Synthesis of 1,8-, 1,6- and 3,6-dichloro-9H-thioxanthen-9-ones

Cyclization of 2-chloro-6-(3-chlorophenyl)thio]benzoic acid ( 2 ) gave a mixture of 1,8-, 3 , and 1,6-dichloro-9H-thioxanthen-9-ones 4 . The mixture was converted to 1,8-diamino- 7 , and 1-amino-6-chloro-9H-thioxanthen-9-ones 8 , from which 3 and 4 were prepared separately, respectively. From a mixture of 4 and 3,6-dichloro-9H-thioxanthen-9-one ( 11 ) obtained by cyclizing 4-chloro-2-(3-chlorophenyl)thio]benzoic acid ( 10 ) was separated 11 by conversion of 4 to 8 .