A new diastereoselective synthesis of alpha-aminophosphonates has been developed, based on the reaction, in the presence of trifluoroacetic acid, of trialkyl phosphites with chiral imines derived from (R)- or (S)-1-(alpha-aminobenzyl)-2-naphthol. The reaction proceeds at room temperature in toluene with high diastereoselectivity. The major diastereomer can be separated by crystallization from an appropriate solvent. The relative configuration of both chiral centers of the major diastereomer was determined by single-crystal X-ray structure analysis. The desired alpha-aminophosphonic acids can be obtained in enantiopure form by treatment of the corresponding diastereomers with HCl.

An improved method for enantioseparation of racemic 1-(a-aminobenzyl)-2-naphthols has been developed by the reaction in situ of Betti base product mixtures with L-(+)-tartaric acid taken in a 1:1 ratio. The products of this reaction are (-)-1-(a-aminobenzyl)-2-naphthol tartrate, the acetal of benzaldehyde and tartaric acid as well as (+)-1,3-diaryl-2,3-dihydro-1H-naphth[1,2-e][1,3]oxazine, which can be easily separated by crystallization.

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