An efficient ruthenium-catalyzed dehydrogenative synthesis of 2,4,6-triaryl-1,3,5-triazines from aryl methanols and amidines

Article abstract of DOI:10.1039/c3ob42589d

By using [RuCl₂(p-Cymene)]₂/Cs₂CO ₃ as an efficient catalyst system, the readily available, inexpensive aryl methanols were firstly employed for dehydrogenative synthesis of aryl substituted 1,3,5-triazine derivatives. Due to the inherent stability of alcohols in contrast with aldehydes, our synthetic protocol is adaptable to a broad substrate scope, there is no need for stringent protection during the whole operation process, and it has the potential to prepare valuable products that are currently inaccessible or challenging to prepare using conventional methods. It is a significantly important complement to the conventional synthetic methodologies. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c3ob42589d

Organic &
Biomolecular Chemistry
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PAPER
An efficient ruthenium-catalyzed dehydrogenative
synthesis of 2,4,6-triaryl-1,3,5-triazines from aryl
methanols and amidines†
Cite this: Org. Biomol. Chem., 2014,
12, 2761
Feng Xie,a,b Mengmeng Chen,a Xiaoting Wang,a Huanfeng Jiangb and Min Zhang*a,b
By using [RuCl2(p-Cymene)]2/Cs2CO3 as an efficient catalyst system, the readily available, inexpensive aryl
methanols were firstly employed for dehydrogenative synthesis of aryl substituted 1,3,5-triazine deriva-
tives. Due to the inherent stability of alcohols in contrast with aldehydes, our synthetic protocol is adapt-
able to a broad substrate scope, there is no need for stringent protection during the whole operation
process, and it has the potential to prepare valuable products that are currently inaccessible or challen-
ging to prepare using conventional methods. It is a significantly important complement to the conven-
tional synthetic methodologies.
Received 3rd January 2014,
Accepted 3rd March 2014
DOI: 10.1039/c3ob42589d
www.rsc.org/obc
(1) the active aldehyde groups may easily suffer from an oxi-
dation reaction, leading to formation of undesirable by-pro-
Introduction
Aryl substituted 1,3,5-triazine derivatives constitute a signifi- ducts unless the synthetic operation follows stringent
cantly important class of nitrogen-containing heterocycles that protection under an inert gas;8 (2) aldehydes could undergo a
exhibit diverse biological activities.1 And they are also powerful decarbonylation reaction under harsh reaction conditions
chelating ligands for the preparation of liquid crystals,2 such as high temperature, which results in low product
organometallic materials3 and efficient hydrogenation cata- yields;9 (3) some aldehydes including heteroaryl ones are of
lysts.4 Despite these extensive functions, only a few methods high cost or not readily available; the method for variation of
have been reported for the preparation of this type of com- products is hence restricted. On the basis of these facts, the
pound. Generally, this goal can be realized by the following search for readily available, inexpensive and stable alternatives
three conventional protocols: (1) Suzuki-coupling reactions of aldehydes would provide a new avenue for the synthesis of
using halogenated 1,3,5-triazines with aryl boronic acids;5 (2) aryl substituted 1,3,5-triazines and is of high importance.
the cyclotrimerization of nitriles;6 (3) the cyclization of aro-
In recent years, the use of abundant and sustainable alco-
matic aldehydes with amidines.7 However, the Suzuki-coupling hols for carbon–carbon (C–C) and carbon–nitrogen (C–N)
reactions require less-environmentally benign halogenated bond formations has received considerable attention.10,11 By
substrates and produce stoichiometric amounts of undesirable employing suitable catalyst systems, the dehydrogenation of
waste. And the cyclotrimerization of nitriles generally needs the alcohols leading to in situ formation of aldehydes (or
excess of amines as the co-catalysts, which could increase the ketones) is recognized as the key point for the formation of
complexity of the work-up procedure. Interestingly, the con- desired products. Inspired by these elegant contributions, we
densation of aromatic aldehydes with amidines has provided a believed that alcohols could also be applied as latent aldehydes
direct pathway for the synthesis of aryl substituted 1,3,5-tri- for the synthesis of aryl substituted 1,3,5-triazines. Compared
azine derivatives. However, the use of aldehydes as the coup- to aldehydes, alcohols have a variety of advantages such as
ling partners could frequently meet some problems as follows: cost-effectiveness, thermodynamic stability, abundance and
sustainability. Replacing aldehydes with alcohols to react with
amidines would allow us to prepare valuable products that are
aSchool of Chemical & Material Engineering, Jiangnan University, Wuxi 214122,
People’s Republic of China. E-mail: minzhang@scut.edu.cn;
Fax: (+86)-020-39925999; Tel: (+86)-13424037838
currently inaccessible or challenging to prepare using conven-
tional methods.
Herein, we wish to develop a new method for the synthesis
of aryl substituted 1,3,5-triazines directly from primary alco-
hols and amidines. To the best of our knowledge, such a syn-
thetic protocol has not yet been reported.
bSchool of Chemistry & Chemical Engineering, South China University of Technology,
381 Wushan Rd, Guangzhou 510641, People’s Republic of China
†Electronic supplementary information (ESI) available: Images of 1H and 13C
NMR of all products. See DOI: 10.1039/c3ob42589d
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Results and discussion
With the above-described idea in mind, we then tried to
examine the possibility of direct synthesis of 2,4,6-triphenyl-
1,3,5-triazine 3a from benzylic alcohol 1a and benzamidine
hydrochloride 2a. The reaction was initially conducted at
110 °C for 16 h using 1 equivalent of K2CO3 in DMSO.
However, we failed to obtain even trace amounts of the
expected product (Table 1, entry 1). Gratifyingly, a 21%
product yield was detected by means of GC analysis while
1 mol% of RuCl3 was introduced into the reaction mixture
under the same conditions (Table 1, entry 2). The exclusive for-
mation of product 2a indicates that intermediate 2,4,6-tri-
Scheme 1 Catalysts employed for the optimization of reaction
conditions.
phenyl-1,2-dihydro-1,3,5-triazine
undergoes
a
thermo- selected [RuCl2(p-Cymene)]2 as our preferred catalyst, Cs2CO3
dynamically favourable dehydrogenation step, forming the as our preferred base, other polar and less-polar solvents were
stable aromatic compound. Encouraged by this result, we then subsequently evaluated, and the results showed that these sol-
performed a thorough ruthenium catalyst screen using the vents are less effective in comparison with DMSO (Table 1,
same reaction as the model (Scheme 1). [RuCl2(p-Cymene)]2 entries 13–15). By using the preferred catalyst, base and
(cat 6) was found to be the best catalyst (Table 1, entries 2–8), solvent, it was found that the decrease of reaction time or the
giving product 3a in 46% yield. Using [RuCl2(p-Cymene)]2 as a increase of reaction temperature would lead to decreased
catalyst, screening various organic and inorganic bases in product yields (Table 1, entries 16 and 17). However, increas-
DMSO indicated that the organic base is ineffective for the for- ing the catalyst loading from 1 mol% to 1.5 mol% resulted in
mation of the product (Table 1, entry 9), while Cs2CO3 gave a an increased yield (Table 1, entry 18), and further increase of
significantly higher product yield (Table 1, entry 10). Thus we catalyst loading did not improve the yield any more (Table 1,
entry 19). Hence, the best reaction conditions are summarized
as follows: 1.5 mol% of [RuCl2(p-Cymene)]2 catalyst, 1 equi-
valent of Cs2CO3, DMSO as the reaction solvent, and at 110 °C
(Table 1, entry 18).
Table 1 Optimization of reaction conditionsa
With the optimized reaction conditions in hand, we then
tested the generality and the limitations of this ruthenium/
Cs2CO3-catalyzed synthetic protocol. Firstly, the reactions of
aryl and alkyl amidines in combination with different substi-
tuted benzylic alcohols were examined. As shown in Table 2,
all the reactions using aryl amidines proceeded smoothly and
furnished desired products in good to excellent isolated yields
(Table 2, entries 1–11). Interestingly, halogen (–Cl) as well as
electron-donating groups (–Me, –OMe) are apparently well-
tolerated (Table 2, entries 2–3 and 7–11). Even benzylic alco-
hols having a strong electron-withdrawing group (–NO2) with
different substitution patterns could also be transformed into
the corresponding products in an efficient manner (Table 2,
entries 4–6), and the meta-substituted one gave the product in
a higher yield; it is conceivable that the meta-substituted sub-
strate is relatively more stable than those of para- and ortho-
substituted ones under the standard conditions. While using
the same amidine, the substituents possessing different elec-
tron properties on the aryl ring of benzylic alcohols slightly
influence the product yields. In general, the electron-rich sub-
strate such as 4-methoxy benzylic alcohol gave the products in
relatively higher yields (Table 2, entries 2, 8 and 10), which
could also be assigned to its inherent stability in comparison
with other benzylic alcohols. However, the reaction of n-amyl
Entry
Catalyst
Base
Solvent
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMF
Toluene
2-Methyl-2-butanol
DMSO
Yieldb % of 3a
1
2
3
4
5
6
7
8
—
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
NEt3
Cs2CO3
t-BuOK
CH3ONa
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
—
21
28
34
30
41
46
41
<10
72
32
28
61
42
21
64
70
85
85
Cat 1
Cat 2
Cat 3
Cat 4
Cat 5
Cat 6
Cat 7
Cat 6
Cat 6
Cat 6
Cat 6
Cat 6
Cat 6
Cat 6
Cat 6
Cat 6
Cat 6
Cat 6
9
10
11
12
13
14
15
16c
17d
18e
19f
DMSO
DMSO
DMSO
a Reaction conditions: unless otherwise specified, all reactions were
carried out without inert gas protection by using 1a (1.5 mmol), 2a alcohol 1g with 2a failed to yield even trace amounts of the
(1 mmol), catalyst (1 mol%), solvent (1 mL), temperature (110 °C),
expected product (Table 2, entry 12). This phenomenon might
be attributable to the dehydrogenation of simple alcohols
being relatively more challenging than that of benzylic
base (1 mmol), reaction time (16 h). b GC yield. c Reaction time (12 h).
d Reaction temperature (130 °C). e Catalyst loading (1.5 mol%).
f Catalyst loading (2 mol%).
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Table 2 Synthesis of aryl substituted 1,3,5-triazine using simple benzylic alcoholsa
Entry
1
Alcohol 1
1a: R1 = Ph
Amidine 2
2a: R2 = Ph
Product
Yieldb (%)
3a, 85
2
1b: R1 = 4-OMe–C6H4
2a
3b, 87
3
4
5
1c: R1 = 4-Cl–C6H4
2a
2a
2a
3c, 78
3d, 65
3e, 80
1d: R1 = 4-NO2− C6H4
1e: R1 = 3-NO2− C6H4
6
7
1f: R1 = 2-NO2− C6H4
2a
3f, 72
3g, 67
1a
2b: R2 = 4-Cl–C6H4
8
1b
2b
3h, 74
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Table 2 (Contd.)
Entry
9
Alcohol 1
Amidine 2
Product
Yieldb (%)
1a
1b
2c: R2 = 4-Me–C6H4
3i, 64
10
11
2c
3j, 68
1c
2c
2a
3k, 61
12
13
3l, —
1a
3m, —
a Reaction conditions: unless otherwise specified, all reactions were carried out without inert gas protection by using 1 (1.5 mmol), 2 (1 mmol),
catalyst (1.5 mol%), solvent (1 mL), temperature (110 °C), base (1 mmol), reaction time (16 h). b Yields of isolated pure product.
alcohols, and the amidines suffer a decomposition prior to the synthetic protocol. Representative heteroaryl substituted
dehydrogenation of alcohols. Similarly, less stable alkyl amidines methanols such as pyridyl methanols (Table 3, see 1h–1k),
such as acetamidine hydrochloride 2d even with benzylic alcohol furyl methanol 1l and thiazol-2-ol 1m were selected as the
1a could not yield the expected product (Table 2, entry 13).
coupling partners for the cyclization reactions with different
Hence, the dehydrogenation rate of alcohols is considered amidines. Gratifyingly, all the reactions proceeded efficiently
to be a key factor for the formation of products. Notably, and furnished the products in moderate to excellent isolated
owing to the aryl groups being ortho to the nitrogen atoms, the yields. Similar to the compounds described in Table 2, the
obtained 2,4,6-triaryl-1,3,5-triazines have the potential to be obtained heteroaryl substituted 1,3,5-triazines could also be
applied as C^N ligands for the preparation of cyclometalated potentially valuable C^N or C^N^C ligands. Additionally, the
organometallic materials12 or C^N^C ligands for the elabor- products arising from pyridin-2-ylmethanol derivatives (see 1j,
ation of pincer complexes.13
1k) and thiazol-2-ylmethanol 1m have the potential to be used
Upon a thorough literature investigation, it was found that as N^N^C ligands for the preparation of novel pincer
the synthesis of heteroaryl substituted 1,3,5-triazines has been complexes.14
scarcely explored with the conventional methods. Herein, we
wish to prepare this type of compounds by employing our as
On the basis of transition metal-induced dehydrogenation
a
substrate activation strategy10,11 as well as the
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Table 3 Synthesis of aryl substituted 1,3,5-triazine using heteroaryl methanolsa
Entry
1
Alcohol 1
Amidine 2
2a: R2 = Ph
Product
Yieldb (%)
3n, 78
2
2a
2a
3o, 74
3
4
3p, 66
3q, 54
1h
5
1i
3r, 63
6
7
2a
2b
3s, 71
3t, 58
1k
1k
8
2c
3u, 65
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Table 3 (Contd.)
Entry
9
Alcohol 1
Amidine 2
Product
Yieldb (%)
2a
2b
3v, 67
10
11
1l
1l
3w, 52
2c
2a
3x, 57
12
3y, 73
a Reaction conditions: unless otherwise specified, all reactions were carried out without inert gas protection by using 1 (1.5 mmol), 2 (1 mmol),
catalyst (1.5 mol%), solvent (1 mL), temperature (110 °C), base (1 mmol), reaction time (16 h). b Yields of isolated pure product.
conventional 1,3,5-triazine syntheses, a plausible pathway for The subsequent inter- and intra-molecular nucleophilic
the generation of 2,4,6-triaryl-1,3,5-triazines from alcohols and addition of the amino group to the electrophilic carbon center
amidines is depicted in Scheme 2. The reaction initiates with would afford intermediate C and racemic aminals D. Then, the
the dehydrogenation of aryl methanol 1 induced by coopera- thermodynamically favourable deamination would release
tive action of the ruthenium catalyst and Cs2CO3; amidine 2′ dihydrotriazine E and ammonia. Finally, the desired product 3
neutralized by Cs2CO3 from its hydrochloride salt 2 then con- is formed via dehydrogenative aromatization of E promoted by
denses with the in situ formed aldehyde A to give azadiene B. the ruthenium catalyst or air oxidation.
Conclusions
In summary, we have presented a new and straightforward
method for the synthesis of 2,4,6-triaryl-1,3,5-triazines by
using commercially available [RuCl2(p-Cymene)]2/Cs2CO3 as a
catalyst system. Abundant and easily available alcohols were
firstly employed as the coupling partners to react with ami-
dines, and the dehydrogenative cyclization process proceeded
efficiently and furnished the products in good to excellent iso-
lated yields. In addition to utilization of simple benzylic alco-
hols, heteroaryl methanols could also be converted into
heteroaryl substituted 1,3,5-triazines. Due to the inherent
Scheme 2 Proposed mechanism for the formation of 2,4,6-triaryl-
1,3,5-triazines from alcohols and amidines.
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stability of alcohols in contrast with aldehydes, our synthetic Science Foundation of Jiangsu Province (BK2011144), Funda-
protocol is adaptable to a broad substrate scope, providing the mental Research Funds for the Central Universities of China
potential to prepare valuable products that are currently inac- (2014ZZ0047), and 333 Talent Project of Jiangsu Province.
cessible or challenging to prepare using the conventional
methods, and there is no need for stringent protection during
the whole operation process. Hence, it is a significantly impor-
tant complement to the conventional synthetic methodologies.
Notes and references
Based on the importance of 2,4,6-triaryl-1,3,5-triazines in
biology, organic and material chemistry, this practical syn-
thetic strategy has the potential to be frequently used.
1 (a) N. Nishimura, A. Kato and I. Maeba, Carbohydr. Res.,
2001, 331, 77–82; (b) B. Klenke, M. Stewart, M. P. Barrett,
R. Brun and I. H. Gilbert, J. Med. Chem., 2001, 44, 3440–
3452; (c) Y. Iino, T. Karakida, N. Sugamata, T. Andoh,
H. Takei, M. Takahashi, S. Yaguchi, T. Matsuno,
M. Takehara, M. Sakato, S. Kawashima and Y. Morishita,
Anticancer Res., 1998, 18, 171–176.
2 (a) S. Kotha, D. Kashinath and S. Kumar, Tetrahedron Lett.,
2008, 49, 5419–5423; (b) C.-H. Lee and T. Yamamoto, Bull.
Chem. Soc. Jpn., 2002, 75, 615–618.
3 P. Paul, B. Tyagi, A. K. Bilakhiya, P. Dastidar and E. Suresh,
Inorg. Chem., 1999, 39, 14–22.
4 (a) M. Hernandez-Juarez, M. Vaquero, E. Alvarez, V. Salazar
and A. Suarez, Dalton Trans., 2013, 42, 351–354;
(b) P. K. Santra and P. Sagar, J. Mol. Catal. A: Chem., 2003,
197, 37–50.
5 (a) H. Tanaka, K. Shizu, H. Miyazaki and C. Adachi, Chem.
Commun., 2012, 48, 11392–11394; (b) J. Liu, K. Wang, F. Xu,
Z. Tang, W. Zheng, J. Zhang, C. Li, T. Yu and X. You, Tetra-
hedron Lett., 2011, 52, 6492–6496; (c) S. Achelle,
Y. Ramondenc, F. Marsais and N. Plé, Eur. J. Org. Chem.,
2008, 3129–3140; (d) S. Ren, Q. Fang, F. Yu and D. Bu,
J. Polym. Sci., Part A: Polym. Chem., 2005, 43, 6554–6561.
6 (a) A. Diaz-Ortiz, A. de la Hoz, A. Moreno, A. Sanchez-Migal-
lon and G. Valiente, Green Chem., 2002, 4, 339–343;
(b) F. Xu, J.-H. Sun, H.-B. Yan and Q. Shen, Synth.
Commun., 2000, 30, 1017–1022; (c) R. D. Spencer and
B. H. Beggs, Anal. Chem., 1963, 35, 1633–1636.
7 (a) S. Biswas and S. Batra, Eur. J. Org. Chem., 2012, 3492–
3499; (b) V. Kumar, M. Gupta and M. P. Mahajan,
Can. J. Chem., 2006, 84, 453–457; (c) E. Haruki, T. Inaike
and E. Imoto, Nippon Kagaku Zasshi, 1966, 87, 206–208.
8 G. V. R. Sharma and A. Robert, Res. Chem. Intermed., 2013,
39, 3251–3254.
9 (a) A. Modak, A. Deb, T. Patra, S. Rana, S. Maity and
D. Maiti, Chem. Commun., 2012, 48, 4253–4255; (b) T. Iwai,
T. Fujihara and Y. Tsuji, Chem. Commun., 2008, 6215–6217.
10 (a) S. Michlik and R. Kempe, Nat. Chem., 2013, 5, 140–144;
(b) S. Michlik and R. Kempe, Angew. Chem., Int. Ed., 2013,
52, 6326–6329; (c) D. Srimani, Y. Ben-David and
D. Milstein, Angew. Chem., Int. Ed., 2013, 52, 4012–4015;
(d) M. Zhang, H. Neumann and M. Beller, Angew. Chem.,
Int. Ed., 2013, 52, 597–601; (e) M. Zhang, X. Fang,
H. Neumann and M. Beller, J. Am. Chem. Soc., 2013, 135,
11384–11388; (f) R. H. Crabtree, Organometallics, 2011, 30,
17–19; (g) T. D. Nixon, M. K. Whittlesey and
J. M. J. Williams, Dalton Trans., 2009, 753–762;
(h) G. Guillena, D. J. Ramón and M. Yus, Chem. Rev.,
2009, 110, 1611–1641; (i) M. H. S. A. Hamid, P. A. Slatford
Experimental
General information
All the obtained products were characterized by melting points
(m.p.), 1H-NMR, infrared spectra (IR), and high resolution
mass spectra (HRMS). The 1H-NMR spectra of known com-
pounds were found to be identical with the ones reported in
the literature. Additionally, all the new compounds were
further characterized by 13C-NMR. Melting points were
measured on an Electrothermal SGW-X4 microscopy digital
melting point apparatus and are uncorrected; IR spectra were
recorded on a FTLA2000 spectrometer; 1H-NMR spectra were
obtained on Bruker-400; high-resolution mass spectra (HRMS)
were recorded on a JEOL JMS-600 spectrometer. Chemical
shifts were reported in parts per million (ppm, δ) downfield
from tetramethylsilane. Proton coupling patterns are described
as singlet (s), doublet (d), triplet (t), multiplet (m). TLC was
performed using commercially prepared 100–400 mesh silica
gel plates (GF254), and visualization was effected at 254 nm.
All the reagents were purchased from commercial sources
(J&KChemic, TCI, Fluka, Acros, SCRC), and used without
further purification.
Typical procedure for synthesis of 2,4,6-triphenyl-1,3,5-triazine
(3a)
To a solution of benzyl alcohol (0.162 g, 1.5 mmol) and benza-
midine hydrochloride (0.156 g,1 mmol) in DMSO (1 mL) were
added [RuCl2-(p-Cymene)]2 (0.015 mmol, 4.5 mg) and Cs2CO3
(0.325 g, 1 mmol). The reaction mixture was heated at 110 °C
for 16 h in a sealed tube without inserting any gas protection.
Afterwards, water (10 mL) and dichloromethane (20 mL) were
added, the layers were separated, and then the aqueous layer
was extracted with dichloromethane (2 × 10 mL). The com-
bined organic layers were dried with anhydrous Na2SO4, and
concentrated under vacuum. The residue was directly purified
by flash chromatography on silica gel eluting with petroleum
ether (60–90 °C)–ethyl acetate (15 : 1) to give 2,4,6-triphenyl-
1,3,5-triazine 3a as a white solid (0.123 g, 85%).
Acknowledgements
The authors are grateful for the funds from the National
Natural Science Foundation of China (21101080), Natural
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and J. M. J. Williams, Adv. Synth. Catal., 2007, 349, 1555–
1575.
11 (a) M. Zhang, S. Imm, S. Bähn, H. Neumann and M. Beller,
Angew. Chem., Int. Ed., 2011, 50, 11197–11201; (b) S. Imm,
(g) X.-T. Wang, M.-M. Chen, F. Xie and M. Zhang, RSC Adv.,
2014, 4, DOI: 10.1039/c4ra00039k; (h) M. Zhang, F. Xie,
X.-T. Wang, F.-X. Yan, T. Wang, M.-M. Chen and Y.-Q. Ding,
RSC Adv., 2013, 3, 6022.
S. Bähn, M. Zhang, L. Neubert, H. Neumann, F. Klasovsky, 12 W. Yang, H. Fu, Q. Song, M. Zhang and Y. Ding, Organo-
J. Pfeffer, T. Haas and M. Beller, Angew. Chem., Int. Ed., metallics, 2010, 30, 77–83.
2011, 50, 7599–7603; (c) S. Bähn, S. Imm, L. Neubert, 13 (a) D. A. Smith, D.-A. Roşca and M. Bochmann, Organo-
M. Zhang, H. Neumann and M. Beller, ChemCatChem,
2011, 3, 1853–1864; (d) G. Guillena, D. J. Ramón and
M. Yus, Chem. Rev., 2009, 110, 1611–1641; (e) G. Guillena,
metallics, 2012, 31, 5998–6000; (b) W. Wei, Y. Qin, M. Luo,
P. Xia and M. S. Wong, Organometallics, 2008, 27, 2268–
2272.
D. J. Ramón and M. Yus, Angew. Chem., Int. Ed., 2007, 46, 14 K. J. H. Young, J. Oxgaard, D. H. Ess, S. K. Meier,
2358–2364; (f) F.-X. Yan, M. Zhang, X.-T. Wang, F. Xie,
M.-M. Chen and H.-F. Jiang, Tetrahedron, 2014, 70, 1193;
T. Stewart, I. I. I. W. A. Goddard and R. A. Periana, Chem.
Commun., 2009, 3270–3272.
2768 | Org. Biomol. Chem., 2014, 12, 2761–2768
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