REGIO-SELECTIVE ULLMANN SYNTHESIS OF 4-BROMO-3-METHYL-5-PROPOXY-THIOPHENE-2-CARBOXYLIC ACID

摘要

This invention is directed to a two step regio-selective Ullmann synthesis of 4-bromo-3- methyl-5-propoxy-thiophene-2-carboxylic acid compound of formula 16 comprising the steps of brominating 3-methyl-thiophene-2-carboxylic acid to yield 4,5-dibromo-3-methyl- thiophene-2-carboxylic acid in appropriate bromination organic solvent, and then effecting the selective Ullmann coupling of the 4,5-dibromo-3-methyl-thiophene-2-carboxylic cid with alkali metal propoxide salt using copper catalyst in propanol to yield the compound of formula 16.