Benzofuran and indole synthesis via Cu(i)-catalyzed coupling of N-tosylhydrazone and o-hydroxy or o-amino phenylacetylene

A general and practical method to synthesize 2-substituted benzofurans and indoles is described. This method employs easily accessible N-tosylhydrazones and o-hydroxy or o-amino phenylacetylenes as substrates. The reaction proceeds through a CuBr-catalyzed coupling–allenylation–cyclization sequence under ligand-free conditions.