Reactions of acyloxiranes with aliphatic ketones

Acyloxiranes react with aliphatic ketones in the presence of boron trifluoride etherate to give the corresponding 4-acyl-1,3-dioxolanes. The corresponding 4,5s-dimethyl-4r-acetyl-1,3-dioxolanes are formed in this case from 2,3t-dimethyl-2r-acetyloxirane, whereas a mixture of cis- and trans-1,3-dioxolanes is formed from trans-2-acetyl-3-phenyloxirane and acetone. The reaction of acyloxiranes with unsymmetrical ketones gives a mixture of the cis- and trans-1,3-dioxolanes with respect to the substituents attached to C-2 relative to the acetyl group, whereas the isomer ratio in this case depends on the effective volumes of the substituents attached to C-2.