Gold-Catalyzed Conversion of Aryl- and Alkyl-Substituted 1-(o-Aminophenyl)-2-propyn-1-ones to the Corresponding 2-Substituted 4-Quinolones

Gold-catalyzed cyclization of alkyl-or aryl-substituted 1-(o-aminophenyl)-2-propyn-1-ones to the corresponding 2-substituted 4-quinolones was studied with various gold salts and complexes. Screening of the different catalysts showed highest performance with cationic Au-I species. In particular PPh3AuNTf2 complex was the most efficient catalyst. Relative to classic quinolone synthesis that requires harsh cyclocondensation conditions, the current method offers a mild and atom-economic alternative. Mechanistically, DFT studies at TPSS-D3/def2-TZVP level suggest that gold operates in an alkynophilic manner rather than through conjugative carbonyl activation.