Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, United States.
New Iridium Incorporated, Boulder, Colorado 80303, United States.
J Am Chem Soc. 2020 Aug 5;142(31):13573-13581. doi: 10.1021/jacs.0c05899. Epub 2020 Jul 28.
The Birch reduction is a powerful synthetic methodology that uses solvated electrons to convert inert arenes to 1,4-cyclohexadienes-valuable intermediates for building molecular complexity. Birch reductions traditionally employ alkali metals dissolved in ammonia to produce a solvated electron for the reduction of unactivated arenes such as benzene ( < -3.42 V vs SCE). Photoredox catalysts have been gaining popularity in highly reducing applications, but none have been reported to demonstrate reduction potentials powerful enough to reduce benzene. Here, we introduce benzo[]perylene imides as new organic photoredox catalysts for Birch reductions performed at ambient temperature and driven by visible light from commercially available LEDs. Using low catalyst loadings (<1 mol percent), benzene and other functionalized arenes were selectively transformed to 1,4-cyclohexadienes in moderate to good yields in a completely metal-free reaction. Mechanistic studies support that this unprecedented visible-light-induced reactivity is enabled by the ability of the organic photoredox catalyst to harness the energy from two visible-light photons to affect a single, high-energy chemical transformation.
硼氢化还原是一种强大的合成方法，它利用溶剂化电子将惰性芳烃转化为 1,4-环己二烯，这是构建分子复杂性的有价值的中间体。硼氢化还原传统上采用溶解在氨中的碱金属来产生溶剂化电子，以还原未活化的芳烃，如苯（< -3.42 V 相对于 SCE）。光氧化还原催化剂在高度还原的应用中越来越受欢迎，但尚未有报道表明它们具有足够强大的还原电位来还原苯。在这里，我们引入苯并[]苝酰亚胺作为新的有机光氧化还原催化剂，用于在环境温度下进行硼氢化还原，并由市售 LED 的可见光驱动。使用低催化剂负载量（<1 摩尔%），苯和其他官能化芳烃在完全无金属的反应中以中等至良好的收率选择性转化为 1,4-环己二烯。机理研究支持，这种前所未有的可见光诱导反应是由有机光氧化还原催化剂能够利用两个可见光光子的能量来影响单一的高能化学转化来实现的。
