Aza-Michael Addition of 2-Aminopyridine with 7-Aza-2-Indolone Chalconides: Synthesis of Functionalized α-Enaminones and One-Pot N-Alkenylation–Dearomatization of Pyridine Ring

Abstract A facile, efficient, and catalyst-free synthetic route for the synthesis of α-enaminones, a motif found in synthetically and biologically active compounds has been developed by the reaction of 2-aminopyridine with 7-aza-2-indolone chalcone derivatives adopting aza-Michael addition as a key reaction. To demonstrate the substrate scope, an array of α-enaminones was synthesized from a number of N-alkylated-3-acylidene-7-aza-2-indolones and aromatic 2-amino azaheterocycles and carbocycles in excellent yields. The structure and relative stereochemistry of representative compounds were established by the single-crystal XRD. Based on control experiments, a plausible and alternate operating mechanism for the formation of the products is also provided. Significantly, the synthetic transformation of the aza-Michael products thus obtained was successfully demonstrated by an unusual heterocyclic functionalization via N-alkenylation and dearomatization of the pyridine ring has also been provided.