Reactivity of the ester group attached isoxazoline, benzisoxazole, and isoxazole: a facial preparation of 3-acyl-substituted these heterocycles

A facile preparation of 3-acyl-substituted isoxazolines, benzisoxazoles, and isoxazoles from the corresponding 3-carboxylate esters is described. The process, involving reaction of the ester derivative of 3-carboxylic acid substituted heterocycles with Grignard or alkynyl lithium reagents, leads to direct generation of the corresponding 3-acyl heterocycle. The presence of α-imino ester moieties in the heterocyclic substrates for the reactions is thought to be a key feature governing the nature of these transformations. The synthetic utility of the new methodology is demonstrated by its application in a two-step route for the preparation of novel linked bis-heterocycles.