[4749-28-4] · C3H5NO2 · 2-Nitro-1-propene · (MW 87.09)
Physical Data: bp 56-57 °C/86 mmHg, 50 °C/60 mmHg; n
Solubility: sol Et2O, THF, acetone, CH2Cl2.
Preparative Methods: by dehydration of 2-nitro-1-propanol (ca. 98% purity commercially or prepared from Nitroethane and formalin, yield 70%2) with phthalic anhydride (73%)3 or Acetic Anhydride-AcONa (85%).4
Handling, Storage, and Precautions: pure 2-nitro-1-propene may be stored in a freezer for several weeks; best prepared immediately before use since it tends to polymerize; this reagent is a powerful lachrymator. Use in a fume hood.
This reagent readily undergoes addition reactions with many different nucleophiles to give saturated nitro compounds,5 which are readily converted into a variety of compounds such as amines or ketones via reduction or the Nef reaction, respectively (eq 1).1
Lewis acid-promoted addition of silyl enol ethers to this reagent provides a very useful method for the preparation of 1,4-diketones (eq 2).4 The 1,4-diketones thus obtained are converted into cyclopentenones in high yields.5
Carboxylic acid dianions or ester enolates react with this reagent to give g-keto acids after hydrolysis (eq 3). However, a low temperature is required to suppress the polymerization of the nitroalkene.6
The base-catalyzed addition of 1,3-diketones to 2-nitropropene followed by heating the initial Michael adducts results in the formation of furans. Thus dimedone and acetylacetone react with 2-nitropropene to give the furans shown in eqs 4 and 5.7
The reaction of this reagent with ketone enolates followed by treatment with Acetic Anhydride gives acetic nitronic anhydrides, which are converted into 1,4-diketones or pyrroles (eq 6).8
The conjugate addition of sulfonyl carbanions to 2-nitropropene, followed by ozonolysis or acid treatment of the resulting nitronates (Nef reaction9) and subsequent elimination of sulfinic acid from b-ketosulfones with 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU), gives a,b-unsaturated ketones (eq 7).10
A unique pyrrole synthesis is realized by the reaction of nitroalkenes with isocyanoacetates. For example, 2-nitropropene condenses with methyl isocyanoacetate in the presence of DBU to produce the pyrrole which is a trail marker pheromone (eq 8).11
A novel electrophilic reagent is formed by diprotonation of nitroalkenes in Trifluoromethanesulfonic Acid. O,O-Diprotonated 2-nitropropene undergoes two alternative electrophilic reactions with benzene which yields a-phenylacetone12 or 4H-1,2-benzoxazine,13 depending on the reaction conditions. These products are not readily synthesized by the conventional Friedel-Crafts reaction. Benzoxazine acts as a precursor of o-benzoquinone methide (eq 9).14
This reagent is an excellent dienophile in the Diels-Alder reaction and it reacts with various dienes.15 The regiochemistry of the Diels-Alder reaction is effectively controlled by the nitro group.16