Thermal Rearrangements of 1-Ethynyl-2-methylcyclopropane: A Computational Study

In this research, a comprehensive theoretical investigation of the thermal rearrangements of 1-ethynyl-2-methylcyclopropane is carried out employing density functional theory (DFT), with the B3LYP functional, and high-level ab initio methods, such as the complete active space self-consistent field (CASSCF), multireference second-order Moller-Plesset perturbation theory (MRMP2), and coupled-cluster singles and doubles with perturbative triples [CCSD(T)]. In all computations Pople's polarized triple-zeta split valence basis set, 6-311G(d,p), is utilized. The potential energy surface (PES) for the relevant system is explored to provide a theoretical account of the experiments by Hopf,(1-4) Ellis and Frey,(5) Huntsman et al.,(6) and Berson.(7) The computational results herein on the target system show that the thermal aromatization reaction does not proceed via conversion of 1,2,5-hexatriene (2) to 1,3,5-hexatriene (10a) as proposed by Hopf.(1-4) Indeed, the reaction proceeds via conversion of 5 and 6 to bicyclo[3.1.0]hexene (9) as suggested by Huntsman et al.(6)