Direct photolysis of ((3-trimethylsilylpropoxy)phenyl)phenyliodonium salts with different counteranions (Cl(-), SbF(6)(-), and B(C(6)F(5))(4)(-)) in methanol leads to products by both heterolytic and homolytic processes. In the presence of 1-naphthol and 1-methoxynaphthalene, products formed by a heterolytic reaction disappear, suggesting an electron-transfer process occurs between excited 1-naphthol/1-methoxynaphthalene and the iodonium salts. In the case of 1-methoxynaphthalene, three phenylated methoxynaphthalene isomers are produced. These are produced as radical coupling products from the phenyl radical and 1-methoxynaphthalene radical cation.
Several new 4-benzoylbenzylammonium borates were prepared in order to study their photochemical properties. It was found that a quantitative yield of biphenyl and a small amount of benzene are formed from photolysis of the title compounds as tetraphenylborates in the absence of oxygen. In addition, amines and methylbenzophenone were detected after the steady-state photolysis. The quantum yields of the photolysis of the title compounds and the formation of biphenyl, amines, and methylbenzophenone were determined. Radical trapping experiments showed that the photogenerated amine is converted to an R-aminoalkyl radical, which is an important initiating species for the polymerization of acrylates when tetraphenylborate is chosen as a counteranion. It was found that even 1-(4-benzoylbenzyl)pyridinium tetraphenylborate is an active photoinitiator, however, indicating that R-aminoalkyl radical is not the only initiating species formed from 4-benzoylbenzylammonium tetraphenylborates. The effect of structure on initiating activity was determined and discussed.
Abstract— Photochemical reactions of 6‐azidocoumarin and 7‐azido‐4‐methylcoumarin in the presence of secondary amines have been investigated for their potential applications in photoaffinity labeling. It was found that the singlet nitrene generated from 6‐azidocoumarin isomerized to a dehydroazepine intermediate that reacted with an amine to yield two isomeric adducts. Photolysis of 7‐azido‐4‐meth‐ylcoumarin, in contrast, gave a triplet nitrene that abstracted hydrogen atoms from secondary amine molecules to form 7‐amino‐4‐methylcoumarin as the major product. The difference in the intersystem crossing rate between the two compounds originates from the azido position relative to the carbonyl group. Because of its ability to form a covalent linkage with a nucleophile, 6‐azidocoumarin is deemed to have a greater potential as a photoaffinity label than 7‐azido‐4‐methylcoumarin.
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