Rh‐Catalyzed Chemodivergent [3+3] Annulations of Diazoenals and α‐Aminoketones: Direct Synthesis of Functionalized 1,2‐Dihydropyridines and Fused 1,4‐Oxazines

Abstract

AbstractNovel rhodium‐catalyzed [3+3] annulations of diazoenals and α‐amino ketones has been disclosed here. The reactivity of diazoenals has been switched from carbenoid to vinylogous NH‐insertion by altering acyclic to cyclic α‐amino ketones. In this direction, we report an efficient strategy to synthesize 1,2‐dihydropyridines (DHPs) and fused 1,4‐oxazines. Mechanistic investigation revealed that the formyl group is necessary for carbenoid [3+3] annulation and the cyclohexyl group is the dictating factor for vinylogous NH‐ insertion. The synthetic utility of 1,2‐dihydropyridines was demonstrated by synthesizing piperidine, pyrido[1,2‐a]indole, and 2‐pyridone scaffolds. Further, structural diversification of fused 1,4‐oxazines resulted in the short synthesis of hexahydroquinolin‐2(1H)‐ones, hexahydro quinolines and tetrahydroquinolinones via ring opening rearrangement and a new oxidative deformylation, respectively.