Nuclear magnetic resonance investigations of carbonium ion intermediates. Part IV. Study of the intermediates involved in the reaction between carboxamides and Lewis acids (extended Vilsmeier reaction) by 1H and 13C nuclear magnetic resonance spectroscopy

Abstract

Structural and dynamic 1H and 13C n.m.r. spectroscopy have been used to study the reaction between N-substituted carboxamides and Lewis acids. The complex kinetics are explained by the formation of new intermediates and selfcondensation compounds whose structure is demonstrated by 13C n.m.r. Hindered rotations around C–N bonds in the starting materials are also measured by 1H and 13C resonance with a view to discussing the nucleophilicity of carboxamides. A second-order exchange reaction is shown to occur in alkyl-substituted iminium salts and activation parameters are computed.