Synthesis of a Novel Heterocyclic System - Pyrimido[5',4':5,6]thiopyrano [2,3-b]indole

An efficient protocol for the synthesis of pyrimido[5',4'p:5,6]thiopyrano[2,3-b]indoles by the cyclocondensation of 1,3-dihydro-2H-indole-2-thione with 6-chloropyrimidine-5-carbaldehydes has been developed. 4-Chloro-2- methylthiopyrimido[5',4':5,6]thiopyrano[2,3-b]indole was found to undergo smooth nucleophilic substitution with various nucleophiles to give 4-substituted pyrimido[5',4':5,6]thiopyrano[2,3-b]indoles.