An efficient protocol for the aza-Diels-Alder reaction of electron-deficient 1,3-dienes with unactivated imines in the presence of a cationic cobalt(III) porphyrin complex was developed. The transformation proceeded smoothly to afford the desired piperidine scaffold within 2 h at ambient temperature. Highly chemoselective cycloaddition of imines with dienes in the presence of a variety of carbonyl compounds was also demonstrated.
FeCl<sub>3</sub> as an Ion-Pairing Lewis Acid Catalyst. Formation of Highly Lewis Acidic FeCl<sub>2</sub><sup>+</sup> and Thermodynamically Stable FeCl<sub>4</sub><sup>–</sup> To Catalyze the Aza-Diels–Alder Reaction with High Turnover Frequency
provided fundamental insights into the disproportionation and structure of the resulting ion-paired iron complex. A theoretical study was performed to analyze the catalytic reaction and better understand the “ion-pairing effect” which transforms simple FeCl3 into a high turnover frequency Lewis acid catalyst in the aza-Diels–Alder reaction of nonactivated dienes and imines.