Diels-Alder reactivities of cycloalkenediones with tetrazine
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Quantum chemical calculations were used to investigate the Diels-Alder reactivities for a series of cycloalkenediones with tetrazine. We find that the reactivity trend of cycloalkenediones toward tetrazine is opposite to cycloalkenes. The electrostatic interactions between the cycloalkenediones and tetrazine become more stabilizing as the ring size of the cycloalkenediones increases, resulting in lower activation energies. The origin of the more favorable electrostatic interactions and the accelerated reactivities of larger cycloalkenediones result from a stabilizing CH/π interaction that is not present in the reaction of the 4-membered cycloalkenedione. The Diels-Alder reactivity trend of cycloalkenediones toward tetrazine is opposite that of cycloalkenes. The increased reactivity of the 5- and 6-membered cycloalkenediones relative to the 4-membered cycloalkenedione is attributed to a stabilizing electrostatic CH/π interaction that is not present in the reaction of the 4-membered cycloalkenedione.
KeywordsDiels-Alder reaction Distortion/interaction-activation strain model Reactivity Electrostatic interactions Density functional theory
We thank the National Science Foundation (NSF CHE-1361104), the National Institute of Health (NIH R01GM109078), and the Netherlands Organization for Scientific Research (NWO) for financial support. We thank Dennis Svatunek for helpful discussions and assistance in generating the ESP maps. Computer time was provided by the UCLA Institute for Digital Research and Education (IDRE) on the Hoffman2 supercomputer. We additionally thank SURFsara for use of the Cartesius supercomputer.
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