23dihydropyrimidine

23dihydropyrimidine, commonly referred to as 2,3-dihydropyrimidine, is a dihydro derivative of pyrimidine. In this non-aromatic six-membered heterocycle, the double bond between the C2 and C3 positions of the parent pyrimidine is reduced, giving a ring that retains two nitrogen atoms at positions 1 and 3. The molecular formula is C4H6N2. Because the ring is no longer aromatic, its electronic structure and reactivity differ from that of pyrimidine.

The core structure remains a heterocycle with two ring nitrogens, but the loss of aromaticity generally reduces stability and alters reactivity toward electrophiles and oxidants. Substituent patterns on the ring can influence basicity and solubility, and the compound can exist in different conformations depending on substitution.

Synthesis of 2,3-dihydropyrimidine typically involves selective hydrogenation of pyrimidine or hydrogenation of substituted derivatives under controlled catalytic conditions. Achieving site-selectivity to stop at the 2,3-dihydro stage can be challenging, and complete over-reduction to saturated rings such as piperidine derivatives is a possibility under more aggressive conditions. The compound can often be interconverted back to pyrimidine by dehydrogenation, or further hydrogenated to more saturated heterocycles.

Applications and occurrence: 2,3-dihydropyrimidine serves mainly as an intermediate in organic synthesis and as a scaffold for medicinal chemistry exploration. Substituted dihydropyrimidines can act as precursors to more complex heterocycles or functionalized amines. While not as widely used as its aromatic counterpart, the 2,3-dihydro form is investigated for properties relevant to drug design and materials science.

See also: pyrimidine, dihydropyrimidine derivatives, hydrogenation.