A similar strain release reaction of MCP was also found by Tantillo and Gagné in the Cope rearrangement of ene-MCPs. In addition, the same phenomenon was also proposed in Diels-Alder reaction of the CP-dienes compared to the common dienes. 8a Here we used quantum chemistry calculations to support that CP diene is more active than dimethyl-diene in D-A reaction with maleic anhydride, by also about 7 kcal/mol in terms of activation free energy, due to the strain release (Scheme 3, reactions c and d). A quantitative understanding of this strain release can use distortion-interaction model , indicating that distortion of MCP in the CP-diene is much less than dimethyl-diene by 11.4 kcal/mol in the [4+2] reaction, whereas interaction energy is nearly identical for both (9.3 vs. 9.4 kcal/mol) (reactions c and d, Scheme 3 and see the Supporting Information).