Alkenes in Diels-Alder reaction

The relative rates of reaction of the singlet TMM derivative 14b with a series of alkenes (32) parallel those of a conjugated diene with the same alkenes in Diels-Alder reactions. These relative rates also are well correlated by the frontier orbital model for a concerted reaction. The absolute rates of the biradical cycloadditions are many orders of magnitude greater than those of the model dienes. The relative rates of the alkenes in the cycloadditions of the triplet biradical 14b, on the other hand, follow the reactivity order of their addition reactions with monoradicals. 

The purely inductive electron-withdrawing character of a fluoroalkyl substituent activates alkenes in Diels-Alder reactions via the interaction of the HOMO of the diene and the LUMO of the fluoroalkyl-containing alkene. 

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