Photochemistry of allyloxybenzophenones: a pseudo-Paternò-Büchi rearrangement accompanied by hydrogen transfer induced 1,5-cyclization

Photochem Photobiol Sci. 2008 Jul;7(7):782-8. doi: 10.1039/b807889k. Epub 2008 May 29.

Abstract

The solution photochemistry of the ortho allyloxy-substituted benzophenone has been investigated in detail. Product analysis revealed formation of a diastereomeric mixture of dihydrobenzofuran derivatives by cyclization via a short-lived intermediate 1,5-biradical and an unusual acetal by a pseudo-Paternò-Büchi rearrangement. The latter reaction pathway was supported by means of laser flash photolysis, where a long-lived intermediate with a maximum absorption band at 380 nm was observed. Besides, theoretical calculations (TD-DFT) of this UV-transient resulted in a band with maximum intensity at 390 nm showing a good correlation between experimental results and theoretical calculations. For comparison, the meta-substituent substrate was also investigated showing preferred triplet-triplet energy transfer.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Absorption
  • Benzophenones / chemistry*
  • Cyclization
  • Electron Transport
  • Hydrogen / chemistry*
  • Photochemistry
  • Photolysis
  • Quantum Theory
  • Spectrophotometry, Ultraviolet
  • Thermodynamics
  • Time Factors

Substances

  • Benzophenones
  • Hydrogen