Donabauer Karsten, Murugesan Kathiravan, Rozman Urša, Crespi Stefano, König Burkhard
Department of Organic Chemistry, University of Regensburg, Universitätsstraße 31, 93053, Regensburg, Germany.
Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, The Netherlands.
Chemistry. 2020 Oct 9;26(57):12945-12950. doi: 10.1002/chem.202003000. Epub 2020 Sep 17.
A metal-free generation of carbanion nucleophiles is of prime importance in organic synthesis. Herein we report a photocatalytic approach to the Corey-Seebach reaction. The presented method operates under mild redox-neutral and base-free conditions giving the desired product with high functional group tolerance. The reaction is enabled by the combination of photo- and hydrogen atom transfer (HAT) catalysis. This catalytic merger allows a C-H to carbanion activation by the abstraction of a hydrogen atom followed by radical reduction. The generated nucleophilic intermediate is then capable of adding to carbonyl electrophiles. The obtained dithiane can be easily converted to the valuable α-hydroxy carbonyl in a subsequent step. The proposed reaction mechanism is supported by emission quenching, radical-radical homocoupling and deuterium labeling studies as well as by calculated redox-potentials and bond strengths.
在有机合成中，无金属生成碳负离子亲核试剂至关重要。在此，我们报道一种光催化的Corey-Seebach反应方法。所提出的方法在温和的氧化还原中性和无碱条件下进行，对官能团具有高耐受性，能给出所需产物。该反应通过光催化和氢原子转移（HAT）催化相结合实现。这种催化合并允许通过氢原子的抽象将C-H活化成碳负离子，随后进行自由基还原。然后生成的亲核中间体能够加成到羰基亲电试剂上。在后续步骤中，所得到的二硫烷可以很容易地转化为有价值的α-羟基羰基化合物。发射猝灭、自由基-自由基自偶联和氘标记研究以及计算得到的氧化还原电位和键强度支持了所提出的反应机理。
