Photochemical aryl-alkyl bond formation

The photolytic cleavage of alkyl aryl sulfoxides has been shown to occur via initial C—S bond homolysis, in accordance with the common mechanistic assumption. Secondary and tertiary alkyl groups show high chemoselectivity for alkyl C—S cleavage. Uniquely, alkene products have been isolated, formed by disproportionation of the initial alkyl radical, with the formation of benzaldehyde and racemization of primary alkyl compounds. An investigation into the photochemical conversion of N-propylsulfobenzoic imides into amides in various solvents revealed a solvent dependence of the observed mechanism. In ethanol, sulfur dioxide extension forms a biradical which abstracts a hydrogen atom from the solvent, whereas in aromatic solvents biradical formation by a single electron transfer is implicated. The photolysis and thermolysis of l,9-bis(alkylthio)dibenzothiophenes and /7-aminophenyl disulfide have been studied. 

Photochemical cleavage of metal-carbon bonds constitutes a brief part of a recent review on the photochemistry of metal carbonyls. Reviews of metal-alkyl and -aryl complexes have also appeared, one of which is concerned solely with metals in Groups IV— VII. The other deals with the formation, stability, and decomposition pathways of transition metal-carbon a-bonds, subjects of much interest in recent years. Consequently the recent isolation of the first stable methylene complex [Ta(Me)(CHa)(jj-C6H6)2] and its unequivocal characterization by a single-crystal JlT-ray diffraction study is of great interest in view of the probability that related derivatives are involved in the recently reported (see Vol, 4, p. 293) examples of a-hydride elimination in metal alkyls. 

Aryl-tellurides undergo radical fragmentation reactions in the presence of methyl radical generated by photochemical decarboxylation of 0-acetyl thiohydroxamate. The driving force of this reaction is the formation of the relatively strong methyl-tellurium bond at the expense of the R-tellurium bond. Conventional radical traps can react with the formed alkyl radical. Scheme 16 shows an application of this reaction in the synthesis of showdomycind ... 

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