INVESTIGADORES
BONESI Sergio Mauricio
congresos y reuniones científicas
Título:
Photo-Fries rearrangement of 7-acyloxypiridoindoles and 2-acyloxycarbazoles A comparative study
Autor/es:
PONCE MARÍA A; BONESI SERGIO M; CABRERIZO FRANCO M; ERRA-BALSELLS ROSA
Lugar:
Salvador do Bahia, Brasil
Reunión:
Congreso; XIV Inter-American Photochemistry Society Conference; 2006
Resumen:
The
photo Fries rearrangement has received considerable attention since its
discovery in 1960 by Anderson and Reese and this photoreaction have been studied
from a synthetic and mechanistic points of view. It is known that the photo
Fries rearrangement takes place in mild conditions, at room temperature and no
hazardous catalysts are needed. Also, this photoreaction gives o-hydroxyketone or o-aminoketone derivatives in moderate to good chemical yields,
which are interesting synthons for the synthesis of a wide variety of natural
products.
Taking
into account that the photo-Fries rearrangement have never been applied to piridoindole
(b-carboline) derivatives, in this
communication we report the photochemical studies of several 7-acyloxyharmoles
and the results are compared with those obtained with 2-acyloxycarbazoles. The
chemical structures of these compounds are shown in Scheme I. All the compounds
have been synthesized for the first time and have been characterized by means
of physical and spectroscopic methods (mp, MS, IR, NMR). In order to prepare o-hydroxy ketone derivatives that show a b-carboline moiety in their structures the photo-Fries rearrangement have been
carried out systematically in different experimental conditions. Thus, the
effects of the solvent, the atmosphere and the excitation wavelength on the
photochemical reaction have been analyzed. Also, the effect of the length of
the hydrocarbon chain on the photochemical reaction has been analyzed. The
photoproducts have been isolated, identified and fully characterized by means
of chromatographic and spectroscopic methods. It
is interesting to mention that as the R
group of the 7-acyloxyharmol changes from methyl or phenyl group to caproyl group,
the photoreaction turns quite inefficient and the conversion of the starting
material is lesser than 5% and harmol is the sole photoproduct detected. In the
case of 2-caproyloxycarbazole the photo-Fries rearrangement takes place
efficiently and the 1,3-migrated photoproducts are formed in moderate to good
chemical yield. Therefore, the distinct photochemical behavior of the b-carboline
derivative could be ascribed to the presence of the pyridine moiety in the b-carboline
structure because an intramolecular electron transfer process between the
pyridine moiety and the ester group competes efficiently with the photo-Fries
rearrangement. Likewise, quenching of the photochemical reaction of
2-caproyloxycarbazole with increasing concentration of pyridine was also
observed and the photochemical reaction turns inefficient.