Visible Light‐Promoted Beckmann Rearrangements: Separating Sequential Photochemical and Thermal Phenomena in a Continuous Flow Reactor

• Yuesu Chen
• David Cantillo
• C. Oliver Kappe

• Karl-Franzens-Universitat Graz, Institute of Chemistry, 8010 Graz, AUSTRIA

The Beckmann rearrangement of oximes to amides typically requires strong acids or highly reactive, hazardous electrophiles and/or high tempertatures 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 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 all side products that were being obtained with the original one‐pot method.

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