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with aryl epoxides and
a,b-epoxy carbonyl compounds, while
modest yields are observed with epoxide substrates without an
adjacent radical-stabilizing group. The preliminary investigation
into the reaction mechanism revealed that the reaction is most
likely initiated by a single electron transfer from zinc to Nb–ep-
oxide complexes. Although more detailed mechanistic studies are
necessary to confirm our proposed reaction mechanism, the suc-
cessful application of our deoxygenation method to a variety of
sulfoxides and amine N-oxides suggests that the low-valent nio-
bium complexes may provide further development of other types
of catalytic reductive C–O/N–O/S–O bond cleavage. Our current
investigation is directed to the generation of highly functionalized
radicals in the presence of chiral ligands around niobium,59 and our
results will be reported in due course.
4. Experimental section
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4.1. Typical procedure for the deoxygenation of epoxides,
sulfoxides, and N-oxides
To NbCl5 (135 mg, 0.5 mmol) under argon atmosphere were
added successively benzene (1.5 mL) and THF (1.5 mL) at ambient
temperature. Zinc dust (163 mg, 2.5 mmol) was added to the pale
yellow solution and stirred for 40 min. The color of the mixture
turned to black upon addition of zinc. A solution of the starting
material (1.0 mmol) in benzene/THF (1:1, 2 mL) was added to the
reaction mixture at ambient temperature and monitored by TLC.
After consumption of the starting material was confirmed via TLC,
water (2 mL) was added and the mixture was stirred for 1 h. The
mixture was filtered over Celite and washed with diethyl ether
(3ꢂ10 mL), dried over sodium sulfate and concentrated in vacuo.
The residue was purified by flash chromatography on silica gel to
give the deoxygenated product. (E)-Stilbene 2a:60 1H NMR
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´
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Acknowledgements
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This work was financially supported by the School of Science
and the Department of Chemistry and Chemical Biology at IUPUI.
The Bruker 500 MHz NMR was purchased via a NSF-MRI award
(CHE-0619254).
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Supplementary data
Supplementary data associated with this article can be found in
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