45Dihydropyrimidine

4,5-Dihydropyrimidine is a partially hydrogenated form of the heterocyclic ring pyrimidine. In this compound, the C4–C5 bond is saturated, leaving carbons 4 and 5 as sp3-hybridized atoms while the ring still contains two nitrogens at positions 1 and 3. The partial saturation removes the aromatic character of pyrimidine, yielding a non-aromatic six-membered heterocycle that remains a versatile scaffold for chemical modification.

Synthesis and availability of 4,5-dihydropyrimidine typically involve selective hydrogenation of pyrimidine or substituted pyrimidines under catalytic conditions, such as hydrogen with a metal catalyst. It can also arise as an intermediate in routes to more complex dihydropyrimidine derivatives, including those prepared via multi-component or cyclization strategies that generate the dihydropyrimidine core.

Reactivity and derivatives of this scaffold are characterized by functionalization at the C4 and C5 positions and by substitutions on the ring nitrogens. The dihydropyrimidine core also serves as a precursor to a variety of functionalized derivatives, including more highly substituted dihydropyrimidines and related heterocycles. The core structure is of interest in medicinal and organic chemistry as a flexible building block for exploring structure–activity relationships.

Applications and significance: 4,5-Dihydropyrimidine and its derivatives are used as core scaffolds in chemical synthesis and drug discovery. Related dihydropyrimidinone derivatives, often accessed from this scaffold in multi-component reactions, have been studied for pharmacological activities and as ligands in coordination chemistry.