Stereoselective Synthesis of Fluorinated Isoxazolidines and 2,3-Dihydroisoxazoles: A Cycloadditive Route to Enantiomerically Pure Amino Fluoro Alcohols

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3-(Fluoroalkyl)isoxazolidines 6 and -2,3-dihydroisoxazoles 8 have been obtained in enantiomerically pure form with good diastereoselectivity by 1,3-dipolar cycloaddition of diethyl fumarate and dimethylacetylene dicarboxylate, respectively, to the chiral fluorinated nitrone (R)-5. The latter has been prepared from the β-fluoromethyl-β-oxo sulfoxide (RS)-1, by a synthetic sequence where the chiral and enantiomerically pure sulfinyl function acts as a removable source of chirality. Reductive opening of isoxazolidines 6 then afforded amino fluoromethyl diols 7 in good yields.