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Synthetic methods of cyclic α-aminophosphonic acids and their esters

“…The labile exocyclic P-N bond of 322d,e was cleaved upon the action of phenol to give the final product diazaphospholidine 323 (Scheme 102). [155][156][157] A highly diastereoselective synthetic procedure for the preparation of enantiopure (2S,5S)-4-benzyl-2-alkoxy-2-oxo-5-phenyl-1,4,2-oxazaphosphinanes [(2S, 5S)-1] (326) from (S)-phenylglycinol (307) was achieved by its condensation with benzaldehyde followed by palladium catalyzed hydrogenation to give N-benzyl-(S)-phenylglycinol (324). The latter compound was condensed with formaldehyde (toluene solvent) and the resulting imminium salt was immediately treated with dialkyl phosphite to afford Mannich products (S)-325.…”