Azomethines 3-aminocarboxylic acid

The reactions of phosphorous acid are paralleled still further by the additions of hypophosphorus acid to azomethines in practice, mixtures of amines and carbonyl reactants may be employed ", but the drawbacks to the procedure found for the synthesis of aminoalkylphosphonic acids may well apply here also. In a valuable publication, Dingwall and coworkers described the syntheses of (aminoalkyl)phosphinic acid analogues of many of the naturally occurring aminocarboxylic acids by the simple treatment of the benzyhydrylimine derivatives of the necessary amines with hypophosphorous acid, formed in situ when diphenylmethylammonium hypophosphite is treated with an appropriate aldehyde this step is followed by removal of the A -protection with 48% aqueous HBr, with 18% aqueous HCl or with trifluoroacetic acid in boiling methoxybenzene any second amino group was protected as the phthalimido derivative. 

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