Phenol Derivatives in Ruthenium-Catalyzed C-H Arylation: A General Synthetic Access to Azole-Based Congested Polyaromatics

Aryl triflates and related phenolates are suitable electrophile coupling partners for the ruthenium-catalyzed direct arylation of heteroaromatic substrates using azole N-directed C-sp(2)-H activation. We report herein convenient conditions for the efficient ortho-C-H functionalization of aryl-pyrazoles, thiazoles and pyridines in which [RuCl2(p-Cym)](2) precatalyst is employed with pivalic acid (PivOH) as co-catalyst. Different phenolate derivatives were successfully coupled, which tolerate a large scope of electron-rich substituents in para-, meta- and highly hindered ortho-position. Electron-withdrawing aryl triflates were found to be less reactive, making the general reactivity of these electrophiles complementary to those of aryl chlorides and deactivated bromides. This cost-effective ruthenium C-H activation/arylation synthesis of poly(hetero)aromatics was concurrently examined using triflates, mesylates, sulfonates, and carbonates, and was also successfully extended to the use of diethyl carbonate as an eco-friendly solvent.