N-Heterocyclic Carbene-Assisted, Bis(phosphine)nickel-Catalyzed Cross-Couplings of Diarylborinic Acids with Aryl Chlorides, Tosylates, and Sulfamates

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• 作者：Haihua Ke ; Xiaofeng Chen ; Gang Zou
• 刊名：Journal of Organic Chemistry
• 出版年：2014
• 出版时间：August 1, 2014
• 年：2014
• 卷：79
• 期：15
• 页码：7132-7140
• 全文大小：371K
• ISSN：1520-6904

文摘

Efficient bis(phosphine)nickel-catalyzed cross-couplings of diarylborinic acids with aryl chlorides, tosylates, and sulfamates have been effected with an assistance of N-heterocyclic carbene (NHC) generated in situ from N,N鈥?dialkylimidazoliums, e.g., N-butyl-N鈥?methylimidazolium bromide ([Bmim]Br), in toluene using K₃PO₄路3H₂O as base. In contrast to bis(NHC)nickel-catalyzed conventional Suzuki coupling of arylboronic acids, mono(NHC)bis(phosphine)nickel species generated in situ from Ni(PPh₃)₂Cl₂/[Bmim]Br displayed high catalytic activities in the cross-couplings of diarylborinic acids. The structural influences from diarylborinic acids were found to be rather small, while electronic factors from aryl chlorides, tosylates, and sulfamates affected the couplings remarkably. The couplings of electronically activated aryl chlorides, tosylates, and sulfamates could be efficiently effected with 1.5 mol % NiCl₂(PPh₃)₂/[Bmim]Br as catalyst precursor to give the biaryl products in excellent yields, while 3鈥? mol % loadings had to be used for the couplings of non- and deactivated ones. A small ortho-substitutent on the aromatic ring of aryl chlorides, tosylates, and sulfamates was tolerable. Applicability of the nickel-catalyzed cross-couplings in practical synthesis of fine chemicals has been demonstrated in process development for a third-generation topical retinoid, Adapalene.