6-Trifluoromethyl-1, 2, 4-triazines and -1, 2, 4-triazin-5-ones were synthesized to investigate the role of the trifluoromethyl group in their thermal as well as photochemical cycloaddition reactions with olefins. In photochemical 2+2 cycloaddition using the triazin-5-ones and -3, 5-diones, the activation of the imine function by the trifluoromethyl group is demonstrated and a new route to azetidine derivatives having a trifluoromethyl group is disclosed. In thermal 4+2 cycloaddition using the corresponding triazines, acceleration of the so-called inverse electron demand Diels-Alder reaction is demonstrated. Clarification of the mechanisms of these reactions and their use in the synthesis of azetidin-2-ones and pyridines having a trifluoromethyl group are also described.