Photochemistry of 2-acyloxycarbazoles. A potential tool in the synthesis of carbazole alkaloids.

S. M. BONESI, L.K. CREVATIN, R. ERRA-BALSELLS

Photochemical and Photobiological Sciences

The Royal Society of Chemistry and Owner Societies

Año: 2004 vol. 3 p. 381 - 388

1474-905X

The photochemistry of two 2-acyloxycarbazoles, 2-acetyl- and 2-benzoyloxycarbazoles, in different solvents has been studied. Irradiation of the 2-acyloxycarbazoles in organic media at 254 nm or 313 nm yields the 1,3-migrated photoproducts, 1-acyl-2-hydroxycarbazole, 3-acyl-2-hydroxycarbazole and 2-hydroxycarbazole. The effects of the solvents, the atmosphere and the intensity of the ligth 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 escited state in terms of fluorescence lifetime and fluorescence quantum yield have been measured in different organic solvents at room temperature. The phot-Fries rearrangement as a mild and claen one-pot reaction for the preparation of an advanced intermediate precursor in the total synthesis of carbazole alkaloids is described.