Stereoselective synthesis of fluorinated isoxazolidines and 2,3-dihydroisoxazoles: A cycloadditive route to enantiomerically pure amino fluoro alcohols

3-(Fluoroalkyl)isoxazolidines 6 and -2,3-dihydroisoxazoles 8 have been obta ined in enantiomerically pure form with good diastereoselectivity by 1,3-di polar cycloaddition of diethyl fumarate and dimethylacetylene dicarboxylate , respectively, to the chiral fluorinated nitrone (R)-5. The latter has bee n prepared from the beta-fluoromethyl-beta-oxo sulfoxide (R-S)-1, by a synt hetic sequence where the chiral and enantiomerically pure sulfinyl function acts as a removable source of chirality. Reductive opening of isoxazolidin es 6 then afforded amino fluoromethyl diols 7 in good yields.