Highly diastereoselective nitrone cycloaddition onto a chiral ketene equivalent: asymmetric synthesis of cispentacin.

A highly diastereoselective intramolecular nitrone cycloaddition onto a chiral ketene equivalent, obtained by Horner−Wadsworth−Emmons olefination of either enantiomer of bis-sulfinyl phosphonate 6, is described. Cycloaddition gave 5,5-disubstituted isoxazolidine 10 in good yield as a single diastereomer. Catalytic hydrogenolysis of 10 furnished either enantiomer of optically pure cis-2-aminocyclopentane-1-carboxylic acid.