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.