Lennart Mçhlmann et al.
COMMUNICATIONS
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as both nucleophile and solvent. Pleasingly, the two
catalytic cycles interacted perfectly with each other
affording a 94% yield of the desired product. In con-
trast to the aza-Henry reactions, the use of acetoni-
trile as solvent did not accelerate the conversion for
these Mannich reactions. Various tetrahydoquinoline
derivatives were reacted with acetone providing the
desired products in good to excellent yields. Use of
sterically more hindered ketones however reduced
the yields significantly (Table 4, entry 2).
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In summary, we have reported a metal-free hetero-
À
geneous system to catalyze oxidative C C bond for-
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mation reactions using visible light, oxygen and in-
soluble carbon nitride photocatalyst, with good quan-
tum yield,[14] providing good to excellent yields under
very mild conditions. This visible light photoredox
catalysis scheme can be further integrated with pro-
line-organocatalysis to achieve catalytic oxidative cas-
cade reactions.
Experimental Section
General Procedure for the Aza-Henry Reaction
Acetonitrile (1 mL), mpg-C3N4 (15 mg), nitroalkane
(5 equiv.) and substrate (0.25 mmol) were added into a 10-
mL Schlenk tube. An O2-balloon was installed at the tube to
provide an oxygen atmosphere. The suspension was then
shaken at room temperature under irradiation with visible
light using a Philips cool daylight energy-saving bulb (60 W)
until all starting material had been consumed.[12] The mpg-
C3N4 was removed either by centrifugation or by filtration
and the solvent was distilled off under reduced pressure.
The residue was purified by column chromatography on
SiO2 to furnish the desired product.
[7] For an example using photoredox catalysis with proline
as a co-catalyst see: M. Rueping, C. Vila, R. M. Koe-
nigs, K. Poscharny, D. C. Fabry, Chem. Commun. 2011,
47, 2360–2362.
À
[8] For selected examples of C C bond formation by pho-
toredox catalysis see: a) D. A. Nicewicz, D. W. C. Mac-
Millan, Science 2008, 322, 77–80; b) M. E. Anzovino, J.
Du, T. P. Yoon, J. Am. Chem. Soc. 2008, 130, 12886–
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Yoon, Chem. Sci. 2011, 2, 2115–2119; i) Z. Lu, M. Shen,
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j) J. D. Nguyen, J. W. Tucker, M. D. Konieczynska,
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For more details, see the Supporting Information.
Acknowledgements
This work was supported by the “Light2Hydrogen” Project
of the BMBF (03IS2071D), and the National Natural Science
Foundation of China (21033003 and 21173043).
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