Ni-Catalyzed Carbocyclization of 1,6-Enynes Mediated by Dialkylzinc Reagents: Me2Zn or Et2Zn Makes a Difference
作者:Gang Zhao、Zhuo Chai、Hai-Feng Wang
DOI:10.1055/s-0029-1217368
日期:2009.7
Unactivated 1,6-enynes were firstly found to undergo different cyclization process under the catalysis of Ni0 species in situ generated from NiII complexes and dialkylzinc reagents. When stoichiometric Me2Zn was used as the reducing agent, only the dimerization products [2+2+2+2] or [2+2+2]} were obtained. On the other hand, reductive cyclization products were obtained solely when 0.6 equivalents of Et2Zn were employed as the reductant under otherwise the same reaction conditions. In the former case, up to 1:7 selectivity in favor of the [2+2+2] products was also achieved with NiCl2(PPh3)2/Me2Zn.
未活化的1,6-炔烃首次被发现能够在由NiII配合物和二烷基锌试剂原位生成的Ni0物种催化下经历不同的环化过程。当使用化学当量的Me2Zn作为还原剂时,仅获得了二聚化产物[2+2+2+2]或[2+2+2]}。另一方面,当在相同反应条件下使用0.6当量的Et2Zn作为还原剂时,仅获得了还原环化产物。在前一种情况下,使用NiCl2(PPh3)2/Me2Zn还实现了对[2+2+2]产物的最高1:7选择性。