Synthesis of Pd^II complexes bearing an enantiomerically resolved seven-membered N

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• 作者：Christopher C. Scarborough ; Ana Bergant ; Graham T. Sazama ; Ilia A. Guzei ; Lara C. Spencer ; Shannon S. Stahl
• 关键词：N-Heterocyclic carbene ; Palladium ; Organometallic chemistry ; Wacker oxidation
• 刊名：Tetrahedron
• 出版年：2009
• 出版时间：27 June 2009
• 年：2009
• 卷：65
• 期：26
• 页码：5084-5092
• 全文大小：540 K

文摘

The development of enantiomerically resolved, axially-chiral seven-membered N-heterocyclic carbene (⁷NHC) ligands for palladium is described. These ⁷NHC ligands are derived from enatiomerically pure 2,2′-diamino-6,6′-dimethylbiphenyl, which is transformed via a synthetic sequence consisting of ortho-arylation, N-alkylation, and cyclization to afford seven-membered-ring amidinium salts. Synthesis of the seven-membered amidinium salts benefits from microwave irradiation, and in-situ metalation of the amidinium salts yields ⁷NHC–Pd^II complexes. The chiral ⁷NHC–Pd complexes were examined as chiral catalysts under aerobic conditions in two intramolecular oxidative amination reactions of alkenes. In one case, enantioselectivities up to 63 % ee were obtained, while the other substrate underwent cyclization to afford essentially racemic products. The catalytic data compare favorably to results obtained with a Pd^II catalyst bearing a chiral five-membered-ring NHC ligand and, thereby, highlight the potential significance of this new class of chiral NHC ligands.