In Synthetic communications, they say: "Since the reaction of nitroalkenes with NaBH4 generally produces Michael adducts (especially with nitrostyrene derivatives), we decided to minimize the side reactions by slowly adding NaBH4 to the nitroalkene dissolved in THF-MeOH (10:1, v/v). The reactions were completed within 40 min. at room temperature (the reaction could be monitored by the disappearance of the yellow color of the nitroalkene."
Yield with phenyl-2-nitrostyrene: 64 %
phenyl-2-nitropropene: 82 %
In Tetrahedron Letters, they have solved the problem of the side reaction that produces those damned dimeric compounds. They say: "Reduction of a variety of nitrostyrenes with NaBH4 in the presence of silica gel in a mixture of chloroform and 2-propanol furnished the corresponding nitroalkanes free of dimers in near quantitative yields. The amount of silica gel required to suppress the formation of dimeric product completely varied but was in the range of 1 - 3 g / mmol of nitrostyrene.
Example: To an efficiently stirred mixture of 2,3-dimethoxyphenyl-2-nitrostyrene (209 mg, 1 mmol), silica gel (2 g, column chromatography grade), 2-propanol (3 ml), chloroform (16 ml) was added NaBH4 (156 mg, 4,1 mmol) in 40 mg portions over a period of 15 min at 25 °C. The mixture was stirred for additional 15 min, by which time the yellow color due to the nitrostyrene has completely disappeard. Excess NaBH4 was decomposed with dilute HCl and the mixture was filtered. The filter was washed with CH2Cl2 and the combined filtrates were washed with brine, dried (Na2SO4) and then evaporated in vacuo to dryness to give 199 mg (94%) of the nitroethane as a colorless oil.
Purity: 1 spot on TLC."
If you do this with P2NP, use 1 g silica gel / mmol nitropropene. Reaction time: 45 min, yield: 93 %
In comparison with Beaker's procedure: the described method has 2 advantages. 1) It uses 2 eq. NaBH4 instead of 4. 2) There is no dimer formation. Therefore, if this procedure can be scaled up, and if you combine this with Beaker's CTH reaction, you will have a kickass reaction path.
Could someone test and scale up this procedure with 2,5-dimethoxynitrostyrene of P2NP? For the moment, I am just a damned theoretical organic chemist