Theoretical study on mechanism of cycloaddition reaction between dimethyl methylene carbene and ethylene

Mechanisms of cycloaddition reaction between singlet dimethyl methylene carbene and ethylene has been investigated with MP2/6-31G∗ method, including geometry optimization and vibrational analysis. Energies for the involved stationary points on the potential energy surface are corrected by zero-point energy and CCSD(T)//MP2/6-31G∗ single-point calculations. From the potential energy surface obtained with the CCSD(T)//MP2/6-31G∗ method for the cycloaddition reaction between singlet dimethyl methylene carbene and ethylene, it can be predicted that reactions (1) and (3) should be two competitive leading channels of cycloaddition reaction between them. The former consists of two steps: (I) the two reactants firstly form an energy-rich intermediate, INT1, which is a barrier-free exothermic reaction; (II) the intermediate INT1 isomerizes to a three-membered ring product P1 via a transition state TS1. The latter proceeds in three steps: (I) the two reactants firstly form a four-membered ring intermediate, INT2, through a barrier-free exothermic reaction; (II) the intermediate INT2 further reacts with ethylene (R2) to form an intermediate, INT3, which is also a barrier-free exothermic reaction; (III) INT3 isomerizes to a polycyclic product P3 via a transition state TS3.