Zinc Halide Mediated Synthesis of 3-Amidoindoles

Significance

Reported is the zinc halide mediated synthesis of 3-amidoindoles through a domino alkyne amination-Fischer indole sequence. The majority of the substrate scope was performed using N-acyl propargylamine, but examples using other N-substituted propargylamines were shown to perform well under a subtle change of conditions. For each example two sets of conditions are shown. It is not clear whether more conditions were examined or if there was a rationale behind choosing these conditions. In contrast to the known instability of many 3-aminoindole products, the obtained compounds are reported to be crystalline stable materials which are easily handled. This process constitutes a complementary route to the synthesis of hydrazone intermediates for the Fischer indole reaction and, in view of the ready availability of alkynes, promises to find broader utility.