A Study of Some Thiophene Analogues of Glycolic Acid

Article abstract of DOI:10.1021/jo00327a009

Reaction of phenyl(3-thienyl)glycolic acid (1) with AlCl3 in benzene solution leads to the formation of 4H-indeno<1,2-b>thiophene-4-carboxylic acid (2) whereas analogous reaction of phenyl(2-thienyl)glycolic acid (4) produces no indenothiophene but only a mixture of 5 and 6.In the case of di-(2-thienyl)glycolic acid (14b) and di-(3-thienyl)glycolic acid (16b) analogous results are obtained, with the former leading to the formation of 15 and the latter producing 17.In the case of the (benzothienyl)phenylglycolic analogues of 1 and 4 the acids were unstable to heat so that the esters, ethyl (2-benzothienyl)phenylglycolate (21) and ethyl (3-benzothienyl)phenylglycolate (20), upon treatment with AlCl3 in benzene led to cyclized products only.The former gave 23 which was saponified and decarboxylated to yield 25 and compared with an authentic sample obtained by synthesis.Ester 20 similarly gave 22 which was similarly converted to the known 24.A mechanistic explanation of these findings is proposed.