The hitherto unknown angular benzo-9-thiafluorenes, 1∶2-benzo-9-thiafluorene (II) and 3∶4-benzo-9-thiafluorene (III) have been synthesized. The former was prepared starting from α-thionaphthol and 2-bromocyclohexanone. Condensation of these compounds gave 2-(α-naphthylmercapto) cyclohexanone (IV) which on cyclization and dehydrogenation gave (II). The constitution of (II) was proved by its unambiguous synthesis starting from 8-chloro-1-thionaphthol and 2-bromocyclohexanone. Starting from β-thionaphthol, (III) was prepared by similar steps. The constitution of (III) followed from its non-identity with 2∶3-benzo-9-thiafluorene.