A highly efficient copper(i) catalyst for the 1,3-dipolar cycloaddition of azides with terminal and 1-iodoalkynes in water: Regioselective synthesis of 1,4-disubstituted and 1,4,5-trisubstituted 1,2,3-triazoles

Article abstract of DOI:10.1039/c0gc00342e

A new water soluble Cu(i) complex that exhibits a versatile and high catalytic activity in the Huisgen cycloadditions of azides and terminal alkynes in aqueous media under mild conditions is the first well-defined Cu(i) catalyst that is active with 1-iodo

Full text of DOI:10.1039/c0gc00342e

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A highly efficient copper(I) catalyst for the 1,3-dipolar cycloaddition of
azides with terminal and 1-iodoalkynes in water: regioselective synthesis of
1,4-disubstituted and 1,4,5-trisubstituted 1,2,3-triazoles†‡
´
Joaqu´ın Garc´ıa-Alvarez,* Josefina D´ıez and Jose´ Gimeno
Received 20th July 2010, Accepted 4th October 2010
DOI: 10.1039/c0gc00342e
A new water soluble Cu(I) complex that exhibits a versatile
and high catalytic activity in the Huisgen cycloadditions
of azides and terminal alkynes in aqueous media under
mild conditions is the first well-defined Cu(I) catalyst
that is active with 1-iodoalkynes in water under aerobic
conditions.
addition to the reaction medium of nitrogen5,6 or phosphorous
ligands7 greatly improves the catalytic performance.8,9 Although,
most of the catalytic processes proceed either in organic solvents
or in mixtures with water (i.e. water/tBuOH), only a few
CuAAC reactions have been performed in pure water as the
reaction medium;8a,8c,8d,9 all of them, however, have used only
terminal alkynes. Despite the strong acceleration effect and
regioselectivity of many organic reactions in aqueous media,10
to the best of our knowledge, only one example of an efficient
catalytic system for the chemo- and regioselective cycloaddition
of azides with internal 1-iodoalkynes has been described to date
in an aqueous medium (see Scheme 2), namely an equimolar
mixture of CuI and TTTA (TTTA = tris((1-tert-butyl-1H-1,2,3-
triazolyl)methyl)amine).6c,11
Among the most genuine examples of “click chemistry”,1 the
copper-catalyzed Huisgen 1,3-dipolar cycloaddition of azides
and terminal alkynes (CuAAC)2 (Scheme 1) has found wide
chemical applications in many fields,3,4 rendering 1,2,3-triazoles
under mild and neutral conditions with high efficiency.
Scheme 1 The copper-catalyzed 1,3-cycloaddition reaction (CuAAC).
Scheme 2 The copper-catalyzed formation of 1,4,5-trisubstituted-
1,2,3-triazoles.
Following on from the seminal catalytic systems, generally
consisting of a Cu(I) species generated in situ from CuSO4 and
sodium ascorbate, important improvements in process efficiency
have since been achieved. In particular, it was discovered that the
Since, 5-iodo-1,2,3 triazoles12 are versatile intermediates for
further functionalization, we believed it to be of interest
to search for an alternative catalyst to avoid the use of
polyamine ligands.13 Herein, we report a novel catalyst for
Huisgen 1,3-dipolar cycloadditions in pure water based on
a PTA-iminophosphorane Cu(I) complex (3) (PTA = 1,3,5-
triaza-7-phosphaadamantane).14 This complex represents the
first example of an isolated copper(I) catalyst for the reaction of
iodoalkynes with azides in aqueous media, the addition of which
shows a remarkable activity and tolerance to functional groups,
giving 1,4,5-trisubstituted-1,2,3-triazoles chemoselectively.15
The catalyst precursor (3) is readily prepared from the reaction
of [Cu(NCCH3)4][PF6] with hydrophilic iminophosphorane 2
(Scheme 3). Ligand 2 is accessible by attaching the water
soluble aminophosphine PTA to the thiophosphoryl azide
(EtO)2P( S)N3 via a classic Staudinger-type reaction.16,17a Com-
pound 2 was fully characterized by IR and NMR spectroscopy
Departamento de Qu´ımica Orga´nica e Inorga´nica, Instituto Universitario
de Qu´ımica Organometa´lica “Enrique Moles” (Unidad Asociada al
CSIC), Facultad de Qu´ımica, Universidad de Oviedo, E-33071, Oviedo,
Spain. E-mail: garciajoaquin@uniovi.es; Fax: +34 985103446; Tel: +34
985102985
† Electronic supplementary information (ESI) available: Synthesis of
compounds 2–9, experimental procedure and crystallographic data for
7a. See DOI: 10.1039/c0gc00342e
‡ Typical procedure for the synthesis of 1,2,3-triazoles; synthesis
of diphenyl(1-(phenylthiomethyl)-1H-1,2,3-triazol-4-yl)methanol (4d):
0.0042
g (0.5 mol%) of catalyst 3 was dissolved in 2 mL of
H2O under air. 1,1-Diphenyl-2-propyn-1-ol (1 mmol, 0.208 g) and
(azidomethyl)(phenyl)sulfane (1 mmol, 0.142 mL) were added in the
presence of 0.012 mL (10 mol%) of 2,6-lutidine. The reaction was stirred
at room temperature for 4 h, after which time a yellow powder had
formed. The crude of the reaction was washed with CH2Cl2 (3 ¥ 10 mL)
and the combined organic fractions were concentrated by evaporation
to give 4d as a white solid (0.354 g, 95%).
1
(details are given in the ESI†). In particular, the 31P{ H} NMR
Typical procedure for the synthesis of 5-iodo-1,2,3-triazoles; synthesis of
5-iodo-4-phenyl-1-(phenylthiomethyl)-1H-1,2,3-triazole (7a): 0.0168 g
(2 mol%) of catalyst 3 was dissolved in 2 mL of H2O under air. 1-Iodo-
phenylacetylene (1 mmol, 0.228 g) and (azidomethyl)(phenyl)sulfane
(1 mmol, 0.142 mL) were added in the presence of 0.012 mL (10 mol%)
of 2,6-lutidine. The reaction was stirred at room temperature for 8 h,
after which time a yellow powder had formed. The crude of the reaction
was washed with CH2Cl2 (3 ¥ 10 mL) and the combined organic fractions
were concentrated by evaporation to give 7a as a white solid (0.377 g,
96%).
spectrum is very informative, showing the presence of two-well
separated doublets (2JPP = 8.9 Hz) at dP -27.92 and 62.38 ppm for
the iminophosphorane and thiophosphoryl groups, respectively.
1
The 1H and 13C{ H} NMR spectra display the expected signals
for the PTA backbone.14 Complex 3 was isolated (81%) as an
air and moisture stable white solid that is soluble in water
(219 mg mL-1)18 and behaves as a 1 : 1 electrolyte in aqueous
solution (KM = 117 X-1 cm-2 mol-1). The coordination of ligand
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Table 1 Synthesis of 1,2,3-triazoles 4–6a
Entry
R
R¢
Product Time/h Yield (%)b
1
2
3
4
5
6
7
8
Ph
n-Bu
PhSCH2
PhSCH2
4a
4b
4c
4d
4e
4f
4g
5a
5b
5c
5d
5e
5f
5g
6a
6b
6c
6d
6e
6
6
5
4
4
5
3
4
4
5
3
3
4
2
16
22
24
24
12
19
8
95
94
93
95
98
97
99
94
97
93
94
93
97
94
98
94
95
99
96
94
96
Cyclohexenyl PhSCH2
C(OH)Ph2
p-F(C6H4)
p-NC(C6H4)
CO2Et
Ph
n-Bu
PhSCH2
PhSCH2
PhSCH2
PhSCH2
PhCH2
Scheme 3 Synthesis of copper(I) complex 3.
1
2 to copper is reflected in the 31P{ H} NMR spectrum of 3 by:
9
PhCH2
(i) slight variations in the P N (Dd = 0.5 ppm) and (RO)2P
S
10
11
12
13
14
15
16
17
18
19
20
21
Cyclohexenyl PhCH2
C(OH)Ph2
p-F(C6H4)
p-NC(C6H4)
CO2Et
Ph
n-Bu
PhCH2
PhCH2
PhCH2
PhCH2
Adamantyl
Adamantyl
(Dd = 2.4 ppm) resonances with respect to those found for
2, suggesting a k-S coordination,17b,c and (ii) conversion of
the doublet signals of the P N and (RO)2P S groups in
the free ligand into two broad signals in complex 3 (see the
ESI†). Although the formation of the formally 1 : 2 adduct of
the starting reagents [Cu·2ligand][PF6] is readily deduced from
their elemental analysis, the real nature of this complex can
only be determined by single-crystal X-ray diffraction methods.
An ORTEP-type drawing of the polymeric chain of complex
3 is shown in Fig. 1, and selected bond distances and angles
are listed in the caption. The coordination sphere around the
copper consists of: (i) two S-coordinated (EtO)2P S units, as
Cyclohexenyl Adamantyl
C(OH)Ph2
p-F(C6H4)
p-NC(C6H4)
CO2Et
Adamantyl
Adamantyl
Adamantayl 6f
Adamantyl 6g
a General conditions: 3 (0.5 mol%), 2,6-lutidine (10 mol%), alkyne
(1 mmol), azide (1 mmol), 2 mL of H2O, under air, r.t. b Isolated yield.
1
suggested by the 31P{ H} NMR data, and (ii) two N-coordinated
The catalytic activity of complex 3 was first evaluated using
the cycloaddition of (azidomethyl)(phenyl)sulfane (PhSCH2N3)
and phenyl acetylene as a model reaction (Table 1, entry 1). In
a typical experiment, the reaction of the alkyne and the azide
was catalyzed in water by using a 0.5 mol% catalyst loading of
complex 3 in the presence of 2,6-lutidine to give the triazole
almost quantitatively as the sole reaction product after 6 h at
amino groups from the aminophosphine ring, displaying a
distorted tetrahedral geometry (range of bond angles from
103.02(8) [N(1)–Cu(1)–S(2)] to 114.77(9)◦ [N(5)–Cu(1)–S(1)]).
The tetracoordinated copper(I) atoms are bridged by two ligands
2
in a k -N,S head-to-tail coordination (see Fig. 1), forming
a sort of dimetala fourteen-membered ring, giving rise to a
polymeric chain. The Cu(1)–S(1) and Cu(1)–S(2) bonds are
1
˚
room temperature (as determined by GC and H NMR). The
very similar in length (2.314(1) and 2.320(1) A, respectively)
addition of an amine ligand to act as a base was crucial, as
no reaction was observed in its absence. The observed rate of
the reaction was strongly dependent on the nature of the amine
ligand. For example, the efficiency of the reaction was markedly
lowered when 2,6-lutidine was replaced by pyridine, TMEDA
(tetramethylethylenediamine), NEt3 or bipyridines such as 1,10-
phenanthroline (see Table ESI-1 in the ESI for details†). It is
also remarkable that the reaction proceeds at a higher rate in
water than in THF (6 vs. 18 h) or in neat conditions (6 vs. 9 h),
thus disclosing a new example of an accelerated organic reaction
in water.10 Catalyst 3 shows a wide applicability for the CuAAC
of a wide variety of alkynes with sulfanyl, benzyl and the bulky
adamantyl azides, leading exclusively to 1,4-disubstituted-1,2,3
triazoles in excellent yields (Table 1). Importantly, catalyst 3
shows a high tolerance to functional groups, being compatible
with the presence of alkenyl (entries 3, 10, and 17), hydroxy
(entries 4, 11 and 18), fluoride (entries 5, 12 and 19), nitrile
(entries 6, 13 and 20) and ester (entries 7, 14 and 21) groups.
In addition, it is worth noting that the high steric demand of
the adamantyl substituent does not affect the outcome of the
cycloaddition.20
and compare well with those previously reported for related
P
N–P( S)(OR)2 units coordinated to Cu(I).19
Fig. 1 ORTEP-type view of the structure of compound 3 showing
the crystallographic labelling scheme. Hydrogen atoms, ethyl groups
-
and PF6 anions have been omitted for clarity. Thermal ellipsoids
˚
are drawn at the 10% probability level. Selected bond lengths (A):
Cu(1)–S(1) = 2.314(1); Cu(1)–S(2) = 2.320(1); Cu(1)–N(1) = 2.1576(3);
Cu(1)–N(5) = 2.131(4). Selected bond angles (◦): N(5)–Cu(1)–N(1) =
117.92(11); N(5)–Cu(1)–S(1) = 114.77(9); N(1)–Cu(1)–S(1) = 103.77(8);
N(5)–Cu(1)–S(2) = 105.16(8); N(1)–Cu(1)–S(2) = 103.02(8); S(1)–Cu(1)–
S(2) = 111.71(4).
The catalytic activity of 3 was then tested in cycloaddition
reactions with 1-iodoalkynes. To our satisfaction, the reactions
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Table 2 Synthesis of 5-iodo-1,2,3-triazoles 7–9a
triazoles. (ii) Its high stability, which allows the reactions to
be performed in air and in aqueous media, precludes either
oxidation or disproportionation, which are generally associated
with most copper(I) catalysts. (iii) The presence of a free thio
moiety in the substrate does not deactivate the catalyst, a fact
generally observed in CuAAC for functionalized substrates
with donor atom groups. Since the reaction is also amenable
to low catalyst loadings and is accessible on a multi-gram
scale, the practical application of this methodology provides
a complementary synthetic tool to familiar CuAAC, providing
an important contribution to click chemistry. Further synthetic
applications of this catalytic methodology in aqueous media and
mechanistic studies to gain insight into the active intermediate
active are presently under way.
We are indebted to the Ministerio de Educacio´n y Ciencia
(MEC) of Spain (Projects CTQ2006-08485/BQU) and Con-
solider Ingenio 2010 (CSD2007-00006 and CTQ2008-00506)
for financial support. J. G.-A. thanks the MEC and the
European Social Fund for the award of a “Juan de la Cierva”
contract.
Entry
R
R¢
Product Time/h Yield (%)b
1
2
3
4
5
6
7
8
Ph
n-Bu
PhSCH2
PhSCH2
7a
7b
7c
7d
7e
7f
8
7
6
6
7
6
5
96
93
94
93
97
95
96
97
94
95
95
97
92
94
96
98
93
97
93
97
92
Cyclohexenyl PhSCH2
C(OH)Ph2
p-F(C6H4)
p-NC(C6H4)
CO2Et
Ph
n-Bu
PhSCH2
PhSCH2
PhSCH2
PhSCH2
PhCH2
7g
8a
8b
8c
8d
8e
8f
6
5
5
5
4
6
4
9
PhCH2
10
11
12
13
14
15
16
17
18
19
20
21
Cyclohexenyl PhCH2
C(OH)Ph2
p-F(C6H4)
p-NC(C6H4)
CO2Et
Ph
n-Bu
PhCH2
PhCH2
PhCH2
PhCH2
Adamantyl 9a
Adamantyl 9b
8g
17
29
27
32
27
31
11
Cyclohexenyl Adamantyl 9c
C(OH)Ph2
p-F(C6H4)
p-NC(C6H4)
CO2Et
Adamantyl 9d
Adamantyl 9e
Adamantyl 9f
Adamantyl 9g
Notes and references
1 H. C. Kolb, M. G. Finn and K. B. Sharpless, Angew. Chem., Int. Ed.,
2001, 40, 2004.
a General conditions: 3 (2 mol%), 2,6-lutidine (10 mol%), alkyne
2 (a) R. Huisgen, Proc. Chem. Soc., 1961, 357; (b) R. Huisgen, R.
Knorr, L. Moebius and G. Szeimies, Chem. Ber., 1965, 98, 4014;
(c) R. Huisgen, G. Szeimies and L. Moebius, Chem. Ber., 1967,
100, 2494; (d) 1,3-Dipolar Cycloaddition Chemistry, ed. R. Huisgen
and A. Pawda, Wiley, New York, 1984, 1–176; (e) R. Huisgen, Pure
Appl. Chem., 1989, 61, 613; (f) M. Meldal, C. Christensen and C. W.
Tornoe, J. Org. Chem., 2002, 67, 3057; (g) K. B. Sharpless, V. V. Fokin,
L. G. Green and V. V. Rostovtset, Angew. Chem., Int. Ed., 2002, 41,
2056.
3 Reviews: (a) Macromol. Rapid Commun., 2008, 29, 943; (b) Special
thematic issue: QSAR Comb. Sci., 2007, 26, 1110; (c) Special thematic
issue: Y. L. Angell and K. Burgess, Chem. Soc. Rev., 2007, 36, 1674;
(d) E. Moses and A. D. Moorhouse, Chem. Soc. Rev., 2007, 36, 1249;
(e) J.-F Lutz, Angew. Chem., Int. Ed., 2007, 46, 1018; (f) P. Wu and
V. V. Fokin, Aldrichim. Acta, 2007, 40, 7; (g) C. O. Kappe and E. Van
der Eicken, Chem. Soc. Rev., 2010, 39, 1325.
4 J. Broggi, S. D´ıez-Gonza´lez, J. L. Petersen, S. Berteina-Raboin, S. P.
Nolan and L. Agrofoglio, Synthesis, 2008, 141.
5 (a) T. R. Chan, R. Hilgraf, K. B. Sharpless and V. V. Fokin, Org.
Lett., 2004, 6, 2853; (b) W. G. Lewis, F. G. Magallon, V. V. Fokin and
M. G. Finn, J. Am. Chem. Soc., 2004, 126, 9152.
6 (a) V. O. Rodionov, S. I. Preloski, S. Gardinier, Y.-H. Lim and M. G.
Finn, J. Am. Chem. Soc., 2007, 129, 12696; (b) V. O. Rodionov, S. I.
Preloski, D. D´ıaz D´ıaz, V. V. Fokin and M. G. Finn, J. Am. Chem.
Soc., 2007, 129, 12705; (c) J. E. Hein, J. C. Tripp, L. B. Krasnova,
K. B. Sharpless and V. V. Fokin, Angew. Chem., Int. Ed., 2009, 48,
8018.
(1 mmol), azide (1 mmol), 2 mL of H2O, under air, r.t. b Isolated yield.
were catalyzed by 3 (2 mol%) at room temperature in pure water
under air, affording quantitatively and chemoselectively the
corresponding 5-iodo-1,2,3-triazoles (Table 2) in excellent yields
(92–98%). This catalytic performance improves that reported
previously, which required 5 mol% of the catalytic system
CuI–TTTA.6c No by-products of 5-H-1,2,3-triazoles or other
compounds arising from reductive dehalogenation were detected
by GC. As for terminal alkynes, the reaction tolerates a diverse
array of functional groups in 1-iodoalkynes (Table 2), including
alkenyl (entries 3, 10, and 17), hydroxy (entries 4, 11 and 18),
fluoride (entries 5, 12 and 19), nitrile (entries 6, 13 and 20) and
ester (entries 7, 14 and 21) groups. Moreover, the formation of
5-iodo-1,2,3-triazoles was unambiguouslyconfirmed byasingle-
crystal X-ray diffraction study of compound 7a (see the ESI†).21
Due to the complete chemoselectivity, straightforward work-
up/purification of the reaction, the mild reaction conditions
and the low catalyst loading, the method is highly amenable to
scaling-up, and the preparation of 7a in multi-gram quantities
is a representative example (see the ESI†).
7 F. Pe´rez-Balderas, M. Ortega-Mun˜oz, J. Morales-Sanfrutos, F.
Herna´ndez-Mateo, F. G. Calvo-Flores, J. A. Calvo-As´ın, J. Isac-
Garc´ıa and F. Santoyo-Gonza´lez, Org. Lett., 2003, 5, 1951.
8 Copper(I) complexes containing N-heterocyclic carbenes have been
described as active catalysts for triazole “click” reactions: (a) S. D´ıez-
Gonza´lez, A. Correa, L. Cavallo and S. P. Nolan, Chem.–Eur. J., 2006,
12, 7558; (b) C. Nolte, P. Mayer and B. Straub, Angew. Chem., Int. Ed.,
2007, 46, 2101; (c) S. D´ıez-Gonza´lez and S. P. Nolan, Angew. Chem.,
Int. Ed., 2008, 47, 8881; (d) S. D´ıez-Gonza´lez, E. D. Stevens and S. P.
Nolan, Chem. Commun., 2008, 4747; (e) J. Broggi, H. Kumamoto,
S. Berteina-Raboin, S. P. Nolan and L. A. Agrofoglio, Eur. J. Org.
Chem., 2009, 1880.
Conclusions
In summary, we have designed a new water soluble, air-stable
and highly efficient catalyst, 3, for CuAAC reactions and the
cycloaddition of 1-iodoalkynes in aqueous media under mild
and aerobic conditions according to “click” laws1 that displays
a broad substrate scope and functional compatibility. It is
important to note the following catalytic features: (i) Catalyst
3 is the first example of an isolated and crystallographically-
characterizedcopper(I) catalyst that is active in the cycloaddition
of 1-iodoalkynes with azides to give exclusively 5-iodo-1,2,3-
9 For Cu(I) catalysts containing N-polydentate ligands, see: (a) S.
¨
Ozc¸ubukc¸u, E. Ozkal, C. Jimeno and M. A. Perica`s, Org. Lett.,
2009, 11, 4680; (b) N. Candelon, D. Laste´roue`res, A. K. Diallo,
J. Ruiz Aranzanes, D. Astruc and J.-M. Vincent, Chem. Commun.,
2008, 741.
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10 (a) Comprehensive Organic Reactions in Aqueous Media, C. H. Li,
T.-H. Chan, Wiley, 2nd edn, 2007; (b) Organic Reactions in Water,
Principles, Strategies and Applications, ed. U. M. Lindstro¨m, Wiley-
Blackwell, 2007; (c) U. M. Lindstro¨m, Chem. Rev., 2002, 102, 2751;
(d) C.-J. Li and L. Chen, Chem. Soc. Rev., 2006, 35, 68; (e) For recent
examples of cycloaddition reactions using water as the solvent, see,
for example: Z.-Y. Yan, Y.-B. Zhao, M.-J. Fan, W.-M. Liu and Y. M.
Liang, Tetrahedron, 2005, 61, 9331; (f) H. W. Lee, F. Y. Kwong and
A. S. C. Chan, Synlett, 2008, 1553; (g) E. Coutouli-Argyropoulou, P.
Sarridis and P. Gkizis, Green Chem., 2009, 11, 1906; (h) I. Kumar, S.
Rana, J. W. Cho and C. V. Rode, Tetrahedron: Asymmetry, 2010, 21,
352.
11 One further example using the internal alkyne 3-hexyne has been
described, but no acceleration rate was observed in water (ref. 8a).
12 Although several syntheses of iodotriazoles are known, stoichio-
metric amounts of copper derivatives and reactive electrophilic
iodinating reagents are required: (a) Y. M. Wu, J. Deng, Y. Li and
Q.-Y. Chen, Synthesis, 2005, 1314; (b) L. Li, G. Zhang, A. Zhu and
L. Zhang, J. Org. Chem., 2008, 73, 3630.
15 Ruthenium-catalyzed azide–internal alkyne cycloaddition reactions
have been reported: (a) L. Zhang, X. Chen, P. Xue, H. H. Y. Sun, I. D.
Williams, K. B. Sharpless, V. V. Fokin and G. Jia, J. Am. Chem. Soc.,
2005, 127, 15998; (b) L. K. Rasmussen, B. C. Boren and V. V. Fokin,
Org. Lett., 2007, 9, 5337; (c) A. Tam, U. Arnold, M. B. Soellner and
R. T. Raines, J. Am. Chem. Soc., 2007, 129, 12670; (d) B. C. Boren, S.
Narayan, L. K. Rasmussen, L. Zhang, H. Zhao, Z. Lin, G. Jia and
V. V. Fokin, J. Am. Chem. Soc., 2008, 130, 8923.
16 H. Staudinger and J. Meyer, Helv. Chim. Acta, 1919, 2, 635.
17 (a) M. Benhammou, R. Kraemer, H. Germa, J. P. Majoral and
J. Navech, Phosphorus Sulfur Relat. Elem., 1982, 14, 105; (b) We
have previously described the synthesis of N-thiophosphorylated
iminophosphoranes complexes of Ag(I) and Ru(II): V. Cadierno, J.
´
D´ıez, J. Garc´ıa-Alvarez and J. Gimeno, Dalton Trans., 2007, 2760;
´
(c) V. Cadierno, J. D´ıez, J. Garc´ıa-Alvarez and J. Gimeno, Dalton
Trans., 2010, 39, 941.
18 This value can be compared to that found in the free ligand 2
(201 mg mL-1).
19 B. Turrin, B. Donnadieu, A.-M. Caminade and J. P. Majoral,
Z. Anorg. Allg. Chem., 2005, 631, 2881.
20 All attempts to recycle the catalytic system (even with the addition
of an extra 10 mol% of lutidine) were unsuccessful.
21 5-Iodo-1,2,3-triazole (7a) was subsequently easily functionalized by
using it in a Suzuki cross-coupling reaction with the organoboronic
acid PhB(OH)2, yielding the corresponding 1-benzyl-4,5-diphenyl-
1H-1,2,3-triazole by using the reaction conditions reported in J.
Deng, Y.-M. Wu and Q.-Y. Chen, Synthesis, 2005, 2730.
13 Cu(I) complexes bearing polyamino ligands are usually rather
reactive in air, limiting their practical interest.
14 (a) D. J. Daigle, A. B. Pepperman Jr. and S. L. Vail, J. Heterocycl.
Chem., 1974, 11, 407; (b) For recent reviews of hydrophilic ligands,
see, for example: A. D. Phillips, L. Gonsalvi, A. Romerosa, F. Vizza
and M. Peruzzini, Coord. Chem. Rev., 2004, 248, 955; (c) K. V.
Shaughnessy, Chem. Rev., 2009, 109, 643; (d) J. Bravo, S. Bolan˜o,
L. Gonsalvi and M. Peruzzini, Coord. Chem. Rev., 2010, 254, 555.
2130 | Green Chem., 2010, 12, 2127–2130
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©