Lin Pao-Shun, Jeganmohan Masilamani, Cheng Chien-Hong
Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan.
Chem Asian J. 2007 Nov 5;2(11):1409-16. doi: 10.1002/asia.200700128.
Various arylboronic acids reacted with activated alkenes in the presence of [Ni(dppe)Br2], ZnCl2, and H2O in CH3CN at 80 degrees C to give the corresponding Mizoroki-Heck-type addition products in good to excellent yields. Furthermore, 1 equivalent of the hydrogenation product of the activated alkene was also produced. By tuning the ligands of the nickel complexes and the reaction conditions, Michael-type addition was achieved in a very selective manner. Thus, various p- and o-substituted arylboronic acids or alkenylboronic acid reacted smoothly with activated alkenes in CH3CN at 80 degrees C for 12 h catalyzed by Ni(acac)2, P(o-anisyl)3, and K2CO3 to give the corresponding Michael-type addition products in excellent yields. However, for m-substituted arylboronic acids, the yields of Michael-type addition products are very low. The cause of this unusual meta-substitution effect is not clear. By altering the solvent or phosphine ligand, the product yields for m-substituted arylboronic acids were greatly improved. In contrast to previous results in the literature, the present catalytic reactions required water for Mizoroki-Heck-type products and dry reaction conditions for Michael-type addition products. Possible mechanistic pathways for both addition reactions are proposed.
在80℃下，各种芳基硼酸在[Ni(dppe)Br2]、ZnCl2和水存在下于乙腈中与活化烯烃反应，以良好至优异的产率得到相应的Mizoroki-Heck型加成产物。此外，还生成了1当量的活化烯烃氢化产物。通过调节镍配合物的配体和反应条件，以非常选择性的方式实现了迈克尔型加成。因此，各种对位和邻位取代的芳基硼酸或烯基硼酸在80℃下于乙腈中，在Ni(acac)2、P(邻茴香基)3和K2CO3催化下与活化烯烃顺利反应12小时，以优异的产率得到相应的迈克尔型加成产物。然而，对于间位取代的芳基硼酸，迈克尔型加成产物的产率非常低。这种不寻常的间位取代效应的原因尚不清楚。通过改变溶剂或膦配体，间位取代芳基硼酸的产物产率得到了极大提高。与文献中先前的结果相反，目前的催化反应对于Mizoroki-Heck型产物需要水，而对于迈克尔型加成产物需要干燥的反应条件。提出了两种加成反应可能的机理途径。
