Abstract：
We report an iron-catalyzed decarboxylative C(sp3)-O bond-forming reaction under mild, base-free conditions with visible light irradiation. The transformation uses readily available and structurally diverse carboxylic acids, iron photocatalyst, and 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) derivatives as oxygenation reagents. The process exhibits a broad scope in acids possessing a wide range of stereoelectronic properties and functional groups. The developed reaction was applied to late-stage oxygenation of a series of bio-active molecules. The reaction leverages the ability of iron complexes to generate carbon-centered radicals directly from carboxylic acids by photoinduced carboxylate-to-iron charge transfer. Kinetic, electrochemical, EPR, UV/Vis, HRMS, and DFT studies revealed that TEMPO has a triple role in the reaction: as an oxygenation reagent, an oxidant to turn over the Fe-catalyst, and an internal base for the carboxylic acid deprotonation. The obtained TEMPO adducts represent versatile synthetic intermediates that were further engaged in C-C and C-heteroatom bond-forming reactions using commercial organo-photocatalysts and nucleophilic reagents.
摘要：
我们报道了在温和条件下铁催化的脱羧C（sp3）-O键形成反应，可见光照射的无碱条件。该转化使用容易获得且结构多样的羧酸，铁光催化剂，和2,2,6,6-四甲基哌啶1-氧基(TEMPO)衍生物作为氧合试剂。该方法在具有宽范围的立体电子性质和官能团的酸中表现出宽范围。所开发的反应被应用于一系列生物活性分子的后期氧合。该反应利用铁络合物通过光诱导的羧酸盐至铁的电荷转移直接从羧酸产生碳为中心的自由基的能力。动力学，电化学,EPR,UV-Vis,HRMS和DFT研究表明，TEMPO在反应中具有三重作用：作为氧合试剂，一种氧化剂来转化铁催化剂，和用于羧酸去质子化的内部碱。所获得的TEMPO加合物代表了通用的合成中间体，这些中间体进一步使用商业有机光催化剂和亲核试剂进行C-C和C-杂原子键形成反应。
