Visible Light-Promoted Beckmann Rearrangements: Separating Sequential Photochemical and Thermal Phenomena in a Continuous Flow Reactor,European Journal of Organic Chemistry

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Visible Light-Promoted Beckmann Rearrangements: Separating Sequential Photochemical and Thermal Phenomena in a Continuous Flow Reactor
European Journal of Organic Chemistry ( IF 2.5 ) Pub Date : 2019-03-08 , DOI: 10.1002/ejoc.201900231
Yuesu Chen _{1,

2} , David Cantillo _{1,

2} , C Oliver Kappe _{1,

2}

Affiliation

The Beckmann rearrangement of oximes to amides typically requires strong acids or highly reactive, hazardous electrophiles and/or elevated temperatures to proceed. A very attractive alternative is the in situ generation of Vilsmeier–Haack reagents, by means of photoredox catalysis, as promoters for the thermal Beckmann rearrangement. Investigation of the reaction parameters for this light‐induced method using a one‐pot strategy has shown that the reaction is limited by the different temperatures required for each of the two sequential steps. Using a continuous flow reactor, the photochemical and thermal processes have been separated by integrating a flow photoreactor unit at low temperature for the electrophile generation with a second reactor unit, at high temperature, where the rearrangement takes place. This strategy has enabled excellent conversions and yields for a diverse set of oximes, minimizing the formation of side products obtained with the original one‐pot method.

中文翻译：

可见光促进的贝克曼重排：分离连续流反应器中的连续光化学和热现象

肟到酰胺的贝克曼重排通常需要强酸或高反应性、危险的亲电子试剂和/或升高的温度才能进行。一个非常有吸引力的替代方案是通过光氧化还原催化原位生成 Vilsmeier-Haack 试剂，作为热贝克曼重排的促进剂。使用一锅策略对这种光诱导方法的反应参数进行的研究表明，该反应受到两个连续步骤中每个步骤所需的不同温度的限制。使用连续流动反应器，通过将用于亲电试剂生成的低温流动光反应器单元与发生重排的高温第二反应器单元集成，将光化学和热过程分开。该策略实现了多种肟的优异转化率和产率，最大限度地减少了原始一锅法获得的副产物的形成。

更新日期：2019-03-08

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