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 efficient synthesis of fused bicyclic tetrahydroisoxazoles bearing exo - and anti -five member heterocyclic rings (76–99% yields) without any catalyst and additive under mild conditions. The 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 highly functionalized compounds.