The terthiophenes in which thienyl groups are attached to the 2-and 3-positions of a central thiophene ring undergo oxidative photocyclization to benzotrithiophenes. A single product, unsymmetrical benzotrithiophene 5, was obtained from 2, 2': 3 ', 2”-and 2, 2': 3', 3''- terthiophenes, and its symmetrical isomer 6 from 2, 3': 2', 3''-terthiophene. However, a mixture of these two products was produced by irradiation of 3, 2 ': 3 ', 3 “-terthiophene, ...