Substituent dependent photochemical rearrangements of halostyrylheterocycles in acid media

New photorearrangement product 2 and hydrolysis product 3 are obtained by irradiating acidic halostyrylheterocycles 1a–f. The competing formal [1,3]hydrogen shift and ring opening of dihydrophenanthrene intermediate is responsible for the product formation. The halogen substituent effect on the product distribution has been studied. Photolysis of 5 can reversibly be converted to 2. Similar photoreactivity for the styrylfuran and styrylthiophene systems is observed.