PPA-mediated C-C bond formation: a synthetic route to substituted indeno[2,1-c]quinolin-6(7H)-ones.

A facile and efficient synthesis of substituted indeno[2,1-c]quinolin-6(7H)-ones from a variety of α-acyl N-arylcinnamamides mediated by polyphosphoric acid (PPA) is described, and a mechanism involving the formation of a dicationic superelectrophile and subsequent double intramolecular nucleophilic cyclization reactions is proposed.