N-Heterocyclic carbene (NHC)-catalyzed intramolecular benzoin condensation-oxidation.

NHC-Catalyzed intramolecular benzoin condensation-oxidation is developed for the expedient synthesis of diverse cyclic 1,2-diketones incorporated in dibenzo-fused seven-membered heterocycles in good to excellent yields, under ambient conditions. The presented carbene-catalyzed transformation appears to proceed through the benzoin intermediate followed by aerobic oxidation.

The base-free van Leusen reaction of cyclic imines on water: synthesis of N-fused imidazo 6,11-dihydro ß-carboline derivatives.

Construction of imidazoles has been demonstrated on water under base-free conditions. The reaction of dihydro ß-carboline imines and p-toluenesulfonylmethyl isocyanides furnished the corresponding substituted N-fused imidazo 6,11-dihydro ß-carboline derivatives in very good yields under ambient conditions. The use of deuterium oxide (D2O) as a solvent enabled the incorporation of deuterium isotopes in the imidazole ring.

N-Heterocyclic carbene (NHC)-catalyzed oxidation of unactivated aldimines to amides via imine umpolung under aerobic conditions.

Herein, we disclose an NHC-catalyzed aerobic oxidation of unactivated aldimines for the synthesis of amides via umpolung of imines proceeding through an aza-Breslow intermediate. We have developed an eco-friendly method for the conversion of imines to amides by using molecular oxygen in air as the sole oxidant and dimethyl carbonate (DMC) as a green solvent under mild reaction conditions. Broad substrate scope, high yields and gram scale syntheses expand the practicality of the developed method.

N-Heterocyclic carbene (NHC)-catalyzed tandem imine umpolung-aza-Michael addition-oxidation of ß-carboline cyclic imines.

Herein we describe an NHC-catalyzed umpolung of ß-carboline-based cyclic imines for their conversion to the corresponding N-substituted cyclic amides. The key to the success of this transformation appears to be that NHC upon reaction with the imine concomitantly goes through the generation of an aza-Breslow intermediate and aza-Michael addition followed by oxidation with molecular oxygen to deliver the N-substituted amide products. The developed method has enabled the synthesis of various biologically relevant ß-carboline-1-one derivatives in good yields.