Synthesis of o-Arylenedizinc Compounds and Their Synthetic Applications

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Structures of arenes, possessing two different side chains at adjacent positions of benzene ring, are observed in numerous organic compounds. One general way to construct such structures might utilize SE or SN type replacement reaction using synthetic equivalents of o-phenylene dianion, dication, or 1-anion 2-cation as benzo segments with appropriate reagents. In this research, we tried to synthesize o-arylenedizinc compounds, intending to use them as the synthetic equivalent of o-arylene dianion in the synthesis of unsymmetrically 1,2-disubstituted arenes.We have already reported on the synthesis of o-phenylenedizinc compound. However, it appeared that similar route will be less effective for the synthesis of o-arylenedizinc compounds because of the limited availability of 1,2-diiodoarenes. Then, new access to o-arylenedizinc compounds was investigated. That is, regioselective iodination of phenols, followed by triflation of the hydroxyl group, affords aryl triflates containing iodo s … More ubstituent at ortho position. Various o-arylenedizinc compounds were obtained in good yields by the reaction of the aryl triflates with zinc powder.Next, the reaction of o-phenylenedizinc compound with electrophilic reagents was examined. When one equivalent of such reagent as iodobenzene or benzoyl chloride was applied to the reaction in the presence of palladium(0) catalyst containing tris(2,4,6-tri-methoxyphenyl)phosphine or tri(o-tolyl)phosphine as a ligand, formal SE reaction took place selectively at one electrophilic side between two possible centers to afford arylzinc compounds in high yields. Further addition of second reagents to the resulting solutions induce the catalytic reactions once again, providing unsymmetrically 1,2-disubsutituted arenes in good yields.For the first time, o-bromophenylzinc compound as a novel synthetic equivalent of o-phenylene 1-anion 2-cation was prepared by the reaction of o-bromoiodobenzene with zinc powder and was applied to the palladium(0)-catalyzed cross-coupling. Its consecutive treatment with electrophilic reagents like aryl halides or aryl halides and then with nucleophilic reagents like potassium cyanide, alkyne, or arylzinc compounds afforded various unsymmetrically 1,2-disubstituted arenes in good yields. Less