Cyclization of 2-alkynylanilines in the presence of NaAuCl4·H2O using [bmim]BF4 as the reaction medium afforded 2-substituted indoles in high yields. The catalyst system was best recycled using n-Bu4NAuCl4. 2,3-Disubstituted indoles could be prepared from 2-alkynylanilines and 3-buten-2-one through a one-flask annulation-alkylation sequence and 1,2,3-trisubstituted indoles were obtained from the same starting materials via an aza-Michael addition-annulation-alkylation process.
Gold(III)-catalyzed annulation of 2-alkynylanilines in EtOH or EtOH-water mixtures at room temperature gives indoles derivatives in good yields. One-flask protocol for the gold-catalyzed conversion of 2-alkynylanilines to 3-bromo and 3-iodoindoles is also reported.