Heck cross-coupling of vinyl heteroaromatic compounds with aryl and heteroaryl halides using Pd(II) complex under phosphine-free conditions

Article abstract of DOI:10.1016/j.tet.2013.10.078

The palladium-catalyzed cross-coupling reaction of vinyl heteroaromatic compounds with aryl bromides and heteroaryl bromides is described using air and moisture stable N,N′,N″,O-tetrafunctional Pd catalyst under phosphine-free conditions. As a result a variety of trans-1,2-disubstituted vinyl heterocycles were obtained in high to good yields.

Full text of DOI:10.1016/j.tet.2013.10.078

Tetrahedron 69 (2013) 10940e10945
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Heck cross-coupling of vinyl heteroaromatic compounds with aryl
and heteroaryl halides using Pd(II) complex under phosphine-free
conditions
Manne Annapurna, P. Vishnuvardhan Reddy, Surya Prakash Singh,
*
Mannepalli Lakshmi Kantam
Inorganic and Physical Chemistry Division, CSIR e Indian Institute of Chemical Technology (CSIR e IICT), Tarnaka, Hyderabad 500007, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 August 2013
Received in revised form 17 October 2013
Accepted 21 October 2013
Available online 31 October 2013
The palladium-catalyzed cross-coupling reaction of vinyl heteroaromatic compounds with aryl bromides
and heteroaryl bromides is described using air and moisture stable N,N0,N00,O-tetrafunctional Pd catalyst
under phosphine-free conditions. As a result a variety of trans-1,2-disubstituted vinyl heterocycles were
obtained in high to good yields.
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
CeC coupling
Heck reaction
Palladium
trans-2-Styrylpyridines
Vinyl heterocycles
1. Introduction
a convenient and efficient catalytic protocol with wide substrate
scope under phosphine-free conditions mainly in view of the
Heck reaction is one of the most popular catalytic processes
used for the construction of C(sp2)eC(sp2) bonds.1 Traditionally,
Heck reaction of aryl halides with alkenes is carried out using
various palladium phosphine catalysts.2 While, significant progress
has been made in the field of Heck coupling of aryl halides or
heteroaryl halides with styrene derivatives; the corresponding
synthesis of trans-2-styrylpyridines derivatives or trans-1,2-
disubstituted vinyl heterocycles by coupling of 2-vinylpyridines
or vinyl functionalized heterocycles with aryl- or heteroaryl ha-
lides is challenging. Earlier, Doucet et al. reported the synthesis of
few selected styrylpyridine derivatives by Heck reaction of aryl
halides with vinylpyridines using [Pd(C3H5)Cl]2/tedicyp catalyst.3
Frech et al. used aminophosphine-based pincer complexes for the
Heck coupling of vinylpyridines with aryl bromides.4 Notably, Li
and Hua demonstrated the synthesis of trans-2-styrylpyridines
derivatives by PdCl2(PCy3)2 catalyzed coupling of 2-vinylpyridine
with aryl chlorides.5 These processes represent important ad-
vancement made in this field; however, it is important to develop
growing significance of styrylpyridine derivatives in material
chemistry,6 biologically active compounds,7 amyloid imaging
agents for Alzheimer’s disease,8 and as ligands in metal complexes.9
In recent years, much emphasis was given for the design and
synthesis of air-stable palladium complexes, which can be used as
an alternate to air-sensitive and toxic palladium phosphine cata-
lysts. In these direction, many palladium complexes comprising N-,
O- and S-centred ligands have been developed amongst, which
N-heterocyclic carbene complexes,10 N-based palladacycles,11 and
carbocyclic carbenes,12 are remarkable. Earlier, we have shown that
palladium complexes containing N-donor ligands with amide
functionality; namely, tetradentate dicarboxyamidate/dipyridyl
palladium, amido/pyridyl carboxylate ligated palladium and uri-
date/pyridyl palladium complexes, increases the thermal stability
and activity of the palladium catalyst for the Heck reaction of
deactivated aryl halides with high turnover number.13 However,
limitations remain with substrate scope of vinyl heterocycles, such
as vinylpyridines, vinyl triazoles and vinyl thiazoles, which are
reported with this communication.
More recently, we have reported the synthesis and application
of palladium(II) complexes of multi-donor and multi-functional
amido/pyridyl/phenolic/amine ligands for the Heck reaction of
* Corresponding author. Tel.: þ91 40 27193510; fax: þ91 40 27160921; e-mail
addresses: mlakshmi@iict.res.in, lkmannepalli@gmail.com (M.L. Kantam).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.10.078

M. Annapurna et al. / Tetrahedron 69 (2013) 10940e10945
10941
Thus the optimum reaction conditions for Heck cross-coupling
of vinyl heteroarenes with aryl halide and heteroaryl halide are
Pd(II) complex/base as Cs2CO3, TBAB as additive and DMA used as
solvent at 150 ꢀC. The results obtained from optimized reaction
conditions by using 2-vinylpyridine with various aryl and hetero-
aryl halides to explore the scope of the reaction and the results are
presented in Table 2.
O
N
NH
O
Pd
N
Catalyst
As can be seen in Table 2, when the reaction performed with
2-vinylpyridine and electron-rich aryl bromides, such as, p-bromoa-
nisole and p-bromotoluene proceeded smoothly to afford the
corresponding desired cross-coupled products as (E)-2-(4-
methoxystyryl)pyridine and (E)-2-(4-methylstyryl)pyridine in good
yields (Table 2, 3a,b). When the reaction conducted with bromo-
benzene the product (E)-2-styrylpyridine was obtained in high yield
90% (Table 2, 3c). Under similar reaction conditions the products were
isolated as (E)-ethyl 4-(2-(pyridin-2-yl)vinyl)benzoate and (E)-2-(4-
(trifluoromethyl)styryl)pyridine in 89% and 85% with electron-
deficient aryl bromides like ethyl 4-bromobenzoate and 1-bromo-4-
(trifluoromethyl)benzene (Table 2, 3d,e). As like above, the reaction
performed with 5-bromo-2-methoxy-1,3-dimethylbenzene and
5-bromobenzo[d][1,3]dioxole the products are isolated in 84% and
89% as (E)-2-(4-methoxy-3,5-dimethylstyryl)pyridine and (E)-2-(2-
(benzo[d][1,3]dioxol-5-yl)vinyl)pyridine (Table 2, 3f,g), respectively.
Notably, the reaction also works for sterically rather hindered sub-
strates like 1-bromonaphthalene and 9-bromophenanthrene gave
good yields of coupled product, such as (E)-2-(2-(naphthalen-1-yl)
Fig. 1. N,N0,N00,O-Tetrafunctional palladium(II) complex.
aryl bromides with substituted styrenes.14 In continuation of
these studies; herein, we report the Heck reaction of vinyl heter-
oaromatic compounds with aryl bromides and heteroaryl bromides
using N,N0,N00,O-tetrafunctional Pd(II) complex (Fig. 1).
2. Results and discussion
Initial studies to evaluate the catalytic activity of palladium
complex for the Heck reaction were performed in a 0.5 mmol scale
using 2-vinylpyridine and 4-bromoanisole as the model substrates
at 150 ꢀC. In the presence of 1.2 mol % catalyst (5.0 mg) and
0.7 mmol of LiOtBu in DMF, the model substrates reacted well to
afford the corresponding cross-coupled product: namely, (E)-2-(4-
methoxystyryl)pyridine in 60% yield (Table 1, entry 1). Addition of
phase transfer catalyst, TBAB enhanced the yield to 70% (Table 1,
entry 2). Thereafter, optimization studies were performed altering
the solvents and bases, and the corresponding results are sum-
marized in Table 1. The solvent screening studies indicated that
polar aprotic solvent like DMF and DMA are superior for this re-
action (Table 1, entries 1e8), whereas non-polar solvents like tol-
uene and o-xylene are less effective (Table 1, entries 9 & 10). In
a similar way, base screening revealed Cs2CO3 as the best base
(Table 1, entries 3e5, 9e11). When the reaction is conducted by
using conventional catalysts for instance Pd(CH3CN)2Cl2 and pal-
ladium(II)acetylacetonate (Pd(C5H7O2)2) poor yields were observed
(Table 1, entries 12 & 13). Upon optimized reaction condition using
uridate/pyridyl palladium complex nearly constant results were
obtained in 42% yield (Table 1, entry 14). However, the present
phosphine-free N,N0,N00,O-tetrafunctional Pd(II) complex system
showed most promising results (Table 1, entry 5).
vinyl)pyridine
and
(E)-2-(2-(phenanthren-9-yl)vinyl)pyridine
with 90% and 92% (Table 2, 3h,i). Afterwards, the scope of the
reaction was tested for several deactivated heteroaryl bromides, such
as
2-bromopyridine,
3-bromopyridine,
2-bromothiophene,
3-bromothiophene and 2-bromoquinoline has given the desired
coupled products as (E)-1,2-di(pyridin-2-yl)ethene, (E)-2,50-(ethene-
1,2-diyl)dipyridine, (E)-2-(2-(thiophen-2-yl)vinyl)pyridine, (E)-2-(2-
(thiophen-3-yl)vinyl)pyridine and (E)-2-(2-(pyridin-2-yl)vinyl)quin-
oline with moderate yields, respectively (Table 2, 3jen). However the
reaction of chlorobenzene was sluggish and gave very poor yield of
(E)-2-(4-methoxystyryl)pyridine (Table 2, 3o).
Based on the palladium catalyzed Heck cross-coupling of 2-
vinylpyridine with various aryl and heteroaryl halides we further
investigated the palladium catalyzed cross-coupling of various
regio-isomers of vinylpyridines and also vinyl-functionalized het-
erocycles with deactivated aryl halides, such as 4-bromoanisole
and bromobenzene were performed and the corresponding re-
sults are summarized in Table 3.
Table 1
Optimization studies for cross-coupling of 2-vinlypyridine with 4-bromoanisolea
OMe
catalyst, base,
It is noteworthy that the reactions of 3-vinylpyridine and
4-vinylpyridine with 4-bromoanisole proceeded smoothly and
furnished the respective cross-coupled products as (E)-3-(4-
methoxystyryl)pyridine and (E)-4-(4-methoxystyryl)pyridine in
good yields, respectively (Table 3, 6a,b). Importantly, the reaction of
vinyl functionalized heterocycles like 1-vinyl-1H-1,2,4-triazole and
4-methyl-5-vinylthiazole with aryl bromides employing LiOtBu base
gave the corresponding coupling products as (E)-1-styryl-1H-1,2,4-
trazole, (E)-1-(4-methoxystyryl)-1H-1,2,4-triazole, (E)-4-methyl-5-
styrylthiazole and (E)-5-(4-methoxystyryl)-4-methylthiazole in
moderate to good yields, respectively (Table 3, 6cef).
The catalytic species involves in the Heck cross-coupling reaction
are Pd(0). Usually, the catalytic cycle involves between the Pd(0) and
Pd(II) oxidation states during the reaction. In our case a precatalyst
(Pd(II) complex) in the Pd(II) oxidation state is used, and it is pre-
sumed to be reduced to Pd(0) in situ, some relevant data has been
obtained only for phosphine assisted catalytic processes.15 In phos-
phine-freecatalyticprocessreductionofPd(II)toPd(0)canbeeffected
by amines and olefins,16 or palladium can be reduced by quaternary
phosphonium and ammonium salts,17 Herrmann reported that the
addition of TBABr eliminated the induction period in the reaction
catalyzed by Pd carbene complex,18 which acts as a reducing agent.
OMe
solvent
N
N
o
Br
TBAB, 150 C ,15 h
Entry
Base
Solvent
Yieldb (%)
1
2
3
4
5
6
7
8
LiOtBu
LiOtBu
Cs2CO3
Cs2CO3
Cs2CO3
K2CO3
DMF
DMF
DMF
DMA
DMA
DMA
DMA
DMA
Toluene
o-Xylene
Cy2NMe
DMA
DMA
DMA
60c
70
80
87
88d
47
55
32
45
48
35
44
35
42
LiOH$H2O
TEA
9
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
10
11
12
13
14
a
Unless otherwise stated, all reactions were performed using 2-vinylpyridine
(0.5 mmol), 4-bromoanisole (0.8 mmol), catalyst (1.2 mol %), base (0.7 mmol),
TBAB (0.5 mmol) in 2.0 mL solvent at 150 ꢀC for 15 h.
b
Isolated yield.
c
Reaction performed in the absence of TBAB.
d
Time 24 h.

10942
M. Annapurna et al. / Tetrahedron 69 (2013) 10940e10945
Table 2
Cross-coupling of 2-vinylpyridine with aryl bromidesa,b
OMe
N
N
N
3a, 87 %
3b, 88 %
3c, 90 %
COOEt
CF3
OMe
N
N
N
N
N
N
3f, 84 %
3e, 85 %
3d, 89 %
O
O
N
N
3h, 90 %
3k, 60 %
3i, 92 %
3g, 89 %
N
S
N
N
N
3l, 55 %
3j, 30 %
S
N
N
N
3o, <5 %, X = Cl
3m, 65 %
3n, 67 %
a
All reactions were performed with 2-vinylpyridine (0.5 mmol), aryl halide (0.8 mmol), catalyst (1.2 mol %), Cs2CO3 (0.7 mmol), TBAB (0.5 mmol) in 2.0 mL DMA at 150 ꢀ
for 15 h.
C
b
Yields are reported after isolation and purification by column chromatography.
3. Conclusion
N,N-dimethylacetamide (2.0 mL). The reaction mixture was heated
at 150 ꢀC for 15 h and the progress of reaction was monitored by
TLC. At the end of the reaction, the reaction mixture was cooled to
room temperature and was diluted with EtOAc (20 mL), washed
with 1 N aq HCl and water. The combined organic phase was dried
over anhydrous Na2SO4. After removal of the solvent, the residue
was subjected to column chromatography on silica gel using ethyl
acetate and hexane to afford the Heck product in high purity.
We have developed palladium-catalyzed cross-coupling of vinyl
heteroaromatic compounds with aryl halides and heteroaryl ha-
lides under phosphine-free conditions. This approach provides an
efficient and convenient route to prepare a wide variety of styr-
ylpyridine derivatives and novel trans-1,2-disubstituted vinyl
heterocycles.
4. Experimental procedure
4.2. Characterization data for the products of the Heck
reaction
4.1. Typical procedure for Heck reaction of vinyl heterocycles
with aryl bromides
4.2.1. (E)-2-(4-Methoxystyryl)pyridine (3a).19a White solid; mp
74e76 ꢀC (lit.,19b 75.5e77 ꢀC); Rf (30% EtOAc/Hexane) 0.54; 1H NMR
The 15 mL sealed tube was charged with aryl bromides
(0.8 mmol), alkenes (0.5 mmol), Cs2CO3 or LiOtBu (0.7 mmol),
TBAB (0.5 mmol) and the catalyst (1.2 mol %, 5.0 mg), in
(500 MHz, CDCl3, TMS):
d
¼3.83 (s, 3H, OCH3), 6.91 (d, J¼8.0 Hz, 2H,
H-300, 500), 7.04 (d, J¼16.0 Hz, 1H, H-10), 7.10 (dd, J¼7.0, 5.0 Hz, 1H,
H-5), 7.35 (d, J¼8.0 Hz,1H, H-3), 7.52 (d, J¼9.0 Hz, 2H, H-200, 600), 7.58

M. Annapurna et al. / Tetrahedron 69 (2013) 10940e10945
10943
7.40 (d, J¼8.0 Hz, 1H, H-3), 7.64e7.72 (m, H-4, H-20, H-200, 600), 8.63
Table 3
Scope of vinyl heteroaromatic compounds with aryl bromidesa,b
(d, J¼4.2 Hz, 1H, H-6); 13C NMR (75 MHz, CDCl3):
¼122.5, 122.6,
d
Catalyst, Cs2CO3, DMA
TBAB, 150 oC, 15 h
124.1 (q, JCeF¼271.7 Hz), 125.6, (d, JCeF¼3.3 Hz), 127.1, 129.9, (q,
JCeF¼32.4 Hz), 130.3, 131.1, 136.6, 140.1, 149.8, 154.9; IR (KBr, cmꢁ1):
2925, 1610, 1579, 1466, 1431, 1328, 1163, 1110, 1064, 979, 831, 740;
ESI-MS (m/z): (MþH)þ¼250; HRMS: calcd for C14H11NF3
(MþH)þ¼250.0838, found: 250.0830.
Ar
R
R
ArX
6
5
4
R = hetero aromatic
compounds
OMe
OMe
N
N
N
4.2.6. (E)-2-(4-Methoxy-3,5-dimethylstyryl)pyridine
(3f). White
N
N
solid; mp 85e87 ꢀC; Rf (30% EtOAc/Hexane) 0.67; 1H NMR
6c, 30, (45)c
6b, 93
6a, 80
(300 MHz, CDCl3, TMS):
d
¼2.31 (s, 6H, CH3), 3.74 (s, 3H, OCH3), 7.06
(d, J¼15.9 Hz,1H, H-10), 7.10e7.15 (m,1H, H-5), 7.25 (s, 2H, H-200, 600),
7.36 (d, J¼8.3 Hz, 1H, H-3), 7.53 (d, J¼15.9 Hz, 2H, H-20), 7.65 (td,
J¼7.6, 2.3 Hz, 1H, H-4), 8.59 (d, J¼3.8 Hz, 1H, H-6); 13C NMR
OMe
OMe
N
N
N
S
N
N
S
6f, (70)c
(75 MHz, CDCl3):
d
¼16.2, 59.7, 121.7, 121.8, 126.8, 127.6, 131.1, 132.1,
6d, 30, (40)c
6e, (75)c
132.3, 136.4, 149.5, 155.8, 157.3; IR (KBr, cmꢁ1): 2995, 2914, 2857,
1633, 1582, 1560, 1470, 1427, 1270, 1218, 1139, 1092, 983, 855;
ESI-MS (m/z): (MþH)þ¼240; HRMS: calcd for C16H18NO
(MþH)þ¼240.1382, found: 240.1376.
aReaction performed with vinyl heteroaromatic compound (0.5 mmol), aryl halide
(0.8 mmol), catalyst (1.2 mol %), Cs2CO3 (0.7 mmol) and TBAB (0.5 mmol) in 2.0 mL
DMA at 150 ꢀC for 15 h.
bYields are reported after isolation and purification by column chromatography.
cYield indicated in the parenthesis is for the reaction performed with LiOtBu.
4.2.7. (E)-2-(2-(Benzo[d][1,3]dioxol-5-yl)vinyl)pyridine
(3g).19a White solid; mp 83e85 ꢀC; Rf (30% EtOAc/Hexane) 0.59; 1H
(d, J¼16.0 Hz, 1H, H-20), 7.63 (td, J¼6.0, 2.0 Hz, 1H, H-4), 8.58 (d,
NMR (300 MHz, CDCl3, TMS):
d
¼6.0 (s, 2H, OCH2O), 6.81 (d,
J¼5.0 Hz, 1H, H-6); 13C NMR (75 MHz, CDCl3):
d
¼55.2, 114.1, 121.6,
J¼8.3 Hz, 1H, H-500), 7.0e7.05 (m, 2H, H-10, H-600), 7.12 (td, J¼6.0,
1.5 Hz, 2H, H-5, H-200), 7.34 (d, J¼7.6 Hz, 1H, H-3), 7.55 (d, J¼15.9 Hz,
1H, H-20), 7.64 (td, J¼7.9,1.5 Hz,1H, H-4), 8.59 (d, J¼4.5 Hz,1H, H-6);
121.7, 125.7, 128.4, 129.3, 132.2, 136.4, 149.5, 155.9, 159.8; IR (KBr,
cmꢁ1): 3005, 2957, 2927, 2836, 1631, 1577, 1507, 1462, 1429, 1294,
1246, 1173, 1140, 1021, 982, 876, 826; ESI-MS (m/z): (MþH)þ¼212;
HRMS: calcd for C14H14NO (MþH)þ¼212.1069, found: 212.1065.
13C NMR (75 MHz, CDCl3):
d¼101.2, 106.0, 108.4, 121.7, 121.9, 122.4,
126.2, 131.1, 132.4, 136.4, 147.9, 148.1, 149.6, 155.7; IR (KBr, cmꢁ1):
3056, 3007, 2905, 2788, 1629, 1583, 1558, 1498, 1441, 1362, 1310,
1249, 1193, 1104, 1033, 963, 924, 868, 806; ESI-MS (m/z):
(MþH)þ¼226; HRMS: calcd for C14H12NO2 (MþH)þ¼226.0862,
found: 226.0860.
4.2.2. (E)-2-(4-Methylstyryl)pyridine (3b).20 White solid; mp
77e79 ꢀC (lit.,20 76e78 ꢀC); Rf (30% EtOAc/Hexane) 0.69; 1H NMR
(500 MHz, CDCl3, TMS):
d
¼2.37 (s, 3H, CH3), 7.11e7.14 (m, 2H, H-10,
H-5), 7.18 (d, J¼8.0 Hz, 2H, H-300, 500), 7.37 (d, J¼8.0 Hz, 1H, H-3), 7.48
(d, J¼8.0 Hz, 2H, H-200, 600), 7.60 (d, J¼16.0 Hz, 1H, H-20), 7.63e7.66
(m, 1H, H-4), 8.59 (d, J¼4.0 Hz, 1H, H-6); 13C NMR (75 MHz, CDCl3):
4.2.8. (E)-2-(2-(Naphthalen-1-yl)vinyl)pyridine
(3h).22 Off-white
solid; mp 37e39 ꢀC (lit.,22 38e40 ꢀC); Rf (30% EtOAc/Hexane) 0.68;
d¼21.3, 121.8, 121.9, 126.9, 127.0, 129.4, 132.6, 133.8, 136.5, 138.3,
1H NMR (300 MHz, CDCl3, TMS):
d
¼7.18e7.26 (m, 2H, H-10, H-5),
149.6, 155.7; IR (KBr, cmꢁ1): 3001, 2922, 2853, 1630, 1577, 1556,
1507, 1463, 1425, 1299, 1174, 1088, 979, 811; ESI-MS (m/z):
(MþH)þ¼196; HRMS: calcd for C14H14N (MþH)þ¼196.1120, found:
196.1114.
7.44e7.58 (m, 4H, H-3, 300, 600, 700), 7.71 (td, J¼7.6, 1.5 Hz, 1H, H-4),
7.82e7.89 (m, 3H, H-200, 400, 500), 8.32 (d, J¼8.3 Hz, 1H, H-800), 8.48 (d,
J¼15.9 Hz, 1H, H-20), 8.66 (d, J¼3.8 Hz, 1H, H-6); 13C NMR (75 MHz,
CDCl3):
d¼122.1, 122.3, 123.9, 125.6, 125.9, 126.2, 128.5, 128.6, 129.8,
130.8, 131.5, 133.7, 134.3, 136.5, 149.7, 155.7; IR (KBr, cmꢁ1): 3052,
3004, 2925, 2853, 1632, 1584, 1563, 1509, 1468, 1430, 1392, 1346,
1253, 1149, 976, 797; ESI-MS (m/z): (MþH)þ¼232; HRMS: calcd for
4.2.3. (E)-2-Styrylpyridine (3c).21 White solid; mp 88e90 ꢀC (lit.,19b
90e90.5 ꢀC); Rf (30% EtOAc/Hexane) 0.64; 1H NMR (300 MHz,
CDCl3, TMS):
d
¼7.12e7.20 (m, 2H, H-10, H-5), 7.29e7.40 (m, 4H, H-4,
C
17H14N (MþH)þ¼232.1120, found: 232.1114.
H-300, 400, 500), 7.57e7.69 (m, 4H, H-3, H-20, H-200, 600), 8.61 (d,
J¼4.7 Hz, 1H, H-6); 13C NMR (75 MHz, CDCl3):
d
¼122.0, 122.1, 127.0,
4.2.9. (E)-2-(2-(Phenanthren-9-yl)vinyl)pyridine (3i). Yellow solid;
mp 82e84 ꢀC; Rf (30% EtOAc/Hexane) 0.65; 1H NMR (300 MHz,
127.9, 128.3, 128.7, 132.6, 136.5, 149.6, 155.5; IR (KBr, cmꢁ1): 3034,
2924, 1629, 1576, 1491, 1465, 1422, 1299, 1142, 1070, 981, 778;
CDCl3, TMS):
d
¼7.18e7.22 (m, 1H, H-5), 7.30 (d, J¼15.7 Hz, 1H, H-10),
ESI-MS (m/z): (MþH)þ¼182; HRMS: calcd for C13H12
N
7.47 (d, J¼7.9 Hz, 1H, H-3), 7.58e7.74 (m, 5H, H-4, H-200, H-300, H-600,
H-700), 7.92 (d, J¼9.1 Hz, 1H, H-800), 8.05 (s, 1H, H-1000), 8.35 (d,
J¼9.4 Hz, 1H, H-100), 8.46 (d, J¼15.7 Hz, 1H, H-20), 8.68 (d, J¼6.4 Hz,
2H, H-400, H-500), 8.75 (d, J¼9.4 Hz, 1H, H-6); 13C NMR (75 MHz,
(MþH)þ¼182.0964, found: 182.0961.
4.2.4. (E)-Ethyl 4-(2-(pyridin-2-yl)vinyl)benzoate (3d). White solid;
mp 92e94 ꢀC; Rf (30% EtOAc/Hexane) 0.52; 1H NMR (300 MHz,
CDCl3):
d
¼122.2, 122.3, 122.5, 123.0, 124.8, 125.0, 126.5, 126.6, 126.7,
CDCl3, TMS):
d
¼1.40 (t, J¼7.1 Hz, 3H, CH3), 4.39 (q, J¼7.1 Hz, 2H,
126.8, 128.8, 130.35, 130.39, 130.43, 130.7, 131.2, 131.7, 133.3, 136.5,
149.7, 155.6; IR (KBr, cmꢁ1): 3060, 2924, 1632, 1579, 1557, 1467,
1425, 1385, 1321, 1265, 1147, 1047, 962, 884, 743; ESI-MS (m/z):
(MþH)þ¼282; HRMS: calcd for C21H16N (MþH)þ¼282.1277, found:
282.1269.
OCH2), 7.16e7.20 (m, 1H, H-5), 7.26 (d, J¼16.1 Hz, 1H, H-10), 7.41 (d,
J¼7.7 Hz, 1H, H-3), 7.62e7.72 (m, 4H, H-4, H-20, H-200, 600), 8.05 (d,
J¼8.3 Hz, 2H, H-300, 500), 8.63 (d, J¼4.5 Hz, 1H, H-6); 13C NMR
(75 MHz, CDCl3):
d¼14.3, 60.9,122.5,126.8,129.8,129.9,130.1,131.5,
136.6, 140.9, 149.7, 155.0, 166.2; IR (KBr, cmꢁ1): 2930, 1702, 1600,
1580, 1465, 1278, 1175, 1101, 1018, 978, 846, 780; ESI-MS (m/z):
(MþH)þ¼254; HRMS: calcd for C16H16NO2 (MþH)þ¼254.1175,
found: 254.1167.
4.2.10. (E)-1,2-Di(pyridin-2-yl)ethene (3j).23 Yellow solid; mp
118e120 ꢀC (lit.,23 118e122 ꢀC); Rf (30% EtOAc/Hexane) 0.18; 1H
NMR (500 MHz, CDCl3, TMS):
d
¼7.17e7.19 (m, 2H, H-5, H-500), 7.43
(d, J¼8.0 Hz, 2H, H-3, H-300), 7.66e7.70 (m, 4H, H-4, H-400, H-10, H-
4.2.5. (E)-2-(4-(Trifluoromethyl)styryl)pyridine (3e). White solid;
mp 116e118 ꢀC; Rf (30% EtOAc/Hexane) 0.66; 1H NMR (300 MHz,
20), 8.63 (d, J¼4.0 Hz, 2H, H-6, H-600); 13C NMR (75 MHz, CDCl3):
d
¼122.6,123.3,131.6, 136.6, 149.7, 154.9; IR (KBr, cmꢁ1): 3045, 2924,
CDCl3, TMS):
d
¼7.17e7.20 (m, 1H, H-5), 7.24 (d, J¼15.9 Hz, 1H, H-10),
2852, 1649, 1582, 1561, 1469, 1429, 1321, 1142, 1084, 988, 959, 888,

10944
M. Annapurna et al. / Tetrahedron 69 (2013) 10940e10945
786; ESI-MS (m/z): (MþH)þ¼183; HRMS: calcd for C12H11N2
(MþH)þ¼183.0916, found: 183.0912.
2H, H-200, H-600), 7.48 (d, J¼8.7 Hz, 2H, H-3, H-5), 8.55 (d, J¼6.2 Hz,
2H, H-2, H-6); 13C NMR (75 MHz, CDCl3):
d¼55.3,114.2,120.5,123.6,
128.3, 128.8, 132.6, 144.9, 150.0, 160.0; IR (KBr, cmꢁ1): 3018, 2966,
2932, 2841, 1633, 1585, 1508, 1456, 1412, 1258, 1171, 1115, 1022, 968,
832; ESI-MS (m/z): (MþH)þ¼212; HRMS: calcd for C14H14NO
(MþH)þ¼212.1069, found: 212.1065.
4.2.11. (E)-2,5’-(Ethene-1,2-diyl)dipyridine (3k). Yellow oil; Rf (30%
EtOAc/Hexane) 0.08; 1H NMR (300 MHz, CDCl3, TMS):
d
¼7.17e7.25
(m, 2H, H-5, H-10), 7.31 (dd, J¼7.9 Hz, J¼4.9 Hz, 1H, H-4), 7.40 (d,
J¼7.7 Hz, 1H, H-3), 7.63 (d, J¼16.2 Hz, 1H, H-20), 7.69 (td, J¼7.6,
1.9 Hz, 1H, H-300), 7.90 (dt, J¼7.9, 1.9 Hz, 1H, H-400), 8.52 (dd, J¼1.5,
1.5 Hz,1H, H-200), 8.63 (d, J¼4.5 Hz,1H, H-6), 8.80 (br d, J¼2.1 Hz,1H,
4.2.17. (E)-1-Styryl-1H-1,2,4-triazole (6c).28 Yellow oil; Rf (30%
EtOAc/Hexane) 0.25; 1H NMR (300 MHz, CDCl3, TMS):
d
¼7.19e7.27
H-600); 13C NMR (75 MHz, CDCl3):
d
¼122.4,122.5,123.6,128.9,129.8,
(m, 2H, H-10, H-400), 7.32 (t, J¼7.32 Hz, 2H, H-300, H-500), 7.39 (d,
132.3, 133.3, 136.7, 148.9, 149.0, 149.7, 154.7; IR (KBr, cmꢁ1): 3051,
2923, 2851, 1640, 1585, 1564, 1472, 1432, 1151, 1024, 970, 804; ESI-
MS (m/z): (MþH)þ¼183; HRMS: calcd for C12H11N2
(MþH)þ¼183.0916, found: 183.0912.
J¼7.32 Hz, 2H, H-200, H-600), 7.46 (d, J¼14.3 Hz, 1H, H-20), 8.01 (s, 1H,
H-5), 8.44 (s, 1H, H-3); 13C NMR (75 MHz, CDCl3):
d
¼121.3, 121.8,
126.5, 128.5, 128.9, 133.7, 142.2, 152.3; IR (KBr, cmꢁ1): 3118, 3081,
3031, 2930, 1660, 1507, 1450, 1422, 1362, 1276, 1196, 1136, 1001, 946,
862, 780, 750; ESI-MS (m/z): (MþH)þ¼172; HRMS: calcd for
4.2.12. (E)-2-(2-(Thiophen-2-yl)vinyl)pyridine (3l).24 Yellow solid,
mp 96e98 ꢀC (lit.,24 99 ꢀC); Rf (30% EtOAc/Hexane) 0.74; 1H NMR
C
10H10N3 (MþH)þ¼172.0869, found: 172.0871.
(300 MHz, CDCl3, TMS):
d
¼6.97 (d, J¼15.9 Hz, 1H, H-10), 7.01e7.04
4.2.18. (E)-1-(4-Methoxystyryl)-1H-1,2,4-triazole (6d). White solid;
mp 82e84 ꢀC; Rf (30% EtOAc/Hexane) 0.24; 1H NMR (300 MHz,
(m, 1H, H-400), 7.11e7.16 (m, 1H, H-5), 7.17 (d, J¼3.0 Hz, 1H, H-300),
7.26 (d, J¼5.2 Hz, 1H, H-500), 7.31 (d, J¼7.6 Hz, 1H, H-3), 7.65 (dt,
J¼7.6, 1.5 Hz, 1H, H-4), 7.79 (d, J¼15.9 Hz, 1H, H-20), 8.58 (d,
CDCl3, TMS):
d
¼3.84 (s, 3H, OCH3), 6.92 (d, J¼8.2 Hz, 2H, H-300,
H-500), 7.21 (d, J¼14.2 Hz, 1H, H-10), 7.38e7.42 (m, 3H, H-20, H-200,
J¼4.5 Hz, 1H, H-6); 13C NMR (75 MHz, CDCl3):
d¼121.9, 122.0, 125.4,
H-600), 8.03 (s, 1H, H-5), 8.29 (s, 1H, H-3); 13C NMR (75 MHz, CDCl3):
125.7, 127.2, 127.7, 136.5, 142.1, 149.6, 155.2; IR (KBr, cmꢁ1): 3108,
3071, 3004, 1623, 1576, 1463, 1417, 1296, 1233, 1192, 1142, 1084,
1040, 971, 825, 769; ESI-MS (m/z): (MþH)þ¼188; HRMS: calcd for
d
¼55.3, 114.4, 120.2, 121.2, 126.3, 127.8, 141.9, 152.1, 159.9; IR
(KBr, cmꢁ1): 3115, 3015, 2970, 2930, 2832, 1656, 1604, 1512, 1462,
1412, 1302, 1254, 1197, 1173, 1139, 1106, 1022, 1000, 932, 836,
803; ESI-MS (m/z): (MþH)þ¼202; HRMS: calcd for C11H12N3O
(MþH)þ¼202.0974, found: 202.0974.
C
11H10NS (MþH)þ¼188.0528, found: 188.0524.
4.2.13. (E)-2-(2-(Thiophen-3-yl)vinyl)pyridine (3m).24 Yellow solid;
mp 82e84 ꢀC (lit.,24 82 ꢀC); Rf (30% EtOAc/Hexane) 0.64; 1H NMR
4.2.19. (E)-4-Methyl-5-styrylthiazole
(6e). Yellow solid; mp
(300 MHz, CDCl3, TMS):
d
¼7.0 (d, J¼16.1 Hz, 1H, H-10), 7.11e7.15 (m,
85e87 ꢀC; Rf (30% EtOAc/Hexane) 0.75; 1H NMR (300 MHz, CDCl3,
1H, H-5), 7.32e7.40 (m, 4H, H-3, H-4, H-20, H-400), 7.61e7.67 (m, 2H,
H-200, H-500), 8.59 (d, J¼4.7 Hz, 1H, H-6); 13C NMR (75 MHz, CDCl3):
TMS):
d
¼2.55 (s, 3H, CH3), 6.83 (d, J¼16.0 Hz, 1H, H-10), 7.18 (d,
J¼16.0 Hz, 1H, H-20), 7.28 (d, J¼7.3 Hz, 1H, H-400), 7.37 (t, J¼7.6 Hz,
d¼121.7, 121.8, 124.1, 125.0, 126.3, 126.7, 127.8, 136.4, 139.5, 149.6,
2H, H-300, H-500), 7.48 (d, J¼7.4 Hz, 2H, H-200, H-600) 8.60 (s, 1H, H-2);
155.7; IR (KBr, cmꢁ1): 3090, 3044, 3002, 1629, 1578, 1557, 1462,
1425, 1301, 1273, 1240, 1144, 1082, 976, 863, 788; ESI-MS (m/z):
(MþH)þ¼188; HRMS: calcd for C11H10NS (MþH)þ¼188.0528,
found: 188.0525.
13C NMR (75 MHz, CDCl3):
d
¼15.3, 118.0, 126.3, 128.0, 128.7, 130.9,
131.4, 136.6, 149.5, 150.2; IR (KBr, cmꢁ1): 3064, 3028, 2924, 2854,
1639, 1514, 1491, 1443, 1404, 1324, 1255, 1181, 1072, 945, 821, 747;
ESI-MS (m/z): (MþH)þ¼202; HRMS: calcd for C12H12NS
(MþH)þ¼202.0685, found: 202.0687.
4.2.14. (E)-2-(2-(Pyridin-2-yl)vinyl)quinoline (3n).25 Yellow solid;
mp 94e96 ꢀC (lit.,25 95e97 ꢀC); Rf (30% EtOAc/Hexane) 0.29; 1H
4.2.20. (E)-5-(4-Methoxystyryl)-4-methylthiazole (6f). Yellow solid;
mp 88e90 ꢀC; Rf (30% EtOAc/Hexane) 0.51; 1H NMR (500 MHz,
NMR (300 MHz, CDCl3, TMS):
d
¼7.20e7.23 (m, 1H, H-5), 7.52 (dd,
J¼8.3 Hz, J¼6.8 Hz, 1H, H-4), 7.58 (d, J¼7.5 Hz, 1H, H-3), 7.67e7.74
(m, 3H, H-300, H-600, H-700), 7.78e7.89 (m, 3H, H-10, H-20, H-800), 8.10
(d, J¼8.3 Hz, 1H, H-500), 8.16 (d, 9.1 Hz, 1H, H-400), 8.66 (d, J¼3.8 Hz,
CDCl3, TMS):
d
¼2.53 (s, 3H, CH3), 3.83 (s, 3H, OCH3), 6.78 (d,
J¼16.0 Hz, 1H, H-10), 6.90 (d, J¼8.0 Hz, 2H, H-300, H-500), 7.03 (d,
J¼16.0 Hz, 1H, H-20), 7.41 (d, J¼9.0 Hz, 2H, H-200, H-600), 8.53 (s, 1H,
1H, H-6); 13C NMR (75 MHz, CDCl3):
d¼120.2, 122.7, 122.8, 126.4,
H-2); 13C NMR (125 MHz, CDCl3):
d
¼15.3, 55.2, 114.1, 116.0, 127.5,
127.5, 129.3, 129.7, 132.5, 133.6, 136.4, 136.6, 148.2, 149.7, 155.0,
155.2; IR (KBr, cmꢁ1): 3053, 2997, 2923, 1642, 1587, 1557, 1500,
1426, 1342, 1137, 1116, 975, 824, 748; ESI-MS (m/z): (MþH)þ¼233;
HRMS: calcd for C16H13N2 (MþH)þ¼233.1073, found: 233.1071.
129.4, 130.8, 131.1, 148.9, 149.7, 159.4; IR (KBr, cmꢁ1): 3069, 3026,
2924, 2839, 1654, 1599, 1507, 1461, 1404, 1325, 1250, 1170, 1109,
1026, 933, 850, 796; ESI-MS (m/z): (MþH)þ¼232; HRMS: calcd for
C
13H14NSO (MþH)þ¼232.0790, found: 232.0787.
4.2.15. (E)-3-(4-Methoxystyryl)pyridine (6a).26 White solid; mp
96e98 ꢀC (lit.,26 98e99 ꢀC); Rf (30% EtOAc/Hexane) 0.33; 1H NMR
Acknowledgements
(300 MHz, CDCl3, TMS):
d
¼3.84 (s, 3H, OCH3), 6.90e6.96 (m, 3H, H-
M.A. thanks University Grants Commission (UGC), New Delhi,
India, for the award of Senior Research Fellowship (SRF).
300, H-500, H-10), 7.12 (d, J¼16.6 Hz, 1H, H-20), 7.27 (dd, J¼8.3 Hz,
J¼4.5 Hz, 1H, H-5), 7.47 (d, J¼8.3 Hz, 2H, H-200, H-600), 7.81 (dt, J¼7.6,
1.9 Hz, 1H, H-4) 8.46 (dd, J¼4.5, 1.5 Hz, 1H, H-6), 8.70 (d, J¼1.5 Hz,
Supplementary data
1H, H-2); 13C NMR (75 MHz, CDCl3):
d¼55.3, 114.2, 122.6, 123.4,
127.9, 129.4, 130.3, 132.3, 133.3, 148.1, 148.2, 159.7; IR (KBr, cmꢁ1):
3013, 2959, 2839, 1600, 1570, 1508, 1451, 1416, 1248, 1172, 1106,
1023, 963, 823; ESI-MS (m/z): (MþH)þ¼212; HRMS: calcd for
Supplementary data related to this article can be found online at
http://dx.doi.org/10.1016/j.tet.2013.10.078.
C
14H14NO (MþH)þ¼212.1069, found: 212.1067.
References and notes
4.2.16. (E)-4-(4-Methoxystyryl)pyridine (6b).27 White solid, mp
132e134 ꢀC (lit.,27 133e135 ꢀC); Rf (30% EtOAc/Hexane) 0.19; 1H
1. (a) Beletskaya, I. P.; Cheprakov, A. V. Chem. Rev. 2000, 100, 3009e3066; (b)
ꢀ
Trzecoak, A. M.; Zio1kowski, J. J. Coord. Chem. Rev. 2005, 249, 2308e2322; (c)
NMR (300 MHz, CDCl3, TMS):
d
¼3.84 (s, 3H, OCH3), 6.85e6.94 (m,
Alonso, F.; Beletskaya, I. P.; Yus, M. Tetrahedron 2005, 61, 11771e11835; (d) Phan,
N. T. S.; Van Der Sluys, M.; Jones, C. W. Adv. Synth. Catal. 2006, 348, 609e679.
3H, H-10, H-300, H-500), 7.26 (d, J¼16.2 Hz, 1H, H-20), 7.33 (d, J¼6.0 Hz,

M. Annapurna et al. / Tetrahedron 69 (2013) 10940e10945
10945
2. (a) Lipshutz, B. H.; Taft, B. R. Org. Lett. 2008, 10, 1329e1332; (b) Moore, L. R.;
Shaughnessy, K. H. Org. Lett. 2004, 6, 225e228; (c) Feuerstein, M.; Doucet, H.;
Santelli, M. J. Org. Chem. 2001, 66, 5923e5925; (d) Littke, A. F.; Fu, G. C. J. Am.
Chem. Soc. 2001, 123, 6989e7000; (e) Lee, D.-H.; Taher, A.; Hossain, S.; Jin, M.-J.
Org. Lett. 2011, 13, 5540e5543.
13. (a) Srinivas, P.; Likhar, P. R.; Maheswaran, H.; Sridhar, B.; Ravikumar, K.;
Kantam, M. L. Chem.dEur. J. 2009, 15, 1578e1581; (b) Kantam, M. L.; Srinivas, P.;
Yadav, J.; Likhar, P. R.; Bhargava, S. J. Org. Chem. 2009, 74, 4882e4885; (c) Sri-
nivas, P.; Srinivas, K.; Likhar, P. R.; Sridhar, B.; Mohan, K. V.; Bhargava, S.;
Kantam, M. L. J. Organomet. Chem. 2011, 696, 795e801; (d) Kantam, M. L.;
Vishnuvardhan Reddy, P.; Srinivas, P.; Bhargava, S. Tetrahedron Lett. 2011, 52,
4490e4493.
3. Berthiol, F.; Feuerstein, M.; Doucet, H.; Santelli, M. Tetrahedron Lett. 2002, 43,
5625e5628.
4. Bolliger, J. L.; Blacque, O.; Frech, C. M. Chem.dEur. J. 2008, 14, 7969e7977.
5. Li, M.; Hua, R. Appl. Organomet. Chem. 2008, 22, 397e401.
6. (a) Cooper, C. G. F.; MacDonald, J. C.; Soto, E.; McGimpsey, W. G. J. Am. Chem. Soc.
2004, 126, 1032e1033; (b) Kim, W.-S.; Ahn, D.-K.; Kim, M.-W. Macromol. Chem.
Phys. 2004, 205, 1932e1937.
14. Kantam, M. L.; Annapurna, M.; Likhar, P. R.; Srinivas, P.; Mirzadeh, N.; Bhargava,
S. K. J. Organomet. Chem. 2013, 723, 129e136.
15. (a) Louie, J.; Hartwig, J. F. Angew. Chem., Int. Ed. 1996, 35, 2359e2361; (b) Beller,
M.; Riermeier, T. H. Eur. J. Inorg. Chem. 1998, 29e35; (c) Luo, F.-T.; Jeevanandam,
A.; Basu, M. K. Tetrahedron Lett. 1998, 39, 7939e7942.
7. (a) Zheng, G.; Dwoskin, L. P.; Deaciuc, A. G.; Zhu, J.; Jones, M. D.; Crooks, P. A.
Bioorg. Med. Chem. 2005, 13, 3899e3909; (b) Wilson, K. J.; Van Niel, M. B.;
Cooper, L.; Bloomfield, D.; O’Connor, D.; Fish, L. R.; MacLeod, A. M. Bioorg. Med.
Chem. Lett. 2007, 17, 2643e2648; (c) Wang, S.-J.; Sihra, T. S. J. Pharmacol. Exp.
Ther. 2004, 309, 951e958.
8. (a) Choi, S. R.; Golding, G.; Zhuang, Z.; Zhang, W.; Lim, N.; Hefti, F.; Benedum, T.
E.; Kilbourn, M. R.; Skovronsky, T.; Kung, H. F. J. Nucl. Med. 2009, 50, 1887e1894;
(b) Kung, H. F.; Choi, S. R.; Qu, W.; Zhang, W.; Skovronsky, D. J. Med. Chem. 2010,
53, 933e941.
16. (a) Beletskaya, I. P.; Kashin, A. N.; Karlstedt, N. B.; Mitin, A. V.; Cheprakov, A. V.;
Kazankov, G. M. J. Organomet. Chem. 2001, 622, 89e96; (b) Tsuji, J. Acc. Chem.
Res. 1969, 2, 144e152.
€
17. (a) Reetz, M. T.; Lohmer, G.; Schwickardi, R. Angew. Chem., Int. Ed. 1998, 37,
481e483; (b) Dullius, J. E. L.; Suarez, P. A. Z.; Einloft, S.; de Souza, R. F.; Dupont,
J.; Fischer, J.; De Cian, A. Organometallics 1998, 17, 815e819.
18. Herrmann, W. A.; Elison, M.; Fischer, J.; Koecher, C.; Artus, G. R. J. Angew. Chem.,
Int. Ed. Engl. 1995, 34, 2371e2374.
€
19. (a) Carran, J.; WaschbUsch, R.; Savignac, P. Phosphorus, Sulfur Silicon Relat. Elem.
9. (a) Spannenberg, A.; Arndt, P.; Baumann, W.; Burlakov, V. V.; Rosenthal, U.;
Becke, S.; Weiss, T. Organometallics 2004, 23, 3819e3825; (b) Klein, H.-F.; Ca-
madanli, S.; Beck, R.; Florke, U. Chem. Commun. 2005, 381e382; (c) Shi, X.-F.;
1997, 123, 209e218; (b) Tsuge, O.; Sone, K.; Urano, S. Chem. Lett. 1980, 9,
977e980.
20. Inomata, S.; Hiroki, H.; Terashima, T.; Ogata, K.; Fukuzawa, S.-I. Tetrahedron
2011, 67, 7263e7267.
21. (a) Shirakawa, E.; Zhang, X.; Hayashi, T. Angew. Chem., Int. Ed. 2011, 50,
4671e4674; (b) Kim, M.; Kwak, J.; Chang, S. Angew. Chem., Int. Ed. 2009, 48,
8935e8939; (c) Chen, C.; Wang, B.; Munoz, B. Synlett 2003, 2404e2406.
22. Hewlins, M. J. E.; Salter, R. Synthesis 2007, 2164e2174.
€
Xing, Z.-Y.; Wu, L.; Zhang, W.-Q. Inorg. Chim. Acta 2006, 359, 603e608.
10. (a) Zhang, X.; Xi, Z.; Liu, A.; Chen, W. Organometallics 2008, 27, 4401e4406; (b)
Meyer, D.; Taige, M. A.; Zeller, A.; Hohlfeld, K.; Ahrens, S.; Strassner, T. Organ-
ometallics 2009, 28, 2142e2149; (c) Selvakumar, K.; Zapf, A.; Beller, M. Org. Lett.
2002, 4, 3031e3033; (d) Yen, S. K.; Koh, L. L.; Hahn, F. E.; Huynh, H. V.; Hor, T. S.
A. Organometallics 2006, 25, 5105e5112; (e) Lee, J.-Y.; Cheng, P.-Y.; Tsai, Y.-H.;
Lin, G.-R.; Liu, S.-P.; Sie, M.-H.; Lee, H. M. Organometallics 2010, 29, 3901e3911.
11. (a) Bedford, R. B.; Cazin, C. S. J.; Holder, D. Coord. Chem. Rev. 2004, 248,
2283e2321; (b) Beletskaya, I. P.; Chepracov, A. V. J. Organomet. Chem. 2004, 689,
4055e4082.
23. Newkome, G. R.; Robinson, J. M. Tetrahedron Lett. 1974, 15, 691e694.
24. Marzinzik, A. L.; Rademacher, P. Synthesis 1995, 1131e1134.
25. (a) Yan, Y.; Xu, K.; Fang, Y.; Wang, Z. J. Org. Chem. 2011, 76, 6849e6855; (b) Li, V.
M.; Gavrishova, T. N.; Budyka, M. F. Russ. J. Org. Chem. 2012, 48, 823e828.
ꢀ
ꢀ
26. Gordillo, A.; Jesus, E.; Mardomingo, C. L. Chem. Commun. 2007, 4056e4058.
27. Najman, R.; Cho, J. K.; Coffey, A. F.; Davies, J. W.; Bradley, M. Chem. Commun.
2007, 5031e5033.
12. (a) Yao, Q.; Zabawa, M.; Woo, J.; Zheng, C. J. Am. Chem. Soc. 2007, 129,
3088e3089; (b) Wass, D. F.; Haddow, M. F.; Hey, T. W.; Orpen, A. G.; Russell, C.
A.; Wingad, R. L.; Green, M. Chem. Commun. 2007, 2704e2706; (c) Herrmann,
28. Taillefer, M.; Ouali, A.; Renald, B.; Spindler, J.-F. Chem.dEur. J. 2006, 12,
€
W. A.; Ofele, K.; Schneider, S. K.; Herdtweck, E.; Hoffmann, S. D. Angew. Chem.
5301e5313.
2006, 118, 3943e3947 Angew. Chem., Int. Ed. 2006, 45, 3859e3862.