An experimental and theoretical investigation of the regio- and stereoselectivity of the polar [3+2] cycloaddition of azomethine ylides to nitrostyrenes

The regio- and stereochemical polar [3+2] cycloaddition of the azomethine ylides, which were generated in situ by the reaction of isatin derivatives and proline, with trans-β-nitrostyrene and (E)-1-phenyl-2-nitropropene were studied using experimental and theoretical methods. In comparison with trans-β-nitrostyrene, when the reactions were performed with (E)-1-phenyl-2-nitropropene, a remarkable inversion in the regioselectively was observed. The regioselectivity of the reactions was investigated using global and local reactivity indices and frontier molecular orbital (FMO) analysis at the B3LYP/6-31G(d,p) level of theory. The effects of the electronic and steric factors on the regioselectivity of the reactions were discussed. The inspection of geometries and energetics of transition states revealed the importance of weak interactions in regioselectivity of the cycloaddition reactions.