Organic Letters
Letter
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and represents the shortest route to the construction of
lamellarin core,7a,8 lamellarin D trimethyl ether, and lamellarin
H7g,13 ever reported in literature.
This one-step, sequential coupling−cyclization reaction was
also utilized to improve the preparation of pentacycles 1 and 12
by reacting 2 directly with 3 and 10 in the presence of a
catalytic amount of Yb(OTf)3 in xylene under reflux conditions
in 70% and 54% yield, respectively (Schemes 2 and 4). We
assumed that the mechanism for the formation of 1 via
Yb(OTf)3-catalyzed reaction involves the Lewis acid promoted
intramolecular proton transfer (rather than light-promoted
hydrogen atom transfer) from the 4-methylene carbon of 4 to
the nearby 3-nitro oxygen atom to afford 6. The remaining
mechanistic steps are similar to those of the visible-light-
promoted reaction as shown in Scheme 3. Compared to the
visible-light-promoted reaction, the Yb(OTf)3-catalyzed route
has the advantages of higher overall yield, one less step, and
being scalable. Nevertheless, the visible-light-promoted cycliza-
tion is more sustainable and environmentally benign and holds
the potential for efficient preparation of novel heterocyclic
aromatic compounds.
In summary, we have demonstrated that coumarin-pyrrole-
isoquinoline-fused pentacycle 12 can be prepared via either
visible-light-promoted cyclization of 4-(isoquinolin-1-ylmeth-
yl)-3-nitrocoumarin (11) or Yb(OTf)3-catalyzed coupling of 4-
chloro-3-nitrocoumarin (2) and 1-methylisoquinoline (10).
The methodology was extended to the one-, two-, and three-
step syntheses of lamellarin core 9 with overall yields of 17%,
15%, and 44%, respectively. Moreover, we have successfully
implemented this method in the synthesis of lamellarin D
trimethyl ether in three steps with an overall yield of 8% and
lamellarin H in four steps.
Bailly, C.; Nevier
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(10) Crystallographic data (excluding structure factors) for 1, 4, and
15 have been deposited with the Cambridge Crystallographic Data
Centre as Supplementary Publication Numbers CCDC-1427920,
-1427919, and -1436089, respectively. These data can be obtained
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: +44 1223 336033.
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2012, 45, 1723−1736.
(12) Ueda, K.; Amaike, K.; Maceiczyk, R. M.; Itami, K.; Yamaguchi, J.
J. Am. Chem. Soc. 2014, 136, 13226−13232.
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Chem. 2015, 80, 11605−11610.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
Synthesis of compounds 1, 4, 9, 11−15, 17, 18, and 20−
22; experimental details; additional spectra (PDF)
X-ray crystal structure details for 1 (CIF)
X-ray crystal structure details for 4 (CIF)
X-ray crystal structure details for 9 (CIF)
X-ray crystal structure details for 15 (CIF)
AUTHOR INFORMATION
Corresponding Author
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the Ministry of Science and Technology of the
Republic of China, Taiwan, for financially supporting this
research under Grant No. MOST 104-2113-M-029-005.
REFERENCES
■
(1) For recent reviews, see: (a) Fukuda, T.; Ishibashi, F.; Iwao, M.
Heterocycles 2011, 83, 491−529. (b) Pla, D.; Albericio, F.; Alvarez, M.
MedChemComm 2011, 2, 689−697. (c) Bailly, C. Mar. Drugs 2015, 13,
1105−1123.
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