The photochemical reaction between 1,4-dicyanonaphtalene and methylbenzenes: Electron transfer and formation of benzylic radicals

The photochemical reaction of 1,4-dicyanonaphtalene (1) in the presence of methylbenzenes (2a–c) in acetonitrile affords 1 - benzyl - 4 - cyanonaphtalenes (3), 1 - benzyl - 1,4 - dicyano - 1,2 - dihydronaphtalenes (4), 2 - benzyl - 1,4 - dicyano - 1,2 - dihydronaphtalenes (5 and 6) and the tetracyclic derivatives 7 and 8. Compounds 3, 7 and 8 are not the products of subsequent transformations of compound 4. No photochemical reaction is observed in non-polar media, in which, on the contrary, exciplex emission is detected. Experiments in the presence of electron acceptors, electron donors and strong acids support the idea that the reaction is initiated by electron transfer from the methylbenzenes to singlet excited 1, followed by protolytic equilibrium of the benzylic radical cation to the corresponding radical, which is the attacking species.