Photoinduced electron-transfer oxidation of olefins with molecular oxygen sensitized by tetrasubstituted dimethoxybenzenes: A non-singlet-oxygen mechanism

Tadashi Mori, Makolo Takamoto, Takehiko Wada, Yoshihisa Inoue

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

α-Methylstyrene (1) was photo-oxidized in the presence of a series of alkylated dimethoxybenzenes as sensitizers in an oxygen-saturated MeCN solution to afford the cleaved ketone 2, epoxide 3, as well as a small amount of the ene product 4 in ca. 1:1:0.04 ratio. The relative rate of conversion was well-correlated with the fluorescence quantum yield of sensitizers. Thus, a non-singlet-oxygen mechanism is proposed, in which an excited sensitizer is quenched by (ground-state) molecular oxygen to produce a sensitizer radical cation and a superoxide ion (O2), the former of which oxidizes the substrate, while the latter reacts with the resulting olefin radical cation (1) to give the major oxidation products. Photodurability of such electron-donating sensitizers is dramatically improved by substituting four aromatic H-atoms in 1,4-dimethoxybenzene with Me or fused alkyl groups, which provides us with an environmentally friendly, clean method of photochemical functionalization with molecular oxygen, alternative to the ene reaction via singlet oxygenation.

Original languageEnglish
Pages (from-to)2693-2707
Number of pages15
JournalHelvetica Chimica Acta
Volume84
Issue number9
DOIs
Publication statusPublished - 2001 Nov 12
Externally publishedYes

ASJC Scopus subject areas

  • Catalysis
  • Biochemistry
  • Drug Discovery
  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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