Copper-catalyzed N-N bond formation by homocoupling of ketoximes via n-o bond cleavage: Facile, mild, and efficient synthesis of azines

Article abstract of DOI:10.1055/s-0031-1290779

A facile, mild, and efficient copper-catalyzed homocoupling of ketoximes involving N-O bond cleavage in the presence of sodium bisulfite (NaHSO has been developed. This reaction shows good functional group tolerance and affords a broad scope of azines in high yields.

Full text of DOI:10.1055/s-0031-1290779

SPECIAL TOPIC
▌1501
sCpeociapl tpopeicr-Catalyzed N–N Bond Formation by Homocoupling of Ketoximes via
N–O Bond Cleavage: Facile, Mild, and Efficient Synthesis of Azines
Homocoupling of Ketoximes via N–O Bond Cleavage
Mi-Na Zhao, Hao Liang, Zhi-Hui Ren, Zheng-Hui Guan*
Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, Department of Chemistry & Materials
Science, Northwest University, Xi’an 710069, P. R. of China
E-mail: guanzhh@nwu.edu.cn
Received: 03.02.2012; Accepted: 05.03.2012
lyzed homocoupling of the oximes, were observed as the
Abstract: A facile, mild, and efficient copper-catalyzed homocou-
main product instead of N-Boc enamines (Scheme 1,
pling of ketoximes involving N–O bond cleavage in the presence of
equation 2). Azines, N–N linked diimines, are extensively
sodium bisulfite (NaHSO3) has been developed. This reaction
shows good functional group tolerance and affords a broad scope of
used as synthetic intermediates,8 and they have received
azines in high yields.
much attention recently due to their interesting optical,9
biological,10 and conductive properties,11 and their poten-
tial application in liquid crystals, nonlinear optical mate-
rials.12 Azines are generally prepared by the condensation
of aldehydes or ketones with hydrazine hydrate in ethanol
solution under reflux conditions;13 hydrazine hydrate is
hazardous and essential for this transformation. Versatile
and efficient methods for the construction of azines using
environmentally friendly and readily available starting
materials remain highly desirable.14 Herein, we report a
facile and practical method for the copper-catalyzed
homocoupling of oximes for the synthesis of azines.
Key words: copper, homocoupling, ketoxime, azine, NaHSO3
Oximes and their derivatives are an important class of
compounds with potential pharmaceutical properties1 and
they are also versatile functional groups.2 Recently, con-
siderable attention has been directed toward transition-
metal-catalyzed coupling reactions using oximes and their
derivatives as substrates in organic synthesis.3 Palladium-
or copper-catalyzed C–O cross-coupling of aryl halides or
arylboronic acids with oximes were recently explored for
the construction of a series of useful O-arylhydroxyl-
amines.4 Accordingly, an attractive, elegant strategy for
the C–N cross-coupling of boronic acids with oxime O-
carboxylates has also been used for the construction of
highly substituted pyridines and N-substituted imines.5
The development of new methodologies for the transition-
metal-catalyzed coupling of oximes remains as a promis-
ing approach for the preparation of various nitrogen-
containing compounds.6
Initially, acetophenone oxime (1a) was used as a model
substrate to optimize the reaction conditions. The desired
azine 2a was obtained in 74% yield when copper(I) iodide
was used as a catalyst in the presence of sodium bisulfite
in toluene (Table 1, entry 1). Various catalysts, reducing
agents, and solvents were then screened in this reaction.
Examining the use of various solvents, 1,4-dioxane and
tetrahydrofuran gave no product and N,N-dimethylform-
amide or acetonitrile gave 2a in lower yield (entries 2–5).
1,2-Dichloroethane was the most suitable solvent for this
reaction, giving azine 2a in an excellent 90% yield (entry
6). Sodium bisulfite is essential as the reducing agent in
this copper-catalyzed homocoupling reaction, other re-
ductants, such as sodium sulfite and sodium dithionite,
were employed, but did not improve the yield of 2a (en-
tries 7–9). Next catalyst was varied, and it was found that
Recently, our group reported a copper-catalyzed reductive
acylation of ketoximes for preparation of enamides in the
presence of sodium bisulfite (Scheme 1, equation 1).7 The
success of this novel methodology encourage us to exam-
ine the formation of N-Boc enamines in the presence of
di-tert-butyl dicarbonate under similar conditions. Unex-
pectedly, azines, which were generated from copper-cata-
Boc
HN
R1
Ar
OH
N
O
R2
H
R1
R2
Ac2O
(Boc)2O
R2
N
Ar
R3
CuI
NaHSO3
CuI
NaHSO3
R2
Ar
R1
Ar
(1)
N
R1
R1
N
Ar
R2
(2)
Scheme 1 Copper-catalyzed reductive coupling of oximes
SYNTHESIS 2012, 44, 1501–1506
Advanced online publication: 30.03.2012
0
0
3
9
-
7
8
8
1
1
4
3
7
-
2
1
0
X
DOI: 10.1055/s-0031-1290779; Art ID: SS-2012-C0109-OP
© Georg Thieme Verlag Stuttgart · New York

1502
M. Zhao et al.
SPECIAL TOPIC
Table 1 Optimization of the Reaction Conditionsa
14 and 15). Based on these studies, the optimal conditions
are copper(I) iodide (10 mol%) and sodium bisulfite (3
equiv) in 1,2-dichloroethane under argon at 140 °C.
OH
With these optimized reaction conditions in hand, we then
examined the substrates scope of this novel copper(I) io-
dide catalyzed homocoupling reaction. The results are
summarized in Table 2. This transformation displayed
good functional group tolerance and gave various azines
in moderate to good yields. Ketoximes 1b–h with methyl,
methoxy, fluoro, chloro, and bromo groups on aryl rings
could easily be converted into the corresponding azines
under the reaction conditions. Electron-donating ketox-
imes were more beneficial for this transformation, while
the yields of electron-withdrawing ketoximes were de-
creased slightly (entries 2–8). Furthermore, the 2-acetyl-
naphthalene oxime (1i) also underwent the desired
reaction to give the corresponding azine 2i in good yield
(entry 9). Similarly, the homocoupling of aryl ethyl ketox-
imes 1j–m and cyclic ketoximes 1n,o also proceeded
smoothly to give the corresponding azines 2j–o in good
yields (entries 10–15).
N
N
N
[M], reductant
(Boc)2O, solvent
1a
2a
Yieldb (%)
Entry Catalyst
Reductant
Solvent
1
2
CuI
NaHSO3
NaHSO3
NaHSO3
NaHSO3
NaHSO3
NaHSO3
–
toluene
DMF
74
53
0
CuI
3
CuI
1,4-dioxane
THF
4
CuI
0
5
CuI
MeCN
DCE
17
90
13
49
71
64
60
21
0
6
CuI
7
CuI
DCE
To gain an insight into the reaction mechanism, the O-
Boc-oxime 3a was first prepared by reacting acetophe-
none oxime (1a) with di-tert-butyl dicarbonate. Then 3a
was refluxed in the presence of copper(I) iodide and sodi-
um bisulfite in 1,2-dichloroethane at 140 °C for 12 hours,
to give the corresponding azine 2a in 82% yield (Scheme
2).
8
CuI
Na2SO3
Na2S2O4
NaHSO3
NaHSO3
NaHSO3
NaHSO3
NaHSO3
NaHSO3
DCE
9
CuI
DCE
10
11
12
13
14
CuBr
CuCl
Cu(OAc)2
Pd(OAc)2
–
DCE
DCE
DCE
On the basis of the results obtained above, a plausible
mechanism for this reaction is depicted in Scheme 3. The
reaction is initiated by the formation of O-Boc-oxime in-
termediate 3 from the acylation of ketoxime 1 by di-tert-
butyl dicarbonate. Next, cleavage of the N–O bond of the
O-Boc-oxime 3 by Cu+ and expulsion of a Cu2+ gives the
imine radical 4,7,15 which is assumed to undergo homo-
coupling rapidly to give azine product 2. The Cu2+ species
is reduced by sodium bisulfite to regenerate the active Cu+
in the reaction.
DCE
DCE
0
15c
n.r.d
CuI
DCE
a Reaction conditions: 1a (0.2 mmol), (Boc)2O (0.4 mmol), catalyst
(10 mol%), reductant (0.6 mmol), solvent (3 mL), under Ar, 140 °C,
12 h.
b Isolate yield.
c The reaction was performed in the absence of (Boc)2O.
d n.r. = no reaction.
In conclusion, we have developed a novel and efficient
protocol for the copper-catalyzed homocoupling of ketox-
imes for the preparation of symmetrical azines. The pro-
cedure shows high functional group tolerance and allows
rapid elaboration of readily available oximes into a variety
of symmetrical substituted azines in good to excellent
yields under mild reaction conditions. The reaction avoids
the use of hazardous hydrazine hydrate and is also envi-
copper(I) iodide was a superior catalyst to other copper or
palladium precursors, such as copper(I) bromide or chlo-
ride, copper(II) acetate, and palladium(II) acetate (entries
10–13). Furthermore, control experiments confirmed that
the formation of 2a was not observed in the absence of ei-
ther copper catalyst or di-tert-butyl dicarbonate (entries
OH
O
O
N
N
N
N
CuI (10 mol%)
NaHSO3
Ot-Bu
(Boc)2O
DCE, 140 °C, 1 h
DCE, 140 °C, 12 h
1a
3a, 98%
2a, 82%
Scheme 2 Investigation of the mechanism
Synthesis 2012, 44, 1501–1506
© Georg Thieme Verlag Stuttgart · New York

SPECIAL TOPIC
Homocoupling of Ketoximes via N–O Bond Cleavage
1503
ronmentally friendly. Investigations of an unsymmetrical
version, the detailed mechanism, and synthetic applica-
tions of this reaction are under way in our laboratory.
Table 2 Copper(I) Iodide Catalyzed Reductive Homocoupling of Ketoximes To Give Azinesa
n
OH
N
N
R
R
CuI, NaHSO3, (Boc)2O
DCE, 140 °C
N
R
n
n
1
2
Yieldb (%)
Entry
1
Oxime 1
Azine 2
Time (h)
12
NOH
N
N
1a
2a
90
NOH
N
N
2
3
4
1b
1c
1d
2b
2c
2d
24
24
24
84
80
73
NOH
N
N
NOH
NOH
N
N
MeO
OMe
MeO
N
5
1e
2e
12
72
N
NOH
F
N
6
7
8
9
1f
2f
2g
2h
2i
24
24
24
9
62
65
67
60
N
F
F
NOH
NOH
Cl
Br
N
1g
1h
1i
N
Cl
Cl
Br
N
N
Br
NOH
N
N
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2012, 44, 1501–1506

1504
M. Zhao et al.
SPECIAL TOPIC
Table 2 Copper(I) Iodide Catalyzed Reductive Homocoupling of Ketoximes To Give Azinesa (continued)
n
OH
N
N
R
R
CuI, NaHSO3, (Boc)2O
DCE, 140 °C
N
R
n
n
1
2
Yieldb (%)
Entry
Oxime 1
Azine 2
Time (h)
NOH
N
N
10
1j
2j
24
72
NOH
N
N
11
12
13
1k
1l
2k
2l
24
24
12
73
75
63
NOH
N
N
NOH
N
N
1m
2m
NOH
NOH
N
N
14
15
1n
1o
2n
2o
12
82
64
N
9
N
a Reaction conditions: 1 (0.4 mmol), (Boc)2O (0.8 mmol), CuI (10 mol%), NaHSO3 (1.2 mmol), DCE (5 mL), under Ar, 140 °C.
b Isolated yield.
Cu+
N
1
R
Column chromatography was carried out on silica gel. H NMR
spectra were recorded on 400 MHz in CDCl3 and 13C NMR spectra
were recorded on 100 MHz in CDCl3. All new products were further
characterized by HRMS. Unless otherwise stated, all reagents and
solvents were purchased from commercial suppliers and used with-
out further purification. The ketoximes were in all cases prepared
from the corresponding ketones according to literature.7,16
OH
O
O
N
N
N
N
(Boc)2O
R
N
Ot-Bu
R
R
R
R
1
3
4
2
Cu2+
NaHSO3
Cu2+
Cu+
Azines 2; General Procedure
A mixture of ketoximes 1 (0.4 mmol), (Boc)2O (0.8 mmol, 174.4
mg), NaHSO3 (1.2 mmol, 124.8 mg), and CuI (10 mol%, 7.6 mg)
was stirred in DCE (5.0 mL) at 140 °C under argon. After comple-
Scheme 3 Proposed mechanism for copper(I) iodide catalyzed ho-
mocoupling of ketoximes
Synthesis 2012, 44, 1501–1506
© Georg Thieme Verlag Stuttgart · New York

SPECIAL TOPIC
Homocoupling of Ketoximes via N–O Bond Cleavage
1505
tion of the reaction (TLC, hexane–EtOAc, 20:1), the mixture was
cooled to r.t., diluted with EtOAc (25 mL), and washed with brine
(20 mL). The organic layers were dried (anhyd Na2SO4), and evap-
orated in vacuo. The desired azines 2 were obtained after purifica-
tion by flash chromatography (silica gel, hexane–EtOAc, 50:1).
13C NMR (100 MHz, CDCl3): δ = 157.3, 137.0, 131.5, 128.1, 124.1,
14.9.
1,2-Bis[1-(naphthalen-2-yl)ethylidene]hydrazine (2i)
Brown solid; yield: 40.6 mg (60%); mp 198–200 °C.
1H NMR (400 MHz, CDCl3): δ = 8.24 (d, J = 10.4 Hz, 4 H), 7.90–
7.84 (m, 6 H), 7.51–7.49 (m, 4 H), 2.47 (s, 6 H).
13C NMR (100 MHz, CDCl3): δ = 157.6, 135.8, 134.0, 133.0, 128.6,
127.9, 127.6, 126.8, 126.6, 126.3, 124.0, 15.0.
1,2-Bis(1-phenylethylidene)hydrazine (2a)
Yellow solid; yield: 42.4 mg (90%); mp 115–116 °C.
1H NMR (400 MHz, CDCl3): δ = 7.93–7.91 (m, 4 H), 7.43–7.41 (m,
6 H), 2.32 (s, 6 H).
13C NMR (100 MHz, CDCl3): δ = 157.6, 138.3, 129.6, 128.3, 126.6,
15.0.
1,2-Bis(1-phenylpropylidene)hydrazine (2j)
Yellow solid; yield: 38.7 mg (72%); mp 59–60 °C.
1H NMR (400 MHz, CDCl3): δ = 7.92–7.90 (m, 4 H), 7.43–7.41 (m,
6 H), 2.90–2.88 (m, 4 H), 1.14–1.11 (t, J = 7.2 Hz, 6 H).
13C NMR (100 MHz, CDCl3): δ = 162.8, 137.3, 129.5, 128.4, 126.8,
1,2-Bis(1-p-tolylethylidene)hydrazine (2b)
Yellow solid; yield: 44.5 mg (84%); mp 127–129 °C.
1H NMR (400 MHz, CDCl3): δ = 7.81 (d, J = 8.8 Hz, 4 H), 7.22 (d,
J = 8.0 Hz, 4 H), 2.39 (s, 6 H), 2.30 (s, 6 H).
21.9, 11.4.
13C NMR (100 MHz, CDCl3): δ = 157.6, 139.6, 135.7, 129.0, 126.5,
21.3, 14.9.
1,2-Bis(1-p-tolylpropylidene)hydrazine (2k)
Yellow solid; yield: 42.7 mg (73%); mp 100–101 °C.
1H NMR (400 MHz, CDCl3): δ = 7.81 (d, J = 8.0 Hz, 4 H), 7.23 (d,
J = 7.2 Hz, 4 H), 2.88–2.86 (m, 4 H), 2.39 (s, 6 H), 1.13–1.09 (m, 6
H).
13C NMR (100 MHz, CDCl3): δ = 163.0, 139.8, 134.9, 129.4, 127.0,
22.1, 21.6, 11.8.
1,2-Bis[1-(3,4-dimethylphenyl)ethylidene]hydrazine (2c)
Yellow solid; yield: 47.4 mg (80%); mp 116–117 °C.
1H NMR (400 MHz, CDCl3): δ = 7.72 (s, 2 H), 7.61 (d, J = 8.0 Hz,
2 H), 7.18 (d, J = 8.0 Hz, 2 H), 2.32 (s, 6 H), 2.30 (s, 6 H), 2.28 (s,
6 H).
13C NMR (100 MHz, CDCl3): δ = 157.3, 138.3, 136.4, 136.1, 129.5,
127.6, 124.1, 19.9, 19.6, 15.0.
1,2-Bis[1-(3,4-dimethylphenyl)propylidene]hydrazine (2l)
Yellow solid; yield: 48.0 mg (75%); mp 61–62 °C.
1H NMR (400 MHz, CDCl3): δ = 7.71 (s, 2 H), 7.61 (d, J = 8.0 Hz,
2 H), 7.18 (d, J = 7.6 Hz, 2 H), 2.88–2.84 (m, 4 H), 2.32 (s, 6 H),
2.30 (s, 6 H), 1.12–1.08 (t, J = 7.6 Hz, 6 H).
13C NMR (100 MHz, CDCl3): δ = 162.4, 138.2, 136.5, 135.0, 129.6,
127.9, 124.3, 21.8, 19.9, 19.6, 11.5.
HRMS (ESI): m/z [M + H]+ calcd for C22H29N2: 321.2325; found:
321.2325.
1,2-Bis[1-(5,6,7,8-tetrahydronaphthalen-2-yl)ethylidene]hy-
drazine (2d)
Yellow solid; yield: 50.0 mg (73%); mp 84–86 °C.
1H NMR (400 MHz, CDCl3): δ = 7.61 (d, J = 8.8 Hz, 4 H), 7.10 (d,
J = 8.0 Hz, 2 H), 2.81 (s, 8 H), 2.26 (s, 6 H), 1.81 (s, 8 H).
13C NMR (100 MHz, CDCl3): δ = 157.3, 138.9, 137.0, 135.7, 129.1,
127.2, 123.7, 29.5, 29.3, 23.1, 23.1, 15.0.
1,2-Bis[1-(5,6,7,8-tetrahydronaphthalen-2-yl)propylidene]hy-
drazine (2m)
1,2-Bis[1-(3-methoxyphenyl)ethylidene]hydrazine (2e)
Yellow solid; yield: 42.6 mg (72%); mp 90–92 °C.
Yellow solid; yield: 47.9 mg (63%); mp 90–91 °C.
1H NMR (400 MHz, CDCl3): δ = 7.50 (s, 2 H), 7.43 (d, J = 7.6 Hz,
2 H), 7.33–7.29 (t, J = 8.0 Hz, 2 H), 6.95 (d, J = 8.0 Hz, 2 H), 3.84
(s, 6 H), 2.27 (s, 6 H).
13C NMR (100 MHz, CDCl3): δ = 159.5, 157.1, 139.7, 129.2, 119.2,
115.6, 111.5, 55.3, 15.1.
1H NMR (400 MHz, CDCl3): δ = 7.61 (d, J = 10.4 Hz, 4 H), 7.11 (d,
J = 8.0 Hz, 2 H), 2.86–2.81 (m, 12 H), 1.81 (s, 8 H), 1.11–1.07 (t,
J = 7.6 Hz, 6 H).
13C NMR (100 MHz, CDCl3): δ = 162.4, 138.8, 137.1, 134.6, 129.1,
127.4, 123.9, 29.5, 29.3, 23.1, 23.1, 21.8, 11.5.
1,2-Bis[1-(4-fluorophenyl)ethylidene]hydrazine (2f)
1,2-Bis[3,4-dihydronaphthalen-1(2H)-ylidene]hydrazine (2n)
Yellow solid; yield: 33.5 mg (62%); mp 125–127 °C.
Yellow solid; yield: 47.2 mg (82%); mp 134–135 °C.
1H NMR (400 MHz, CDCl3): δ = 7.90–7.86 (m, 4 H), 7.10–7.05 (t,
J = 8.8 Hz, 4 H), 2.29 (s, 6 H).
13C NMR (100 MHz, CDCl3): δ = 163.7 (d, JC,F = 248.9 Hz), 157.4,
134.5, 128.5 (d, JC,F = 8.3 Hz), 115.3 (d, JC,F = 22.0 Hz), 14.9.
1H NMR (400 MHz, CDCl3): δ = 8.30–8.29 (m, 2 H), 7.29–7.25 (m,
4 H), 7.17–7.15 (m, 2 H), 2.82–2.81 (m, 4 H), 2.77–2.74 (m, 4 H),
1.93–1.90 (m, 4 H).
13C NMR (100 MHz, CDCl3): δ = 157.0, 140.4, 132.8, 129.4, 128.6,
126.2, 125.4, 29.9, 27.3, 22.1.
1,2-Bis[1-(4-chlorophenyl)ethylidene]hydrazine (2g)
Pale yellow solid; yield: 39.3 mg (65%); mp 154–155 °C.
1,2-Bis(2,3-dihydroinden-1-ylidene)hydrazine (2o)
Yellow solid; yield: 33.2 mg (64%); mp 164–166 °C.
1H NMR (400 MHz, CDCl3): δ = 7.90 (d, J = 7.6 Hz, 2 H), 7.38–
7.29 (m, 6 H), 3.07–3.01 (m, 8 H).
1H NMR (400 MHz, CDCl3): δ = 7.82 (d, J = 8.0 Hz, 4 H), 7.36 (d,
J = 8.4 Hz, 4 H), 2.27 (s, 6 H).
13C NMR (100 MHz, CDCl3): δ = 157.2, 136.6, 135.7, 128.5, 127.9,
14.9.
13C NMR (100 MHz, CDCl3): δ = 169.9, 149.7, 138.3, 131.0, 126.9,
125.6, 122.5, 28.5, 28.2.
1,2-Bis[1-(4-bromophenyl)ethylidene]hydrazine (2h)
Yellow solid; yield: 52.5 mg (67%); mp 161–162 °C.
1H NMR (400 MHz, CDCl3): δ = 7.75 (d, J = 8.0 Hz, 4 H), 7.52 (d,
J = 8.8 Hz, 4 H), 2.26 (s, 6 H).
Acknowledgment
This research was supported by National Natural Science Founda-
tion of China (NSFC-21002077).
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2012, 44, 1501–1506

1506
M. Zhao et al.
SPECIAL TOPIC
Med. Chem. Lett. 2010, 20, 6920. (c) Cohen, R.;
Rybtchinski, B.; Gandelman, M.; Shimon, L. J. W.; Martin,
J. M. L.; Milstein, D. Angew. Chem. Int. Ed. 2003, 42, 1949.
(d) Ferguson, L. N.; Goodwin, T. C. J. Am. Chem. Soc. 1949,
71, 633.
References
(1) Ashani, Y.; Silman, I. In The Chemistry of Hydroxylamines,
Oximes and Hydroxamic Acids; Rappoport, Z.; Liebman, J.
F., Eds.; Wiley: New York, 2008, 609.
(2) (a) Nakamura, I.; Iwata, T.; Zhang, D.; Terada, M. Org. Lett.
2012, 14, 206. (b) Ramón, R. S.; Bosson, J.; Díez-González,
S.; Marion, N.; Nolan, S. P. J. Org. Chem. 2010, 75, 1197.
(c) Ganguly, N. C.; Mondal, P. Synthesis 2010, 3705.
(d) Augustine, J. K.; Atta, R. N.; Ramappa, B. K.;
Boodappa, C. Synlett 2009, 3378.
(3) Ren, Z.-H.; Zhang, Z.-Y.; Yang, B.-Q.; Wang, Y.-Y.; Guan,
Z.-H. Org. Lett. 2011, 13, 5394; and references therein.
(4) (a) Maimone, T. J.; Buchwald, S. L. J. Am. Chem. Soc. 2010,
132, 9990. (b) Nonappa, P. D.; Pandurangan, K.; Maitra, U.;
Wailes, S. Org. Lett. 2007, 9, 2767. (c) Feng, X.-H.; Zhang,
G.-Z.; Chen, C.-Q.; Yang, M.-Y.; Xu, X.-Y.; Huang, G.-S.
Synth. Commun. 2009, 39, 1768. (d) Abdelselam, A.; Meyer,
A. G.; Tuck, K. L. Synlett 2009, 955. (e) Wang, L.; Huang,
C.; Cai, C. Catal. Commun. 2010, 11, 532.
(9) (a) Tang, W.; Xiang, Y.; Tong, A. J. Org. Chem. 2009, 74,
2163. (b) Rajendiran, N.; Balasubramanian, T. Spectrochim.
Acta, Part A 2007, 68, 894. (c) Lewis, M.; Glaser, R. J. Org.
Chem. 2002, 67, 1441. (d) Nalwa, H. S.; Kakuta, A.;
Mukoh, A. J. Appl. Phys. 1993, 73, 4743.
(10) (a) Kurteva, V. B.; Simeonov, S. P.; Stoilova-Disheva, M.
Pharmacology & Pharmacy 2011, 2, 1;
http://www.scirp.org/journal/pp/. (b) Kuznetsova, Y. A.;
Romakh, V. B. Appl. Biochem. Biotechnol. 1996, 61, 205.
(11) (a) Cianga, I.; Ivanoiu, M. Eur. Polym. J. 2006, 42, 1922.
(b) Euler, W. B.; Cheng, M.; Zhao, C. Chem. Mater. 1999,
11, 3702. (c) Kesslen, E. C.; Euler, W. B. Chem. Mater.
1999, 11, 336. (d) Euler, W. B. Chem. Mater. 1990, 2, 209.
(12) Wu, C. Y.; Chen, Y.; Jing, S. Y.; Lee, C. S.; Dinda, J.;
Hwang, W. S. Polyhedron 2006, 25, 3053.
(5) (a) Liu, S.; Liebeskind, L. S. J. Am. Chem. Soc. 2008, 130,
6918. (b) Liu, S. B.; Yu, Y.; Liebeskind, L. S. Org. Lett.
2007, 9, 1947.
(13) (a) Kolb, V. M.; Kuffel, A. C.; Spiwek, H. O.; Janota, T. E.
J. Org. Chem. 1989, 54, 2771. (b) Brun, P.; Tenalglia, A.;
Waegell, B. Tetrahedron 1985, 41, 5019.
(6) (a) Tan, Y.; Hartwig, J. F. J. Am. Chem. Soc. 2010, 132,
3676. (b) Gerfaud, T.; Neuville, L.; Zhu, J. Angew. Chem.
Int. Ed. 2009, 48, 572. (c) Parthasarathy, K.; Jeganmohan,
M.; Cheng, C.-H. Org. Lett. 2008, 10, 325. (d) Zaman, S.;
Mitsuru, K.; Ab, A. D. Org. Lett. 2005, 7, 609. (e) Too, P.
C.; Chua, S. H.; Wong, S. H.; Chiba, S. J. Org. Chem. 2011,
76, 6159.
(7) Guan, Z.-H.; Zhang, Z.-Y.; Ren, Z.-H.; Wang, Y.-Y.; Zhang,
X. J. Org. Chem. 2011, 76, 339.
(8) (a) Nanjundaswamy, H. M.; Pasha, M. A. Synth. Commun.
2007, 37, 3417. (b) Manikannan, R.; Venkatesan, R.;
Muthusubramanian, S.; Yogeeswari, P.; Sriram, D. Bioorg.
(c) Nanjundaswamy, H. M.; Pasha, M. A. Synth. Commun.
2007, 37, 3417. (d) Safari, J.; Gandomi-Ravandi, S. Synth.
Commun. 2011, 41, 645.
(14) (a) Lee, B.; Lee, K. H.; Cho, J.; Nam, W.; Hur, N. H. Org.
Lett. 2011, 13, 6386. (b) Laouiti, A.; Rammah, M. M.;
Rammah, M. B.; Marrot, J.; Couty, F.; Evano, G. Org. Lett.
2012, 14, 6.
(15) (a) Narasaka, K.; Kitamura, M. Eur. J. Org. Chem. 2005,
4505. (b) Narasaka, K. Pure Appl. Chem. 2002, 74, 143.
(16) Zhao, H.; Vandenbossche, C. P.; Koenig, S. G.; Singh, S. P.;
Bakale, R. P. Org. Lett. 2008, 10, 505.
Synthesis 2012, 44, 1501–1506
© Georg Thieme Verlag Stuttgart · New York