Microwave-Promoted Catalyst- and Solvent-Free Aza-Diels–Alder Reaction of Aldimines with 6-[2-(Dimethylamino)vinyl]-1,3-dimethyluracil

A microwave-promoted aza-Diels–Alder reaction
between 6-[2-(dimethylamino)­vinyl]-1,3-dimethyluracil
and aldimines has been developed for the construction of dihydropyrido­[4,3-d]­pyrimidines. Urea is effectively employed as an environmentally
benign source of ammonia in the absence of any catalyst or solvent.
The key step in the reaction is in situ generation and trapping of
the reactive aldimine formed from urea and aldehyde by the diene system
of the uracil. The reaction is clean, and excellent yields are obtained
in a matter of a few minutes.