UPDATES
NBS-Mediated Radical Cyclization of 3-Arylallyl Azides
Innovative Entrepreneurial Training Program of Lanzhou
University (No. 201310730090) for financial support.
References
Scheme 4. Proposed mechanism for the formation of 7 f.
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sulted from further oxidation of the corresponding
iminyl radical. We speculate that 7 f might be formed
by the mechanism illustrated in Scheme 4. The pres-
ence of a cyano group might render the a-hydrogen
in intermediate D more acidic,[20] and thus deprotona-
tion of D could take place to form E. On the other
hand, the reaction of 5h gave compounds 6h-1 and
6h-2 in a combined yield of 69% (Table 3, entry 8),
which is much better than that of 1k (Table 1,
entry 11).
In summary, we have developed a new protocol for
the synthesis of quinoline-3-carboxylic acid deriva-
tives. This method makes use of methyl 2-(azidometh-
yl)-3-arylpropenoates and 2-(azidomethyl)-3-arylacry-
lonitriles as precursors, and features the cyclization of
iminyl radicals as the key step. The iminyl radicals
can be conveniently generated by the reaction of pre-
cursors with NBS under visible light irradiation. The
present reactions, while enriching the radical chemis-
try of organic azides and derived iminyl radicals,
could likely find further applications in heterocylic
synthesis.
Experimental Section
General Procedure for NBS-mediated reaction of
1 and 5
Compound 1 (0.5 mmol) and NBS (178 mg, 1.0 mmol) was
dissolved in 25 mL of dry CH2Cl2 contained in a 50 mL
pyrex tube. The solution was deaerated by bubbling with
argon gas for 30 min., and then sealed with a stopper. The
solution was irradiated with a household fluorescent lamp
(45 W) at ambient temperature. The progress of reaction
was monitored by TLC (2 to 5 h). After reaction the solvent
was removed under reduced pressure, and the residue was
separated by silica gel column chromatography (eluted with
hexane/EtOAc (8:1~15:1)) to yield the product(s).
The reaction of compound 5 was performed following the
same procedure.
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Acknowledgements
The authors thank the National Natural Science Foundation
of China (No. 21372108) and the National College Studentsꢀ
Adv. Synth. Catal. 0000, 000, 0 – 0
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