The synthesis and chemistry of azolenines. Part 2. A general synthesis of pyrrole-2-carboxylic acid derivatives by the reaction of 2H-azirines with enamines, and the crystal and molecular structure of ethyl 3-phenyl-4,5,6,7-tetrahydroindole-2-carboxylate
A new general synthesis of 1H-pyrrole-2-carboxylic acid derivatives is described. Reaction between appropriately substituted 2H-azirines and enamines gives a mixture of 2,3- and 3,4-dihydropyrroles, which on acid treatment yields the title compounds in moderate to high yields. Attempts to extend the reaction to the preparation of 2H- and 3N-pyrroles were unsuccessful; reasons are discussed. The crystal and molecular structure of ethyl 3-phenyl-4,5,6,7-tetrahydroindole-2-carboxylate has been determined. The molecules pack in highly coplanar, centrosymmetric, hydrogen-bonded pairs.