ASYMMETRIC-SYNTHESIS OF 3-CHLORO-3-FLUORO-2,4-DISUBSTITUTED AND 3-FLUORO-2,4-DISUBSTITUTED TETRAHYDROFURANS BY THE FLUORINATED SULFOXIDE CHIRON ROUTE

An efficient procedure for the preparation of the title compounds in moderate to high enantiomeric purity has been realized starting from olefins tethered on the fluoriated sulfinyl chiron 6, prepared from methyl 4-methylphenyl sulfoxide and ethyl dichlorofluoroacetate. Radical-promoted cyclization of intermediates 9 according to the tributyltin hydride method afforded 3-chloro-3-fluorotetrahydrofuran derivatives 12, from which the corresponding 3-fluorotetrahydrofurans 15 were obtained by reductive dechlorination. Structural assignments have been done on the basis of H-1, C-13 and F-19 NMR data and NOE difference experiments.