Ruthenium-Sulfonamide-Catalyzed Direct Dehydrative Condensation of Benzylic C–H Bonds with Aromatic Aldehydes

The first catalytic dehydrative condensation of the benzylic C–H bonds of toluene and p-xylene with aromatic aldehydes is reported herein. This protocol provides highly atom-economical access to stilbene and p-distyrylbenzene derivatives, whereby water is the sole byproduct. The reaction is based on the deprotonation–functionalization of benzylic C–H bonds through η6-complexation of the arenes, which is realized for the first time using a catalytic amount of a transition metal activator. The key to the success of this method is the use of a sulfonamide anion as a catalyst component, which appears to facilitate not only the deprotonation of the benzylic C–H bonds but also the formation of a C–C bonds via an electrophilic tosylimine intermediate.