Dual Reactivity of Hydroxy- and Methoxy- Substituted o-Quinone Methides in Aqueous Solutions: Hydration versus Tautomerization
Dual Reactivity of Hydroxy- and Methoxy- Substituted o-Quinone Methides in Aqueous Solutions: Hydration versus Tautomerization
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DOI：
10.1021/jo101613t
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发表时间：
2010-11-05
影响因子：
3.6
通讯作者：
Popik, Vladimir V.
中科院分区：
文献类型：
--
作者：
Arumugam, Selvanathan;Popik, Vladimir V.
4-羟基-6-亚甲基-2,4-环己二烯-1-酮 (1) 和 4-甲氧基-6-亚甲基-2,4-环己二烯-1-酮 (2) 通过 2-(羟甲基)苯-1,4-二醇 (3a) 的高效 (Phi = 0.3) 光脱水生成 分别为2-(羟甲基)-4-甲氧基苯酚(4a)。邻醌甲基化物 1 和 2 可以作为与乙基乙烯基醚的 Diels-Alder 加合物被定量捕获，或者被良好的亲核试剂拦截，例如叠氮离子 (k(N3)(1) = 3.15 x 10(4) M-1 s(-1) 和 k(N3)(2) = 3.30 x 10(4) M-1 s(-1))。在水溶液中，邻醌甲基化物 2 快速加水以再生起始材料（tau(H2O)(2) = 7.8 ms，25°C）。该反应由特定酸 (k(H1)(2) = 8.37 x 10(3) s(-1) M-1) 和特定碱 (k(OH)-(2) = 1.08 x 10(4) s(-1) M-1) 催化，但没有表现出明显的一般酸/碱催化作用。与此形成鲜明对比的是，邻醌甲基化物 1 通过两种竞争途径衰变（25°C 时 tau(H2O)(1) = 3.3 ms）：亲核水合形成起始材料 3a 和互变异构化产生甲基对苯醌。或1的消失不仅表明特定酸（k(H+)(1) = 3.30 x 10(4) s(-1) M-1）和特定碱催化（k(OH)-(1) = 3.51 x 10(4) s(-1) M-1），而且还显示一般酸和碱的明显催化作用。邻醌甲基化物 1 和 2 也是通过 2-(乙氧基甲基)苯-1,4-二醇 (3b) 和 2-(乙氧基甲基)-4-甲氧基苯酚 (4b) 以及 (2,5-二羟基-1-苯基)甲基-(3c) 和 (2-羟基-5-甲氧基-1-苯基)甲基三甲基碘化铵(4c)。在 3a、b 和 4a、b 的激光闪光光解中检测到邻醌甲基化物 1 和 2 的短寿命（tau（25 摄氏度）约 20 μs）前体。根据它们的反应性，苯并氧酯结构已被指定给这些
4-Hydroxy-6-methylene-2,4-cyclohexadien-1-one (1) and 4-methoxy-6-methylene-2,4-cyclohexadien-1-one (2) were generated by efficient (Phi = 0.3) photodehydration of 2-(hydroxymethyl)benzene-1,4-diol (3a) and 2-(hydroxymethyl)-4-methoxyphenol (4a), respectively. o-Quinone methides 1 and 2 can be quantitatively trapped as Diels-Alder adducts with ethyl vinyl ether or intercepted by good nucleophiles, such as azide ion (k(N3)(1) = 3.15 x 10(4) M-1 s(-1) and k(N3)(2) = 3.30 x 10(4) M-1 s(-1)). In aqueous solution, o-quinone methide 2 rapidly adds water to regenerate starting material (tau(H2O)(2) = 7.8 ms at 25 degrees C). This reaction is catalyzed by specific acid (k(H1)(2) = 8.37 x 10(3) s(-1) M-1) and specific base (k(OH)-(2) = 1.08 x 10(4) s(-1) M-1) but shows no significant general acid/base catalysis. In sharp contrast, o-quinone methide 1 decays (tau(H2O)(1) = 3.3 ms at 25 degrees C) via two competing pathways: nucleophilic hydration to form starting material 3a and tautomerization to produce methyl-p-benzoquinone. The disappearance or 1 shows not only specific acid (k(H+)(1) = 3.30 x 10(4) s(-1) M-1) and specific base catalysis (k(OH)-(1) = 3.51 x 10(4) s(-1) M-1) but pronounced catalysis by general acids and bases as well. The o-quinone methides 1 and 2 were also generated by the photolysis of 2-(ethoxymethyl)benzene-1,4-diol (3b) and 2-(ethoxymethyl)-4-methoxyphenol (4b), as well as from (2,5-dihydroxy-1-phenyl)methyl-(3c) and (2-hydroxy-5-methoxy-1-phenyl)methyltrimethylammonium iodides (4c). Short-lived (tau(25 degrees C) approximate to 20 mu s) precursors of o-quinone methides 1 and 2 were detected in the laser flash photolysis of 3a,b and 4a,b. On the basis of their reactivity, benzoxete structures have been assigned to these in