Boronic acids and their derivatives are some of the most useful reagents in the chemical sciences1, with applications spanning pharmaceuticals, agrochemicals and functional materials. Catalytic C-H borylation is a powerful method for introducing these and other boron groups into organic molecules because it can be used to directly functionalize C-H bonds of feedstock chemicals without the need for substrate pre-activation1-3. These reactions have traditionally relied on precious-metal catalysts for C-H bond cleavage and, as a result, display high selectivity for borylation of aromatic C(sp2)-H bonds over aliphatic C(sp3)-H bonds4. Here we report a mechanistically distinct, metal-free borylation using hydrogen atom transfer catalysis5, in which homolytic cleavage of C(sp3)-H bonds produces alkyl radicals that are borylated by direct reaction with a diboron reagent. The reaction proceeds by violet-light photoinduced electron transfer between an N-alkoxyphthalimide-based oxidant and a chloride hydrogen atom transfer catalyst. Unusually, stronger methyl C-H bonds are borylated preferentially over weaker secondary, tertiary and even benzylic C-H bonds. Mechanistic studies indicate that the high methyl selectivity is a result of the formation of a chlorine radical-boron 'ate' complex that selectively cleaves sterically unhindered C-H bonds. By using a photoinduced hydrogen atom transfer strategy, this metal-free C(sp3)-H borylation enables unreactive alkanes to be transformed into valuable organoboron reagents under mild conditions and with selectivities that contrast with those of established metal-catalysed protocols.

中文翻译：

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烷烃的无金属光诱导 C(sp3)-H 硼酸化

硼酸及其衍生物是化学科学中最有用的试剂之一，其应用范围涵盖药物、农用化学品和功能材料。催化 CH 硼酸化是将这些和其他硼基团引入有机分子的有效方法，因为它可用于直接官能化原料化学品的 CH 键，而无需底物预活化1-3。这些反应传统上依赖贵金属催化剂进行 CH 键断裂，因此，与脂肪族 C(sp3)-H 键相比，芳族 C(sp2)-H 键的硼化显示出高选择性。在这里，我们报告了使用氢原子转移催化的机械上独特的无金属硼化反应 5，其中 C(sp3)-H 键的均裂产生的烷基自由基通过与二硼试剂直接反应而被硼化。该反应通过基于 N-烷氧基邻苯二甲酰亚胺的氧化剂和氯氢原子转移催化剂之间的紫光光诱导电子转移进行。不同寻常的是，更强的甲基 CH 键优先于较弱的二级、三级甚至苄基 CH 键被硼化。机理研究表明，高甲基选择性是形成氯自由基 - 硼酸盐复合物的结果，该复合物选择性地切割空间不受阻碍的 CH 键。通过使用光致氢原子转移策略，