Intramolecular Interactions in Carbenes Derived During the Pyrolysis of N-Alkenylisoxazolones

Abstract

Flash vacuum pyrolysis of ethyl 3-(3-methyl-5-oxo-2,5-dihydroisoxazole-2-yl)-3-phenylpropenoate yields 4-ethoxy-3-hydroxy-2-methyl-5-phenylpyridine in addition to the expected pyrrole. The structure assignment is based on two-dimensional NMR and computational evidence. The pyrolysis of the corresponding dimethyl amide gives a mixture of three 3-hydroxypyridines, in addition to the pyrrole. Evidence is presented for the formation of intermediate 1,4-oxazepines by a six-electron electrocyclic reaction of a carbene with ester or amide carbonyl groups.