Elimination−Addition Mechanism for Nucleophilic Substitution Reaction of Cyclohexenyl Iodonium Salts and Regioselectivity of Nucleophilic Addition to the Cyclohexyne Intermediate
作者:Morifumi Fujita、Wan Hyeok Kim、Yuichi Sakanishi、Koji Fujiwara、Sayaka Hirayama、Tadashi Okuyama、Yasuhiro Ohki、Kazuyuki Tatsumi、Yasunori Yoshioka
DOI:10.1021/ja0496672
日期:2004.6.23
intermediate. The cyclohexyne formation was confirmed by deuterium labeling and trapping to lead to [4 + 2] cycloadducts and a platinum-cyclohexyne complex. Cyclohexyne can also be generated in the presence of some other mild bases such as fluoride ion, alkoxides, and amines, though amines are less effective bases for the elimination. Kinetic deuterium isotope effects show that the anionic bases induce the E2
4-取代的环己-1-烯基(苯基)碘鎓四氟硼酸盐与四丁基乙酸铵的反应在非质子溶剂中得到ipso和cine乙酸盐取代产物。异构的5-取代的碘鎓盐也产生相同的异构乙酸盐产物混合物。该反应最好通过消除加成机制来解释,其中 4-取代的环己炔作为常见的中间体。环己炔的形成通过氘标记和捕获得到证实,导致 [4 + 2] 环加合物和铂-环己炔配合物。环己炔也可以在一些其他弱碱(如氟离子、醇盐和胺)的存在下生成,尽管胺是不太有效的消除碱。动力学氘同位素效应表明阴离子碱诱导 E2 消除 (k(H)/k(D) > 2),而胺允许在氯仿中形成环己烯基阳离子,从而导致 E1 和 S(N)1 反应(k(H)/k(D) 大约为 1)。碱在甲醇中的效果要差得多,而甲醇盐是唯一能有效提供环己炔中间体的碱。亲核试剂与环己炔反应以产生比例取决于环取代基的区域异构产物。观察到的取代环己炔亲核加成的区域选择性是从计算的 LUMO