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 alpha,alpha-dibromo beta-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.

Automated summary

The additive-free copper(I)-bromide-mediated radical cyclization reactions of alpha,alpha-dibromo beta-iminoesters successfully enabled the synthesis of a series of 5- or 6-brominated 2-aryl-1H-indole-3-carboxylates in moderate to good yields. Mechanistic study revealed the bromine atom originated from the substrates and the bromination might be related to a 3-bromo-3H indole intermediate.