Acetolysis of Cyclic Acetals: Regioselective Acylative Cleavage of Cyclic Formals

Article abstract of DOI:10.1021/jo00199a040

The acid-catalyzed reaction of cyclic acetals with acetic anhydride has been investigated.Acylative cleavage of cyclic formals has been found to be a clean, high-yield reaction involving rupture of the C(2)-O bond with loss of stereochemical integrity at the C(2)-position to give hemiacetal acetate products.Ring cleavage of unsymmetrically substituted cyclic formals with either acetic anhydride or acetyl chloride occurs via preferential rupture of the less congested C(2)-O bond (Scheme I, path A).Such cleavage is totally regiospecific for 1,3-dioxanes and displays high (75-85percent) regioselectivity for smaller and larger ring systems.Acetolysis of cyclic acetals other than formals is a slow process that leads to loss of the aldehyde derived fragment and formation of simple diacetates.These results are rationalized in terms of rate-limiting electrophilic attack that is acutely sensitive to steric effects engendered by substituents located at positions adjacent to ring oxygens.