Tetracyanobenzenes photoreactions

Previously, Ohashi and his co-workers reported the photosubstitution of 1,2,4,5-tetracyanobenzene (TCNB) with toluene via the excitation of the charge-transfer complex between TCNB and toluene [409], The formation of substitution product is explained by the proton transfer from the radical cation of toluene to the radical anion of TCNB followed by the radical coupling and the dehydrocyanation. This type of photosubstitution has been well investigated and a variety of examples are reported. Arnold reported the photoreaction of p-dicyanobenzene (p-DCB) with 2,3-dimethyl-2-butene in the presence of phenanthrene in acetonitrile to give l-(4-cyanophenyl)-2,3-dimethyl-2-butene and 3-(4-cyanophenyl)-2,3-dimethyl-l-butene [410,411], The addition of methanol into this reaction system affords a methanol-incorporated product. This photoreaction was named the photo-NO-CAS reaction (photochemical nucleophile-olefin combination, aromatic substitution) by Arnold. However, a large number of nucleophile-incorporated photoreactions have been reported as three-component addition reactions via photoinduced electron transfer [19,40,113,114,201,410-425], Some examples are shown in Scheme 120. 

Keywords tetracyanobenzene, benzyl cyanide, two-component crystal, photoreaction... 

The photosubstitution of 1,4-dicyanobenzene by use of allyl-trimethylsilane in acetonitrile giving l-allyl-4-cyanobenzene is atypical example as shown in Scheme iP Similar photoreactions of 1,2-and 1,4-dicyanobenzenes and 1,2,4,5-tetracyanobenzene using tetraalkylsilanes, benzylsilanes, and disilanes occur to give substitution products regioselectively. The photoreaction of 1,4-dicyanobenzene with 3-methyl-2-butenyltrimethylsilane gives both a- and y-allylated products in a 2 3 ratio. This ratio is not dependent on the solvent used or the presence of additives. These results clearly support a mechanism involving formation of allyl and benzyl radicals as intermediates. 

Electron-donating silyl ethers such as ketene silyl acetals and cyclopropanone silyl acetals also can be used as latent carbon-functional groups. The photoreactions of 1,2,4,5-tetracyanobenzene with dimethyl ketene silyl acetal and 2,2-dimethylcyclopropanone silyl methyl acetal afford substituted products in good yields, respectively. 

PET reactions of benzylic silanes with polycyano-aromatic compounds have been applied to photoresist and electron-beam resist technologies. "" The photoreaction of poly(4-trimethylsilyl-methylstyrene) in benzene-acetonitrile with DCB affords insoluble polymer via photo-cross-linking, which contains 4-cyanophenyl-methyl groups. In the case of 1,2,4,5-tetracyanobenzene, soluble 2,4,5-tricyanophenylmethyl-substituted polystyrene is produced. But,... 

Photoreactions of charge-transfer compounds formed between poly(l-raethyl styrene) and tetracyanobenzene degraded the polymer on exposure to radiation not directly absorbed by it. Radical-induced photo-oxidation of solutions of poly (1-methyl styrene) in chlorobenzene has been studied. In a series of papers Weir and co-workers have investigated the photolysis of polymers of 4-amino-, 4-nitro-, 4-fluoro-, 4-chloro-, 4-bromo-, and 4-(2,2-dimethylethyl)-styrene. ... 

Tsujimoto, K., Nakao, N., and Ohashi, M., Electron-donating behavior of aliphatic carboxylic acids in the photoreaction with 1,2,4,5-tetracyanobenzene,/. Chem. Soc., Chem. Commun., 366, 1992. 

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