Solvent and Base in One: Tetra-n-butylammonium Acetate as a Multi-Purpose Ionic Liquid Medium for Ru-Catalyzed Directed Mono- and Di-o-C-H Arylation Reactions

Ru-catalyzed directed o-C-H arylation reactions of 2-phenylpyridine, N-phenylpyrazole, acetophenone N-(p-methoxyphenyl)imine, and 2-phenyloxazoline proceed in good to excellent yields with a number of functionalized aryl and heteroaryl bromides in neat Bu4NOAc at 120 degrees C. The acetate ion acts as the base and the relatively low melting point Bu4N salts (a mixture of acetate and bromide) behave as an ionic liquid. Arylation reactions of 2-phenyloxazoline proceed with concomitant oxazolidine cleavage to give 2-(N-acetylamino)ethyl benzoates promoted by side product CH3COOH. The dual-purpose ionic liquid medium is compatible with both ligandless Ru for di-arylation (optimal pre-catalyst: RuCl3xH2O) and Ru-phosphane (optimal pre-catalyst: [RuCl2(p-cymene)](2)/P(p-Tol)(3) 1:4) catalysts (1-5 mol-%) for selective mono-arylation.