Lewis Acid-Catalyzed Nucleophilic Addition of Indoles to in Situ-Generated 2-Amidoallyl Cations.

We report herein the first Lewis acid-catalyzed generation of 2-amidoallyl cations through ring-opening of 4-benzylidene-2-oxazolines with Sc(OTf)3. Upon nucleophilic addition of indoles, indolylenamides were obtained with yields of 60-99% and excellent (Z)-selectivity. In addition, the novel strategy was also successfully applied to pyrroles and naphthols as π-nucleophiles. A Brønsted acid-catalyzed process using TfOH formed in situ was ruled out by control experiments.