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

• The preparation of perfluoro cis-1,2-dimethyl butadienyl copper reagent.
• Preparation of perfluoro cis-1,2-dimethyl butadienyl benzenes from copper reagent and aryl iodides.
• Photocyclization to give novel naphthalene derivatives and 1,4-dihydronaphthalenes.
• Naphthalene derivative prepared by treatment of 1,4-dihydronaphthalene with DABCO.

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-bistrifluoromethyl-3,4-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.

The preparation of perfluoro cis-1,2-dimethyl butadienyl copper reagent and subsequent coupling with aryl iodides are described. Photocyclization of the corresponding butadienyl benzenes gives novel naphthalene derivatives and 1,4-dihydronaphthalenes. Additionally, naphthalene derivatives are prepared by treatment of 1,4-dihydronaphthalenes with DABCO.Figure optionsDownload as PowerPoint slide