Scheme 3. Plausible reaction mechanism. Theoretical investigations on the reaction pathways for the formation of product 3g (Table 2, entry 7): relative free energies (ΔG _sol, in kcal mol^–1) of key intermediates and transition states were computed at the M06/6-31+G(d)/SDD level in 1,2-dichloroethane at 298 K.