Pyrido[1′,2′:1,2]pyrimido[5,4-d]indoles. A new heterocyclic ring system

The preparation of the novel pyrido1′,2′:1,2]pyrimido5,4-b]indole ring system is described -via fusion at 180° of ethyl 3-amino-1H-indole-2-carboxylate 8a and several 6-chloronicotinic acid derivatives. Similar fusion of 8a and thiourea yielded a 2-mercaptopyrimido5,4-b]indole 18 .