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Catalytically Generated Meerwein’s Salt-Type Oxonium Ions for Friedel–Crafts C(sp2)–H Methylation with Methanol
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2023-02-01 , DOI: 10.1021/jacs.2c13341 Tao He 1 , Hendrik F T Klare 1 , Martin Oestreich 1
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2023-02-01 , DOI: 10.1021/jacs.2c13341 Tao He 1 , Hendrik F T Klare 1 , Martin Oestreich 1
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A catalytic protocol for a Friedel–Crafts-type direct C(sp2)–H methylation of various arenes with methanol is disclosed. The reaction is initiated by counteranion-stabilized silylium or arenium ions, which form Meerwein’s salt-like oxonium ions with methanol as the active methylating agents. The silylated methyloxonium ions are stronger electrophiles than their protonated congeners, allowing the Friedel–Crafts alkylation to proceed more efficiently and at a lower reaction temperature. The regeneration of these superelectrophiles within the catalytic cycle is accomplished by the addition of a tetraorganosilane additive, i.e., trimethyl(phenyl)silane or tetraethylsilane, that releases a silylium ion through protodesilylation by the Brønsted acidic Wheland intermediate, thereby acting as a productive “proton-into-silylium ion” generator. By this method, even the C–H methylation of electronically deactivated aryl halides with methanol is achieved. The protocol is also applicable to nonactivated primary as well as π-activated benzylic alcohols. Dialkyl ethers are also competent alkylating agents in the presence of the quaternary phenylsilane additive.
中文翻译：
催化生成的 Meerwein 盐型氧鎓离子用于 Friedel-Crafts C(sp2)-H 甲基化与甲醇
Friedel–Crafts 型直接 C(sp 2)的催化方案)–H甲基化各种芳烃与甲醇的公开。该反应由抗衡阴离子稳定的硅烷离子或砷离子引发，它们与甲醇作为活性甲基化剂形成 Meerwein 盐状氧鎓离子。甲硅烷基化的甲基氧鎓离子比它们的质子化同系物具有更强的亲电性，使 Friedel-Crafts 烷基化能够在较低的反应温度下更有效地进行。这些超级亲电子试剂在催化循环中的再生是通过添加四有机硅烷添加剂（即三甲基（苯基）硅烷或四乙基硅烷）来实现的，它们通过布朗斯台德酸性 Wheland 中间体的原脱甲硅烷基化作用释放出甲硅烷基离子，从而充当生产性“质子” -转化为硅基离子”发生器。通过这种方法，甚至用甲醇实现了电子失活的芳基卤化物的 C-H 甲基化。该协议也适用于未激活的伯醇和 π 激活的苄醇。在季苯基硅烷添加剂存在下，二烷基醚也是有效的烷基化剂。
更新日期：2023-02-01
中文翻译：
催化生成的 Meerwein 盐型氧鎓离子用于 Friedel-Crafts C(sp2)-H 甲基化与甲醇
Friedel–Crafts 型直接 C(sp 2)的催化方案)–H甲基化各种芳烃与甲醇的公开。该反应由抗衡阴离子稳定的硅烷离子或砷离子引发，它们与甲醇作为活性甲基化剂形成 Meerwein 盐状氧鎓离子。甲硅烷基化的甲基氧鎓离子比它们的质子化同系物具有更强的亲电性，使 Friedel-Crafts 烷基化能够在较低的反应温度下更有效地进行。这些超级亲电子试剂在催化循环中的再生是通过添加四有机硅烷添加剂（即三甲基（苯基）硅烷或四乙基硅烷）来实现的，它们通过布朗斯台德酸性 Wheland 中间体的原脱甲硅烷基化作用释放出甲硅烷基离子，从而充当生产性“质子” -转化为硅基离子”发生器。通过这种方法，甚至用甲醇实现了电子失活的芳基卤化物的 C-H 甲基化。该协议也适用于未激活的伯醇和 π 激活的苄醇。在季苯基硅烷添加剂存在下，二烷基醚也是有效的烷基化剂。
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