A theoretical study on the mechanism of cycloaddition reaction between vinylidene and acetone

Mechanisms of cycloaddition reaction between singlet vinylidene and acetone have been investigated with MP2/6-31G* method. Energies for the involved conformations are further improved using CCSD(T)//MP2/6-31G* and MP2/6-311G**//6-31G* for the geometries optimized with MP2/6-31G* method. On the basis of the potential energy surface profile, it can be predicted that the dominant reaction pathway for the reaction consists of three steps: (1) the two reactants firstly form an active four-membered ring intermediate, INT2, which is a barrier-free exothermic reaction, ΔE=−81.6 kJ/mol (−95.0 kJ/mol, MP2/6-311G**//6-31G*); (2) the intermediate INT2 further reacts with acetone to form a polycyclic intermediate, INT3, through a barrier-free exothermic reaction, ΔE=−31.0 kJ/mol (−32.3 kJ/mol, MP2/6-311G**//6-31G*); (3) INT3 isomerizes to a polycyclic product P3 via a transition state TS3 with an energy barrier of 25.1 kJ/mol (21.2 kJ/mol, MP2/6-311G**//6-31G*).