The Research Of Palladium-catalyzed Desulfitative C-H Arylation Of Azoles And Synthesis Of Quinolines From Nitroarenes

The formation of C-C and C–heteroatom bond has been one of the major topics inthe arena of organic synthesis for many decades. In recent years, transition-metalcatalyzed cross-coupling reaction using halides and organometallic reagents havebeen largely developed. The preparation of halides need to be corresponding C-Hbonds functionalized and the reaction byproducts such as acids are environmentallyunfriendly. Therefore, the direct use of C-H activation affords an more efficient andgreen route. The construction of C-N bond is becoming focus of study andconsiderable progress has been achieved. The research found that the nitro group canuse the hydrogen released by the alcohol oxidation step to achieve in-situ reduction inthe absence of any additive. So it’s a very green approach for construction of C-Cbond. This paper did some exploration about a more efficient way for construction ofC-C and C-N bond. Herein, we reported the research of palladium-catalyzeddesulfitative C-H arylation of azoles and one-pot synthesis of quinolines. Somedetailed research was described as follows:We described a palladium-catalyzed desulfitative arylation of azoles with aromaticsodium sulfinates via C-H activation. The reaction proceeded well for a range ofdifferent substrates using Pd(OAc)2as catalyst and Cu(OAc)2as oxidant at120oC.After experimental analysis of the catalyst, oxidants, solvent and temperature, theoptimum conditions were found. We then explored the scope and generality of thistransformation in the presence of a variety of functional groups of substrates. Variousazoles bearing weak electron-withdrawing or donating substituents afforded theadducts in moderate to good yields. A series of functional groups on aromatic sulfinicacids including fluoro, chloro, bromo and trifluoromethyl were tolerated under theoptimal reaction conditions, and the desired products were obtained in moderate togood yields. A plausible mechanism to rationalize this transformation is found.A series of quinolines were synthesized in moderate yields by one-pot reaction ofnitroarenes and trialkylamines in the presence of a catalytic amount of rutheniumtrichloride catalyst together with tricyclohexylphosphonium tetrafluoroborate ligand.This method is convenient without extra reductant, and nitroarenes are cheap andhighly available. It affords an more efficient route to synthetize quinolines.