Copper-Mediated Halocyclization Route to 3-Haloindoles

Significance

Reported is the synthesis of 3-­chloro- and 3-bromoindoles utilizing a modification of a previously reported procedure (S. Tang, Y.-X. Xie, J.-H. Li, N.-X. Wang Synthesis 2007, 1841). In comparison to that procedure, the modification consists of adding base to the mixture, changing the solvent (DCE → DMSO) and the N-protecting group (Ac → Ms, Ts). The methods complement each other to some extent, as in the present method when R^² = Ac (or H), no reaction occurs. Furthermore, the reaction is unsuccessful when R^¹ = TMS. Both chloro- and bromoindoles were prepared in high yields except when R^¹ = H, which led to a drastic decrease in yield (22%). The substrate scope was poorly studied in terms of ­aromatic ring substitution.