AM1 STUDY OF THE CYCLOADDITION OF SINGLET METHYLENE TO BUTADIENE AND THE VINYLCYCLOPROPANE REARRANGEMENT

The addition of singlet methylene to 1,3-butadiene was studied theoretically by using the Austin Model 1 (AM1) semi-empirical method. The concerted pathway of the 1,4-cycloaddition on the AM1 hypersurface was found not to be an actual minimal energy reaction pathway, and the 1,2-addition was found to take place with no activation. The path between the reactants and the 1,4-adduct must pass by the minimum of the 1,2-adduct. The transition state of the transformation of the 1,2-adduct into the 1,4-adduct was also determined and the energy barriers of the mutually competitive 1,2- and 1,4-processes were analysed.