Facile synthesis of 1-(isoquinolin-1-yl)ureas by silver triflate catalyzed tandem reactions of 2-alkynylbenzaldoximes with carbodiimides

Article abstract of DOI:10.1002/ejoc.201001040

2-Alkynylbenzaldoximes react with carbodiimides under mild conditions and silver triflate catalysis in DMF, leading to a diverse range of 1-(isoquinolin-1-yl)ureas in good to excellent yields. This transformation involves tandem 6-endo cyclization, [3+2]

Full text of DOI:10.1002/ejoc.201001040

FULL PAPER
DOI: 10.1002/ejoc.201001040
Facile Synthesis of 1-(Isoquinolin-1-yl)ureas by Silver Triflate Catalyzed
Tandem Reactions of 2-Alkynylbenzaldoximes with Carbodiimides
Shengqing Ye,[a] Huanhuan Wang,[a] and Jie Wu*[a,b]
Keywords: Alkynes / Fused-ring systems / Cycloaddition / Cyclization / Rearrangement / Silver
2-Alkynylbenzaldoximes react with carbodiimides under
mild conditions and silver triflate catalysis in DMF, leading
to a diverse range of 1-(isoquinolin-1-yl)ureas in good to ex-
cellent yields. This transformation involves tandem 6-endo
cyclization, [3+2] cycloaddition, and subsequent rearrange-
ment.
isocyanide co-catalyzed by silver triflate and bismuth tri-
flate, which afforded N-(isoquinolin-1-yl)formamides in
good yields.[11f] Meanwhile, Shin and co-workers disclosed
the gold-catalyzed cascade reactions of 2-alkynylbenzaldox-
imes.[11a] In the above reaction processes, isoquinoline N-
oxide was believed to be the key intermediate, which was
generated from 2-alkynylbenzaldoxime through 6-endo cy-
clization in the presence of suitable Lewis acids or electro-
philes.[11] Prompted by these results and with an expectation
to generate a focused library of isoquinolines, we conceived
that carbodiimides 2 should also be suitable substrates in
the reaction of 2-alkynylbenzaldoximes 1. As described in
Scheme 1, we expected that [3+2] cycloaddition reaction
would occur after generation of isoquinoline N-oxides 3
through 6-endo cyclization of 2-alkynylbenzaldoximes 1 in
the presence of a metal catalyst, leading to the correspond-
ing fused isoquinoline compounds 4. With these considera-
tions in mind, thus we started to explore the possibility of
this transformation.
Introduction
It is well recognized that natural product like compounds
can be used to dissect the circuitry of cells in a way that is
analogous to the use of mutations in genetics.[1] One of the
most efficient ways to generate such small molecules cap-
able of modulating any pathway or process of interest is
using diversity-oriented synthesis.[2] Among the strategies
using diversity-oriented synthesis to produce a collection of
structurally complex and diverse compounds, tandem reac-
tions using simple starting materials provide an efficient
and powerful tool.[3,4] As a privileged skeleton, the isoquin-
oline core structure is found in a wide variety of biologically
active natural products and pharmaceuticals.[5] In addition,
isoquinoline derivatives with iridium complexes are found
applications in organic light-emitting diodes.[6] Thus, in-
tense interest has been directed toward the development of
new methods for the isoquinoline construction.[7–10] Al-
though there are several routes to isoquinolines, it is still of
high demand to develop novel and efficient pathways for
efficient assembly of functionalized isoquinolines with
novel structures under mild conditions, especially in a com-
binatorial format.
Recently, 2-alkynylbenzaldoxime was discovered as a use-
ful building block for the formation of nitrogen-containing
heterocycles.[11] For example, we reported the generation of
an isoquinoline-based azomethine ylide through a cascade
reaction of 2-alkynylbenzaldoxime and DMAD with bro-
mide or iodine.[11g] Subsequently, 2-alkynylbenzaldoxime
was also found to be a suitable partner in the reaction of
Scheme 1. Proposed synthetic route for tandem reaction of 2-alk-
ynylbenzaldoximes 1 with carbodiimides 2.
[a] Department of Chemistry, Fudan University,
220 Handan Road, Shanghai 200433, China
Fax: +86-21-65641740
E-mail: jie_wu@fudan.edu.cn
[b] State Key Laboratory of Organometallic Chemistry,
Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences,
Results and Discussion
The initial attempt was carried out with 2-alkynylbenz-
aldoxime 1a with N-[(cyclohexylimino)methylene]cyclo-
hexanamine (DCC 2a) in the presence of 10 mol-% of Lewis
354 Fenglin Road, Shanghai 200032, China
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201001040.
View this journal online at
wileyonlinelibrary.com
6436
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2010, 6436–6439

Silver Triflate Catalyzed Synthesis of 1-(Isoquinolin-1-yl)urea
acid in various solvents at 60 °C (Table 1). At the outset,
As described above in the reaction process, isoquinoline
the reaction was stopped at the formation of isoquinoline N-oxide 3 was demonstrated to be the key intermediate, and
N-oxide 3a (30% yield), and no further transformation was indeed, this compound, which was generated from 2-alk-
detected when CuI was used as the catalyst in 1,2-dichloro- ynylbenzaldoxime through 6-endo cyclization in the pres-
ethane (DCE; Table 1, Entry 1). Similar results were ob-
served when Cu(OTf)2 (25% yield) or Zn(OTf)2 (80% yield)
was employed as a replacement (Table 1, Entries 2 and 3).
A trace amount of product was generated when Bi(OTf)3
was utilized as the catalyst under the conditions (Table 1,
Entry 4). In contrast, the use of silver triflate as a catalyst
in the reaction led to the formation of a product with 80%
isolated yield (Table 1, Entry 5). The result could not be
improved when the reaction was catalyzed by PdCl2 or
FeCl3 (Table 1, Entries 6 and 7). However, structural identi-
fication discovered that the compound obtained was the un-
expected 1,3-dicyclohexyl-1-(3-phenylisoquinolin-1-yl)urea
(5a), instead of the corresponding product 4a. With this
promising result in hands, we further tested the reaction
in other solvents by using AgOTf as the catalyst (Table 1,
Scheme 2. Possible pathway for AgOTf-catalyzed tandem reaction
Entries 8–13). Interestingly, compound 5a could be ob-
of 2-alkynylbenzaldoxime 1 with carbodiimide 2.
tained in 94% yield when the reaction was performed in
DMF (Table 1, Entry 10). Lower yields were generated
Table 2. Silver triflate catalyzed tandem reaction of 2-alkynyl-
when the reaction was carried out in other solvents. We also
benzaldoximes 1 with carbodiimides 2.
examined the reaction catalyzed by 5 mol-% of silver triflate
in DMF at 60 °C, which resulted in lower yield. An inferior
result was displayed when the reaction was carried out at
25 °C (data not shown).
Table 1. Initial studies for tandem reaction of 2-alkynylbenzaldox-
ime 1a with carbodiimide 2a.
Entry 2-Alkynylbenzaldoxime 1 Carbodiimide 2 Product % Yield[a]
1
2
3
4
5
6
7
8
1a
1a
1b
1b
1c
1d
1d
1e
1e
1f
2a
2b
2a
2b
2b
2a
2b
2a
2b
2a
2b
2a
2b
2a
2b
2b
2a
2b
2a
2b
2a
2b
2a
2b
2a
2b
2b
2b
2a
2b
5aa
5ab
5ba
5bb
5cb
5da
5db
5ea
5eb
5fa
94
96
90
99
99
71
70
90
99
90
84
83
85
97
96
92
90
96
94
91
97
93
96
99
77
95
88
95
97
90
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
1f
5fb
1g
1g
1h
1h
1i
1j
1j
1k
1k
1l
5ga
5gb
5ha
5hb
5ib
5ja
5jb
5ka
5kb
5la
Entry
Lewis acid
Solvent
% Yield of 5[a]
1
2
3
4
5
6
7
8
9
10
11
12
13
CuI
Cu(OTf)2
Zn(OTf)2
Bi(OTf)3
AgOTf
PdCl2
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
MeCN
n.d.
n.d.
n.d.
trace
80
trace
1l
5lb
1m
1m
1n
1n
1o
1p
1q
1q
5ma
5mb
5na
5nb
5ob
5pb
5qa
5qb
FeCl3
complicated
AgOTf
AgOTf
AgOTf
AgOTf
AgOTf
AgOTf
73
63
94
31
80
69
toluene
DMF
EtOH
THF
1,4-dioxane
[a] Isolated yield based on 1a.
[a] Isolated yield based on 1.
Eur. J. Org. Chem. 2010, 6436–6439
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
6437

S. Ye, H. Wang, J. Wu
FULL PAPER
Figure 1. 2-Alkynylbenzaldoximes 1.
ence of silver triflate, was highly stable and could be iso-
lated. As carbodiimide was a good electrophile in the reac-
tion, the subsequent [3+2] cycloaddition would occur lead-
ing to corresponding adduct 4, which then underwent intra-
molecular rearrangement to give rise to unexpected 1-(iso-
quinolin-1-yl)urea 5 (Scheme 2).
Conclusions
In summary, we have described a novel and facile route
for the generation of 1-(isoquinolin-1-yl)ureas through a sil-
ver triflate catalyzed tandem reaction of 2-alkynylbenz-
aldoximes with carbodiimides under mild conditions. The
good substrate generality, mild reaction conditions, and
high efficiency of this synthetic route would be attractive
and beneficial for the construction of a focused library.
Under the optimized conditions [silver triflate (10 mol-
%), DMF, 60 °C], we then examined the generality of this
reaction, and the results are shown in Table 2. The reaction
was found to afford good to excellent yields of the desired
products. For instance, treatment of 2-alkynylbenzaldoxime
1a with 2b gave rise to the corresponding product 5ab in
96% yield (Table 2, Entry 2). Almost quantitative yield of
compound 5bb or 5cb was obtained when 2-alkynylbenz-
aldoxime 1b or 1c was used in the reaction of carbodiimide
2b under the standard conditions (Table 2, Entries 4 and 5).
From these results, it seemed that in addition to the aro-
matic groups attached to the CϵC triple bond, alkyl groups
were also found to be suitable to cleanly generate the de-
sired products. When a cyclopropyl group was attached to
the triple bond, the expected products were generated in
slightly lower yields (Table 2, Entries 6 and 7). This meth-
odology could also be extended to other 2-alkynylbenz-
aldoximes with various substituents on the aromatic ring.
For example, reactions of fluoro-, chloro-, or methoxy-sub-
stituted 2-alkynylbenzaldoxime 1 (Figure 1) with carbodi-
imide 2a or 2b (Figure 2) worked well to afford the desired
products in good to excellent yields; the electronic nature
of the aromatic backbone of the substrates did not seem to
exert any influence.
Experimental Section
General Procedure for Silver Triflate Catalyzed Tandem Reaction
of 2-Alkynylbenzaldoximes 1 with Carbodiimides 2: Silver triflate
(0.02 mmol, 10 mol-%) was added to a solution of 2-alkynylbenz-
aldoxime 1 (0.2 mmol) and carbodiimide compound 2 (0.4 mmol,
2 equiv.) in DMF (2.0 mL). The solution was stirred at 60 °C in air
overnight. After completion of the reaction as indicated by TLC,
the reaction was quenched by the addition of saturated aqueous
NH4Cl (5.0 mL), and the mixture was extracted with EtOAc
(3ϫ4.0 mL). The combined organic layer was dried with Na2SO4
and concentrated in vacuo. The residue was purified by column
chromatography on silica gel to provide product 5.
1,3-Dicyclohexyl-1-(3-phenylisoquinolin-1-yl)urea (5aa): 1H NMR
(400 MHz, CDCl3): δ = 0.68–2.03 (m, 20 H), 3.61–3.68 (m, 2 H),
4.56–4.60 (m, 1 H), 7.43 (t, J = 7.3 Hz, 1 H), 7.51–7.57 (m, 3 H),
7.69 (t, J = 7.3 Hz, 1 H), 7.91 (d, J = 8.3 Hz, 1 H), 8.08–8.11 (m,
2 H), 8.18 (d, J = 8.3 Hz, 2 H) ppm. 13C NMR (100 MHz, CDCl3):
δ = 24.7, 25.4, 25.6, 26.1, 32.0, 33.3, 116.3, 125.8, 126.3, 126.7,
127.3, 127.6, 128.8, 130.8, 138.5, 138.9, 149.9, 152.3, 156.0 ppm.
HRMS: calcd. for C28H33N3O [M + H]+ 428.2702; found 428.2709.
1,3-Diisopropyl-1-(3-phenylisoquinolin-1-yl)urea (5ab): 1H NMR
(400 MHz, CDCl3): δ = 0.89 (d, J = 6.3 Hz, 6 H), 1.29 (d, J =
7.0 Hz, 6 H), 3.64 (d, J = 7.7 Hz, 1 H), 3.95–4.01 (m, 1 H), 4.97–
5.01 (m, 1 H), 7.43 (t, J = 7.3 Hz, 1 H), 7.51–7.59 (m, 3 H), 7.70
(t, J = 8.3 Hz, 1 H), 7.91 (d, J = 8.0 Hz, 1 H), 8.06 (d, J = 8.7 Hz,
1 H), 8.11 (s, 1 H), 8.18 (d, J = 7.3 Hz, 2 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 21.5, 23.0, 42.3, 49.0, 116.2, 125.6, 126.0,
126.7, 127.4, 127.6, 128.8, 130.8, 138.5, 138.9, 149.9, 152.2,
156.0 ppm. HRMS: calcd. for C22H25N3O [M + Na]+ 370.1895;
found 370.1894.
Figure 2. Carbodiimides 2.
6438
www.eurjoc.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2010, 6436–6439

Silver Triflate Catalyzed Synthesis of 1-(Isoquinolin-1-yl)urea
b) for a review on the synthesis of isoquinoline alkaloids, see:
M. Chrzanowska, M. D. Rozwadowska, Chem. Rev. 2004, 104,
3341–3370; c) Y.-N. Niu, Z.-Y. Yan, G.-L. Gao, H.-L. Wang,
X.-Z. Shu, K.-G. Ji, Y.-M. Liang, J. Org. Chem. 2009, 74,
2893–2896; d) Y.-Y. Yang, W.-G. Shou, Z.-B. Chen, D. Hong,
Y.-G. Wang, J. Org. Chem. 2008, 73, 3928–3930; e) D. Fischer,
H. Tomeba, N. K. Pahadi, N. T. Patil, Z. Huo, Y. Yamamoto,
J. Am. Chem. Soc. 2008, 130, 15720–15725; f) M. Movassaghi,
M. D. Hill, Org. Lett. 2008, 10, 3485–3488; g) T. Blackburn,
Y. K. Ramtohul, Synlett 2008, 1159–1164; h) G. Pandey, M.
Balakrishnan, J. Org. Chem. 2008, 73, 8128–8131; i) S. Su, J. A.
Porco, Org. Lett. 2007, 9, 4983–4986; j) M. Mori, H. Wakam-
atsu, K. Tonogaki, R. Fujita, T. Kitamura, Y. Sato, J. Org.
Chem. 2005, 70, 1066–1069; k) Z. Xiang, T. Luo, K. Lu, J. Cui,
X. Shi, R. Fathi, J. Chen, Z. Yang, Org. Lett. 2004, 6, 3155–
3158.
a) S. Obika, H. Kono, Y. Yasui, R. Yanada, Y. Takemoto, J.
Org. Chem. 2007, 72, 4462–4468 and references cited therein;
b) N. Asao, S. Yudha, S. T. Nogami, Y. Yamamoto, Angew.
Chem. Int. Ed. 2005, 44, 5526–5528; c) R. Yanada, S. Obika,
H. Kono, Y. Takemoto, Angew. Chem. Int. Ed. 2006, 45, 3822–
3825; d) N. Asao, K. Iso, S. Yudha, Org. Lett. 2006, 8, 4149–
4151; e) N. Asao, C. S. Chan, K. Takahashi, Y. Yamamoto,
Tetrahedron 2005, 61, 11322–11326; f) M. Ohtaka, H. Naka-
mura, Y. Yamamoto, Tetrahedron Lett. 2004, 45, 7339–7341; g)
B. Witulski, C. Alayrac, L. Tevzadze-Saeftel, Angew. Chem. Int.
Ed. 2003, 42, 4257–4260; h) I. Yavari, M. Ghazanfarpour-Dar-
jani, M. Sabbaghan, Z. Hossaini, Tetrahedron Lett. 2007, 48,
3749–3751; i) A. Shaabani, E. Soleimani, H. R. Khavasi, Tetra-
hedron Lett. 2007, 48, 4743–4747; j) G.-W. Wang, J.-X. Li, Org.
Biomol. Chem. 2006, 4, 4063–4064; k) J. L. Diaz, M. Miguel,
R. Lavilla, J. Org. Chem. 2004, 69, 3550–3553; l) A. B. Beeler,
S. Su, C. A. Singleton, J. A. Porco Jr., J. Am. Chem. Soc. 2007,
129, 1413–1419.
Supporting Information (see footnote on the first page of this arti-
cle): Experimental procedures, characterization data, and 1H and
13C NMR spectra of compound 5.
Acknowledgments
Financial support from the National Natural Science Foundation
of China (No. 20972030) and the Science & Technology Commis-
sion of Shanghai Municipality (09JC1404902) is gratefully ac-
knowledged.
[1] a) T. J. Mitchison, Chem. Biol. 1994, 1, 3–6; b) S. L. Schreiber,
Bioorg. Med. Chem. 1998, 6, 1127–1152; c) C. M. Crews, U.
Splittgerber, Trends Biochem. Sci. 1999, 24, 317–320.
[2] a) D. P. Walsh, Y.-T. Chang, Chem. Rev. 2006, 106, 2476–2530;
b) P. Arya, D. T. H. Chou, M.-G. Baek, Angew. Chem. Int. Ed.
2001, 40, 339–346; c) S. L. Schreiber, Science 2000, 287, 1964–
1969; d) M. R. Spaller, M. T. Burger, M. Fardis, P. A. Bartlett,
Curr. Opin. Chem. Biol. 1997, 1, 47–53.
[3] For reviews, see: a) J. Montgomery, Angew. Chem. Int. Ed.
2004, 43, 3890–3908; b) E. Negishi, C. Coperet, S. Ma, S. Y.
Liou, F. Liu, Chem. Rev. 1996, 96, 365–394; c) L. F. Tietze,
Chem. Rev. 1996, 96, 115–136; d) R. Grigg, V. Sridharan, J.
Organomet. Chem. 1999, 576, 65–87; e) T. Miura, M. Murak-
ami, Chem. Commun. 2007, 217–224; f) M. Malacria, Chem.
Rev. 1996, 96, 289–306; g) K. C. Nicolaou, T. Montagnon,
S. A. Snyder, Chem. Commun. 2003, 551–564; h) K. C. Nico-
laou, D. J. Edmonds, P. G. Bulger, Angew. Chem. Int. Ed. 2006,
45, 7134–7186; i) D. Enders, C. Grondal, M. R. Hüttl, Angew.
Chem. Int. Ed. 2007, 46, 1570–1581; j) L. F. Tietze, G. Brasche,
K. Gericke, K. Domino Reactions in Organic Synthesis, Wiley-
VCH, Weinheim, Germany, 2006.
[8]
[4] For recent selected examples, see: a) F. Shi, X. Li, Y. Xia, L.
Zhang, Z.-X. Yu, J. Am. Chem. Soc. 2007, 129, 15503–15512;
b) S. W. Youn, J.-Y. Song, D. I. Jung, J. Org. Chem. 2008, 73,
5658–5661; c) K.-G. Ji, X.-Z. Shu, J. Chen, S.-C. Zhao, Z.-J.
Zheng, L. Lu, X.-Y. Liu, Y.-M. Liang, Org. Lett. 2008, 10,
3919–3922; d) A. B. Beeler, S. Su, C. A. Singleton, J. A.
Porco Jr., J. Am. Chem. Soc. 2007, 129, 1413–1414; e) L.-Q.
Lu, Y.-J. Cao, X.-P. Liu, J. An, C.-J. Yao, Z.-H. Ming, W.-J.
Xiao, J. Am. Chem. Soc. 2008, 130, 6946–6948; f) X.-L. Sun,
Y. Ta n g , Acc. Chem. Res. 2008, 41, 937–948; g) S. H. Cho, S.
Chang, Angew. Chem. Int. Ed. 2008, 47, 2836–2839; h) S. H.
Cho, S. Chang, Angew. Chem. Int. Ed. 2007, 46, 1897–1900; i)
E. J. Yoo, S. H. Park, S. Chang, Org. Lett. 2009, 11, 1155–1158.
[5] For selected examples, see: a) K. W. Bentley, The Isoquinoline
Alkaloids, Harwood Academic, Australia, 1998, vol. 1; b) J. D.
Phillipson, M. F. Roberts, M. H. Zenk, The Chemistry and Bio-
logy of Isoquinoline Alkaloids, Springer, New York, 1985.
[6] For selected examples, see: a) K.-H. Fang, L.-L. Wu, Y.-T. Hu-
ang, C.-H. Yang, I.-W. Sun, Inorg. Chim. Acta 2006, 359, 441–
450; b) S.-J. Liu, Q. Zhao, R.-F. Chen, Y. Deng, Q.-L. Fan, F.-
Y. Li, L.-H. Wang, C.-H. Huang, W. Huang, Chem. Eur. J.
2006, 12, 4351–4361; c) Q. Zhao, S. Liu, M. Shi, C. Wang, M.
Yu, L. Li, F. Li, T. Yi, C. Huang, Inorg. Chem. 2006, 45, 6152–
6160; d) A. Tsuboyama, H. Iwawaki, M. Furugori, T. Mukaide,
J. Kamatani, S. Igawa, T. Moriyama, S. Miura, T. Takiguchi,
S. Okada, M. Hoshino, K. Ueno, J. Am. Chem. Soc. 2003, 125,
12971–12979.
[9]
a) Q. Huang, R. C. Larock, J. Org. Chem. 2003, 68, 980–988;
b) G. Dai, R. C. Larock, J. Org. Chem. 2003, 68, 920–928; c)
G. Dai, R. C. Larock, J. Org. Chem. 2002, 67, 7042–7047; d)
Q. Huang, J. A. Hunter, R. C. Larock, J. Org. Chem. 2002, 67,
3437–3444; e) K. R. Roesch, R. C. Larock, J. Org. Chem. 2002,
67, 86–94; f) K. R. Roesch, H. Zhang, R. C. Larock, J. Org.
Chem. 2001, 66, 8042–8051; g) K. R. Roesch, R. C. Larock,
Org. Lett. 1999, 1, 553–556; h) G. Dai, R. C. Larock, Org. Lett.
2001, 3, 4035–4038.
For selected examples, see: a) Z. Chen, Q. Ding, X. Yu, J. Wu,
Adv. Synth. Catal. 2009, 351, 1692–1698; b) Z. Chen, M. Su,
X. Yu, J. Wu, Org. Biomol. Chem. 2009, 7, 4641–4646; c) Z.
Chen, X. Yang, J. Wu, Chem. Commun. 2009, 3469–3471; d)
X. Yu, Z. Chen, X. Yang, J. Wu, J. Comb. Chem. 2010, 12,
374–378; e) X. Yu, J. Wu, J. Comb. Chem. 2009, 11, 895–899;
f) X. Yu, X. Yang, J. Wu, Org. Biomol. Chem. 2009, 7, 4526–
4530; g) X. Yu, Q. Ding, Z. Chen, J. Wu, Tetrahedron Lett.
2009, 50, 4279–4282.
a) H.-S. Yeom, J.-E. Lee, S. Shin, Angew. Chem. Int. Ed. 2008,
47, 7040–7043; b) H.-S. Yeom, S. Kim, S. Shin, Synlett 2008,
924–928; c) Z. Huo, H. Tomeba, Y. Yamamoto, Tetrahedron
Lett. 2008, 49, 5531–5534; d) Q. Ding, Z. Wang, J. Wu, Tetra-
hedron Lett. 2009, 50, 198–200; e) Q. Ding, J. Wu, Adv. Synth.
Catal. 2008, 350, 1850–1854; f) Z. Chen, X. Yu, M. Su, X.
Yang, J. Wu, Adv. Synth. Catal. 2009, 351, 2702–2708; g) Q.
Ding, Z. Wang, J. Wu, J. Org. Chem. 2009, 74, 921–924; h) H.-
S. Yeom, Y. Lee, J. Jeong, E. So, S. Hwang, J.-E. Lee, S. S. Lee,
S. Shin, Angew. Chem. Int. Ed. 2010, 49, 1611–1615.
Received: July 22, 2010
[10]
[11]
[7] For selected examples, see: a) M. Balasubramanian, J. G. Keay,
“Isoquinoline Synthesis” in Comprehensive Heterocyclic Chem-
istry II (Eds.: A. E. McKillop, A. R. Katrizky, C. W. Rees,
E. F. V. Scrivem), Elsevier, Oxford, 1996, vol. 5, pp. 245–300;
Published Online: October 7, 2010
Eur. J. Org. Chem. 2010, 6436–6439
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
6439