Expeditious Synthesis of 2,3,6-Trisubstituted 2H-1,3-Oxazin-4(3H)-ones via the Tertiary Amine-Induced Reaction of 2-Diazo-3-oxoalkanals and Imines Under Mild Conditions

A series of 2,3,6-trisubstituted 2H-1,3-oxazin-4(3H)-one derivatives were conveniently synthesized in satisfactory to good yields by the reaction of imines with 2-diazo-3-oxoalkanals in the presence of a catalytic amount of a tertiary amine during several seconds under mild condition. Different bases and α-diazo-β-dicarbonyl compounds were also evaluated and a reaction mechanism is proposed. Compared with the corresponding thermal- and photo-induced­ reactions, the current method is a metal-free, mild, highly regioselective, and more efficient approach for the synthesis of 2H-1,3-oxazin-4(3H)-one derivatives.