Duan Lingfei, Lin Yunzhi, An Qing, Zuo Zhiwei
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Shanghai 200032, China.
J Am Chem Soc. 2025 Apr 30;147(17):14785-14796. doi: 10.1021/jacs.5c03711. Epub 2025 Apr 18.
Ligand-to-metal charge transfer (LMCT) excitation has emerged as a potent strategy for the selective generation of heteroatom-centered radicals, yet its full potential in modulating open-shell radical pathways remains underexplored. Here, we present a photocatalytic methylative cross-coupling reaction that capitalizes on the synergistic interplay between LMCT and Ni catalysis, enabling the use of -butanol as an efficient and benign methylating reagent. The electron-deficient ligand 2,6-ditrifluoromethyl benzoate facilitates Ce(IV)-mediated bond scission of -butanol, generating a methyl radical that is subsequently captured by the Ni catalytic cycle to form C-CH bonds. Under mild reaction conditions, this strategy affords efficient methylation of sp carbons adjacent to carbonyls and sp centers, demonstrating broad functional group tolerance and applicability in late-stage functionalization of bioactive molecules. Additionally, trideuteromethylative coupling can be facilely achieved using commercial -butanol-. This approach circumvents the need for traditional -butoxy radical precursors, such as peroxides, while strategically modulating the radical pathway to favor β-scission and suppress unwanted -butoxy radical formation in solution. Mechanistic studies reveal that the benzoate ligand plays a crucial role in enabling LMCT excitation and facilitating methyl radical generation, supporting a concerted Ce-OR and β-C-C bond homolysis mechanism, further evidenced by the modulation of regioselectivity in alkoxy radical-mediated β-scission.
配体到金属的电荷转移(LMCT)激发已成为选择性生成以杂原子为中心的自由基的有效策略,但其在调节开壳自由基途径方面的全部潜力仍未得到充分探索。在此,我们展示了一种光催化甲基化交叉偶联反应,该反应利用了LMCT和镍催化之间的协同相互作用,使得能够使用叔丁醇作为一种高效且良性的甲基化试剂。缺电子配体2,6 - 二(三氟甲基)苯甲酸酯促进铈(IV)介导的叔丁醇的键断裂,生成一个甲基自由基,该自由基随后被镍催化循环捕获以形成C - C键。在温和的反应条件下,该策略实现了与羰基和sp中心相邻的sp碳的高效甲基化,展示了广泛的官能团耐受性以及在生物活性分子后期功能化中的适用性。此外,使用市售的叔丁醇 - d₃可以轻松实现氘代甲基化偶联。这种方法避免了对传统叔丁氧基自由基前体(如过氧化物)的需求,同时策略性地调节自由基途径以有利于β - 断裂并抑制溶液中不需要的叔丁氧基自由基的形成。机理研究表明,苯甲酸酯配体在实现LMCT激发和促进甲基自由基生成方面起着关键作用,支持协同的Ce - OR和β - C - C键均裂机制,这在烷氧基自由基介导的β - 断裂中的区域选择性调节中得到进一步证明。
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