Stereoselective 1,3-dipolar cycloadditions of nitrile oxides to sugar olefins. Synthesis of acyclic-sugar isoxazoline C-nucleoside analogs

Abstract

The cycloaddition 1,3-dipolar of nitrile oxides to sugar nitro olefins and α,β-unsaturated carbonyl olefins has been investigated. The reaction is less regioselective that the cycloaddition of diazoalkanes to the same olefins and while nitrile oxides with bulky substituents afford the sterically less hindered cycloadducts, other nitrile oxides yield a mixture of the two possible regioisomers. However, the reactions seem to be highly stereoselective and single diastereomers were obtained in all the cases studied.