1-Methyl-3,5-dinitro-2-pyridone serves as an excellent substrate for nucleophilic-type ring transformation because of the electron deficiency and presence of a good leaving group. In this review, we focus on the three-component ring transformation (TCRT) of dinitropyridone involving a ketone and a nitrogen source. When dinitropyridone is allowed to react with a ketone in the presence of ammonia, TCRT proceeds to afford nitropyridines that are not easily produced by alternative procedures. Ammonium acetate can be used as a nitrogen source instead of ammonia to undergo the TCRT, leading to nitroanilines in addition to nitropyridines. In these reactions, dinitropyridone serves as a safe synthetic equivalent of unstable nitromalonaldehyde.
Heterocyclic Compounds/chemical synthesis , Nitrogen/chemistry , Pyridones/chemistry , Acetates/chemistry , Heterocyclic Compounds/chemistry , Ketones/chemistry , Stereoisomerism
When 2-(phenylethynyl)pyridine was oxidized, the formed N-oxide immediately cyclized at the ethynyl group to form isoxazolo[2,3-a]pyridinium salt. This salt underwent Reissert-Henze-type reactions with alcohol in the presence of a base to afford 6-substituted 2-phenacylpyridines, which are not easily synthesized through alternative procedures. When acetonitrile was used as a solvent, an amide functional group was introduced into the phenacylpyridine framework. Moreover, a hetero-atom at the 6-position facilitated the oxidation of the phenacyl group to afford α-diketones upon simple exposure of the reaction mixture to air.
A metal-free, mild and efficient method for the synthesis of 2-methylquinolines was successfully developed by condensation of anilines with vinyl ethers in the presence of catalytic amount of iodine. Modification of both pyridine and benzene moieties was easily achieved by changing only the vinyl ether and aniline. In this reaction, the iodine species was revealed to show dual behavior; molecular iodine serves as an oxidant, while its reduced form, hydrogen iodide, activates the vinyl ether. The redox reaction between these iodine species enables the use of a catalytic amount of iodine in this synthetic method.
Aniline Compounds/chemistry , Iodine/chemistry , Quinaldines/chemistry , Vinyl Compounds/chemistry , Catalysis , Magnetic Resonance Spectroscopy , Molecular Structure , Oxidation-Reduction , Quinaldines/chemical synthesis
An alternative method for the synthesis of 3-alkylated/arylated 5-nitropyridines was developed involving a three-component ring transformation of 3,5-dinitro-2-pyridone on treatment with aldehyde in the presence of ammonium acetate. This method facilitates the modification of the substituent at the 3-position by changing the precursor aldehyde. The use of solid ammonium acetate instead of ammonia as the nitrogen source renders the synthetic method more practical and user-friendly.
