"Continuous-Flow N-Heterocyclic Carbene Generation and Organocatalysis"

Lorenzo Di Marco, Morgan Hans, Lionel Delaude, and Jean-Christophe M. Monbaliu

Journal Cover
          source: Chemistry - A European Journal
            year: 2016
          volume: 22
      first page: 4508
       last page: 4514
             doi: 10.1002/chem.201505135

graphical abstract

Abstract: Two methods were assessed for the generation of common N-heterocyclic carbenes (NHCs) from stable imidazol(in)ium precursors using convenient and straightforward continuous-flow setups with either a heterogeneous inorganic base (Cs2CO3 or K3PO4) or a homogeneous organic base (KN(SiMe3)2). In-line quenching with carbon disulfide revealed that the homogeneous strategy was most efficient for the preparation of a small library of NHCs. The generation of free nucleophilic carbenes was next telescoped with two benchmark NHC-catalyzed reactions; namely, the transesterification of vinyl acetate with benzyl alcohol and the amidation of N-Boc-glycine methyl ester with ethanolamine. Both organocatalytic transformations proceeded with total conversion and excellent yields were achieved after extraction, showcasing the first examples of continuous-flow organocatalysis with NHCs.

Keywords: Carbenes, Continuous-Flow, Microreactors, Organocatalysis, Transesterification

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