Full Paper
obtained commercially. The visualization of spots on TLC plates
was effected by exposure to UV. Column chromatography was per-
formed over Silica gel (200 mesh) using the relevant eluent. High
Performance Liquid Chromatography (HPLC) was performed on an
Agilent HP1100 chromatograph equipped with a DAD detector de-
tector using a fused XB-C18 capillary column (Welch Ultimate,
25.0 cmꢃ4.6 mmꢃ5.0 mm). A standard program was used for all
HPLC analysis: eluent concentration of acetonitrile water solution
was increased from the initial concentration 70% to 95% with
2.5% per minute, eluent flow rate was 1 mLminÀ1, and monitoring
wavelength was at 254.4 nm. 1H (400 MHz) and 13C (100 MHz)
NMR-spectra were recorded on Bruker UltraShield spectrometers at
ambient temperature in CDCl3 or [D6]DMSO. Chemical shifts are re-
ported in ppm downfield to tetramethyl silane. Coupling constants
are reported and expressed in Hz, splitting patterns are designated
as s (singlet), d (doublet), t (triplet) and m (multiplet). NMR Fourier
transform, integration and peak picking were done with MestRe-
Nova software. Infrared absorption spectra were recorded on Nico-
let-20DXB spectrometer and the absorption bands are reported in
reciprocal centimeters (cmÀ1). High resolution mass spectra (HRMS)
were recorded at Micromass GCT-TOF, and Ultraviolet-Visible (UV/
Vis) spectra were recorded at Ultraviolet-Visible Absorption Spec-
troscopy, PerkinElmer Lambda 35 (190–1100 nm).
cleavage happens on neighbor SÀC bond to generate B, which
conduct O-rearrangement to carry out C. Oxidation of C via
this oxidative system affords PBS (or HPBS in buffer) and re-
generates porphyrin iron (III) that re-enters a new catalytic
cycle. A can be trapped by HTEMPO to afford corresponding
intermediate (ESI, S21), and Imidazole as a good axial ligand D
can resist DBTO from porphyrin iron (III), both of them can
end this catalytic cycle.
Conclusions
In conclusion, we have uncovered a dibenzothiopenic C-S
bond incision reaction via regioselective insertion of an oxygen
atom within sulfoxide-carbon linkage, a thia-analog of the
Baeyer–Villiger oxidation. The reaction led to cyclic sulfinate
ester PBS, and subsequent hydrolysis generated the corre-
spounding HPBS. Porphyrin iron(III) catalyst, hydroperoxide ox-
idant and ultraviolet light are indispensable for this reaction
success. Using high-pressure mercury lamp in the presence of
o-TCPPFeCl and tBuOOH, photoreaction of DBT at 30.08C in
2.5 h lead to 100% conversion of DBT and 91.9% yield of PBS
based on the HPLC analysis, and 83.2% isolated yield obtained
by column chromatography on silica gel. Placing the methyl
substituents at the 4,6-position of DBT had a little impact on
the yield of correspounding PBS, although DMDBT is a particu-
larly inert substrate against stringent conditions in hydrodesul-
furization. The impressive result was emphasized by residen-
tially germicidal UV-Lamp-254 (6 W) irradiation reaction per-
formed in mixed solvent of the phosphatic buffer (pH 7.8) and
methanol, which promoted DBT and DMDBT to completey
convert and to give outstanding yields, 91.3% and 87.2% re-
spectively for each desired HPBS. The isotopic exchange ex-
periment supports that the present photoreactions is an oxida-
tive incision reaction by an intra oxygen rearrangement and in-
sertion within sulfoxide-carbon bond. Int0so complex impor-
tance in diverting the reaction pathway and leading to the
thia-Baeyer–Villiger product was emphasized by the axial
ligand replacement experiment. The radical trap experiment
suggests that radical intermediate was involved in the photo-
reaction by 0.1 equiv HTEMPO on DBTO retarded the photore-
action of DBTO upon 59.7%. A plausible mechanism is pro-
posed according to the present results.
Procedure for DBTO sunlight photoreaction
To a 100 mL round-bottomed quartz flask fitted with a water con-
denser, introduced DBTO (10.0 mg, 50.0 mmol), tBuOOH (3.2 equiv.
on DBTO) and o-TCPPFeCl (2 mg, 2.4 mmol) in CH3OH (10 mL). Irra-
diating this mixture for 14 h was proceeded at ambient tempera-
ture under the sunlight without stirring.
General procedure for DBTs or DBTs sulfoxides photoreac-
tion irradiated by artificial lights
In a 200 mL three-necked and round-bottomed flask, added a solu-
tion of DBT sulfoxide or DBT (150.0 mmol) and catalyst (7.2 mmol)
in CH3OH (30.0 mL). Light lamp was carefully set in a quartz tube
(length: 28 cm, diameter: 3.8 cm) and then together installed in
the middle of the round-bottomed flask. The reactor was equipped
with the water condenser on the one neck of the flask and 2/3
flask immersed in the 30.08C water bath with integrated tempera-
ture control. Initial 0.8 equiv. tBuOOH (2.4 equiv. if DBT serviced as
the substrate) was dropwised into the solution after switched on
magnetic stirring and water recycling. The reactor was covered
with tinfoil before turn on the lamp. After irradiating the reaction
mixture for 0.5 h, turned off the lamp, rapidly took a sample
(150.0 mL) and added tBuOOH (0.8 equiv.) into reaction solution
only if examined no tBuOOH left by iodometry method and re-
started the lamp to irradiate reaction solution for another 0.5 h.
Repeat the last step until the designed time, wherein catalyst
(2.4 mmol) was added at 2 h if reaction time is more than 2 h. After
evaporating the solvent, the crude product was purified by
column chromatography on silica gel.
Experimental Section
General information
All experiments using artificial lights were performed in the built-in
lamp photoreactor with magnetic stirrer and cooling water con-
denser. DBTs and TPPFeCl were used as received. Solvents were
redistilled. tert-butylhydroperoxide (tBuOOH, 80% in water) was ti-
trated by iodometry method before used. meso-tetrakis(o-chloro-
phenyl)porphine iron (III) chloride (o-TCPPFeCl) and meso-tetra-
kis(p-chlorophenyl)porphine iron (III) (p-TCPPFeCl) were synthe-
sized according to the references reported.[7] High-pressure mercu-
ry lamp (Giguang, 250 Wt), residentially germicidal ultraviolet lamp
(UV-Lamp-254, Philips TUV-TL, l=254 nm, 6 W) and insect trap ul-
traviolet lamp (UV-Lamp-365, Philips TUV-TL, l=365 nm, 6 W) were
Acknowledgements
The authors are grateful to the National Natural Science Foun-
dations of China (No. 21076036) for financial support; Shuang
Lv, Xian Chen, Feng Yuan and Zhaoguo Wang for preliminary
tests and materials preparation.
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Chem. Asian J. 2020, 00, 0 – 0
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ÝÝ These are not the final page numbers!