Aspects of tautomerism. Part 15. Investigations on oxo-participation in δ-oxocarboxylic acid chlorides during their formation and alcoholysis

Abstract

Oxalyl chloride converts ring-substituted 4-benzoylbutyric acids into a mixture of normal and pseudo-acid chlorides by two independent and competing pathways. Pseudoacid chlorides are formed by a concerted 2_σ+ 2_π+ 2_σ pathway. It is suggested that the reaction of acid chlorides with a poor nucleophile involves a transition state wherein the attacking nucleophile and the departing group make an angle of ca. 45 ° to the plane of the carbonyl group. There is evidence against involvement of any common transition state or an equilibration process during the formation of normal and pseudoacid chlorides. Alcoholysis of normal acid chlorides derived from the above mentioned acids does not involve oxo-participation.