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ABSTRACT: Selective synthesis of 1,2,4,5-tetrasubstituted benzenes was achieved via formation of 2,5-bis(trimethylsilyl)zirconacyclopentadienes from 2 equiv of TMS-substituted alkynes with Cp(2)ZrBu(2) and Cu-mediated formation of 1,4-disilylbenzene by cycloaddition of zirconacyclopentadienes to disubstituted alkynes. Preparation of 1,2,3,4,9,10-hexasubstituted pentacene and 2,3,6,11-tetrasubstituted naphthacene derivatives were demonstrated by a homologation or coupling method using tetrasubstituted benzene.
Organic Letters 08/2009; 11(15):3318-21. · 5.86 Impact Factor
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ABSTRACT: Multi-substituted pentacenes, such as 1,2,3,4,6,8,9,10,11,13-decasubstituted pentacenes (Type I), 1,2,3,4,6,13-hexasubstituted pentacenes (Type II), 1,2,3,4-tetrasubstituted pentacenes (Type III), and 2,3-disubstituted pentacenes (Type IV), 1,2,3,4,6,11-hexasubstituted naphthacenes (Type V), 1,2,3,4-tetrasubstituted naphthacenes (Type VI), and 2,3-disubstituted naphthacenes (Type VII), were prepared by a homologation method. The homologation method involved the conversion of phthalic acid ester derivatives to two ring extended phthalic acid ester derivatives via diynes and metallacyclopentadienes using transition metals, such as Zr and Rh. For the formation of pentacenes of Type III and Type IV and naphthacenes of Type VII, trimethylsilyl-substituted diynes were used for zirconocene-mediated cyclization. Elimination of the trimethylsilyl groups after the cyclization afforded nonsubstituted position on pentacenes or naphthacenes. Structures of 1,4,6,8,9,10,11,13-octaethyl-2,3-bis(methoxycarbonyl)pentacene (9a) and 8,9,10,11-tetraethyl-2,3-bis(methoxycarbonyl)-1,4,6,13-tetrapropylpentacene (9b) were determined by X-ray analysis. The structure of 9a had the herringbone packing system in the crystal like nonsubstituted pentacene. However, 9b, whose substituents at 1,4,6,13-positions were changed from Et to Pr at 1,4,6,13-positions of 9a, had the face parallel plane system in the crystal.
The Journal of Organic Chemistry 11/2006; 71(21):7967-77. · 4.45 Impact Factor
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ABSTRACT: Direct addition of alkylzirconocenes to activated alkenes was found, for the first time. Octyl- and decylzirconocene chloride reacted with benzylidenemalononitrile to give the corresponding addition products after hydrolysis in 86% and 79% yield, respectively. Zirconacyclopentanes showed a similar reactivity toward activated alkenes with a two-electron-withdrawing group. On the other hand, treatment of the reaction mixture of zirconacyclopentanes and ylidenemalononitriles with iodine afforded six-membered cyclic compounds in high yields. The diastereoselectivity of the cyclized compound was remarkably high and the high selectivity originated from the Zr-promoted cyclization. The structures of cyclic compounds 10b and the major diastereoisomer of 10d were determined by X-ray analysis. Zirconacyclopentenes reacted with ylidenemalononitrile with high chemoselectivity in which the sp(3)-carbon attached to zirconium reacted with ylidenemalononitrile.
The Journal of Organic Chemistry 11/2002; 67(20):7019-28. · 4.45 Impact Factor
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10/1999;
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Tetrahedron. 58(36):7327-7334.
