The synthesis of the 12-methyl derivative of a novel hcterocyclic ring system, namely benzo[h][l]benzothi­eno[2,3-c][1,6]naphthyridine (8) was prepared by photocyclization of 3-chloro-N-(2'-methyl-4'-quinolyl)benzo­[h]thiophene-2-carboxamide (5) to 12-methylbenzo[h][1]benzothieno[2,3-c][1,6]nalththyridin-6(5N}one(6).Chlorination of 6 afforded 6-chloro-12-methylbenzo[h][1]benzothieno[2,3-c][1,6]naphthyridine (7) which upon dechlorination provided the novel title compound 8.