Base-catalysed intramolecular nucleophilic keto-group participation in the solvolysis of the hindered ester, 2-acetylphenyl mesitoate: acetal formation under basic conditions as a mechanistic consequence of such participation

Abstract

Under comparable conditions in aqueous ethanol the hindered ester, 2-acetylphenyl mesitoate (IV) was hydrolysed 130 times more rapidly than the 4-isomer (V) as a result of participation by the keto-carbonyl group. Such participation in anhydrous methanol was shown to result in the formation of the dimethyl acetal (IX) of 2-hydroxy-acetophenone under basic conditions and to support a mechanism involving intramolecular nucleophilic attack by the conjugate base of the solvated keto-carbonyl group upon the ester carbonyl group of the ester (IV). That this attack is, in part, rate determining, was shown by the much greater susceptibility to intramolecular cyclisation of the unhindered ester, 2-acetylphenyl benzoate (X).