Nucleophile-Controlled Trapping of Gold Carbene by Nitriles and Water: Synthesis of 5 H -Pyrimido[5,4- b ]indoles and 2-Benzylidene-3-indolinones.

A gold-catalyzed, nucleophile-controlled cascade reaction of N -(2-azidophenyl-ynyl)methanesulfonamides with nitriles and water is described that provides structurally diverse 5 H -pyrimido[5,4- b ]indoles and 2-benzylidene-3-indolinones in good to excellent yields. Mechanistic studies indicate that the β-sulfonamido-α-imino gold carbene is the key intermediate which is generated through the gold-catalyzed cyclization of N -(2-azidophenyl-ynyl)methanesulfonamides and undergoes formal [4 + 2] cascade annulation with nitriles and intramolecular S N 2' type reaction with water, respectively.