Cupric Halide‐Mediated Intramolecular Halocyclization of N‐Electron‐Withdrawing Group‐Substituted 2‐Alkynylanilines for the Synthesis of 3‐Haloindoles

A convenient and efficient method for the synthesis of 3‐haloindoles has been developed. Both 3‐chloro‐ and 3‐bromoindole derivatives can be obtained in high yields by the reaction of N‐electron‐withdrawing group‐substituted 2‐alkynylanilines with cupric halide in dimethyl sulfoxide (DMSO) within a short period of time. Investigation of the reaction mechanism reveals that two equivalents of cupric halide are necessary.