Nitroacetonitrile and Its Synthetic Equivalents

Nitroacetonitrile (NAN) serves as a cyano(nitro)methylating agent facilitating the construction of polyfunctionalized compounds; however, its explosive property is a significant drawback in terms of practical handling. Alkali metal salts of NAN are thermally stable, but their insolubility in organic solvents restricts their use as a synthetic reagents. On the contrary, dipyrrolidinium cyano-aci-nitroacetate is soluble in common organic solvents and thermally stable, allowing for its use as an alternative synthetic equivalent of nitroacetonitrile for the construction of polyfunctionalized frameworks via cyano(nitro)methylation.

Comparison of Substituting Ability of Nitronate versus Enolate for Direct Substitution of a Nitro Group

α-Nitrocinnamate underwent the conjugate addition of an active methylene compound such as nitroacetate, 1,3-dicarbonyl compound, or α-nitroketone, and the following ring closure afforded functionalized heterocyclic frameworks. The reaction of cinnamate with nitroacetate occurs via nucleophilic substitution of a nitro group by the O-attack of the nitronate, which results in isoxazoline N-oxide. This protocol was applicable to 1,3-dicarbonyl compounds to afford dihydrofuran derivatives, including those derived from direct substitution of a nitro group caused by O-attack of enolate. It was found the reactivity was lowered by an electron-withdrawing group on the carbonyl moiety. When α-nitroketone was employed as a substrate, three kinds of products were possibly formed; of these, only isoxazoline N-oxide was identified. This result indicates that the substituting ability of nitronate is higher than that of enolate for the direct S_N2 substitution of a nitro group.

Nitroacetonitrile as a versatile precursor in energetic materials synthesis

Nitroacetonitrile is the simplest α-nitronitrile; it possesses a single central carbon attached to two strong electronegative, electron-withdrawing groups allowing extensive chemistry through the active methylene center. Free nitroacetonitrile has purification and stability issues, however stable salts of nitroacetonitrile possess the same reactivity as the free acid and are much more stable. Nitroacetonitrile serves as a versatile synthetic precursor in the formation of heterocyclic and polyfunctional aliphatic products and can allow for straightforward conversion to amino, acyl, and other functional groups. A main advantage of using nitroacetonitrile in the formation of heterocyclic-based energetics is its ability to add vicinal amino and nitro moieties onto fused ring structures, a common structural motif in insensitive energetic materials. In this minireview we discuss the preparation of nitroacetonitrile and its stable salts, as well as discuss the range of energetic materials this versatile precursor has found use in.

Nitroacetonitrile is a useful synthetic precursor capable of participating in a wide range of reactions and enables the simple synthesis of annulated heterocyclic systems which are rapidly becoming promising new energetic materials.