Free-radical cyclization approach to polyheterocycles containing pyrrole and pyridine rings.

A wide range of derivatives with new pyrido[2,1-]pyrrolo[3,4-]isoquinoline skeleton was synthesized by free-radical intramolecular cyclization of -bromophenyl-substituted pyrrolylpyridinium salts using the (TMS)SiH/AIBN system. The cyclization provides generally good yields of pyrido[2,1-]pyrrolo[3,4-]isoquinoline hydrobromides having no additional radical-sensitive substituents. The free bases can be obtained from the synthesized hydrobromides in quantitative yield by basification at room temperature.

Synthesis of Pyrrolotriazoloisoquinoline Frameworks by Intramolecular Cu-Mediated or Free Radical Arylation of Triazoles.

The cyclization of (2-bromophenyl)pyrrolyl-1,2,4-triazoles via copper-mediated intramolecular direct C-arylation of 1,2,4-triazoles was first accomplished under triazole-NHC control to give unknown fused heterocyclic skeletons, pyrrolo[3,2-c][1,2,4]triazolo[5,1-a] or [3,4-a]isoquinolines. The primary products underwent a triazole ring opening under the basic arylation conditions, providing N-(1H-pyrrolo[3,2-c]isoquinolin-5-yl)cyanamides. The formation of the cyanamides from isomeric pyrrolo[3,2-c][1,2,4]triazolo[3,4-a]isoquinolines involves, besides the triazole ring opening, the unusual migration of the cyano group.