(DHQD)2PHAL ligand-accelerated Cu-catalyzed azide-alkyne cycloaddition reactions in water at room temperature

Article abstract of DOI:10.1039/c4ra12572j

Herein, we have described, a 'Click Chemistry' protocol for the rapid synthesis of 1,2,3-triazoles in water. (DHQD)₂PHAL has been found to be an excellent accelerating ligand for the copper(i)-catalyzed azide-alkyne cycloaddition reaction under

Full text of DOI:10.1039/c4ra12572j

RSC Advances
View Article Online
View Journal | View Issue
COMMUNICATION
(DHQD)2PHAL ligand-accelerated Cu-catalyzed
azide–alkyne cycloaddition reactions in water at
room temperature
Cite this: RSC Adv., 2014, 4, 64388
a
a
b
a
Received 17th October 2014
Accepted 17th November 2014
*
Abdul Aziz Ali, Mitali Chetia, Prakash J. Saikia and Diganta Sarma
DOI: 10.1039/c4ra12572j
www.rsc.org/advances
Herein, we have described, a ‘Click Chemistry’ protocol for the rapid approaches for the preparation of ve membered heterocycles6
synthesis of 1,2,3-triazoles in water. (DHQD)2PHAL has been found to which proceeds very slowly even at high temperatures, and gives
be an excellent accelerating ligand for the copper(I)-catalyzed azide– a mixture of 1,4- and 1,5-disubstituted 1,2,3-triazoles. In 2002,
alkyne cycloaddition reaction under air. The procedure is simple, the groups of Meldal7 and Sharpless8 independently discovered
efficient, environmentally-friendly and the products were isolated in that copper(I) was an excellent catalyst for the regioselective
excellent yields with high purity.
preparation of 1,4-substituted 1,2,3 triazoles. Since then copper-
catalyzed azide–alkyne 1,3-dipolar cycloaddition (CuAAC) reac-
tion has been termed as a “click reaction” and numerous
applications of the click reaction have been reported in the eld
of organic synthesis, drug discovery, polymer chemistry, uo-
rescent imaging, molecular biology, and materials science.9–12
The development of copper(I) catalytic systems for CuAAC
reactions has been found in numerous literature. Due to the
known instability of simple copper(I) salts, the active species are
oen generated in situ from a copper(II) salt and a reducing
agent (most oen sodium ascorbate). These systems can be
enormously efficient, but they are inherently limited to water-
tolerant substrates.13 It has been found that certain Cu-
binding ligands accelerate the CuAAC reaction up to several
thousand times over the ligand-free process.14 The CuAAC
reaction has been proven to be accelerated by Cu(I) species
supported by nitrogen,15 sulfur,16 N-heterocyclic carbenes
NHC,17,18 polydentate ligands,19 simple monodentate phosphine
complexes – Cu(P(OEt)3)3I,20 Cu(PPh3)3Br,21,22 and Cu(PPh3)2OAc,23
monodentate phosphoramidite24 and thioethers,25 and histi-
dine derivatives.26 The use of ligands in this context protects the
copper(I) center from oxidation or disproportionation and
enhances its catalytic activity allowing for smoother reaction
conditions or broader applicability. Although most of these
ligands help speeding up the reaction, but still fall short of the
requisite reaction times for labelling of biological targets with
short-lived radioisotopes. Others shortcomings involve high
catalyst loadings, tricky synthetic route, long reaction time, use
of organic solvent etc.
Water is the solvent of nature; it attracts enormous attention
due to its important additional benets: it is cheap, nonam-
mable, nontoxic, and an environmentally benign solvent. Water
has unique physical and chemical properties such as a high
dielectric constant, optimum oxygen solubility to maintain
aquatic life forms, high cohesive energy density compared with
most organic solvents and has a network of hydrogen bonds
which can inuence the reactivity of substrates.1 This unique
nature of water is also essential for most biochemical reactions
in living systems.2 From the viewpoint of international
consensus on green chemistry, it is desirable to use water
instead of organic solvents as a reaction solvent.3 Therefore, the
design and development of environmentally benign chemical
processes is oen regarded as a goal for synthetic chemists.
The 1,2,3-triazoles are N-heterocyclic compounds which do
not occur in nature, although the synthetic molecules that
contain 1,2,3-triazole units show a spacious applications
ranging from industrial applications to a large number found in
pharmaceutical compounds.4 The 1,2,3-triazole has the bene-
cial properties like high chemical stability (generally inert to
severe hydrolytic, oxidizing, and reducing conditions, even at
high temperature), strong dipole moment (4.8–5.6 Debye),
aromatic character, and hydrogen bond accepting ability.5
Several synthetic methods have been developed for the
preparation of 1,2,3-triazole derivatives. Among them, Huisgen
1,3-dipolar azide–alkyne cycloaddition is the most general
(DHQD)2PHAL
or
hydroquinidine-1,4-phthalazinediyl
aDepartment of Chemistry, Dibrugarh University, Dibrugarh-786004, Assam, India.
E-mail: dsarma22@gmail.com; dsarma22@dibru.ac.in
bAnalytical Chemistry Division, CSIR-North East Institute of Science & Technology,
diether (Fig. 1) is a phthalazine class of ligand and it was rst
introduced by Sharpless et al. for asymmetric dihydroxylation of
alkenes.27 This reagent is readily available and air stable
Jorhat-785006, Assam, India
64388 | RSC Adv., 2014, 4, 64388–64392
This journal is © The Royal Society of Chemistry 2014

View Article Online
Communication
RSC Advances
results were well supported by earlier ndings. F. Li and T. S. A.
Hor reported the use of copper coordinated nitrogen tetra-
dentate ligands for CuAAC reaction.19 They performed the
azide–alkyne cycloaddition reactions in presence of one equiv-
alent each of CuI and ligand in MeCN : water (1 : 1 ratio) solvent
system for 10 h at room temperature to achieve almost quan-
titative yields. Wang et al. developed a ‘on water’ protocol for
copper catalyzed cycloaddition of water-insoluble aliphatic/aryl
azides and alkynes at room temperature using 10 mol% catalyst
(CuBr) and 50 mol% ligand (PhSMe).16 B. L. Feringa and his
research group described the accelerating nature of mono-
dentate phosphoramidite ligands for CuAAC reaction yielding a
wide variety of functionalized 1,4-disubstituted-1,2,3-triazoles.24
Their methodology involved the CuAAC reaction carried out in
presence of 1 mol% copper sulphate (in presence of sodium
ascorbate) and 1.1 mol% ligand in DMSO : water (1 : 3 ratio)
solvent system.
Fig. 1 (DHQD)2PHAL ligand.
polydentate ligand. Considering the virtues of ligands, we
describe here a (DHQD)2PHAL stabilized copper(I) catalyst,
without the requirement of immobilization on a polymeric or
an inorganic support, for the synthesis of 1,2,3-triazoles in
aqueous media at room temperature.
Encouraged by the high activity of our catalytic system, we
then next performed the CuAAC reaction of benzyl azide and
phenyl acetylene in presence of CuI catalyst in different solvent
systems (Table 1, entries 9–16). Unlike earlier literature reports,
the reaction proceeded in excellent yields (90%) under aqueous
conditions (Table 1, entry 10). Taking into account the interest
of environmental concerns and economic considerations, all
CuAAC reactions were performed under aqueous conditions. As
water was found to be the best solvent for the reaction under
this reaction condition, we next investigated catalyst loading
(Table 2, entries 1–3) and gratifyingly, upon lowering the cata-
lyst concentration to 0.5 mol% the reaction still proceeded
within 10 min giving 88% yields (Table 2, entry 2). Therefore, a
Results and discussion
We initialized our studies with the cycloaddition of benzyl azide
with phenylacetylene as model reaction under standard cyclo-
addition conditions. The reaction of benzyl azide and phenyl
acetylene catalyzed by copper sulphate in presence of sodium
ascorbate and (DHQD)2PHAL ligand in a mixture of water : t-
BuOH (1 : 1) solvent system afforded 1,2,3-triazoles in 50%
yields (Table 1, entry 1). Optimization studies revealed that the
CuAAC reaction could be performed with moderate yields using
various copper sources (Table 1, entries 2–7). Interestingly,
when CuI (1 mol%) was used as the catalyst the reaction pro-
ceeded smoothly under air to afford 1-benzyl-4-phenyl-1,2,3-
triazole regioselectively in 75% yields (Table 1, entry 8). Our
Table 1 Solvent and catalyst optimization studiesa
Entry
Copper source
Solvent
Time (min)
Yieldb (%)
1
2
3
4
5
6
7
8
CuSO4 + sodium ascorbate
H2O/t-BuOH (1 : 1)
H2O/t-BuOH (1 : 1)
H2O/t-BuOH (1 : 1)
H2O/t-BuOH (1 : 1)
H2O/t-BuOH (1 : 1)
H2O/t-BuOH (1 : 1)
H2O/t-BuOH (1 : 1)
H2O/t-BuOH (1 : 1)
THF
H2O
DMSO
DMF
Acetone
60
60
60
60
60
60
60
20
60
5
40
60
50
60
60
60
50
55
65
60
50
48
55
75
70
90
65
68
65
50
52
0c
CuCl
Cu(OAc)
CuOTf
Cu powder
CuCN
CuBr
CuI
CuI
CuI
CuI
CuI
9
10
11
12
13
14
15
16
CuI
CuI
CuI
CuI
Toluene
DCM
H2O
a
Reagents and reaction conditions: 1a (1 mmol), 2a (1.1 mmol), catalyst (1 mol%) and ligand (1 mol%) in the given solvent was stirred at room
temperature in open air otherwise stated. b Isolated yields aer reduced pressure distillation. Absence of ligand.
c
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 64388–64392 | 64389

View Article Online
RSC Advances
Communication
Table 2 CuAAC with different loading of catalysta
smoothly giving excellent isolated yields of the corresponding
triazoles aer simple extraction and crystallization, irrespective
of the substitution either on the starting azides or on the
alkynes. The results indicated that benzyl (entries 1, 6 and 9,
Table 3), aryl (entries 2–4, 7–8, and 10–12, Table 3), and alkyl
azides (entry 5, Table 3) generated the 1,4-disubstituted 1,2,3-
triazoles in excellent yields. Of the alkynes, aromatic (entries 1–
5, Table 3) and aliphatic alkynes (entries 6–8, Table 3) – all
worked efficiently toward this click conversion and the hydroxyl-
functionalized alkyne (entries 9–12, Table 3) was also a good
coupling partner resulting in 87–92% yields of the desired
triazoles.
Entry
CuI (mol%)
Time (min)
Yieldb (%)
1
2
3
1
0.5
2
10
10
10
90
88
91
a
Reagents and reaction conditions: 1a (1 mmol), 2a (1.1 mmol), and
b
catalyst CuI (0.5–2 mol%), and ligand (1 mol%) in water. Isolated
yields.
Conclusions
In conclusion, we have successfully developed a quick, versatile,
highly efficient and environmentally friendly catalytic system
for CuAAC reactions in water. This protocol provides a wide
scope for the synthesis of desired 1,4-disubstituted-1,2,3-
triazoles in excellent yields within a few minutes by using
(DHQD)2PHAL as an accelerating ligand at room temperature.
The operational ease of this protocol and the purity of the
recovered products make it attractive for tremendous applica-
tions in various research elds.
catalyst loading of 0.5 mol% appeared to be optimal with
respect to yields and short reaction times. Signicantly, under
these optimized conditions, no undesirable byproduct could be
detected. However, in absence of ligand, no triazole formation
was observed under this reaction condition, highlighting the
key role of the ligand (Table 1, entry 16).
With optimized parameters in hand, exploration of the scope
of the catalyst system for CuAAC reaction was performed in
water at room temperature without the exclusion of air with a
variety of organic azides and acetylenes. The results are exem-
plied in Table 3 (entries 1–12). All reactions proceeded
Experimental
All reactions were carried out in oven dried glassware under
atmospheric conditions otherwise noted. Reagents and solvents
were obtained from commercial suppliers and used without
further purication. All reported yields are isolated yields. Thin
layer chromatography (TLC) was carried out using aluminium
sheets pre-coated with silica gel 60F254 (Merck) and was visu-
Table 3 Copper(I) catalysed azide–alkyne cycloaddition of a variety of
azides and alkynes in water at room temperaturea
Entry Azide
1
Alkyne
Product Time (min) Yieldb (%)
1
alized under 254 nm UV light. H NMR (300 MHz), 13C NMR
3a
5
88
(100 MHz) were measured on a Brucker Avance 400 MHz spec-
trometer. Chemical shis are reported in parts per million
(ppm, d) downeld from residual solvents peaks and coupling
constants are reported as Hertz (Hz). Splitting patterns are
designated as singlet (s), doublet (d), triplet (t), quartet (q),
broad (br) etc., splitting patterns that could not be interpreted
or easily visualized are designated as multiplet (m). ESI-MS
spectra were recorded on an Agilent 6510 ESI-QTOF LC/MS
mass spectrometer. Melting points were measured with a
2
3
3b
3c
30
15
82
85
4
5
3d
3e
20
25
87
82
6
3f
30
84
¨
Buchi B-540 melting point apparatus.
7
8
3g
3h
30
25
82
86
Synthesis of azide
All azides were synthesized according to the reported
procedure.28
9
3i
20
90
A typical CuAAC procedure for the preparation of 1,2,3-tri-
zole. To a mixture of CuI (0.95 mg, 0.5 mol%), (DHQD)2PHAL
(7.7 mg, 0.01 mmol) and azide (1 mmol) in deionised water (2
mL), alkyne (1.1 mmol) was added at room temperature. The
resultant mixture was stirred continuously until the reaction
system solidied completely. Then ethyl acetate (20 mL) was
added to dissolve the crude product. The organic layer was
washed with H2O, 0.25 N HCl (10 mL) and brine, and dried over
10
11
3j
30
25
92
90
3k
12
3l
20
87
a
All reactions were carried out using azide (1 mmol), alkynes
(1.1 mmol), CuI (0.5 mol%), and (DHQD)2PHAL (0.01 mmol) in H2O
(2 mL) at room temp. b Isolated yields.
64390 | RSC Adv., 2014, 4, 64388–64392
This journal is © The Royal Society of Chemistry 2014

View Article Online
Communication
RSC Advances
anhydrous Na2SO4. Removal of the solvent yielded a residue,
which was washed with petroleum ether (50 mL) to furnish the
product triazoles.
1-Benzyl-4-phenyl-1H-1,2,3-triazole (3a). White solid, mp
128–130 ꢀC, 88% yield. 1H NMR (300 MHz, CDCl3): d 7.80 (d, J ¼
7.35 Hz, 2H), 7.66 (s, 1H), 7.42–7.29 (m, 5H), 5.57 (s, 2H); 13C
NMR (100 MHz, CDCl3): d 148.2, 134.6, 130.4, 129.1, 128.8,
128.2, 128.0, 125.7, 119.5, 54.2. MS (ESI) m/z: 236 [M + H]+, cal.
236.3.
(1-Phenyl-1H-[1,2,3]triazol-4-yl)-methanol (3j). White solid,
mp 115–118 ꢀC. 92% yield. 1H NMR (300 MHz, DMSO-d6): d 8.68
(s, 1H), 7.92 (d, J ¼ 7.8 Hz, 2H), 7.61–7.45 (m, 3H), 4.64 (d, J ¼ 5.2
Hz, 2H), 2.50 (br, 1H); 13C NMR (100 MHz, DMSO-d6): d 149.6,
137.2, 130.3, 128.9, 121.4, 120.4, 55.4. MS (ESI) m/z: 176
[M + H]+, cal. 176.2.
[1-(4-Chloro-phenyl)-1H-[1,2,3]triazol-4-yl]-methanol
(3k).
Yellowish solid, mp 146–148 ꢀC, 90% yield, 1H NMR (300 MHz,
CDCl3): d 8.01 (s, 1H), 7.68 (d, J ¼ 8.5 Hz, 2H), 7.50 (d, J ¼ 8.5 Hz,
2H) 4.88 (s, 2H), 2.35 (br, 1H); 13C NMR (100 MHz, CDCl3):
148.7, 135.5, 134.6, 129.9, 121.7, 56.2. MS (ESI) m/z: 211
[M + H]+, cal. 210.6.
1-(4-Diphenyl)-1H-1,2,3-triazole (3b). Pale yellow solid, mp
1
183–184 ꢀC, 82% yield. H NMR (300 MHz, CDCl3): d 8.19 (s,
1H), 7.92 (d, J ¼ 7.34 Hz, 2H), 7.80 (d, J ¼ 7.73 Hz, 2H), 7.64–7.19
(m, 6H); 13C NMR (100 MHz, CDCl3): d 148.9, 137.2, 130.6, 129.5,
129.1, 128.8, 126.2, 120.6, 118.4; MS (ESI) m/z: 222 [M + H]+, cal.
222.3.
[1-(4-Bromo-phenyl)-1H-[1,2,3]triazol-4-yl]-methanol
(3l).
Yellowish solid, mp 135–137 ꢀC, 87% yield. 1H NMR (300 MHz,
CDCl3): d 8.00 (s, 1H), 7.72–7.59 (m, 4H), 4.89 (s, 2H), 2.14 (br,
1H); 13C NMR (100 MHz, CDCl3): 148.2, 136.8, 134.3, 130.9,
121.3, 54.6. MS (ESI) m/z: 255 [M + H]+, cal. 255.1.
1-(4-Bromophenyl)-4-phenyl-1H-1,2,3-triazole (3c). White
1
ꢀ
solid, mp 231–233 C, 85% yield. HNMR (300 MHz, CDCl3): d
8.17 (s, 1H), 7.91–7.35 (m, 9H). 13C NMR (100 MHz, CDCl3): d
149.1, 133.3, 136.4, 130.4, 129.4, 129.0, 126.3, 122.8, 122.3,
117.7. MS (ESI) m/z: 301 [M + H]+, cal. 301.2.
Acknowledgements
1-(4-Chlorophenyl)-4-phenyl-1H-1,2,3-triazole (3d). Yellow
solid, mp 225–227 ꢀC, 87% yield. 1H NMR (300 MHz, CDCl3): d
8.17 (s, 1H), 7.92 (d, J ¼ 7.5 Hz, 2H), 7.77 (d, J ¼ 8.6 Hz, 2H),
7.54–7.36 (m, 5H). 13C NMR (100 MHz, CDCl3): d 135.6, 134.4,
129.8, 128.8, 128.4, 125.7, 121.5, 117.2. MS (ESI) m/z: 257 [M +
H]+, cal. 256.7.
DS is thankful to CSIR, New Delhi for a research grant [no.
02(0154)/13/EMR-II]. The authors also acknowledge the
Department of Science and Technology for nancial assistance
under DST-FIST programme and UGC, New Delhi for Special
Assistance Programme (UGC-SAP) to the Department of
Chemistry, Dibrugarh University.
1-Octyl-4-phenyl-1H-1,2,3-triazole (3e). White solid, mp 74–
1
ꢀ
76 C, 82% yield. H NMR (300 MHz, CDCl3): d 7.84 (d, J ¼ 7.3
Hz, 2H), 7.74 (s, 1H), 7.44–7.29 (m, 3H), 4.40 (t, J ¼ 7.2 Hz, 2H),
1.96 (t, J ¼ 7.0 Hz, 2H), 1.34–1.26 (m, 10H), 0.89 (t, J ¼ 6.9 Hz,
3H); 13C NMR (100 MHz, CDCl3): d 147.5, 130.6, 129.0, 128.7,
127.9, 125.5, 119.3, 50.3, 31.5, 30.2, 28.9, 28.8.0, 26.3, 22.4, 13.9.
MS (ESI) m/z: 258 [M + H]+, cal. 258.4.
References
1 A. Chanda and V. V. Fokin, Chem. Rev., 2009, 109, 725–748.
2 S. Kobayashi and K. Manabe, Acc. Chem. Res., 2002, 35, 209–
217.
3 P. T. Anastas and J. C. Warner, Green Chemistry: Theory and
Practice, Oxford University Press, Oxford, 1998.
4 (a) V. P. Krivopalov and O. P. Shkurko, Russ. Chem. Rev.,
2005, 74, 339–379; (b) M. G. Finn and V. V. Fokin, Chem.
Rev., 2010, 39, 1231–1232; (c) B. Saikia, P. P. Saikia,
A. Goswami, N. C. Barua, A. K. Saxena and N. Suri,
Synthesis, 2011, 19, 3173.
1-Benzyl-4-butyl-1H-1,2,3-triazole (3f). White solid, mp 64–
1
ꢀ
66 C, 84% yield. H NMR (300 MHz, CDCl3): d 7.41–7.21 (m,
6H), 5.50 (s, 2H), 2.73 (t, J ¼ 7.5 Hz, 2H), 1.68–1.58 (m, 2H), 1.42–
1.30 (m, 2H), 0.93 (t, J ¼ 7.5 Hz, 3H); 13C NMR (100 MHz, CDCl3):
d 148.2, 134.9, 128.2, 128.4, 127.2, 120.4, 53.6, 31.4, 25.2, 22.3,
14.7. MS (ESI) m/z: 216 [M + H]+, cal. 216.3.
4-Butyl-1-phenyl-1H-1,2,3-triazole (3g). Colorless liquid, 82%
5 J. E. Hein and V. V. Fokin, Chem. Soc. Rev., 2010, 39, 1302–
1315.
6 R. Huisgen, 1,3-Dipolar Cycloaddition Chemistry, ed. A.
Padwa, Wiley, New York, 1984, pp. 1–176.
7 C. W. Tornøe, C. Christensen and M. Meldal, J. Org. Chem.,
2002, 67, 3057–3064.
1
yield. H NMR (300 MHz, CDCl3): d 7.73 (d, J ¼ Hz, 2H), 7.53–
7.39 (m, 3H), 7.27 (s, 1H), 2.83–2.78 (t, 2H), 1.77–1.67 (m, 2H),
1.49–1.37 (m, 2H), 0.98 (t, J ¼ 7.2 Hz, 3H); 13C NMR (100 MHz,
CDCl3): d 151.3, 130.5, 128.5, 127.9, 126.6, 119.4, 50.1, 32.4,
19.7, 14.4. MS (ESI) m/z: 202 [M + H]+, cal. 202.3.
1-(4-Bromo-phenyl)-4-butyl-1H-[1,2,3]triazole (3h). White
solid, mp 69–71 ꢀC, 86% yield. 1H NMR (300 MHz, DMSO-d6): d
8.61 (s, 1H), 7.88 (d, J ¼ 8.8 Hz, 2H), 7.80 (d, J ¼ 8.8 Hz, 2H), 2.72
(t, J ¼ 7.4 Hz, 2H), 1.70–1.60 (m, 2H), 1.43–1.35 (m, 2H), 0.94 (t, J
¼ 7.3 Hz, 3H); 13C NMR (100 MHz, DMSO-d6): d 148.8, 136.4,
133.1, 122.1, 121.3, 127.82, 120.5, 55.3, 31.3, 25.1, 22.1, 14.1. MS
(ESI) m/z: 281 [M + H]+, cal. 281.2.
(1-Benzyl-1H-1,2,3-triazol-4-yl) methanol (3i). White solid,
mp 75–78 ꢀC, 90% yield. 1H NMR (300 MHz, DMSO-d6): d 8.02 (s,
1H), 7.40–7.31 (m, 5H), 5.57 (s, 2H), 4.52 (s, 2H), 2.50 (br, 1H);
13C NMR (100 MHz, DMSO-d6): d 148.7, 136.6, 129.1, 128.5,
128.3, 123.2, 55.5, 53.1. MS (ESI) m/z: 190 [M + H]+, cal. 190.2.
8 V. V. Rostovtsev, L. G. Green, V. V. Fokin and K. B. Sharpless,
Angew. Chem., Int. Ed., 2002, 41, 2596–2599.
9 (a) M. Meldal and C. W. Tormøe, Chem. Rev., 2008, 108,
2952–3015; (b) J. E. Moses and A. D. Moorhouse, Chem.
Soc. Rev., 2007, 36, 1249–1262; (c) H. C. Kolb and
K. B. Sharpless, Drug Discovery Today, 2003, 8, 1128–1137.
10 (a) S. Chuprakov, S. W. Kwok and V. V. Fokin, J. Am. Chem.
Soc., 2013, 135, 4652–4655; (b) M. Zibinsky and
V. V. Fokin, Angew. Chem., 2013, 125, 1547–1550; Angew.
Chem., Int. Ed., 2013, 52, 1507–1510; (c) A. V. Gulevich,
A. S. Dudnik, N. Chernyak and V. Gevorgyan, Chem. Rev.,
2013, 113, 3084–3213.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 64388–64392 | 64391

View Article Online
RSC Advances
Communication
11 J. C. Jewett and C. R. Bertozzi, Chem. Soc. Rev., 2010, 39,
1272–1279.
J. Isac-Garcia and F. Santoyo-Gonzalez, Org. Lett., 2003, 5,
1951–1954.
12 A. Qin, J. W. Y. Lam and B. Z. Tang, Chem. Soc. Rev., 2010, 39, 21 P. Wu, A. K. Feldman, A. K. Nugent, C. J. Hawker, A. Scheel,
2522–2544.
B. Voit, J. Pyun, J. M. J. Frechet, K. B. Sharpless and
´
´
13 S. Dıez-Gonzalez, Catal. Sci. Technol., 2011, 1, 166–178.
V. V. Fokin, Angew. Chem., Int. Ed., 2004, 43, 3928–3932.
´
14 S. I. Presolski, V. Hong, S. H. Cho and M. G. Finn, J. Am. 22 S. Lal and S. Dıez-Gonzalez, J. Org. Chem., 2011, 76, 2367–
Chem. Soc., 2010, 132, 14570–14576. 2373.
´
15 (a) V. O. Rodionov, S. I. Presolski, S. Gardinier, Y. H. Lim and 23 Z. Gonda and Z. Novak, Dalton Trans., 2010, 39, 726–729.
M. G. Finn, J. Am. Chem. Soc., 2007, 129, 12696–12704; (b) 24 L. S. Campbell-Verduyn, L. Mirfeizi, R. A. Dierckx,
V. O. Rodionov, S. I. Presolski, D. D. Diaz, V. V. Fokin and
M. G. Finn, J. Am. Chem. Soc., 2007, 129, 12705–12712.
P. H. Elsinga and B. L. Feringa, Chem. Commun., 2009,
2139–2141.
16 F. Wang, H. Fu, Y. Y. Jiang and Y. F. Zhao, Green Chem., 2008, 25 S. Q. Bai, L. L. Koh and T. S. A. Hor, Inorg. Chem., 2009, 48,
10, 452–456. 1207–1213.
17 S. Dıez-Gonzalez and S. P. Nolan, Angew. Chem., Int. Ed., 26 K. Tanaka, C. Kageyama and K. Fukase, Tetrahedron Lett.,
2008, 47, 8881–8884. 2007, 48, 6475–6479.
18 J. M. Collinson, J. D. E. T. Wilton-Ely and S. Dıez-Gonzalez, 27 K. B. Sharpless, W. Amberg, Y. L. Bennani, G. A. Crispino,
´
´
´
Chem. Commun., 2013, 49, 11358–11360.
19 F. Li and T. S. A. Hor, Chem.–Eur. J., 2009, 15, 10585–
10592.
J. Hartung, K. S. Jeong, H. L. Kwong, K. Morikawa,
Z. M. Wang, D. Xu and X. L. Zhang, J. Org. Chem., 1992, 57,
2768–2771.
20 F. Perez-Balderas, M. Ortega-Munoz, J. Morales-Sanfrutos, 28 J. McNulty and K. Keskar, Eur. J. Org. Chem., 2012, 5462–
F. Hernandez-Mateo, F. G. Calvo-Flores, J. A. Calvo-Asin,
5470.
64392 | RSC Adv., 2014, 4, 64388–64392
This journal is © The Royal Society of Chemistry 2014