The selectivity of the reduction of some trifluoroacetyl-1,3-dioxanes and 1,3-dioxolanes with DIBAH or L-Selectride was studied and compared with that of the corresponding methylketones; the results-in accordance with literature- show an important steric hindrance of the CF 3 group. The selectivity observed in these reductions led to good yields in the syntheses of 5,5,5-trifluorinated derivatives of D and L-pentofuranoses; a new method for the preparation of some functionalized trifluoromethylketones is described.