Superacid-Catalyzed Reaction of Substituted Benzaldehydes with Benzene

Benzaldehydes bearing an electron-withdrawing group reacted with 2 equiv of benzene in the presence of a superacid, trifluoromethanesulfonic acid, to give substituted triphenylmethane in good yields. On the other hand, benzaldehydes bearing an electron-donating or a neutral group reacted under the similar conditions to give unsubstituted diphenylmethane and triphenylmethanol, together with substituted benzene. We propose a new mechanism of this reaction, which involves transalkylation as the key step.