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General procedure for PtCl4-catalyzed intramolecular
hydroamination of N-acetyl-2-alkynylaniline substrates for the
synthesis of N-acetyl-2-substituted indole derivatives (Procedure
A): A solution of N-acetyl-2-phenylethynyllaniline (1a) (60.1
mg, 0.2554 mmol, 1.00 equiv) in DCM (5.0 mL) was added with
PtCl4 (1.6 mg, 0.0060 mmol, 0.02 equiv) in one portion. The
resulting reaction mixture was allowed to stir at room
temperature until the reaction was complete as monitored by
TLC. Upon completion, the reaction mixture was filtered through
a short plug of silica gel while rinsing with DCM to remove the
catalyst. The filtrate solution was concentrated under reduced
pressure to give 59.4 mg (99 %) of analytically pure indole 2a.
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General procedure for PtCl4-catalyzed intramolecular
hydroamination of N-acetyl-2-alkynylaniline substrates for the
synthesis of N-acetyl-2-substituted indole derivatives (Procedure
B): A solution of N-(5-fluoro-2-(phenylethynyl)phenyl)acetamide
(1k) (52.8 mg, 0.2085 mmol, 1.00 equiv) in DCE (5.0 mL) was
added with PtCl4 (1.2 mg, 0.0045 mmol, 0.02 equiv) in one
portion. The resulting reaction mixture was equipped with a
condenser and heated at reflux until the reaction was complete as
monitored by TLC. Upon completion, the reaction mixture was
filtered through a short plug of silica gel while rinsing with DCM
to remove the catalyst. The filtrate solution was concentrated
under reduced pressure to give 51.7 mg (98 %) of analytically
pure indole 2k.
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Acknowledgments
This research work was supported in part by grants from
Chulabhorn Research Institute (CRI), Chulabhorn Graduate
Institute (CGI), Mahidol University, the Center of Excellence on
Environmental Health and Toxicology, Science & Technology
Postgraduate Education and Research Development Office
(PERDO), Ministry of Education. We would also like to
gratefully acknowledge the assistance in this work by Mr.
Auttaphon Chachavalvuttikul (2016 undergraduate summer
intern from Chiang-Mai University, Chiang-Mai, Thailand) and
Mr. Itthinan Duangngam (2017 undergraduate summer intern
from Chulalongkorn University, Bangkok, Thailand).
−4001.
3994
6. For preparation of compound 1a, and other compounds, as well as
their characterization data, please see supporting information.
7. (a) Müller, T. E.; Beller, M. Chem. Rev. 1998, 98, 675–703. (b)
Beller, M.; Seayad, J.; Tillack, A.; Jiao, H. Angew. Chem. Int. Ed.
2004, 43, 3368–3398. (c) Chianese, A. R.; Lee, S. J.; Gagné, M.
R. Angew. Chem. Int. Ed. 2007, 46, 4042–4059.
8. For some recent examples, please see: (a) Fürstner, A.; Hannen, P.
Chem. Eur. J. 2006, 12, 3006–3019. (b) Lu, L.; Liu, X.-Y.; Shu,
X.-Z.; Yang, K.; Ji, K.-G.; Liang, Y.-M. J. Org. Chem. 2009, 74,
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2013, 11, 4488–4502. (d) Kwon, Y.; Kim, I.; Kim, S. Org. Lett.
2014, 16, 4936−4939.
A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at
9. The generation of HCl and the HCl-induced proto-deplatination of
reactions involving organoplatinum species within a catalytic
cycle have been studied and proposed previously, please see: (a)
Kong, W.; Cui, J.; Yu, Y.; Chen, G.; Fu, C.; Ma, S. Org. Lett.
2009, 11, 1213–1216. (b) Bender, C. F.; Brown, T. J.;
Widenhoefer, R. A. Organometallics 2016, 35, 113−125.
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