Reaction of tetrahydrofuroisoxazoles with molybdenum hexacarbonyl. A new route to preparation of 3-substituted tetrahydro- and dihydrofuran derivatives

Abstract

3-(4-X-Phenyl)-3a,4,6,6a-tetrahydrofuro[3,4-d]isoxazoles Ia-If (X = H, CH3, CH3O, Cl, F, C6H5) react with molybdenum hexacarbonyl to give not only the expected cis-3-aroyl-4-hydroxytetrahydrofuran III, but also its trans isomer IV and 3-aroyl-2,5-dihydrofuran II. This paper concerns a new preparation of 3-aroyl-2,5-dihydrofuran derivatives starting from 2,5-dihydrofuran via 1,3-dipolar cycloaddition of nitrile oxides, cleavage with molybdenum hexacarbonyl and dehydratation with p-toluenesulfonic acid. The structure of cis-(III) and trans-(IV) derivatives was deduced from both the γ-effect in the 13C NMR and the DQ COSY experiment in the 1H NMR spectra.