dihydropyrimidine

Dihydropyrimidine refers to a class of heterocyclic compounds derived from pyrimidine by partial saturation of the ring. The parent ring is a six-membered heteroaromatic system containing two nitrogen atoms at positions 1 and 3. In dihydropyrimidines one of the double bonds present in pyrimidine is reduced, yielding a non-aromatic, partially saturated ring. Two principal isomers are commonly recognized: 2,3-dihydropyrimidine and 4,5-dihydropyrimidine, depending on which carbon–carbon bond is hydrogenated.

Occurrence and synthesis: Dihydropyrimidines are typically prepared synthetically rather than isolated as natural products. They can be produced by catalytic hydrogenation of pyrimidines or by condensation reactions such as the Biginelli reaction, which furnishes dihydropyrimidinone derivatives (DHPMs) that are versatile intermediates for further modification. Other synthetic routes include cyclization of suitably functionalized beta-dicarbonyl compounds with amidines or related partners.

Properties and applications: The partial saturation of the ring reduces aromatic stabilization and alters the electronic and steric properties compared with pyrimidine. Dihydropyrimidines and related dihydropyrimidinones are valuable building blocks in medicinal chemistry and materials science, with numerous derivatives explored for potential pharmaceutical activity and as intermediates in the synthesis of more complex targets.

See also: Pyrimidine, Dihydropyrimidinone, Biginelli reaction.