Reaction of o-carboxyphenyl sulfoxides with acetic anhydride : Kinetic studies on the neighboring group effect of ortho-carboxyl group in the oxygen exchange and Pummerer reactions

Abstract

Kinetic studies on the concurrent oxygen exchange and racemization reactions and Pummerer reaction of o-carboxyphenyl sulfoxides with acetic anhydride were carried out. In the reaction of o-carboxyphenyl phenyl sulfoxide, ortho-carboxyl group was found to enhance the rates of both oxygen exchange and racemization about 180 times, and the rate of racemization was nearly twice that of oxygen exchange. In the reaction of alkyl o-carboxyphenyl sulfoxides, an intramolecular Pummerer reaction took place to give 3,1-benzoxathian-4-one derivatives, and the Pummerer reaction was accelerated about 140 times that of the usual unassisted Pummerer reaction of aryl methyl sulfoxide. A very small deuterium kinetic isotope effect (k H/k D = 1.07 with trideuterated-methyl o-carboxyphenyl sulfoxide) and the rate-enhancing effect of α-alkyl group were also noticed. The markedly large rate-enhancement of both oxygen exchange and the Pummerer reactions is undoubtedly caused by the neighboring group participation of carboxyl group in the rate-determining intramolecular acylation of sulfinyl O atom.