Iron-catalyzed oxidative tandem reactions with TEMPO oxoammonium salts: Synthesis of dihydroquinazolines and quinolines

摘要

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 FeCl_3 led to better results for the synthesis of quinolines. This divergent approach implies that, for both syntheses, direct oxidative functionalization of a α-C(sp~3)-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.