Reduction of Nitrostyrenes to Nitroalkanes with Borohydride Exchange Resin (BER)
We wish to report that nitroalkenes are selectively reduced to nitroalkanes by borohydride supported on an ion exchange resin in MeOH at room temperature. Borohydride bound resin was prepared by stirring commercially avaliable anion exchange resin, Amberlite IRA-400 (Cl- form) with aqueous sodium borohydride solution. The reaction procedure involves the addition of borohydride ion exchange resin to a methanolic solution of the nitroalkene. The reactions are complete in 60 minutes and can be monitored by TLC (and in some cases by the disapperance of the yellow color of the nitroalkene). The product nitroalkanes are isolated by removal of the ion exchange resin by filtration and evaporatin of the filtrate under reduced pressure. The resin may be reused by rinsing the spent material with dilute hydrochloric acid followed by regeneration with aqueous sodium borohydride solution.
Borohydride bound ion exchange resin
An aqueous solution of sodium borohydride (0,5 M, 100 ml) was stirred with 10 g of wet chloride form resin (Amberlite IRA-400) for one hour. The resulting resin was washed thoroughly with distilled water until free from excess sodium borohydride. The borohydride bound exchange resin was dried in vacuo at 65°C for 5 hours. The dried resin was analyzed for borohydride content by hydrogen evolution on acidification with 0,05 N HCl; the average capacity of the ion exchange resin was found to be 2,5 mmol BH4-/g of resin.
General procedure for the synthesis of nitroalkanes
The preparation of 2-(2-nitropropyl)thiophene is representative of the procedure employed.
2-(2-Nitropropenyl)thiophene (2 mmol 0,338 g) was dissolved in MeOH (40 ml) in a 100 ml Erlenmeyer flask containing a magnetic stirring bar. Borohydride supported ion exchange resin (2,2 mmol, 0,88 g) was then added at room temperature to the well stirred solution. A mildely exothermic reaction ensued with the gradual disapperance of the yellow coloration. The reaction mixture was stirred for 60 minutes at room temperature and the the resin was filtered off, washed twice with MeOH (2x10 ml). Removal of the MeOH under reduced pressure yielded 0,265 g (78%) of pure 2-(2-nitropropyl)thiophene as an oil.
 Kabalka et. al., Synthetic Communications, 19 (5&6), 805-811 (1989)