Selective synthesis of indazoles and indoles via triazene–alkyne cyclization switched by different metals?

Organic & Biomolecular Chemistry Pub Date: 2013-12-03 DOI: 10.1039/C3OB42088D

Abstract

We described two orthogonal heterocycle syntheses, where an arene bearing both an alkyne and a triazene functionality underwent two distinct cyclization pathways mediated by different transition metals. Starting from the same substrates, a synthesis of 2H-indazole was accomplished by a Cu(II) salt promoted oxidative cyclization, while 2-substituted indoles could be accessed via a Ag(I) salt mediated N–N bond cleavage. This method represents the first synthesis of indoles from alkynyl triazenes. Computational analysis was performed for both reaction pathways, supporting a Lewis acid role for Cu and a π-acid catalysis for Ag.

Graphical abstract: Selective synthesis of indazoles and indoles via triazene–alkyne cyclization switched by different metals
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