Stereoselective cycloaddition of nitrile oxides to a dispiroketal-protected but-3-ene-1,2-diol

Article abstract of DOI:10.1016/0957-4166(95)00362-S

The influence of a dispiroketal protecting group on the π-facial selectivity of nitrile oxide cycloaddition of S-but-3-ene-1,2-diol has been investigated. Ethoxycarbonylformonitrile oxide and benzonitrile oxide undergo regiospecific and diasteroeselective addition to alkene 7 to afford isoxazolines 11 and 12. The major adducts (11a and 11b) are formed with 44% and 50% d.e. respectively, and in each case have S-configuration at C-5, the new stereogenic centre.