Cyclic diketo sulfides 4 (n= 3-8, lO) were condensed with glyoxal to give thiophenophanediones 6. The NMR, IR, and UV spectral data of 6 are consistent with the following picture. The thiophene-2, 5-dicarbonyl moiety in 6 (n= 10) is in the mean molecular plane and, unlike the corresponding open chain compounds, in an O, S, O trans, trans conformation. As n decreases, the benzene rings gradually become face-to-face as ...