Asymmetric Synthesis of α‐Aminophosphonic Acids by Cycloaddition of N ‐Glycosyl‐ C ‐dialkoxyphosphonoylnitrones

Addition of dialkyl phosphites to the nitrone 6 , formed in situ from the oxime 5 and formaldehyde gave the hydroxylamines 7 (86%) and 8 (88%), which reacted with p ‐benzoquinone in the presence of ethylene via the C ‐dialkoxyphosphonoylnitrones 9 and 10 to yield the cycloaddition products 11 – 14 (80–85%) with a diastereoselectivity of about 50%. The cycloaddition products were transformed into the monoisopropylidene derivatives 15 – 18 and the diacetates 19 – 22 . Comparison of the NMR spectra and the specific rotations of the compounds 19 – 22 with those of the corresponding α‐ammo‐acid derivatives 23 – 26 of known configuration indicated preferential formation of the L ‐isomers. The cycloaddition products were transformed in good yield into the L ‐α‐aminophosphonic acids 29 , 30 , 36 , and 39 .