The photochemistry of two 2-acyloxycarbazoles, 2-acetyl- and 2-benzoyloxycarbazole, in different solvents has been studied. Irradiation of the 2-acyloxycarbazoles in organic media at 254 or 313 nm yields the [1,3]-migrated photoproducts, 1-acyl-2-hydroxycarbazole, 3-acyl-2-hydroxycarbazole and 2-hydroxycarbazole. The effects of the solvent, the atmosphere and the intensity of the light source on the photochemistry of 2-acyloxycarbazole have been studied. Laser flash photolysis as well as photosensitization experiments were performed in order to determine the photoreactive excited state. Electronic spectra (absorption, fluorescence and phosphorescence emission spectra) of the 2-acyloxycarbazoles have been recorded in homogeneous media at 298 K and in solid matrices at 77 K. The dynamic properties of the lowest singlet excited state in terms of fluorescence lifetime and fluorescence quantum yield have been measured in different organic solvents at room temperature. The photo-Fries rearrangement as a mild and clean one-pot reaction for the preparation of an advanced intermediate precursor in the total synthesis of carbazole alkaloids is described.
Systematic studies on the photo-Fries rearrangement of different 9H-carbazol-2-yl sulfonates 2 have shown that this type of conversion can be readily used for the preparative-scale introduction of alkyl-or arylsulfonyl groups into polycyclic aromatic compounds under very mild conditions. A series of new 1-sulfonyl-(3) or 3-sulfonyl-9H-carbazoles (4) were prepared in medium-to-good yields, and characterized by UV/VIS, 1 H-NMR, and 13 C-NMR spectroscopy, as well as by elemental analysis. Effects of irradiation wavelength, solvent polarity, presence or absence of O 2 , and photosensitizers were studied in detail.
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