Synthesis of 6,7,8,9-tetrahydropyrido[2,3-b]indolizine and 3,4-dihydro-2H-pyrido[2′,3′:4,5]pyrrolo[2,1-b][1,3]oxazine derivatives as new melatonin receptor ligands

The synthesis of new tricyclic azaindolic analogs of the hormone melatonin is described. Treatment of 1-(4-bromobutyl)pyrrolo[3,2-b]pyridine derivative with tributyltin hydride and AIBN results in radical cyclisation to give the 6,7,8,9-tetrahydropyrido[2,3-b]indolizine ring system. A new synthetic approach of pyridopyrrolo[2,1-b][1,3]oxazine moiety is shown to be accomplished readily from 1-(3-bromopropyl)-2-oxopyrrolopyridine derivative with sodium hydride in N,N-dimethylformamide.