Theoretical study on the reaction mechanism of cyclopropenylidene with azacyclopropane: ring expansion process

The reaction mechanism between cyclopropenylidene and azacyclopropane has been systematically investigated by employing the second-order Moller–Plesset perturbation theory (MP2) method to better understand the reactivity of cyclopropenylidene with the three-membered ring compound azacyclopropane. Geometry optimization and vibrational analysis have been performed for the stationary points on the potential energy surfaces of the system. It was found that, in the first step of this reaction, cyclopropenylidene can insert into azacyclopropane at its C–N bond to form a spiro intermediate. In the second, ring-opening step, a carbene intermediate is formed. Through the following two H-transfer steps, the carbene intermediate forms an allene [pathway (1)] or alkyne [pathway (2)] product. From the kinetic viewpoint, the pathway with alkyne formation is easier than that with allene formation. From the thermodynamic viewpoint, the allene is the dominant product because the reaction is exothermic (287.8 kJ mol−1). .