Medium-sized cyclophanes. Part XVI. Substitution versus transannular reaction of [2.2]metacyclophanes with benzoyl peroxide and cupric chloride. Importance of a cation radical intermediate in the transannular dehydrogenation
作者:Kozaburo Nishiyama、Kazuo Hata、Takeo Sato
DOI:10.1039/p29740000577
日期:——
treated with benzoyl peroxide (BPO) and cupric chloride in acetonitrile; one is nuclear substitution giving the 4-benzoate and the 8-cyanomethyl derivatives, each formed by a radical attack via a cyclohexadienyl intermediate, and the other is transannular dehydrogenation to give pyrene and hydropyrenes. The latter reaction occurs with BPO alone or with other metal halides. Transannular dehydrogenation is
用过氧化苯甲酰(BPO)和氯化铜在乙腈中处理[2.2]甲基环已(1)时,会发生两种类型的反应;一种是核取代,产生4-苯甲酸酯和8-氰基甲基衍生物,它们分别是通过自由基攻击通过环己二烯中间体,另一种是环环脱氢,得到pyr和氢吡喃。后者与单独的BPO或与其他金属卤化物发生反应。对于(1)的烷基衍生物而言,环过氢脱氢是有利的。5,13-二甲基衍生物(12a)没有发生核取代。对于(1),(12a),二乙基衍生物(12b)和四甲基衍生物(19),由氯化铜引起的脱氢的相对速率分别为1、160、120和40。这些速率与电离势和中间体的稳定性有关。通过单电子转移过程形成的阳离子自由基中间体的重要性得到提高。