以价廉易得的烷烃为烷基化试剂, 发展了一种基于配体-金属电荷转移(ligand-to-metal charge transfer)机制的可见光诱导铁催化苯并噁嗪-2-酮烷基化新方法. 以氯化铁为光催化剂, 空气为氧化剂, 四丁基氯化铵为氢原子转移促进剂, 在390 nm可见光诱导下实现了苯并噁嗪-2-酮C(sp²)—H键和烷烃C(sp³)—H键之间的交叉脱氢偶联反应, 构建新的C(sp²)—C(sp³)键, 实现烷基化苯并噁嗪-2-酮衍生物的高效合成. 该方法具有反应条件绿色温和、位点选择性高、操作简单等优点, 在生物活性分子后续结构修饰中具有较高的应用价值.

Homogeneous visible-light photoredox catalysis has emerged as a powerful tool in modern organic synthesis, which utilizes inexhaustible light to facilitate carbon-carbon and carbon-heteroatom bond formation under eco-friendly and mild conditions. Due to the incapablity of most organic compounds to absorb visible light, homogeneous photocatalysts such as precious metals (rhodium and iridium-complexes) and elaborate organic dyes were often employed through their visible light-driven electron/energy transfer to sensitize organic molecules in photoredox catalysis. However, these photocatalysts are not conducive to large-scale production due to the relatively high cost. Iron is an ideal candidate for economical and eco-friendly catalysis because of its abundant availability and nontoxicity. Recently, iron-photocatalyzed bond formation reactions via ligand-to-metal charge transfer (LMCT) have attracted huge attention. Functionalized benzoxazin-2-ones are important N-heterocycles found in many natural products, bioactive molecules and pharmaceuticals. Among these benzoxazin-2-one derivatives, alkylated benzoxazin-2-ones have received significant attention due to their valuable biological and pharmacological activities. From a synthetic point of view, the direct C—H alkylation of benzoxazin-2-ones represents one of the most straightforward and efficient methods for producing alkylated benzoxazin-2-ones due to its high atom and step economy. Alkanes are low cost and abundant feedstock materials, which have been widely used as the alkylation reagents in organic synthesis. In the present work, we report the development of iron-catalyzed C—H alkylation of benzoxazin-2-ones with alkanes via photoinduced LMCT. With FeCl₃ as the photocatalyst, ambient air as the oxidant, tetrabutylammonium chloride as the promoter, a series of 3-alkylbenzoxazin-2-ones were efficiently synthesized under mild and eco-friendly conditions. The chlorine radical generated in situ serves as a hydrogen atom-transfer reagent. In addition, the present reaction can be smoothly scaled-up to gram level, which indicates it could be applied in industrial synthesis of pharmaceuticals.