1,3-Dipolar Cycloaddition Reaction of Benzyl Azide with Cyclohex2-en-1-one. Experimental and Computational Study

It has been found that 1,3-dipolar cycloaddition reaction of benzyl azide with cyclohex-2en- 1-one leads to the formation of 1,2,3-triazole in ethanol and at room temperature. The isolated and purified product was characterized by spectral methods IR, 1H-NMR, 13C-NMR, Cosy, Dept-135 and MS. Ab initio calculations were carried out with the Complete Basis Set (CBS-4M) Model Chemistry of Petersson and coworkers in order to obtain very accurate energies. Geometry optimization and vibrational frequency calculations were performed on reactants, adducts, final products, and the transition states using CBS-4M model. CBS-4M begins with a HF/3-21G(d) geometry optimization. The zero point energy is computed at the same level. It then uses a large basis set SCF calculation as a base energy, and an MP2/6-31+ G calculation with a CBS extrapolation to correct the energy through second order. An MP4(SDQ)/6-31+(d, p) calculation is used to approximate higher order contributions. Enthalpies, free energies, rate constants, and the accompanying activation energies of the initial steps in the two possible routes of 1,3-dipolar cycloaddition reaction of the benzyl azide with cyclohex-2-en-1-one in the gas-phase were evaluated at the CBS-4M level of theory. The energies of the all adducts were obtained at this level confirming that the exo(1) adduct in route(1) is more stable then endo(1), but in route (2) the endo(2) adduct is more stable than exo(2). In addition, product (1) has lower energy, than product (2). In summary, it has been found that the thermodynamic and kinetic adducts in step(1) are exo(1) and endo(1), respectively, while in route(2) the thermodynamic and kinetic adduct is endo(2).