Kumar Puneet, Thakur Ashish, Hong Xin, Houk K N, Louie Janis
Department of Chemistry, University of Utah , 315 South 1400 East, Salt Lake City, Utah 84112-0850, United States.
J Am Chem Soc. 2014 Dec 24;136(51):17844-51. doi: 10.1021/ja5105206. Epub 2014 Dec 5.
A Ni/N-heterocyclic carbene catalyst couples diynes to the C(α)-C(β) double bond of tropone, a type of reaction that is unprecedented for metal-catalyzed cycloadditions with aromatic tropone. Many different diynes were efficiently coupled to afford [5-6-7] fused tricyclic products, while [5-7-6] fused tricyclic compounds were obtained as minor byproducts in a few cases. The reaction has broad substrate scope and tolerates a wide range of functional groups, and excellent regioselectivity is found with unsymmetrical diynes. Theoretical calculations show that the apparent enone cycloaddition occurs through a distinctive 8π insertion of tropone. The initial intramolecular oxidative cyclization of diyne produces the nickelacyclopentadiene intermediate. This intermediate undergoes an 8π insertion of tropone, and subsequent reductive elimination generates the [5-6-7] fused tricyclic product. This initial product undergoes two competing isomerizations, leading to the observed [5-6-7] and [5-7-6] fused tricyclic products.
镍/氮杂环卡宾催化剂将二炔与卓酮的C(α)-C(β)双键偶联，这种反应对于金属催化的与芳香族卓酮的环加成反应来说是前所未有的。许多不同的二炔都能有效地偶联，得到[5-6-7]稠合三环产物，而在少数情况下，[5-7-6]稠合三环化合物作为次要副产物得到。该反应具有广泛的底物范围，能耐受多种官能团，对于不对称二炔具有优异的区域选择性。理论计算表明，明显的烯酮环加成反应是通过卓酮独特的8π插入发生的。二炔的初始分子内氧化环化产生镍环戊二烯中间体。该中间体经历卓酮的8π插入，随后的还原消除生成[5-6-7]稠合三环产物。该初始产物经历两种相互竞争的异构化反应，导致观察到的[5-6-7]和[5-7-6]稠合三环产物。
