Synthesis of Orthogonally Protected Angular Nitrogen Polyheterocycles via CpCo-Catalyzed Pyridine Formation

Abstract

Unprecedented nitrogen polyheterocycles have been prepared by means of intramolecular Co-catalyzed [2+2+2] cycloaddition of two alkynes to one nitrile. They exhibit two nitrogencontaining rings fused in an angular fashion to one pyridine unit. Several relative positions of the nitrogen atoms have been studied, giving rise to eight different new scaffolds. In order to allow selective functionalization of the two amino groups, orthogonal protecting groups (PG 1 and PG 2 ) were introduced prior to cyclization. Eleven combinations of seven different protecting groups (Bn, COCF 3 , Cbz, Boc, Ts, SO 2 -2-py, Ns) were tested, most of them being perfectly tolerated under the cyclization conditions.