Phosphonium Salt Catalyzed Henry Nitroaldol Reactions

Trihexyl(tetradecyl)phoshonium decanoate was shown to be an effective promoter for the Henry nitroaldol reaction of nitromethane with aromatic aldehydes. A mechanism is proposed involving Lewis acid activation of the carbonyl group proceeding through a trigonal-bipyramidal intermediate. Evidence in accord with the postulated pathway as opposed to a base or phase transfer-mediated route involving proton transfer from the nitroalkane is presented.