Copper-catalyzed synthesis of 4-Aryl-1H-1,2,3-triazoles from 1,1-dibromoalkenes and sodium azide

Article abstract of DOI:10.1002/ejoc.201101204

A new methodology for the Cu-catalyzed synthesis of 1H-1,2,3-triazoles from 1,1-dibromoalkenes and sodium azide is presented. Aryl dibromoolefins were efficiently converted into the corresponding 1,2,3-triazoles. A comprehensive number of functional group

Full text of DOI:10.1002/ejoc.201101204

FULL PAPER
DOI: 10.1002/ejoc.201101204
Copper-Catalyzed Synthesis of 4-Aryl-1H-1,2,3-triazoles from
1,1-Dibromoalkenes and Sodium Azide
Xiaokun Wang,[a] Chunxiang Kuang,*[a] and Qing Yang[b]
Keywords: 1,2,3-Triazoles / Heterocycles / Copper / 1,1-Dibromoalkene / Sodium azide / Synthesis design
A new methodology for the Cu-catalyzed synthesis of 1H-
1,2,3-triazoles from 1,1-dibromoalkenes and sodium azide is
presented. Aryl dibromoolefins were efficiently converted
into the corresponding 1,2,3-triazoles. A comprehensive
number of functional groups were compatible with this reac-
tion. 1,2,3-Triazoles were obtained in moderate to excellent
yields.
been generated by simple debrominative decarboxylation in
the presence of bases, which was catalyzed by Pd2(dba)3 and
Xantphos. Zhu and Ma[15] have reported that the coupling
reaction of vinyl iodides with sodium azide under CuI/l-
proline catalysis provides only vinyl azides at relatively low
temperatures (Scheme 1a). Some reactions of halogen al-
kynes with azide have also been reported (Scheme 1b and
c).[16] These vinyl halides or haloalkynes were easily ob-
tained from 1,1-dihaloalkenes, and we need to find a new
method to generate 4-aryl-1H-1,2,3-triazoles using less ex-
pensive substrates.
Introduction
1,2,3-Triazoles are important heterocycles,[1] which are
widely used in pharmaceuticals and agrochemicals. 1,2,3-
Triazoles have a wide spectrum of biological activities,[2]
such as antibacterial,[3] herbicidal, fungicidal, antiallergic,
and anti-HIV[4] properties. 4-Aryl-1H-1,2,3-triazoles have
been used as human methionine aminopeptidase
(hMetAP2) and indoleamine 2,3-dioxygenase (IDO) inhibi-
tors, and are expected to become medicines to treat cancers,
AIDS, Alzheimer’s disease, tristimania, cataracts, and some
other serious diseases.[5]
The Huisgen dipolar cycloaddition of alkynes to organic
azides has been greatly developed.[6] Catalytic azide–alkyne
cycloaddition methods for the copper(I)-catalyzed[7] synthe-
sis of 1,4- or ruthenium(II)-catalyzed[8] 1,5-disubstituted
1,2,3-triazoles are reliable means of assembling diversely
substituted 1,2,3-triazoles. Terminal alkynes react with both
organic[9] and inorganic azides[10] to generate 4-aryl-1,2,3-
triazoles.
In 2008, Lu[11] first reported the copper-catalyzed synthe-
sis of 1H-1,2,3-triazoles from phenylacetylene and sodium
azide. Other routes to 1H-1,2,3-triazoles include the reac-
tion of sodium azide with nitroalkenes[12] and alkenyl brom-
ides. Barluenga et al.[13] have reported the effective synthesis
of 1H-1,2,3-triazoles from (E)-β-arylvinyl bromides and so-
dium azide, which is catalyzed by Pd2(dba)3 and Xantphos.
Likewise, we[14] have reported the one-pot synthesis of 4-
aryl-1H-1,2,3-triazoles from sodium azide and anti-3-aryl-
2,3-dibromopropanoic acids. (Z)-β-Arylvinyl bromides have
Scheme 1. Reaction of vinyl halide or haloalkyne with sodium
azide.
Results and Discussion
We report the results of the Cu-catalyzed synthesis of 4-
aryl-1H-1,2,3-triazoles from 1,1-dibromoalkenes and so-
dium azide. The catalyst was CuI with sodium ascorbate in
dimethyl sulfoxide (DMSO) and K2CO3.
In a preliminary set of experiments, the reaction of 1a
with sodium azide was studied under different conditions.
The copper catalyst and the base were first selected.
Cu(OAc)2 and CuI (Table 1, Entries 1–3 and 7–8) were used
together with different bases, such as Cs2CO3, K2CO3, and
[a] Department of Chemistry, Tongji University,
Siping Road 1239, Shanghai 200092, China
Fax: +86-21-65983191
E-mail: kuangcx@tongji.edu.cn
[b] Department of Biochemistry, School of Life Sciences, Fudan
University,
Handan Road 220, Shanghai 200433, China
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201101204 or from
the author.
424
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2012, 424–428

Cu-Catalyzed Synthesis of 4-Aryl-1H-1,2,3-triazoles
Table 1. Screening for optimum reaction conditions.
Entry Cu salt (20%)
Additive (50%)
Base (1.0 equiv.)
Solvent
Temp. [°C]
Time [h]
Yield of 2a[a] [%]
1
2
3
4
5
6
7
8
9
Cu(OAc)2
Cu(OAc)2
CuI
Na ascorbate
Na ascorbate
Na ascorbate
l-proline
Cs2CO3
K2CO3
–
K2CO3
K2CO3
K2CO3
K2CO3
DBU
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
120
120
120
120
120
120
120
120
80
12
12
12
12
12
12
12
12
12
12
12
40
70
0
65
78
trace
83
64
28
trace
45
CuI
CuI
CuI
CuI
CuI
CuI
CuI
CuI
Na ascorbate + l-proline
–
Na ascorbate
Na ascorbate
Na ascorbate
Na ascorbate
Na ascorbate
K2CO3
K2CO3
K2CO3
10
11
CH3CN
butanol/H2O
80
120
[a] Isolated yield.
1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The best pair Table 2. Synthesis of 4-aryl-1H-1,2,3-triazoles (2) from 1,1-dibro-
moalkenes (1) and sodium azide.[a]
was found to be CuI and K2CO3, which gave a product
yield of 83% (Table 1, Entry 7). The ligand specificity of
the reaction was also remarkable; compound 2a was not
detected without sodium ascorbate (Table 1, Entry 6).
Other ligands were tried, but the yields were lower (Table 1,
Entries 4 and 5). Sodium ascorbate was specifically proven
to promote the reaction (Table 1, Entry 5). The effects of
different solvents (Table 1, Entries 10 and 11) and reaction
temperature were then examined. DMSO was found to be
the best solvent, which produced 2a in 83% yield (Table 1,
Entry 7). Reducing the tempreature from 120 to 80 °C re-
sulted in a lower product yield (Table 1, Entry 9).
The scope of the reaction was examined with the opti-
mized experimental conditions (Table 2). The formation of
triazoles 2 occurred in very high yields by using 1,1-dibro-
moalkenes. The substitution on the aromatic ring had little
effect on the outcome of the reaction, and systems substi-
tuted with neutral, electron-withdrawing, or electron-donat-
ing groups provided similar results. From the experimental
results presented, there are higher yields for electron-rich
aryl olefins and lower yields for electron-poor ones. The
reaction tolerated sensitive functional groups substituted in
the aromatic ring, such as methyl ester, nitro, and trifluoro-
methyl groups. Compounds 1i and 1l, which contain ortho
Entry
R
Product
Overall yield [%][b]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
4-MeC6H4
Ph
4-iPrC6H4
2a
2b
2c
2d
2e
2f
2g
2h
2i
2j
2k
2l
2m
2n
2o
2p
2q
2r
2s
83
74
79
81
86
80
81
65
63
62
66
61
68
63
67
68
60
70
74
3-MeOC6H4
4-MeOC6H4
3,4-(MeO)2C6H3
3,4,5-(MeO)3C6H2
4-BrC6H4
2-ClC6H4
3-ClC6H4
4-ClC6H4
2-FC6H4
4-FC6H4
2,4-Cl2C6H3
4-NO2C6H4
4-MeO2CC6H4
4-CF3C6H4
2-naphthyl
3-pyridine
[a] Reaction conditions: 1 (0.2 mmol), NaN3 (0.6 mmol), K2CO3
(0.2 mmol), CuI (20%), Na ascorbate (50%), DMSO (2.5 mL), N2,
120 °C, 12 h. [b] Isolated yield based on 1.
Considering that alkynyl azides do not undergo cycliza-
groups, gave 2i and 2l in 63 and 61% yield, respectively. The tion to 1,2,3-triazoles upon heating, the Cu catalyst should
reaction of the pyridyl-substituted 1s gave 2s in 74% yield. promote the electrocyclization of the intermediate alkynyl
The proposed pathways for these debrominative and 1,5- azide. To validate his mechanistic hypothesis, several experi-
electrocyclization reactions are shown in Scheme 2. Com- mental studies were conducted (Scheme 3). First, alkynyl
plex IV was probably formed in two ways: the first was bromide 3 was substituted for dibromoalkene under the
when dibromoalkene I underwent β-elimination to form same reaction conditions to yield 2a.[18] Interestingly, 1a
propargyl bromide compounds II. The second was when was transformed into 1-(bromoethynyl)-4-methylbenzene
dibromoalkene I first produced complex III from oxidative 3.[19] This transformation indicated that alkynyl bromide ac-
addition with complex VIII, which was eliminated to form tually participated in the reaction and was not protonated
complex IV.[17] The azide was substituted with bromine to to alkynes.
form complex V. 1,5-Electrocyclization followed to produce
In order to confirm the proposed mechanism, 1-(bromo-
complex VI. Finally, 1,2,3-triazoles VII were formed by re- ethynyl)-4-methylbenzene (3) was treated with sodium azide
leasing VIII.[12]
in DMSO with Pd(PPh3)4. As expected, 5-bromo-4-p-tolyl-
Eur. J. Org. Chem. 2012, 424–428
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
425

X. Wang, C. Kuang, Q. Yang
FULL PAPER
1H-1,2,3-triazole (4) was obtained, which proved that cop-
per was crucial to promote the reaction.
Some deuterium labeling experiments were also per-
formed to determine the hydrogen source. When 1a was
treated in [D6]DMSO under reaction conditions similar to
those reported in Table 2, undeuterated 2a was obtained.
The addition of D2O (0.1 mL) to DMSO (2 mL) in the re-
action of 1c under the same conditions led to the formation
of 2c and 2c-D in 67% yield and a 1:1 ratio. When we in-
creased the amount of water in the solvent, 2a was obtained
in a very low yield. When water was the solvent, no product
was observed. Furthermore, a very small amount of 4, the
reaction byproduct, was produced. These results revealed
that a small amount of water in DMSO, rather than DMSO
itself, may be the hydrogen source for 4. In summary, these
reactions (Scheme 3) verified our mechanism proposed in
Scheme 2.
Some experiments on 1,1-dibromoalkenes and organic
azides were also conducted.[20] Compound 1a reacted as ex-
pected with 1-azido-4-methylbenzene (5) to yield 1,4-di-p-
tolyl-1H-1,2,3-triazole (6, Scheme 4). The proposed path-
way is similar to that shown in Scheme 2.
Conclusions
A new methodology for the Cu-catalyzed synthesis of
1H-1,2,3-triazoles from 1,1-dibromoalkenes and sodium
Scheme 2. Proposed mechanism for the Cu-catalyzed formation of
triazoles from dibromoalkenes and sodium azide.
Scheme 3. Evidence for the proposed mechanism.
Scheme 4. Cu-catalyzed formation of triazoles from dibromoalkenes and organic azides.
426
www.eurjoc.org
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2012, 424–428

Cu-Catalyzed Synthesis of 4-Aryl-1H-1,2,3-triazoles
Supporting Information (see footnote on the first page of this arti-
azide has been reported. The starting substrates 1 were eas-
ily obtained from aromatic aldehydes.[21] Further studies to
prove the proposed mechanism are expected.
1
cle): Copies of the H and 13C NMR spectra.
Acknowledgments
The present work was supported by the National Natural Science
Foundation of China (No. 30873153), the Key Projects of Shanghai
in Biomedicine (No. 08431902700), and the Scientific Research
Foundation of the State Education Ministry for Returned Overseas
Chinese Scholars. We would also like to thank the Center for In-
strumental Analysis, Tongji University, China.
Experimental Section
General Considerations: 1H NMR spectra were recorded with an
AM-500 spectrometer in CDCl3 with SiMe4 as the internal stan-
dard. Commercially obtained reagents were used without further
purification. DMSO (AR, water Յ 0.2%) was used as received.
Column chromatography was carried out with 300–400 mesh silica
gel.
[1] a) A. R. Katritzky, Y. Zhang, S. K. Singh, Heterocycles 2003,
60, 1225; b) K. A. DeKorver, H. Li, A. G. Lohse, R. Hayashi,
Z. Lu, Y. Zhang, R. P. Hsung, Chem. Rev. 2010, 110, 5064; c)
N. R. Candeias, L. C. Branco, P. M. P. Gois, C. A. M. Afonso,
A. F. Trindade, Chem. Rev. 2009, 109, 2703; d) S. Díez-
González, N. Marion, S. P. Nolan, Chem. Rev. 2009, 109, 3612.
[2] a) Y. M. Chabre, R. Roy, Curr. Top. Med. Chem. 2008, 8, 1237;
b) M. Colombo, I. Peretto, Drug Discovery Today 2008, 13,
677; c) R. Hanselmann, G. E. Job, G. Johnson, R. L. Lou, J. G.
Martynow, M. M. Reeve, Org. Process Res. Dev. 2010, 14, 152;
d) R. Moumne, V. Larue, B. Seijo, T. Lecourt, L. Micouin, C.
Tisne, Org. Biomol. Chem. 2010, 8, 1154.
[3] a) M. J. Genin, D. A. Allwine, D. J. Anderson, M. R. Barba-
chyn, D. E. Emmert, S. A. Garmon, D. R. Graber, K. C.
Grega, J. B. Hester, D. K. Hutchinson, J. Morris, R. D. Re-
ischer, D. Stper, B. H. Yagi, J. Med. Chem. 2000, 43, 953; b) W.
Li, Y. Xia, Z. Fan, F. Qu, Q. Wu, P. Ling, Tetrahedron Lett.
2008, 49, 2804.
General Procedure for the Synthesis of 4-Aryl-1H-1,2,3-triazoles (2):
A reaction tube was charged with 2-aryl-1,1-dibromoalkenes 1
(0.2 mmol), NaN3 (26 mg, 0.4 mmol), CuI (0.04 mmol), Na ascorb-
ate (0.10 mmol), K2CO3 (0.4 mmol), and DMSO (2 mL). The mix-
ture was heated to 120 °C with stirring for 12 h. The mixture was
allowed to cool to room temperature and was quenched with H2O
(10 mL). The mixture was extracted with EtOAc (3ϫ10 mL), and
the organic layer was washed with brine (5 mL). The combined
organic layers were dried with Na2SO4, concentrated under reduced
pressure, and dried under high vacuum. Purification by column
chromatography on silica gel (EtOAc/hexane, 2:1) afforded 4-aryl-
1H-1,2,3-triazole 2.
4-(4-Isopropylphenyl)-1H-1,2,3-triazole (2c): Yield: 79%. Slightly
1
yellow oil. H NMR (500 MHz, CDCl3): δ = 7.94 (s, 1 H), 7.74 (d,
J = 8.2 Hz, 2 H), 7.32 (d, J = 8.2 Hz, 2 H), 2.98–2.93 (m, 1 H),
1.29 (d, J = 6.9 Hz, 6 H) ppm. 13C NMR (125 MHz, CDCl3): δ =
149.7, 146.9, 129.2, 127.1, 126.2, 126.1, 34.0, 23.8 ppm. ESI-MS:
m/z (%) = 187 ([M]+, 100). HRMS: calcd. for C11H13N3 [M + H]+
187.1111; found 187.1110.
[4] a) R. Alvarez, S. Velazquez, A. San-Felix, S. Aquaro, E.
De Clercq, C. F. Perno, A. Karlsson, J. Balzarini, M. J. Camar-
asa, J. Med. Chem. 1994, 37, 4185; b) F. da Silva, M. C. B. V.
de Souza, I. I. P. Frugulhetti, H. C. Castro, O. S. L. de Souza,
T. M. L. de Souza, D. Q. Rodrigues, A. M. T. Souza, P. A. Ab-
reu, F. Passamani, C. R. Rodrigues, V. F. Ferreira, Eur. J. Med.
Chem. 2009, 44, 373.
4-(3,4-Dimethoxyphenyl)-1H-1,2,3-triazole (2f): Yield: 80%. Yellow
1
oil. H NMR (400 MHz, CDCl3): δ = 3.92 (s, 3 H), 3.96 (s, 3 H),
[5] a) L. S. Kallander, Q. Lu, W. Chen, T. Tomaszek, G. Yang, D.
Tew, T. D. Meek, G. A. Hofmann, C. K. Schulz-Pritchard,
W. W. Smith, C. A. Janson, M. D. Ryan, G. Zhang, K. O.
Johanson, R. B. Kirkpatrick, T. F. Ho, P. D. Fisher, M. R. Mat-
tern, R. K. Johnson, M. J. Hansbury, J. D. Winkler, K. W.
Ward, D. F. Veber, S. K. Thompson, J. Med. Chem. 2005, 48,
5644; b) U. F. Rohrig, O. L. Awad, O. A. Grosdidier, P. Larrieu,
V. Stroobant, D. Colau, V. Cerundolo, A. J. G. Simpson, P. Vo-
gel, B. J. Van den Eynde, V. Zoete, O. Michielin, J. Med. Chem.
2010, 53, 1172.
[6] a) V. V. Rostovtsev, L. G. Green, V. V. Fokin, K. B. Sharpless,
Angew. Chem. 2002, 114, 2708; Angew. Chem. Int. Ed. 2002,
41, 2596; b) P. Wu, A. K. Feldman, C. J. Hawker, A. Scheel, B.
Voit, J. Pyun, K. B. Sharpless, V. V. Fokin, Angew. Chem. Int.
Ed. 2004, 43, 4018; c) P. Wu, A. K. Feldman, C. J. Hawker, A.
Scheel, B. Voit, J. Pyun, K. B. Sharpless, V. V. Fokin, Angew.
Chem. 2004, 116, 4018; Angew. Chem. Int. Ed. 2004, 43, 3928;
d) E. J. Yoo, M. Ahlquist, S. H. Kim, I. Bae, V. V. Fokin, K. B.
Sharpless, S. Chang, Angew. Chem. Int. Ed. 2007, 46, 1760; e)
Yoo, E. J. M. Ahlquist, S. H. Kim, I. Bae, V. V. Fokin, K. B.
Sharpless, S. Chang, Angew. Chem. 2007, 119, 1760; Angew.
Chem. Int. Ed. 2007, 46, 1730; f) D. Kumar, V. B. Reddy, R. S.
Varma, Tetrahedron Lett. 2009, 50, 2065.
6.93 (d, J = 8.5 Hz, 1 H), 7.34–7.42 (m, 2 H), 7.85 (br. s, 1 H) ppm.
13C NMR (100 MHz, CDCl3): δ = 150.2, 148.8, 148.5, 135.8, 128.2,
118.8, 111.4, 109.2, 56.0 ppm. ESI-MS: m/z (%) = 205 (100) [M]+.
HRMS: calcd. for C10H12N3O2 [M + H]+ 206.0930; found
206.0929.
Synthesis of 5-Bromo-4-p-tolyl-1H-1,2,3-triazole (4): A reaction
tube was charged with 1-(bromoethynyl)-4-methylbenzene (3)
(0.2 mmol), NaN3 (26 mg, 0.4 mmol), Pd(PPh3)4 (0.04 mmol), and
DMSO (2 mL). The mixture was heated to 120 °C with stirring for
12 h. The mixture was allowed to cool to room temperature and
was quenched with H2O (10 mL). The mixture was extracted with
EtOAc (3ϫ10 mL), and the organic layer was washed with brine
(5 mL). The combined organic layers were dried with Na2SO4, con-
centrated under reduced pressure, and dried under high vacuum.
Purification by column chromatography on silica (EtOAc/hexane,
2:1) afforded 4.
Synthesis of 1,4-Di-p-tolyl-1H-1,2,3-triazole (6): A reaction tube
was charged with dibromoolefin 1a (55 mg, 0.2 mmol), NaN3
(26 mg, 0.4 mmol), CuI (0.04 mmol), Na ascorbate (20 mg,
0.10 mmol), K2CO3 (58 mg, 0.4 mmol), and DMSO (2 mL). The
mixture was heated to 120 °C with stirring for 12 h. The mixture
was allowed to cool to room temperature and was quenched with
H2O (10 mL). The mixture was extracted with EtOAc (3ϫ10 mL),
and the organic layer was washed with brine (5 mL). The combined
organic layers were dried with Na2SO4, concentrated under reduced
pressure, and dried under high vacuum. Purification by column
chromatography on silica gel (EtOAc/hexane, 2:1) afforded 6.
[7] a) C. W. Tornøe, C. Christensen, M. Meldal, J. Org. Chem.
2002, 67, 3057; b) V. V. Rostovtsev, L. G. Green, V. V. Fokin,
K. B. Sharpless, Angew. Chem. 2002, 114, 2708; Angew. Chem.
Int. Ed. 2002, 41, 2596; c) F. Fazio, M. C. Bryan, O. Blixt, J. C.
Paulson, C. H. Wong, J. Am. Chem. Soc. 2002, 124, 14397; d)
Q. Wang, R. C. Chan, R. Hilgraf, V. V. Fokin, K. B. Sharpless,
M. G. Finn, J. Am. Chem. Soc. 2003, 125, 3192; e) S. Löber, P.
Rodriguez-Loaiza, P. Gmeiner, Org. Lett. 2003, 5, 1753; f) F.
Eur. J. Org. Chem. 2012, 424–428
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
427

X. Wang, C. Kuang, Q. Yang
FULL PAPER
Perez-Balderas, M. Ortega-Munoz, J. Morales-Sanfrutos, F.
Hernández-Mateo, F. G. Calvo-Flores, J. A. Calvo-Asin, J.
Isac-Garcia, F. Santoyo-González, Org. Lett. 2003, 5, 1951.
[12] a) N. S. Zefirov, N. K. Chapovskaya, V. V. Kolesnikov, J. Chem.
Soc. D 1971, 13, 1001; b) B. Quiclet-Sire, S. Z. Zard, Synthesis
2005, 19, 3319.
[13] J. Barluenga, C. Valdes, G. Beltrn, M. Escribano, F. Aznar,
Angew. Chem. 2006, 118, 7047; Angew. Chem. Int. Ed. 2006,
45, 6893.
[14] W. Zhang, C. Kuang, Q. Yang, Synthesis 2010, 2, 283.
[15] W. Zhu, D. Ma, Chem. Commun. 2004, 7, 888.
[16] a) J. E. Hein, J. C. Tripp, L. B. Krasnova, K. B. Sharpless, V. V.
Fokin, Angew. Chem. 2009, 121, 8162; Angew. Chem. Int. Ed.
2009, 48, 8018; b) E. Prochnow, A. Alexander, A. A. Auer, K.
Banert, J. Phys. Chem. A 2007, 111, 9945.
[17] A. Coste, F. Couty, G. Evano, Synthesis 2010, 9, 1500.
[18] C. Spiteri, J. E. Moses, Angew. Chem. 2010, 122, 33; Angew.
Chem. Int. Ed. 2010, 49, 31.
[19] L. Shu, M. Mayor, Chem. Commun. 2006, 39, 4134.
[20] a) J. Yoon, J. Ryu, Bioorg. Med. Chem. Lett. 2010, 20, 3930; b)
S. Ozcubukcu, E. Ozkal, C. Jimeno, M. A. Pericas, Org. Lett.
2009, 11, 4680; c) W. S. Brotherton, H. A. Michaels, J. T. Sim-
mons, R. J. Clark, N. S. Dalal, L. Zhu, Org. Lett. 2009, 11,
4954.
[8]
a) L. Zhang, X. Chen, P. Xue, H. H. Sun, I. D. Williams, K. B.
Sharpless, V. V. Fokin, G. Jia, J. Am. Chem. Soc. 2005, 127,
15998; b) M. M. Majireck, S. M. Weinreb, J. Org. Chem. 2006,
71, 8680; c) B. C. Boren, S. Narayan, L. K. Rasmussen, L.
Zhang, H. Zhao, Z. Lin, G. Jia, V. V. Fokin, J. Am. Chem. Soc.
2008, 130, 8923; d) L. K. Rasmussen, B. C. Boren, V. V. Fokin,
Org. Lett. 2007, 9, 5337; e) A. Tam, U. Arnold, M. B. Soellner,
R. T. Raines, J. Am. Chem. Soc. 2007, 129, 12670.
a) P. Fabbrizzi, S. Cicchi, A. Brandi, E. Sperotto, G. van Koten,
Eur. J. Org. Chem. 2009, 5423; b) B. Schulze, C. Friebe, M. D.
Hager, W. Günther, U. Köhn, B. O. Jahn, H. Görls, U. S. Schu-
bert, Org. Lett. 2010, 12, 2710; c) I. S. Park, M. S. Kwon, Y.
Kim, J. S. Lee, J. Park, Org. Lett. 2008, 10, 497; d) S. Lee, Y.
Hua, H. Park, A. H. Flood, Org. Lett. 2010, 12, 2100; e) J. Li,
M. Hu, S. Q. Yao, Org. Lett. 2009, 11, 3008.
[9]
[10] a) S. B. Ferreira, A. C. R. S. Odero, M. F. C. Cardoso, E. S.
Lima, C. R. Kaiser, F. P. Silva, V. F. Ferreira, J. Med. Chem.
2010, 53, 2364; b) J. Li, D. Wang, Y. Zhang, J. Li, B. Chen,
Org. Lett. 2009, 11, 3024.
[21] E. J. Corey, P. L. Fuchs, Tetrahedron Lett. 1972, 13, 3769.
Received: August 16, 2011
Published Online: November 16, 2011
[11] L. Lu, J. Wu, C. Yang, J. Chin. Chem. Soc. 2008, 55, 414.
428
www.eurjoc.org
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2012, 424–428