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Asymmetric Synthesis of α-Amino Phosphonic Acids Using Stable Imino Phosphonate as a Universal Precursor.

A practical method for synthesizing chiral α-amino phosphonic acid derivatives was developed. Readily available and stable N-o-nitrophenylsulfenyl (Nps) imino phosphonate was utilized as a substrate for a highly enantioselective Friedel-Crafts-type addition of indole or pyrrole nucleophiles catalyzed by chiral phosphoric acid. The resulting adduct was easily converted to N-9-fluorenylmethyloxycarbonyl (Fmoc) amino phosphonic acid, which is useful for synthesizing peptides containing an amino phosphonic acid.