Difference in photochemical behavior in 3,6- and 2,5-di-tert-butyl-3H-azepine: The first photochemical bond formation between 2- and 6-position of 3H-azepine ring

Different photochemical behavior between 3,6- and 2,5-di-t-butyl-3H-azepine was observed. The former gave wavelength dependent products 3,5-di-t-butylpyridine on irradiation through Pyrex filter via photolysis and 4,7-di-t-butyl-2-azabicyclo[3.2.0]hepta-2,6-diene on irradiation through quartz filter via photo-isomerization. Meanwhile, 2,5-di-t-butyl derivative gave exclusively a labile 2,5-di-t-butyl-6-azabicyclo-[3.2.0]hepta-2,6-diene on irradiation through Pyrex filter via hitherto unknown photoisomerization mode of the bond formation between 2- and 6-position of the ring.