Synthesis of arylzinc compounds in ethereal solvent and application to organic synthesis

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As a reactive and chemoselective Ar-supplying reagent, arylzinc compounds, ArZnX, are extensively utilized in organic synthesis. Compared with the conventional synthetic method of the compounds from ArLi or ArMgX and ZnX_2,the recently developed one of treating ArX with Zn powder in polar solvents such as HMPA, DMF, or TMU is far more convenient and atom economic. Here it is to be noted that, because of the liability of the organozinc compounds to moisture, the solution containing ArZnX is used in subsequent reaction as obtained. Consequently, a given solvent must be appropriate not only for the preparation but also for the utilization of ArZnX. In this context, the polar solvents might limit the utility of ArZnX, since or ganometallic reactions are often carried out in less polar solvent such as THF. In this research, we attempted to synthesize the ArZnX through the direct reaction in ethereal solvents. Such compounds, if available, must provide the extremely valuable sources of Ar^- … More for organic synthesis from viewpoints of functional group tolerance and atom economy (new zinc effect). We found that the reactions of ArI containing electron-withdrawing groups such as CO_2CH_3,CN, Br, or CF_3 at the ortho-position with Zn powder in THE at 70℃ proceed well to afford the desired ArZnI in good yields. For the reactions of An containing similar electron-withdrawing groups at the meta- or para-position or electron-donating groups like CH_3,OCH_3,or H, the heating at 100 or 130 in diglyme was required, respectively. Pd(dba)_2 exhibited an outstanding efficient catalytic effect for the cross-coupling of these ethereal solution of ArZnX with allylic halides to afford a variety of functionalized allylbenzenes in high yields ; the reactions were mostly carried out at 0℃ for 5-30 min in the presence of 5 mol% of catalyst. In addition, TiCl_2(O-i-Pr)_2 mediated the reactions between aldehydes and ArZnX in ethereal solvents, too. Since the titanium compound failed in mediating the reactions in TMU, the utility of ethereal solvents is essential for the successful reaction. Less