Theoretical predication of Diels-Alder reactions of highly strained dienophiles

Using density functional theory M06-2X functional in combination with 6-311 + +G ** basis set, we have obtained six types of highly strained dienophiles (1-6). The Diels-Alder reactions of 1-6 with butadiene (A), cyclopentadiene (B) and 3,6-bis(trifluoromethyl)-tetrazine (C) have been investigated. Calculated results show that these Diels-Alder reactions are both thermodynamically and kinetically feasible. The endo Diels-Alder reactions of 1-6 with A and B are more favorable than their exo Diels-Alder reactions, which originates from the distortion energy differences of A and B. The low activation energy of the Diels-Alder reactions of 1-6 with C arises from the electron-withdrawing group CF3 in C, which is consistent with the previous results (J. Am. Chem. Soc. 2013, 135, 15642). The Diels-Alder reactions of 1-6 with the three dienes give a family of novel propellanes but not six-membered carbocycles.