Cycloaddition of nitrile oxides to cyclic and acyclic α,β-unsaturated amides. Frontier orbital interactions and an unexpected steric drift determine regiochemistry
The regiochemistry of the cycloadditions of nitrileoxides to α,β-unsaturated amides is determined by frontier orbital interactions and by a regiochemical drift due to steric effects. Cycloadditions to α,β-unsaturated lactames afford mainly 4-carboxamido-isoxazolines with high regioselectivity. In cycloadditions to acyclic α,β-unsaturated amides the regioselectivity relaxes and finally reverses in