Dienamine Activation of Diazoenals: Application to the Direct Synthesis of Functionalized 1,4‐Oxazines

A novel rhodium‐catalyzed dienamine activation of diazoenals resulted in a new class of γ‐functionalized donor–acceptor dienamines. The synthetic utility of these dienamines has been demonstrated in a cooperative rhodium(II)/Brønsted acid and gold(I)‐catalyzed direct [3+3] annulation of enaldiazo ketones with N‐propargyl anilines, thus leading to highly substituted enal‐functionalized 1,4‐oxazines. The reaction is proposed to involve dienamine activation through the diacceptor rhodium enalcarbenoid NH‐insertion and a gold‐catalyzed intramolecular site‐selective 6‐exo‐dig heterocyclization. The methodology was applied to the efficient synthesis of structurally complex [1,4]oxazino[4,3‐a]quinolone, which is present in the antibacterial agent PNU‐286607.