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Visible Light‐Promoted Beckmann Rearrangements: Separating Sequential Photochemical and Thermal Phenomena in a Continuous Flow Reactor
Author(s) -
Chen Yuesu,
Cantillo David,
Kappe C. Oliver
Publication year - 2019
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201900231
Subject(s) - beckmann rearrangement , chemistry , electrophile , reagent , photochemistry , thermal , flow (mathematics) , reactive intermediate , catalysis , organic chemistry , thermodynamics , physics , geometry , mathematics
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.