Construction of push—pull systems using β-formyl-β-nitroenamine

Abstract

The review is focused on the application of β-formyl-β-nitroenamines, one of the push—pull alkenes, having the biased electron density as well as an electrophilic formyl group and a nucleophilic amino group in the organic synthesis. Due to the multi-functionality, β-formyl-β-nitroenamines exhibit versatile reactivity to facilitate the synthesis of polyfunctionalized compounds possessing push—pull property. Nitroenamines serve as a synthetic equivalent of unstable nitromalonaldehyde to afford nitropyrazoles, nitropyrimidines, nitrodiazepines, and nitrophenoles upon treatment with dinucleophiles such as hydrazines, amidines, 1,2-diamines, and ketones, respectively. When active methylene compounds allowed reacting with the nitroenamines, polyfunctionalized pyridones and 2-amino-5-nitropyridines are obtained. In addition, nitroenamines undergo [4+2] self-condensation to afford 3,5-dinitropyridinium ion, which is easily trapped by benzene derivatives leading to 4-arylated 1,4-dihydropyridines.