Bu₄NOAc For Ru-catalyzed Directed Functionalization O-C-H Arylation Reactions

Of all the transition-metal-catalyzed cross-coupling reactions,the use of simple(hetero)arene as substrates by direct C-H arylation instead is a hot research topic currently due to the reason that organic-metal reagents synthesized with multi-steps and some times along with practical challenges are necessary in the traditional cross-coupling reactions.Finding alternatives for the replacerment of the hazardous organic solvents is an important goal of green chemistry.In this article,cheap and readily available Bu4NOAc was used as an alternative instead of toxic and hazardous organic solvents.RuCl3·xH2O(the cheapest source of Ru)was used as a catalyst to catalyze a series of C-H direct arylation of heteroatom-containing directing groups(DG)aromatic and aryl halides.The result suggested that this is a highly reaction protocol.The result showed that the Ru-catalyzed directed o-C-H arylation reactions of 2-phenylpyridine,N-phenylpyrazole,acetophenone N-(p-meth-oxyphenyl)imine,and 2-phenyloxazoline proceed smoothly to give monoarylated and diarylated products with a number of functionalized aryl and hetero-aryl bromides in good yields(99%-50%)in neat Bu4NOAc at 120 ℃.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.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 the selective mono-arylation.Direct arylation makes the synthesis of biaryl compounds more succinct and economical,and the synthetic strategy has established its position in the synthetic chemistry.Solvent-free ruthenium catalyzed direct o-C-H arylation reaction has also shown great potential in the synthesis of green natural products and exploration of organic functional materials,enriching the research content of organic chemistry and green chemistry.