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Redox-Active Thiocarbonyl Auxiliaries in Ni-Catalyzed Cross-Couplings of Aliphatic Alcohols
Accounts of Chemical Research ( IF 16.4 ) Pub Date : 2023-12-04 , DOI: 10.1021/acs.accounts.3c00541
John J Monteith 1 , Sophie A L Rousseaux 1
Affiliation  

The Barton–McCombie deoxygenation reaction first established the use of O-alkyl thiocarbonyl derivatives as powerful redox-active agents for C(sp3)–O reduction. In recent years, first-row transition metals capable of engaging with alkyl radical intermediates generated from O-alkyl thiocarbonyl derivatives using alternative stoichiometric radical precursors have been developed. Given the ability of select Ni catalysts to both participate in single-electron oxidative addition pathways and intercept alkyl radical intermediates, our group has investigated the use of O-alkyl thiocarbonyl derivatives as electrophiles in novel cross-coupling reactions. After describing related work in this area, this Account will first summarize our entry point into this field. Here, we used the cyclopropane ring as a reporter of leaving group reactivity to aid in the design and optimization of a novel redox-active O-thiocarbamate leaving group for C(sp3)–O arylation. Motivation for this pursuit was driven by the propensity of the cyclopropane ring to undergo ring opening under polar (2e) oxidative addition pathways or to be maintained under single-electron (1e) conditions. Using these guiding principles, we developed a method for the deoxygenative arylation of cyclopropanol derivatives using a Ni catalyst without the need for a stoichiometric external reductant or photocatalyst. We next summarize our evaluation of an alternative redox-active O-thiocarbonyl imidazole auxiliary in a related deoxygenative cross-coupling. This work demonstrated an extension of our initial approach to the deoxygenative arylation of primary and secondary aliphatic alcohol derivatives. A brief mechanistic investigation revealed that this reaction likely proceeds via a distinct mechanism involving direct homolytic C(sp3)–O bond cleavage. We conclude this Account with a summary of work aimed toward a unique approach for thiocarboxylic acid derivative synthesis. This project was inspired by the efficiency of thionoester generation under most of the reaction conditions evaluated in our prior investigations. Using alcohol, amine, or thiol starting materials, which were activated with convenient thiocarbonyl sources in a single step, we optimized for a Ni-catalyzed cross-coupling capable of providing access to a range of thionoester, thioamide, or dithioester products. In summary, our work has revealed the potential of redox-active thiocarbonyl auxiliaries in Ni-catalyzed cross-couplings with C(sp3)–O electrophiles. We anticipate that the continued investigation of aliphatic thiocarbonyl derivatives as radical precursors with alternative single-electron inputs will be an area of continued growth in the years to come.

中文翻译:


镍催化脂肪醇交叉偶联中的氧化还原活性硫代羰基助剂



Barton-McCombie 脱氧反应首先确立了使用O -烷基硫代羰基衍生物作为 C(sp 3 )–O 还原的强大氧化还原活性剂。近年来,已经开发出能够与使用替代化学计量自由基前体由O-烷基硫代羰基衍生物产生的烷基自由基中间体结合的第一行过渡金属。鉴于精选的Ni催化剂既能参与单电子氧化加成途径又能拦截烷基自由基中间体的能力,我们的小组研究了在新型交叉偶联反应中使用O-烷基硫代羰基衍生物作为亲电子试剂。在描述了该领域的相关工作后,本账户将首先总结我们进入该领域的切入点。在这里,我们使用环丙烷环作为离去基团反应性的报告子,以帮助设计和优化用于 C(sp 3 )–O 芳基化的新型氧化还原活性O -硫代氨基甲酸酯离去基团。这一追求的动机是由环丙烷环在极性(2e)氧化加成途径下进行开环或在单电子(1e)条件下保持的倾向所驱动。利用这些指导原则,我们开发了一种使用镍催化剂对环丙醇衍生物进行脱氧芳基化的方法,无需化学计量的外部还原剂或光催化剂。接下来,我们总结了对相关脱氧交叉偶联中替代氧化还原活性O-硫代羰基咪唑辅助剂的评估。这项工作证明了我们最初的方法对伯和仲脂肪醇衍生物的脱氧芳基化的扩展。 一项简短的机理研究表明,该反应可能通过涉及直接均裂 C(sp 3 )–O 键断裂的独特机制进行。我们总结了旨在合成硫代羧酸衍生物的独特方法的工作总结。该项目的灵感来自于我们之前研究中评估的大​​多数反应条件下硫代酸酯的生成效率。使用醇、胺或硫醇起始材料,通过方便的硫代羰基源一步活化,我们优化了镍催化的交叉偶联,能够提供一系列硫代酸酯、硫代酰胺或二硫代酯产品。总之,我们的工作揭示了氧化还原活性硫代羰基助剂在 Ni 催化与 C(sp 3 )–O 亲电子试剂交叉偶联中的潜力。我们预计,对脂肪族硫代羰基衍生物作为具有替代单电子输入的自由基前体的持续研究将是未来几年持续增长的领域。
更新日期:2023-12-04
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