School of Chemistry and Chemical Engineering, Jinan University, Jinan, Shandong 250022, China

The mechanism of a cycloaddition reaction between singlet alkylidenestannylene and ethylene has been investigated with MP2/3-21G* and B3LYP/3-21G* methods, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. Energies for the involved conformations were calculated by CCSD(T)//MP2/3-21G* and CCSD(T)//B3LYP/3-21G* methods, respectively. The results show that the dominant reaction pathway of the cycloaddition is that an intermediate (INT) is firstly formed between the two reactants through a barrier-free exothermic reaction of 39.7 kJ/mol, and the intermediate then isomerizes to a four-membered ring product (P_2.1) via a transition state TS_2.1with a barrier of 66.8 kJ/mol.