Synthesis and Structure of Condensed Heterocycles Derived from Intramolecular 1,3-Dipolar Cycloaddition of Transient and Enantiomerically Pure α-Allylamino Nitrones and Nitrile Oxides in a High Level of Diastereoselectivity

A series of typical nitrone and nitrile oxide derivatives was generated in situ from the corresponding sulfonylated α-allylamino aldehydes and aldoximes, which afforded isoxazolidine and isoxazoline fused heterocycles by intramolecular 1,3-dipolar cycloaddition reactions with a high degree of diastereoselectivity. The structure as well as the absolute stereochemistry of the products were confirmed by extensive 2D-NMR spectroscopy and single crystal X-ray analyses and the reasons for the observed selectivity were explained by the energy calculations of the transition states using semiempirical (MOPAC AM1 and MOPAC PM3) and ab initio methods (3-21G* and 6-31G*).

1,3-dipolar cycloaddition - nitrones - nitrile oxides - transition states - diastereoselectivity