The synthesis of the previously reported thianinhydrin (12) was achieved from 3-methylthiophene via the corresponding 5,6-dihydrocyclopenta[b]thiophen-4,6-dione (10). Conversion of 10 to the tricarbonyl (12) proceeded in good yield using dimethydioxirane oxidation of 5,6-dihydro-5-dimethyl aminomethylenecyclopenta[b]thiophen-4,6-dione (14). The fluorescence intensity of the zinc salt of the product of 12 and glycine was similar to that obtained from the product of ninhydrin and the same amino acid.