REGIOSELECTIVE AND STEREOSELECTIVE SYNTHESIS OF TRIFLUOROMETHYLATED ISOXAZOLIDINES BY 1,3-DIPOLAR CYCLOADDITION OF 1,1,1-TRIFLUORO-3-PHENYLSULFONYLPROPENE WITH NITRONES, AND THEIR CONVERSION INTO TRIFLUOROMETHYLATED SYN-3-AMINO ALCOHOLS

1,1,1-Trifluoro-3-phenylsulfonylpropene 1, a useful synthetic precursor for trifluoromethylated compounds, has been prepared from methyl phenyl sulfone 2 and ethyl trifluoroacetate. The 1,3-dipolar cycloaddition of 1 with various nitrones 5a-f gave 5-trifluoromethylisoxazolidines 6a-f with a high degree of regio- and stereoselectivity, The adducts 6a-f were converted into trifluoromethylated syn-3-amino alcohols 8a-d by desulfonylation with Na-Hg, followed by reductive cleavage of the N-O bond by catalytic hydrogenation. Conversion of 8a and 8d into the cyclic carbamates 10a and 10d confirmed the assigned stereochemistry of 8 and, hence, of the cycloadduct 6a-f.