Reactions of Quinolinecarbaldehydes with Arenes under Superelectrophilic Activation. NMR and DFT Studies of Dicationic Electrophilic Species

N , O -Diprotonated forms (dications) of various quinolinecarbaldehydes were theoretically studied by DFT calculations. It was found that the most reactive electrophilic dications are expected to be generated from 2- and 4-quinolinecarbaldehydes compared to the other quinolinecarbaldehydes. Experimental studies of protonation of quinoline-2(6,8)-carbaldehydes in Brønsted acids (CF 3 SO 3 H, H 2 SO 4 ) by means of 1 H, 13 C, and 15 N NMR revealed the formation of the corresponding N -protonated O -protosolvated species. Reactions of quinoline-2(6,8)-carbaldehydes with arenes in the presence of Brønsted (TfOH) and Lewis acids (AlX 3 , X = Cl, Br) or acidic zeolites led to the formation of the corresponding 2(6,8)-(diarylmethyl)quinolines. However, 6- and 8-quinolinecarbaldehydes gave additionally unusual products – 6(8)-(arylmethyl)quinolines.