Rcf. Jones et al., 1,3-DIPOLAR CYCLOADDITION ROUTE TO OXYGEN HETEROCYCLIC TRIONES, Journal of the Chemical Society. Perkin transactions. I, (3), 1998, pp. 411-416
1,3-Dipolar cycloadditon of nitrile oxides, formed in situ by dehydrat
ion of primary nitro compounds, with pyrrolidine enamines of protected
gamma-hydroxy-beta-keto esters affords isoxazole-4-carboxylates; thes
e are subjected to N-O bond cleavage and lactonisation to afford 3-acy
ltetronic acids and 3-acyl-4-hydroxytetrahydropyran-2-ones.