What controls regiochemistry in 1,3-dipolar cycloadditions of münchnones with nitrostyrenes?

The distinct experimentally observed regiochemistries of the reactions between mesoionic münchnones and ß-nitrostyrenes or phenylacetylene are shown by DFT/BDA/ETS-NOCV analyses of the transition states to be dominated by steric and reactant reorganization factors, rather than the orbital overlap considerations predicted by Frontier Molecular Orbital (FMO) Theory.