Iron-Catalyzed Oxidative Tandem Reactions with TEMPO Oxoammonium Salts: Synthesis of Dihydroquinazolines and Quinolines

A straightforward iron-catalyzed divergent oxidative tandem synthesis of dihydroquinazolines and quinolines from N-alkylanilines using a TEMPO oxoammonium salt as a mild and nontoxic oxidant has been developed. Fe­(OTf)₂ was the Lewis acid catalyst of choice for the formation of dihydroquinazolines, whereas FeCl₃ led to better results for the synthesis of quinolines. This divergent approach implies that, for both syntheses, direct oxidative functionalization of a α-C­(sp³)–H bond of the N-alkylanilines occurs, leading to C–N bond formation or C–C bond formation upon homocondensation or reaction with simple olefins, respectively. Cyclization followed by a final oxidation generates these classes of interesting bioactive heterocycles in one synthetic transformation. Additionally, the one-pot multicomponent synthesis of quinolines from anilines, aldehydes, and olefins has also been successfully developed under these mild oxidative conditions.