Theoretical Study of Mechanism of Cycloaddition Reaction Between Dimethylmethylene Carbene and Formaldehyde

The cycloaddition mechanism of forming a polycyclic compound between singlet dimethylmethylene carbene(R1) and formaldehyde(R2) has been investigated with MP2/6-31G* method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated with CCSD(T)//MP2/6-31G* method. From the potential energy profile, it can be predicted that the dominant reaction pathway of the cycloadditional reaction between singlet dimethylmethylene carbene and formaldehyde consists of two steps: (I) the two reactants(R1, R2) firstly form an energy-enricheded intermediate (INT1a) through a barrier-free exothermic reaction of Delta E = 11.3 kJ/mol. (2) Intermediate (INT1a) then isomerizes to a three-membered product (P1) via a transition state (TS1a) with an energy barrier of 20.0 kJ/ mol. The dominant reaction has an excellent selectivity and differs considerably from its competitive reactions in reaction rate. (C) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 110: 1273-1278, 2010