title: Cationic arylation through photo(sensitised) decomposition of diazonium salts. Chemoselectivity of triplet phenyl cations.
abstract: The photodediazoniation of some 4-X-phenyldiazonium tetrafluoborates in MeCN leads to the singlet phenyl cations (X = H, tert-butyl, NMe2, CN), which add to the solvent yielding the corresponding acetanilides. Triplet sensitisation, however, leads to the triplet phenyl cation, which is reduced in neat solvent and is trapped by pi nucleophiles (allyltrimethylsilane and benzene), resulting in an ionic analogue of the Meerwein or Gomberg arylations. With the 4-nitro derivative intersystem crossing prevails over dediazoniation from the singlet and with the 4-cyano competes with it, so that in those cases the triplet phenyl cation is formed also upon direct irradiation.
authors.affiliation: Dipartimento di Chimica Organica, Università, V. Taramelli 10, 27100 Pavia, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Milanesi
authors.forename: Maurizio
authors.initials: M
authors.lastname: Fagnoni
authors.forename: Angelo
authors.initials: A
authors.lastname: Albini