutanone acetals and their reaction with boron tribromide

Nine 2-substituted cyclobutanone acetals, in addition to the parent cyclobutanone acetal, were synthesized from their corresponding cyclobutanones and subsequently treated with boron tribromide. The substituents were either alkyl chains or a phenyl and a benzyl group, respectively. The major compounds obtained in these reactions were, in most cases, the geminal dibromocyclobutanes which were obtained in yields between 50 and 73%. A 2-fold excess of BBr3 and a reaction time of 3 h at -78 degreesC afforded the best yields. In four cases no dibromide formation was observed at all, and the cyclobutanone acetals were hydrolyzed to the corresponding cyclobutanone. This is probably due to increased steric hindrance of the acetal and BBr3 in the transition state.