Shukla Paritosh, Hsu Yun-Chu, Cheng Chien-Hong
Department of Chemistry, National Tsing Hua University, Hsinchu 30043, Taiwan.
J Org Chem. 2006 Jan 20;71(2):655-8. doi: 10.1021/jo052065w.
[reaction: see text] An efficient cobalt-catalyzed reductive coupling reaction of alkyl halides with electron-withdrawing alkenes (CH(2)=CR(1)EWG, EWG = electron-withdrawing group) in the presence of water and zinc powder in acetonitrile to give the corresponding Michael-type addition product (RCH(2)CR(1)EWG) was described. The methodology is versatile such that unactivated primary, secondary, and tertiary alkyl bromides and iodides and various conjugated alkenes including acrylates, acrylonitrile, methyl vinyl ketone, and vinyl sulfone all successfully participate in this coupling reaction. For the alkyl halides used in the reaction, the iodides generally gave better yields compared to those of the corresponding bromides. It is a unique method employing CoI(2)dppe, zinc, and alkyl halides, affording conjugate addition products in high yields. Mechanistically, the reaction appears to follow an oxidative addition driven route rather than the previously reported radical route.
[反应：见正文] 描述了一种在乙腈中，水和锌粉存在下，钴催化卤代烃与吸电子烯烃（CH(2)=CR(1)EWG，EWG = 吸电子基团）进行的有效还原偶联反应，生成相应的迈克尔型加成产物（RCH(2)CR(1)EWG）。该方法具有通用性，未活化的伯、仲、叔烷基溴化物和碘化物以及各种共轭烯烃，包括丙烯酸酯、丙烯腈、甲基乙烯基酮和乙烯基砜，都能成功参与此偶联反应。对于反应中使用的卤代烃，碘化物的产率通常比相应的溴化物更好。这是一种使用CoI(2)dppe、锌和卤代烃的独特方法，能以高产率得到共轭加成产物。从机理上讲，该反应似乎遵循氧化加成驱动的途径，而非先前报道的自由基途径。
