THE PHOTOCHEMICAL-REACTION BETWEEN AROMATIC NITRILES AND ALLYLSILANE

The results obtained from the irradiation of aromatic nitriles and allyltrimethylsilane (ATMS) depend on the redox parameters of these molecules and their singlet energies. The reaction between 1-naphthalenecarbonitrile (NN) and ATMS in apolar solvents leads to [2 + 2] cycloaddition at positions 1 and 2 (via the exciplex); in polar solvents, electron transfer becomes a possibility, and loss of the trimethylsilyl cation followed by allylation of NN at positions 2 and 4 is also observed. When naphthalene-1,4-dicarbonitrile (NDN) is used, electron-transfer-initiated allylation (both addition and cyano group substitution) is the main pathway, but in apolar solvents cycloaddition at positions 4a and 5 occurs as a minor pathway. The reaction with benzene-1,2,4,5-tetracarbonitrile (BTN) gives substitution of an allyl for a cyano group as the only process. Finally, with both NDN and BTN and a high ATMS concentration in apolar solvents, the reaction pathway changes to photosensitized [2 + 2] dimerization of ATMS, proposed to occur via a terplex. Rationalizations for the observed reactions (including regiochemistry of addition and cycloaddition and nature of the intermediates) are offered.