Interestingly, using the popular DFT M08HX level (Minnesota density functional theory) with the MG3S basis set (equivalent to the 6-311++G(3d2f,2p) basis set) which uses analytical second energy derivatives, the cyclic structure was not found, although the approach was not linear either. At this level (with energy improved by single-point calculations at the CCSD(T)-F12/aug-cc-pVTZ level) the reactant complex is stabilized by 0.47 kcal mol -1 with respect to the reactants, in agreement with the previous results.