The Gewald syntheses were employed to prepare a series of 2-amino-3-carboethoxythiophenes, and the syntheses of two of these, namely, the 3,4-trimethylene (If) and 3,4tetramethylene (Ig) derivatives, were examined in detail. In two preparations of If, octahydro-6a~4morpholinyl~2-thioxocyclopent~~]pyrro~e~3-carboxylic acid (7) was a co-product. The structure of 7 was ascertained from its 300 MHz 'H nmr and 'X nmr spectra, and by its conversion to 1,4,5,6-tetrahydro-2-mercaptocyclopent~~]pyrrole-3-carboxylic acid ethyl ester (8). Isolation of 7 and other observations led to postulated mechanisms for three of the Gewald thiophene syntheses.