In connection with one of the projects in this Laboratory a number of 2, 3-and 3, 4- dicarboxylic acids of furan, pyrrole and thiophene were desired. Although several of the dicarboxylic acids of this group are known, the methods of preparation are generally difficult and unsatisfactory. Recently a convenient synthesis of the 3, 4-dicarboxylic acids like I was described involving as intermediates the potential 1, 4-dicarbonyl esters 11.'
