Phenol Derivatives in Ruthenium-Catalyzed C-H Arylation: A General Synthetic Access to Azole-Based Congested Polyaromatics
Résumé
Aryl triflates and related phenolates are suitable electrophile coupling partners for the ruthenium-catalyzed direct arylation of heteroaromatic substrates using azole N-directed sp 2-C-H activation. We report herein convenient conditions in the efficient ortho-C-H functionalization of aryl-pyrazoles, thiazoles and pyridines where [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 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.
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