Total Synthesis of Pyrrolnitrin. II. Synthesis of Ethyl 3-Aryl-5-methyl-2-pyrrolecarboxylate. (1)

Abstract

Ethyl 3-aryl-5-methyl-2-pyrrolecarboxylate (XXIII), a desirable intermediate for chlorination to prepare pyrrolnitrin, was derived from ethyl 3-aryl-5-methyl-4-pyrrolecarboxylate (I) by following two routes. At first, it was undertaken to introduce a second ester group to the 2-position of I before the first ester group at the 4-position of I was eliminated. Then the first ester group was hydrolysed selectively and the resulting carboxyl group was removed by decarboxylation. Secondly, the ester group of I was eliminated at first, affording 3-aryl-5-methylpyrrole (XIV). Introduction of an ester group to 2-position of XIV was carried out successively by two methods via a cyano group or a carbonyl chloride group.