“Back-to-Front” Indole Synthesis Using Silver(I) Catalysis: Unexpected C-3 Pyrrole Activation Mode Supported by DFT

An efficient silver(I)-catalyzed method is reported for the synthesis of substituted indoles, most notably 5-hydroxy-derivatives, via π-acidic alkyne activation. Most methods for the preparation of indoles involve annulation of a benzene precursor, but the method reported herein is unusual in that pyrrole precursors are used. Density Functional Theory (DFT) studies suggest that these reactions proceed via initial activation of the pyrrole C-3 position before undergoing subsequent rearrangement, contradicting the conventional wisdom that pyrroles are more nucleophilic through C-2.