Evaluation of the n-phthaloyl moiety as protecting group in aminoacylphosphonic derivatives

Reaction of dimethyl benzoylphosphonate with hydrazine hydrate gave exclusively benzhydrazide. Reaction of methyl lithium benzoylphosphonate with hydrazine hydrate gave the corresponding hydrazone (3) as a 65:35 mixture of E and Z isomers. Reaction of hydrazine hydrate with diisopropyl 4-phthalimidobutanoylphosphonate gave mainly products resulting from nucleophilic attack of hydrazine on the carbonyl of the acylphosphonate and only a small percentage of phthalhydrazide. From our results it appears that the N-phthaloyl protecting group is not suitable for the transient protection of amino groups during attempts to synthesize aminoacylphosphonates.