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An efficient pot and step economic protocol for synthesis of pyrido[2,3-d]pyrimidine derivatives from a multicomponent aza-Diels–Alder reaction of uracil analogues, aromatic aldehydes and acetophenones in the presence of Na2CO3 in DMF was developed. The key step of the reaction is in situ generation of the reactive dienophile from aldehyde and acetophenone and their subsequent reaction with diene to give the desired product.

A mild and efficient protocol for the synthesis of various tetrahydroquinazolinedione and dihydropyrido[2,3-d]pyrimidine-2,4-dione templates from uracil derivatives utilizing a [4+2]-cycloaddition strategy in a one-pot reaction has been developed.

Dienophiles generated in situ from aldehydes and acetophenones undergo aza-Diels—Alder reaction with uracil derivative (I) followed by oxidative aromatization to give pyridopyrimidines.

In situ generated enimines undergo Diels—Alder reactions with morpholinovinyl- or dimethylaminovinyl substituted uracil derivatives, followed by elimination of the amino group and aromatization to give the title compounds (IV) in good yields.

Uracil derivatives (I) and (IV) are employed as diene components for the reaction with aromatic nitroalkenes.

A facile synthesis of the title compounds is achieved by microwave promoted three-component aza-Diels—Alder reaction of uracil derivative (I), aldehydes, and amines.

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.