European Journal of Organic Chemistry
10.1002/ejoc.201600772
COMMUNICATION
Although comprehensive study detailing the mechanistic
underpinning of this reaction will require further investigation,
based on preceding discussion (Scheme 5 and Table 1), a
plausible reaction mechanism is outlined in Scheme 6. The 8-
aminoquinoline complex A is converted to B after single electron
transfer (SET), which on reaction with diaryl diselenide 2
produces the intermediate C. In the presence of Ag(I), aryl
selenium radical is reduced to corresponding anion, which
deprotonates to give Cu(I)-complex D. After that, complex D is
reoxidized to produce E, which on exchange with another
molecule of 1 delivers the product 3 and generate complex A to
continue the catalytic cycle.
Keywords: quinolines • selenylation • copper • radical
homogeneous catalysis • C–H functionalization
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Scheme 6. Plausible reaction mechanism.
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2
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Conclusions
In summary, we have unfolded an efficient copper-catalyzed
direct selenylation of quinolines with an excellent degree of
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regioselectivity at the C5-position. This protocol is operationally [6]
simple, scalable, displays a broad substrates scope, and uses
readily available diaryl diselenides as selenium precursors.
Mechanistic studies revealed that the reaction is chelation-
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a single electron transfer (SET)
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mechanism for remote C–H bond functionalization. Additional
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Experimental Section
5
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General Procedure: The 8-amidoquinolines 1 (0.20 mmol), diselenide
derivatives 2 (0.40 mmol), silver carbonate (1 equiv.), Cu(OTf) (20
2
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mol%) and selectfluor (0.10 mmol) were taken in a dried schlenk tube
with a magnetic stir bar under nitrogen atmosphere. Then DCE (3 mL)
was added with a syringe and the resulting mixture was heated at 100 ºC
for 48 h. After completion of the reaction (TLC monitored), it was cooled
to room temperature and transferred to a round bottom flask after dilution
with CH Cl . The solvent was evaporated to dryness and the crude
2 2
reaction mixture was loaded directly onto silica gel column and purified to
provide pure selenylation products 3-4.
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Acknowledgements
We gratefully acknowledge CSIR New Delhi for the financial
support (02(0212)/14/EMR-II). H. K. S. thanks IIT-Madras for
HTRA and A. M. thanks UGC for a JRF. We also thank the
department of chemistry, IIT-Madras for instrumental facilities.
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