Fraile José María, Mayoral José Antonio, Salvatella Luis
Instituto de Sı́ntesis Quı́mica y Catálisis Homogénea-ISQCH, CSIC-Universidad de Zaragoza , Pedro Cerbuna 12, 50009 Zaragoza, Spain.
J Org Chem. 2014 Jul 3;79(13):5993-9. doi: 10.1021/jo5003888. Epub 2014 Jun 16.
The mechanisms of the BF3-catalyzed Meinwald rearrangement reactions of five epoxides in dichloromethane solution have been studied at the M062X/6-311++G(2df,2pd) level. Accordingly, the Lewis acid-epoxide complex can react through several alternative pathways, though three phases (ring opening, C-C bond rotation, and hydrogen or alkyl group migration) are required in any path. In some cases, a concerted pathway (involving all three successive phases) is found. Otherwise, the reaction takes place through a reaction mechanism involving a zwitterion or a BF3 addition compound (formed by fluoride transfer from the BF3 moiety to the incipient carbocationic center generated by C-O bond rupture) or both as reaction intermediate(s). The BF2-bound fluorohydrin yields the reaction product through a concerted process involving fluoride transfer from the C-F bond to the OBF2 group and hydrogen or alkyl group migration, as first demonstrated in this work. Effects of a number of features (solvent effects, concurrent hydrogen/alkyl group migration, carbocation substitution, benzylic conjugation) are also discussed.
在M062X/6-311++G(2df,2pd)水平上研究了二氯甲烷溶液中BF₃催化的五种环氧化合物的Meinwald重排反应机理。因此，路易斯酸-环氧化合物络合物可以通过几种不同的途径反应，尽管任何途径都需要三个阶段（开环、C-C键旋转以及氢或烷基迁移）。在某些情况下，会发现一种协同途径（涉及所有三个连续阶段）。否则，反应通过一种反应机理进行，该机理涉及两性离子或BF₃加成化合物（由氟从BF₃部分转移到由C-O键断裂产生的初始碳正离子中心形成）或两者作为反应中间体。与BF₂相连的氟代醇通过一个协同过程生成反应产物，该过程涉及氟从C-F键转移到OBF₂基团以及氢或烷基迁移，这是本文首次证明的。还讨论了许多特征（溶剂效应、并发氢/烷基迁移、碳正离子取代、苄基共轭）的影响。
