Total Syntheses of β‐Carboline‐Based Natural Alkaloids Including Secofascaplysin A, Strychnocarpine, Rutaecarpine and Euxylophoricine A Using NHC‐Catalyzed Imine Umpolung‒Oxidation

Despite N-heterocyclic carbene (NHC) organocatalysis proceeding through umpolung reactivity mode, which has been widely explored using aldehydes, the conspicuous use of imines is still an underdeveloped area. Oxidation of imines to amides using organocatalysis is an attractive topic. Herein, we have demonstrated the application of NHC-catalyzed oxidation of a cyclic imine to the corresponding cyclic amide, proceeding through imine umpolung, as a key step in the total syntheses of biologically active natural β-carboline alkaloids of marine/plant origin, including secofascaplysin A, strychnocarpine, rutaecarpine, euxylophoricine A and also an mGluR1 antagonist.