Unusual photocyclization of perfluoro cis-1,2-dimethyl-1,3-butadienyl benzenes as a means to synthesize partially fluorinated naphthalenes

Photoirradiation of the titled compounds perfluoro-cis-1,2-dimethyl-butadienyl benzenes (1), which were prepared in several steps from perfluorovinyl bromide, results in the formation of the corresponding novel naphthalene derivatives and 1,4-dihydronaphthalenes. Isolated 1,1,2-trifluoro-3,4-bis(trifluoromethyl)-1,4-dihydronaphthalene (3a) could be converted into 1,2-bistrifluoromethy13,4-difluoronaphthalene (2a) by base treatment (DABCO); however, 3a did not lead to 2a by photoreaction, suggesting 3a was not a possible photochemical precursor. Competitive photoreaction studies suggest that varying the substituent on benzene ring (e.g. methyl or trifluoromethyl) does not significantly affect the reaction rate. Presently, this reaction mechanism is not yet clearly understood. (C) 2016 Published by Elsevier B.V.