Department of Chemistry, National Tsing Hua University, Hsinchu, 30013, Taiwan.
Chemistry. 2012 Sep 10;18(37):11771-7. doi: 10.1002/chem.201200779. Epub 2012 Aug 2.
A cobalt-catalyzed reductive coupling of terminal alkynes, RC≡CH, with activated alkenes, R'CH=CH(2), in the presence of zinc and water to give functionalized trans-disubstituted alkenes, RCH=CHCH(2)CH(2)R', is described. A variety of aromatic terminal alkynes underwent reductive coupling with activated alkenes including enones, acrylates, acrylonitrile, and vinyl sulfones in the presence of a CoCl(2)/P(OMe)(3)/Zn catalyst system to afford 1,2-trans-disubstituted alkenes with high regio- and stereoselectivity. Similarly, aliphatic terminal alkynes also efficiently participated in the coupling reaction with acrylates, enones, and vinyl sulfone, in the presence of the CoCl(2)/P(OPh)(3)/Zn system providing a mixture of 1,2-trans- and 1,1-disubstituted functionalized terminal alkene products in high yields. The scope of the reaction was also extended by the coupling of 1,3-enynes and acetylene gas with alkenes. Furthermore, a phosphine-free cobalt-catalyzed reductive coupling of terminal alkynes with enones, affording 1,2-trans-disubstituted alkenes as the major products in a high regioisomeric ratio, is demonstrated. In the reactions, less expensive and air-stable cobalt complexes, a mild reducing agent (Zn) and a simple hydrogen source (water) were used. A possible reaction mechanism involving a cobaltacyclopentene as the key intermediate is proposed.
钴催化的末端炔烃 RC≡CH 与活化烯烃 R'CH=CH(2) 在锌和水存在下的还原偶联反应，生成官能化的反式二取代烯烃 RCH=CHCH(2)CH(2)R'，本文对此进行了描述。在 CoCl(2)/P(OMe)(3)/Zn 催化剂体系存在下，各种芳香族末端炔烃与包括烯酮、丙烯酸酯、丙烯腈和乙烯砜在内的活化烯烃进行还原偶联反应，以高区域和立体选择性得到 1,2-反式二取代烯烃。类似地，脂肪族末端炔烃也能与丙烯酸酯、烯酮和乙烯砜在 CoCl(2)/P(OPh)(3)/Zn 体系存在下高效参与偶联反应，以高产率提供 1,2-反式和 1,1-二取代官能化末端炔烃产物的混合物。该反应的范围还通过 1,3-烯炔和乙炔气与烯烃的偶联反应得到了扩展。此外，本文还证明了无膦配体钴催化的末端炔烃与烯酮的还原偶联反应，以高区域异构体比得到主要产物 1,2-反式二取代烯烃。在这些反应中，使用了更廉价、空气稳定的钴配合物、温和的还原剂（Zn）和简单的氢源（水）。提出了一种可能的反应机理，涉及钴环戊烯作为关键中间体。
