Abstract
For clarification of the photochemical reactivities of 2-pyridones toward ethylenes, quenching phenomena of the fluorescence of 2-pyridones by the ethylenes were measured, and the direct photoreactions between various 2-pyridones and ethylenes were analyzed. It has been found that 2-pyridones are fluorescent unless they have electron-withdrawing substituents and some electron-poor ethylenes quench the fluorescence to give photoadducts. The photoadditions occurred when the quenching constants (kqτ) were 0<kqτ <7.6 and the main products were regio- and stereoselective [2+2]cycloadducts across the 3, 4-positions of 2-pyridones. The reactions were concluded to proceed via exciplexes between the 2-pyri dones and the ethylenes, but to give no adducts when the CT properties of the exciplexes were too large. The main reaction was explained on the basis of MO theory. We also revised some descriptions on the fluorescence of 2-pyridone in our previous report.
