Synthesis of 4‑Substituted 3,5-Dinitro-1,4-dihydropyridines by the Self-Condensation of β‑Formyl-β-nitroenamine

3,5-Dinitro-1,4-dihydropyridines
(DNDHPs) are readily constructed
by the acid-promoted self-condensation of β-formyl-β-nitroenamines.
In the DNDHPs, one molecule of the nitroenamine serves as a C3N1 building
block and the other serves as a C2 block. This synthetic method does
not require any special reagents and conditions. When the reaction
is conducted in the presence of electron-rich benzene derivatives,
arylation at the 4-position of DNDHP is achieved by trapping the 3,5-dinitropyridinium
ion intermediate.