Practically Usable C3 Building Blocks for the Syntheses of Nitro Heterocycles

Abstract

-Nitromalonaldehyde (NMA-H) is one of useful synthons for synthesizing nitro compounds. However, NMA-H itself cannot be practically employed because of its unstable property. Therefore, sodium salt of NMA-H (NMA-Na) has been used as its synthetic equivalent from old time, and NMA-Na is still important even now albeit several restrictions with regard to safety and treatability. On the other hand, dinitropyridone, nitropyrimidinone and dinitropyrazole can be employed in place of NMA-Na for the same purpose, and furthermore azadienamines, formylnitroenamines and dinitropyrazole also serve as the synthetic equivalents of NMA-H, which are usable in common organic solvents with safety. These reagents condense with dinucleophiles to afford various kinds of nitro compounds.

Activation of 1-Methyl-5-nitro-2-pyrimidinone by Dearomatization Using a Secondary Amine

“…Ring opening reaction of adduct (7) leading to nitroenamine (8), N-formylpyrrolidine (9) and N-methylurea (10). Yields were determined based on pyrimidinone (1). When adducts (7a) and (7b) were stood in acetonitrile at room temperature for 1 day, the ring opening reaction also proceeded to afford nitroenamine (8), 6 N-formylpyrrolidine (9) and N-methylurea (10) in 17%, 16% and 12% yields, respectively.…”

“…1 1-Methyl-5-nitro-2-pyrimidinone (1) is one of such compounds used for the present purpose that is easily prepared by condensation of N-methylurea and 1,1,3,3-tetramethoxypropane under acidic conditions followed by nitration. 2 The highly electron-deficient property of 1 facilitates the aminolysis to afford azadienamines (2) 3 used as unique bidentate ligands, 4 and half hydrolysis of 2 yields β-formyl-β-nitroenamines (3) which serve as a useful building block for versatile aza-heterocyclic compounds (Scheme 1).…”

Synthesis of Nitroaromatic Compounds via Three-Component Ring Transformations

“…Instead, its sodium salt ( NMA-Na ) has been widely used, although it should be handled carefully because of the explosive impurities [ 14 ]. Thus, it is necessary to develop a safe synthetic equivalent of NMA-H [ 15 ]. From this perspective, a nucleophilic-type ring transformation using pyridone 1 is a useful synthetic method for versatile nitro compounds because of its higher safety.…”

Tailor‐Made Synthesis of N,N,2,6‐Tetrasubstituted 4‐Nitroanilines by Three‐Component Ring Transformation of Dinitropyridone

“…Ring transformation reactions provide a unique method for the synthesis of functionalized heterocyclic compounds, which are not easily prepared by other methods 1,2. We have reported an alternative method for the synthesis of nitropyridines 3 by the three‐component ring transformation (TCRT) of dinitropyridone 1 with aromatic ketones 2 in the presence of ammonium acetate (Scheme ),2 wherein dinitropyridone 1 serves as the synthetic equivalent of unstable nitromalonaldehyde 3. This reaction is initiated by the nucleophilic attack of the enol form of 2 followed by conversion to enamine 4 .…”