Utilizing Fukui's development of Frontier Molecular Orbital theory, Woodward & Hoffman attempted to 
Utilizing Fukui's development of Frontier Molecular Orbital theory, Woodward & Hoffman attempted to explain this broad class of reactions. They showed that if the LUMO and the HOMO were phase matched for the reactants, this type of reaction would be allowed under symmetry. One formal type of this reaction occurs between enone and an enamine by n-butylithium. In order to reduce bond strain, Cope rearrangements can often follow this type of reaction. Thermal types usually have four n plus 2 pi electrons participating in the starting material.  Typically resulting in the conversion of pi-bonds into sigma-bonds, for 10 points, name this type of pericyclic chemical reaction of which 1,3-dipolar and Diels-Alder are common types.
Utilizing Fukui's development of Frontier Molecular Orbital theory, Woodward & Hoffman attempted to explain this broad class of reactions.
Cycloaddition reaction