Additive-Free Copper(I)-Mediated Synthesis of 5- or 6‑Brominated 2‑Aryl‑1H‑Indole-3-Carboxylates from α,α-Dibromo β‑Iminoesters

Additive-free copper­(I)-bromide-mediated radical cyclization reactions of α,α-dibromo β-iminoesters were investigated, enabling the synthesis of a series of 5- or 6-brominated 2-aryl-1H-indole-3-carboxylates in moderate to good yields. The mechanistic study showed that (i) the bromine atom originated from the substrates and (ii) the bromination might be related to a 3-bromo-3H indole intermediate via an electrophilic bromine atom transfer. Furthermore, the practicality of this method was demonstrated by gram-scale synthesis and the potential for product derivatization toward other valuable multisubstituted indoles.