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

Abstract

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.

Fluorescence spectroscopy of a naturally occurring carbazole alkaloid: murrayanine

“…These type of compounds are biologically active, possessing significant antibiotic, anti-carcinogenic, anti-viral and anti-inflammatory properties [6]. Incidentally, most of the research activity on carbazole alkaloids has been devoted towards the development of synthetic strategies [1,2], along with some reports on their physiological effects [3][4][5]. However, their fluorescence spectroscopic properties remain by and large obscure, in spite of the fact that these properties can provide valuable information about the structure and dynamics of a molecule and its interactions with its environment [7].…”

“…1), a carbazole alkaloid isolated from the root bark of Murraya koenigii Spreng (Indian curry-leaf plant) [2,3]. The experiments were performed both in homogeneous alcohol solvents as well as in aqueous micelles.…”

“…Carbazole alkaloids obtained from naturally occurring sources have been the subject of extensive research, mainly because of their widespread application in traditional medicine [1][2][3][4][5]. These type of compounds are biologically active, possessing significant antibiotic, anti-carcinogenic, anti-viral and anti-inflammatory properties [6].…”

Fries rearrangement of dibenzofuran-2-yl ethanoate under photochemical and Lewis-acid-catalysed conditions

“…2,3 The thermal Fries reaction involves the formation of a solvent caged ion pair, 4 whereas the photoreaction occurs via radical intermediates. 2,5 In the latter case, electronic excitation is followed by homolytic cleavage to yield aryloxy and acyl radical pairs, 6 and calculations indicate that this involves the excited singlet state.…”

Photo‐Fries Rearrangement of Carbazol‐2‐yl Sulfonates: Efficient Tool for the Introduction of Sulfonyl Groups into Polycyclic Aromatic Compounds

“…In continuation of our research on photo-Fries reactions [16], we herein report a protocol for the efficient synthesis of various sulfonates of 9H-carbazol-2-ol (1), as well as their isolation and full characterization by means of physical and spectroscopic methods.…”