Cremeens Matthew E, Hughes Thomas S, Carpenter Barry K
Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, NY 14853-1301, USA.
J Am Chem Soc. 2005 May 11;127(18):6652-61. doi: 10.1021/ja0445443.
Myers et al. pyrolyzed (Z)-1,2,4-heptatrien-6-yne (1) in methanol at 100 degrees C and observed benzylmethyl ether (2) as a major product and 2-phenylethanol (3) as a minor product. If a biradical intermediate, such as the open-shell singlet state of alpha,3-didehydrotoluene (4), was the only intermediate generated by the cyclization, then reaction with methanol might be expected to afford 2-phenylethanol as the principal product. The question that has been of interest since its first discovery is the origin of the principal product of the title reaction, benzylmethyl ether. This report considers three mechanisms for formation of the benzylmethyl ether: direct methanol participation in the cyclization of the reactant, partial ether formation from the biradical 4, or involvement of the closed-shell zwitterionic state of alpha,3-didehydrotoluene (5). A fourth mechanism, involving a cyclic allene intermediate, has been ruled out by earlier studies. In the present work, the first two mechanisms are ruled out by experiment and/or calculation. The remaining one, involving the zwitterion, is shown to be consistent with experimental and computational data only if a component of the reaction follows a nonadiabatic course.
迈尔斯等人在100摄氏度下于甲醇中对（Z）-1,2,4-庚三烯-6-炔（1）进行热解，观察到苄基甲基醚（2）是主要产物，2-苯乙醇（3）是次要产物。如果双自由基中间体，如α,3-二脱氢甲苯（4）的开壳单重态，是环化产生的唯一中间体，那么与甲醇反应可能会预期以2-苯乙醇作为主要产物。自首次发现以来一直令人感兴趣的问题是标题反应的主要产物苄基甲基醚的来源。本报告考虑了苄基甲基醚形成的三种机制：甲醇直接参与反应物的环化、双自由基4形成部分醚、或α,3-二脱氢甲苯（5）的闭壳两性离子态参与。涉及环状丙二烯中间体的第四种机制已被早期研究排除。在本工作中，前两种机制通过实验和/或计算被排除。剩下的涉及两性离子的机制只有在反应的一个组分遵循非绝热过程时才与实验和计算数据一致。
