1,3-Dipolar Cycloaddition of Nitrones to Oxa(aza)bicyclic Alkenes
A new 1,3-dipolar cycloaddition of oxa(aza)bicyclic alkenes with nitrones has been developed. The operationally simple cycloaddition allows us for the efficient synthesis of fused bicyclic tetrahydroisoxazole bearing exo- and anti-five member heterocyclic ring (76–99% yields) without any catalyst and additive under mild conditions. A proposed concerted mechanism and the observed selectivity are investigated by DFT calculations of the reaction pathways. This mild and practical [3+2] cycloaddition provides an efficient route to access to highly functionalized compounds.