Synthesis of a novel resorcin[4]arene-glucose conjugate and its catalysis of the CuAAC reaction for the synthesis of 1,4-disubstituted 1,2,3-triazoles in water

Article abstract of DOI:10.1039/c9ra00972h

The Cu(i)-catalyzed azide-alkyne cycloaddition (CuAAC) in aqueous media using resorcin[4]arene glycoconjugate (RG) is reported. The eight β-d-glucopyranoside moieties constructed on the resorcin[4]arene upper rim provide a pseudo-saccharide cavity that offers a suitable host environment for water-insoluble hydrophobic azido and/or alkyne substrates in water. The utility of RG was established as an efficient inverse phase transfer catalyst for the CuAAC in water as a green approach for the synthesis of 1,4-disubstituted 1,2,3-triazole species. The catalytic utility of RG (1 mol%) was demonstrated in a multicomponent one-pot CuAAC for various azido/alkyne substrates. The RG acts as a molecular host and a micro-reactor resulting in the 1,4-disubstituted 1,2,3-triazoles in excellent yield.

Full text of DOI:10.1039/c9ra00972h

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Synthesis of a novel resorcin[4]arene–glucose
conjugate and its catalysis of the CuAAC reaction
for the synthesis of 1,4-disubstituted 1,2,3-triazoles
in water†
Cite this: DOI: 10.1039/c9ra00972h
*
Ali A. Husain and Kirpal S. Bisht
The Cu(I)-catalyzed azide–alkyne cycloaddition (CuAAC) in aqueous media using resorcin[4]arene
glycoconjugate (RG) is reported. The eight b-D-glucopyranoside moieties constructed on the resorcin[4]
arene upper rim provide a pseudo-saccharide cavity that offers a suitable host environment for water-
insoluble hydrophobic azido and/or alkyne substrates in water. The utility of RG was established as an
efficient inverse phase transfer catalyst for the CuAAC in water as a green approach for the synthesis of
1,4-disubstituted 1,2,3-triazole species. The catalytic utility of RG (1 mol%) was demonstrated in
a multicomponent one-pot CuAAC for various azido/alkyne substrates. The RG acts as a molecular host
and a micro-reactor resulting in the 1,4-disubstituted 1,2,3-triazoles in excellent yield.
Received 5th February 2019
Accepted 5th March 2019
DOI: 10.1039/c9ra00972h
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and can be carried out in aqueous conditions. From review of
literature, it is easy to conclude that water is an appropriate
Introduction
The classical Huisgen1 cycloaddition reaction for the synthesis
of 1,2,3-triazole involves thermal 1,3-dipolar cycloaddition of
organic azides with alkynes, though in low yield and mixed
regioselectivity. Sharpless'2 and Meldal's3 research groups later
independently developed the improved procedure involving the
copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition reaction,
which is the widely studied ‘click’ reaction (Scheme 1). The
impact of the copper catalyzed azide–alkyne click reaction in
various branches of science is increasing exponentially as evi-
denced from numerous recent reviews available in the literature
since 2010.4
The three most common facile protocols for CuAAC include
(i) use of copper(I) salts (mostly in organic solvents), (ii) the
reduction of a copper(II to I), and (iii) oxidation of Cu(0 to I). Of
the three protocols described above, the method employing in
situ reduction of copper(II) salts is known to be more practical
choice as a solvent for the CuSO4/sodium ascorbate catalyzed
click protocol, which results in the formation of the triazole in
high yields and with excellent regioselectivity. However, despite
the efficiency of the CuAAC reaction, there are limitations to
using the procedure especially when the substrates are not
water-soluble. The protocol in essence requires deoxygenated
conditions in the presence of mixed aprotic organic solvents
such as THF, CH3CN, CH2Cl2, toluene, etc. and due to the
oxidative tendency of the copper(I), a higher catalyst concen-
tration throughout the reaction is needed. To stabilize the
catalyst, several phosphine-based complexes and amine-based
(bound with different heterocyclic donors) ligands have been
used for rate acceleration.5 Additionally, a number of hetero-
geneous Cu catalysts,6 including amberlyst resin-supported,7
polymer-supported,8 and zeolite-supported9 have been explored
to catalyze the triazole formation. To speed up the azide–alkyne
reaction, use of surfactants and phase transfer catalyst,10 the
microwave11 and ultrasound irradiations12 have also been
reported.13
Recently, our research group reported resorcin[4]arene cav-
itand glycoconjugates (RCGs)14 as inverse phase transfer cata-
lysts with abilities to catalyze organic reactions in aqueous
media. We also reported on the RCGs ability to catalyze the
formation of 1,4-disubstituted 1,2,3-triazoles in water without
the addition of any co-organic solvents.14 It is noteworthy to
mention that we were the rst to establish the concept of the
spatial directionality of b-D-glycopyranoside units on the
resorcin[4]arene rigid structure “cavitand”. The RCGs possesses
a unique molecular host system “pseudo-saccharide bucket”
Scheme 1 Azide–alkyne cycloaddition (AAC) reaction under different
reaction conditions.
Department of Chemistry, University of South Florida, 4202 East Fowler Avenue, CHE
205, Tampa, FL 33620, USA. E-mail: kbisht@usf.edu
† Electronic supplementary information (ESI) available: NMR spectra for new
compounds are included. See DOI: 10.1039/c9ra00972h
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Fig. 1 Resorcin[4]arene glycoconjugate (RG & RCGs14).
Fig. 2 Partial 1H-, 13C- and DEPT NMR spectra (250 and 62.5 MHz,
CDCl3) of 2.
which can encapsulate organic substrates and catalyze chemical
reactions in water.14
In this manuscript, we describe the synthesis of a resorcin[4]
arene glycoconjugate (RG) (Fig. 1) and its application as a micro-
reactor for the synthesis of 1,4-disubstituted 1,2,3-triazole
species in aqueous media via the CuAAC reaction. RG structure
consists of eight b-D-glucopyranoside moieties constructed on the
phenolic parts on the resorcin[4]arene upper rim via multiple 1,4-
disubstituted 1,2,3-triazole linkages. The eight arm resorcin[4]
arene glycoconjugate offers an enlarged exible pseudo-
saccharide cavity that can act as a molecular vessel for water-
insoluble azido and/or alkyne substrates in aqueous environment.
Scheme 3 Synthesis of 3.
Results and discussion
Synthesis of eight arm resorcin[4]arene glycoconjugate (RG)
For the synthesis of the novel RG, resorcin[4]arene 1 (ref. 14 and
15) was rst synthesized upon the acid-catalyzed cyclo-
condensation reaction of methyl resorcinol with heptanal.
Compound 1 was then treated with propargyl bromide in the
presence of potassium carbonate in reuxing acetone to achieve
the octa-propargyl resorcin[4]arene intermediate 2 (Scheme 2).
Resorcin[4]arene 2 was characterized conclusively from its
Scheme 4 Synthesis of RG.
measurement using ESI-Q-TOF HRMS: observed 1207.7034 (M +
Na)+, calculated 1207.7003 (M + Na)+.
2-Azidoethyl b-D-glucopyranoside tetraacetate (3) was
prepared following the typical procedures found in literature
(Scheme 3) and unambiguously characterized.14,16
1
NMR and spectral data. In its H-NMR spectrum, the benzylic
protons (–CH3, Ha) were found as a singlet at 2.25 ppm. The
alkyne protons (–C^CH, Hf) were observed as a triplet at
2.50 ppm (J ¼ 2.4 Hz) and the propargyl methylene protons
Octa-propargyl resorcin[4]arene 2 and azido glucopyranoside
3 were then coupled together via the CuAAC reaction. The
reaction was carried out in reuxing chloroform in presence of
CuI (10 mol%) and DIPEA (6.0 equiv.) to yield the octaacetoxy-
RG (4) in excellent yield. Global deacetylation using NaOMe
solution (0.1 M) resulted in RG in gram quantity (Scheme 4).
The structures of the RG and its octaacetoxy precursor 4 were
established from the respective 1H- and 13C-NMR data. Namely,
the absence of the alkyne protons (Hf), the emergence of the
triazole protons (1H, at 7.69 ppm) and the shi of the propargyl
protons (Hc, from 4.11 ppm to 4.50 ppm) conrmed the struc-
ture of 4 (Fig. 3). In the 1H-NMR spectra of RG (Fig. 3b), the
disappearance of the acetate protons (–OCOCH3, OAc) from the
region of 1.70–2.10 ppm was conrmatory of its structure. The
molecular weight of the products {for 4 m/z (ESI-Q-TOF):
observed 2283.8955 (M + 2Na)2+, calculated 2283.8984 (M +
0
(–OCH2C^, Hc,c ) showed as two set of double doublets with J ¼
15.3 and 2.4 Hz at 4.20 and 4.36 ppm. Its 13C-NMR spectrum
had resonances for the alkyne carbons Ce and Cf at 74.8 and
79.5 ppm, respectively, and the propargyl methylene carbons
(–OCH2C^, Cc) were at 60.3 ppm (Fig. 2). The molecular
formula (C80H96O8) of compound 2 was conrmed from its m/z
Scheme 2 Synthesis of octa-alkyne resorcin[4]arene 2.
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Table
1
CuAAC of substituted benzyl azides 1a–4a and alkyne
a
substrates 1b–4b in the presence of RG
1
Fig. 3 Partial H-NMR spectra of (a) 4 (500 MHz, CDCl3) and (b) RG
(500 MHz, DMSO-d6).
a
Reaction condition: benzyl azide derivative (1 mmol) and alkyne
substrates (1.05 mmol), Cu(II) (1 mol%), Na-L-ascorbate (3 mol%), RG
(1 mol%), water (10 mL), 80 ꢀC. b Isolated yield.
chemical structure (Fig. 4). Remarkably, the CuAAC reaction
was almost completed with more than 93% conversion only in
10 minutes when RG (1 mol%) was added but only 26%
conversion was observed in its absence (no catalyst). Obviously,
the fast CuAAC in the presence of RG indicates that it provides
a unique molecular environment that is capable of catalyzing
the CuAAC reaction efficiently.
Fig. 4 CuAAC of benzyl azide and phenyl acetylene at 80 ꢀC. RCG
catalyst structures in Fig. 1.
2Na)2+; for RG m/z (ESI-Q-TOF): observed 1611.7374 (M + 2Na)2+
,
Scoping the CuAAC in water using RG
calculated 1611.7294 (M + 2Na)2+} conrmed the respective
To scope the CuAAC reactions catalyzed by RG in aqueous
media, we have investigated coupling of substituted benzyl
azides 1a–4a with aromatic and aliphatic alkynes 1b–4b
(Table 1).
molecular formula.
Optimizing CuAAC in water catalyzed by RG
The CuAAC reactions was investigated to examine the catalytic
As recorded in Table 1, the RG catalyzed CuAAC reactions of
activity in aqueous environment. For optimization, the CuAAC a variety of substituted benzyl azides in water and all reactions
reaction of benzyl azide (1.0 mmol) with phenyl acetylene (1.05 led to the desired 1,4-disubstituted 1,2,3-triazole products (2c–
equiv.) with/without the addition of a catalyst (1 mol%) was 16c) in high yields (>90% isolated). Not surprisingly, it was
carried out (Fig. 4). The reactions were performed in the pres- determined that the reaction took longer to reach completion as
ence of copper sulfate (1 mol%) and sodium L-ascorbate the hydrophobicity of the substrate pair increased, as evidenced
(3 mol%) in 10 mL of distilled deionized water at 80 ꢀC (Fig. 4). by their clog P values (Table 1). For example, the coupling
The chemical structures and synthetic procedure for RCG between the 4-bromo benzyl azide (4a, clog P ¼ 4.13) and 1-
catalysts evaluated in Fig. 4 have been previously reported by hexyne (4b, clog P ¼ 2.51) took nearly 65 minutes to completion
our research group.14
while the reactions between propargyl alcohol (1b, clog P ¼
The coupling reaction was much slower in absence of added ꢁ0.34) and 3-methoxy benzyl azide (1a, clog P ¼ 3.18) was
RCG catalyst and in presence of compound 14 (Fig. 1),14 which completed in 15 minutes.
lacks the spatial directionality of the RCGs. While the RCGs
To further evaluate the effectiveness of the RG as a catalyst in
catalyzed the CuAAC reaction between benzyl azide and phenyl CuAAC of hydrophobic substrates, we carried out the coupling
acetylene, there were signicant differences in substrate of phenyl acetylene (3b) with alkylated ortho-azido phenols (5a–
conversion to suggest a dependence of catalytic activity on 9a) of increasing steric bulk and clog P values from 2.55–4.95. A
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Table 2 CuAAC of o-azido phenol derivatives (5a–9a) with phenyl Table 3 Di-CuAAC of di-alkynes 5b–7b with benzyl azide derivatives
a
a,b
acetylene 1b with/without RG
1a–4a in water in the presence of RG
Catalyst
(% yield)b
Entry Azide (clog P value) Product
Time (min) None RG
1
2
5a R ¼ OH (2.55)
6a R ¼ OMe (3.18)
30
30
64
22
96
97
3
4
7a R ¼ OEt (3.71)
8a R ¼ OBu (4.77)
30
30
16
12
98
98
a
Reaction condition: di-alkyne derivative (1 mmol) and azides (2.1
mmol), Cu(II) (1 mol%), Na-L-ascorbate (3 mol%), RG (1 mol%), water
b
(10 mL), 45 min, 80 ꢀC. Isolated yields.
5
9a R ¼ OBn (4.95)
30
<10
99
been alternative methods employed for their in situ synthesis.
The azides can be prepared from their corresponding halides
upon the addition of sodium azide. Hence, a multicomponent
one-pot CuAAC reaction between in situ generated azide from its
corresponding precursor and alkyne is highly desirable.18
We have investigated the multicomponent one-pot CuAAC
reactions of phenyl acetylene 3b with the aryl bromides and
sodium azide catalyzed by the RG. Complete conversion were
accomplished within 25–55 minutes even for a bulkier aryl
system (naphthyl) to achieve the 1,2,3-triazoles in excellent
isolated yield (90–96%) (Table 4, entries 1–5). In addition,
reaction with a-bromo acetophenones (entries 6 and 7), a-bro-
moesters (entry 8) and ally bromide (entry 9) led to quantitative
conversion within 25–30 min to the desired triazoles 35c–37c in
91–95% isolated yield. However, the multi component CuAAC
failed when saturated aliphatic bromides were used as
substrates, i.e., butyl, heptyl and dodecyl bromides (entries 10–
12). We suspect the p–p interactions play an important role in
the encapsulation, in water, of the substrates molecule in the
hydrophobic cavity of the RG and the lack of these interactions
in the aliphatic alkyl bromide does not allow their encapsula-
tion in the RG cavity and hence no observed reaction.
a
Reaction condition: azidophenol derivative (1 mmol) and phenyl
acetylene 1b (1.05 mmol), Cu(II) (1 mol%), Na-L-ascorbate (3 mol%),
cat. (1 mol%), water (10 mL), 80 ꢀC. b Isolated yield.
comparative study of the CuAAC reaction in absence and pres-
ence of the RG is shown in Table 2.
As expected, the coupling of o-azido phenols (5a, clog P ¼
2.44) with phenyl acetylene 1b catalyzed by RG resulted in tri-
azole 17c in 96% yield and even without added catalyst the yield
was 64% due to its higher hydrophilicity (entry 1). However,
replacing the hydroxyl functionality with alkoxy groups, i.e.
–OMe, –OEt, –OBu, –OPh of progressively higher bulk, hydro-
phobicity, and clog P value led to much slower reactions in
absence of the RG. The reactions catalyzed by the RG resulted in
near quantitative conversion in about 30 minutes irrespective of
the bulk or hydrophobicity of the azide substrates, attesting to
its effectiveness as a catalyst in the CuAAC reactions in water
even for the much bulkier and hydrophobic substrates.
Di-CuAAC reactions in water using RG
Simultaneous multiple CuAAC reactions have found interest in
synthesis of the polymers and dendrimers and the need for
efficient catalyst that can catalyze reactions in water has never
been greater.17 We have therefore investigated RG for catalyzing
the di-CuAAC reactions in water of di-propargyl benzene deriv-
atives 5b–7b with substituted benzyl azides 1a–4a (Table 3).
Interestingly, the di-CuAAC reaction were completed within
45 min resulting in the desired bis-1,2,3-triazole products 22c–
33c in gram quantities.
Inclusion complex of RG with benzyl azide (2a) and phenyl
acetylene (3b) in D2O
We set out to probe the encapsulation of the substrates by the RG.
Specically, we have studied the encapsulation of benzyl azide
and phenyl acetylene by RG using NMR. The 1H-NMR spectra of
the guest (2a & 3b) were recorded in the presence of the host (RG)
in a 1 : 1 molar ratio for 2 mM concentrated solution in D2O at
25 ꢀC (Fig. 5). In the 1H-NMR, the aromatic protons (H2, H3, H4)
in 2a were shied up eld from 7.35 ppm to 6.90 ppm upon
Multicomponent one-pot CuAAC reactions in water
Organic azides are not always considered safe for handling addition of the RG (Fig. 5a). Similarly, the aromatic protons (H6,
because of their toxic and shock sensitive nature and there have H7, H8) in 3b were shied upeld from 7.35 and 7.45 ppm to 6.98
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Table 4 Multicomponent one-pot CuAAC of phenyl acetylene, aryl/
a
alkyl bromides and sodium azides in the presence of RG
Entry
1
Product
Time (min)
25
Yieldb (%)
92
1
Fig. 5 Partial H-NMR spectra (250 MHz, D2O, 2 mM) at 25 ꢀC of (a)
benzyl azide and benzyl azide + RG (1 : 1); (b) phenylacetylene and
phenylacetylene + RG (1 : 1).
2
3
4
5
30
30
50
55
94
96
90
91
6
7
30
30
92
95
8
25
93
9
25
91
10
11
200
200
<10
N/A
12
200
N/A
Fig. 6 Proposed mechanism for the CuAAC in aqueous media cata-
lyzed by RG.
a
Reaction condition: phenyl acetylene (1 mmol), bromide derivative
(1.05 mmol) and sodium azide (1.1 mmol), RG (1 mol%), water (10
b
mL), 80 ꢀC. Isolated yields, N/A ¼ not isolated.
Conclusion
In conclusion, a new resorcinarene sugar conjugate (RG) is re-
ported. It was determined that RG is an efficient catalyst for the
and 7.15 ppm, respectively upon addition of RG (Fig. 5b). The CuAAC reaction in water at only 1 mol%. Based upon the reaction
shielding of the guest 1H NMR resonances upon addition of RG catalysis and the encapsulation observed, RG catalytic mecha-
indicated their encapsulation in the RG cavity. The encapsulation nism, we believe, begins with inclusion of the alkyne and azide
of the substrates in the RG cavity may explain the catalytic activity substrates resulting in the copper–triazole complex followed by
of the RG. In addition, the observation that the CuAAC reactions protonation and dissociation to the desired 1,4-di substituted
of the aromatic and p bond containing azides were accelerated in 1,2,3-triazole. RG was found to catalyze the coupling of the
the presence of RG (Table 4), the encapsulation of the guest most alkyne/azide pair and also of the multicomponent alkyl bromide/
likely involves p–p host–guest interactions.
sodium azide/alkyne to the 1,4-disubstituted 1,2,3-triazole prod-
ucts in excellent yield within short period of time in water.
Proposed mechanism for the CuAAC using RG
Based upon the reaction catalysed and the encapsulation
observed, the proposed mechanism for the CuAAC reaction
catalyzed by RG may proceed via step shown in Fig. 6. Starting
Experimental section
General
with inclusion of the alkyne and azide substrates in the pseudo-b-D- 1H- and 13C-NMR spectra were recorded on a Bruker DRX-250,
glucopyranoside cavity of RG. The closed proximity of the alkyne a Inova-400 and a DD-500 spectrometers. Sample concentra-
and azide in the presence of Cu(I) catalyst accelerate the cycload- tions were about 10% (w/v) in CDCl3 or DMSO-d6 and the J
dition process resulting in the copper–triazole complex followed by values are given in Hz. The mass spectral analyses were per-
protonation and dissociation of the desired 1,4-di substituted 1,2,3- formed on an Aligent Technologies 6540 UHD Accurate-Mass Q-
triazole (Fig. 6).19 The binding of the Cu(I) to the multiple triazoles in TOF LC/MS. The clog P values were calculated using ChemDraw
the RG may also facilitate the coupling reaction inside the RG cavity. Professional, Version 15.1.0.144.
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1H NMR (250 MHz, DMSO-d6) d ¼ 0.79 (t, J ¼ 6.6 Hz, 12H),
1.14–1.36 (m, 32H), 2.27 (bm, 8H), 2.27 (bs, 12H), 2.98 (t, J ¼
8.1 Hz, 8H), 3.05 (ddd, J ¼ 3.3, 9.2, 18.3 Hz, 8H), 3.11–3.19 (m,
16H), 3.41–3.47 (m, 8H), 3.67 (d, J ¼ 10.6 Hz, 8H), 3.89 (bs, 8H),
4.07 (bs, 8H), 4.24 (d, J ¼ 7.0 Hz, 8H), 4.53 (bs, 24H), 4.63 (bs,
16H), 7.93–8.39 (bs, 12H); 13C NMR (62.5 MHz, DMSO-d6) d ¼
11.1, 14.0, 22.2, 28.1, 29.1, 31.4, 34.8, 37.8, 49.6, 61.1, 65.4,
67.3, 70.0, 73.3, 76.6, 77.0, 102.9, 123.8, 124.3, 124.7, 142.9,
143.1; HRMS [M + 2Na]2+ calcd for C144H216N24O56Na2
1611.7294, found 1611.7374.
Materials and reagents
All reagents were used with no further purication unless
otherwise specied. 2-Methyl resorcinol (98%) was purchased
from Acros Organics Chemical Company. Octa-hydroxy resorcin
[4]arene (1) and 2-azidoethyl b-D-glucopyranoside tetraacetate
(3) were synthesized following synthetic procedures reported
previously.14–16
Octa-propargyl resorcin[4]arene (2). Compound 1 (5 g, 5.7
mmol) was dissolved in 110 mL acetone. Potassium carbonate
(6.26 g, 45 mmol) was added into the solution and allowed to
stir for 10 min at room temperature. Propargyl bromide (8.1 mL,
90 mmol) was then added and the reaction mixture was reuxed
overnight. Aer completion, the reaction mixture was cooled at
room temperature and the salt was ltered out followed by the
concentration of acetone. The product was puried by column
chromatography as a pale yellow solid using 10% EA/hexane
yielding 6.04 g (90%) yield. 1H NMR (250 MHz, CDCl3) d ¼
0.85 (t, J ¼ 6.5 Hz, 12H), 1.25–1.36 (m, 16H), 1.36 (m, 16H), 1.82–
1.94 (m, 8H), 2.25 (s, 12H), 2.50 (t, J ¼ 2.4 Hz, 4H), 4.11 (d, J ¼
15.3 Hz, 8H), 4.25 (d, J ¼ 15.3 Hz, 8H), 4.45 (t, J ¼ 7.1 Hz, 4H),
6.39 (s, 4H); 13C NMR (62.5 MHz, CDCl3) d ¼ 11.1, 14.0, 22.7,
28.5, 29.5, 31.9, 34.9, 38.3, 60.3, 74.8, 79.5, 124.3, 124.3, 133.9,
154.0; HRMS [M + Na]+ calcd for C80H96O8Na 1207.7003, found
1207.7034.
Typical procedure for screening and scoping the CuAAC in
water catalyzed by RG
Aryl azide (1 mmol) and aryl/alkyl alkyne (1.05 equiv.) were
added to a solution of copper(II) sulfate pentahydrates, Na-
ascorbate and RG (1 : 3 : 1 mol%) in 10 mL de-ionized
ꢀ
distilled water. The reaction mixture was then heated to 80 C
for 15–65 min. Aer completion, the solid reaction product was
ltered off, dried, and weighed to calculate the isolated yield.
When the product was not solid (10c and 11c), the reaction
mixture was extracted with DCM (2 ꢂ 5 mL). The combined
organic layer was collected and dried over MgSO4. DCM was
then removed using a rotary evaporator and 1H-NMR was taken
in CDCl3 or DMSO-d6.
Octa-sugar acetate resorcin[4]arene (6). Compound 2 (1 g,
0.84 mmol) was dissolved in 30 mL chloroform. CuI (32 mg,
0.17 mmol) and DIPEA (0.88 mL, 5 mmol) were then added to
the solution. Sugar azide 3 (5.6 g, 13.5 mmol) was then added
to the solution. The reaction mixture was then reuxed over-
night. Aer completion, the reaction was worked up using
ammonium hydroxide solution and the organic phase was
extracted and dried using Na2SO4. Chloroform was evaporated
and the product was puried by column chromatography
using 5% MeOH/DCM in order to separate the product from
the excess sugar azide. The product was collected as yellow oil
that solidied slowly to pale yellow solid in 3.48 g (91%) yield.
1H NMR (500 MHz, CDCl3) d ¼ 0.80 (t, J ¼ 6.6 Hz, 12H), 1.15–
1.35 (m, 32H), 1.78–1.85 (bs, 12H), 1.88 (s, 12H), 1.93 (s, 12H),
1.98 (s, 24H), 2.04 (s, 12H), 2.04 (s, 12H), 2.07–2.16 (bs, 12H),
2.37 (bm, 8H), 3.71–3.77 (m, 8H), 3.91–4.00 (m, 8H), 4.06–4.14
(m, 8H), 4.22 (t, J ¼ 2.9 Hz, 8H), 4.25 (dd, J ¼ 2.9, 4.4 Hz, 4H),
4.49 (bs, 16H), 4.55 (d, J ¼ 8.1 Hz, 8H), 4.58 (t, J ¼ 8.1 Hz, 4H),
4.93 (t, J ¼ 7.7 Hz, 8H), 5.03 (ddd, J ¼ 3.3, 9.5, 13.2 Hz, 8H), 5.13
(q, J ¼ 9.9, 19.1 Hz, 8H), 7.69 (s, 8H); 13C NMR (125 MHz,
CDCl3) d ¼ 10.7, 14.0, 20.3, 20.4, 20.4, 20.6, 22.7, 28.6, 29.6,
31.8, 35.2, 38.0, 49.5, 61.6, 65.9, 67.5, 68.1, 70.7, 71.7, 72.4,
100.4, 123.7, 124.1, 124.2, 144.3, 144.5, 169.3, 170.0, 170.5;
HRMS [M + 2Na]2+ calcd for C208H280N24O88Na2 2283.8984,
found 2283.8955.
Typical procedure for three component one-pot CuAAC
catalyzed by RG
Phenyl acetylene 1b (1 mmol) and aryl/alkyl bromides (1.05
equiv.) with sodium azide (1.1 equiv) were added to a solution of
copper(II) sulfate pentahydrates, Na-ascorbate and RG
(1 : 3 : 1 mol%) in 10 mL de-ionized distilled water. The reac-
tion mixture was then heated to 80 ꢀC for 20–55 min. Aer
completion, the solid reaction product was ltered off, dried,
and weighed to calculate the isolated yield. When the conver-
sion was low (entries 10–12, Table 4), the reaction mixture was
extracted with DCM (2 ꢂ 5 mL). The combined organic layer was
collected and dried over MgSO4. The solvent was then removed
1
using a rotary evaporator and H-NMR was taken in CDCl3.
4-((Benzyloxy)methyl)-1-(2-methylbenzyl)-1H-1,2,3-triazole
1
(6c). White solid (98%); H NMR (400 MHz, CDCl3) d 2.25 (s,
3H), 4.55 (s, 2H), 4.62 (s, 2H), 5.48 (s, 2H), 7.11–7.13 (m, 1H),
7.15–7.21 (m, 2H), 7.24 (d, J ¼ 7.0 Hz, 2H), 7.29 (m, 4H), 7.33 (s,
1H); 13C NMR (100 MHz, CDCl3) d 18.9, 52.2, 63.6, 72.4, 126.5,
127.7, 127.8, 128.3, 129.0, 129.4, 130.9, 132.3, 136.8, 137.6.
4-Butyl-1-(2-methylbenzyl)-1H-1,2,3-triazole (7c). White solid
(90%); 1H NMR (400 MHz, CDCl3) d 0.87 (t, J ¼ 7 Hz, 3H), 1.27–
1.36 (m, 2H), 1.54–1.61 (m, 2H), 2.23 (s, 3H), 2.64 (t, J ¼ 7.8 Hz,
2H), 5.45 (s, 2H), 7.15–7.18 (m, 2H) 7.22–7.26 (m, 1H); 13C NMR
(100 MHz, CDCl3) d 13.7, 18.9, 22.2, 25.3, 31.4, 51.0, 120.2,
126.5, 128.8, 129.1, 130.8, 132.7, 136.8.
4-((Benzyloxy)methyl)-1-(3-methoxybenzyl)-1H-1,2,3-triazole
(10c). Brown oil (94%); 1H NMR (400 MHz, CDCl3) d 3.71 (s, 2H),
4.54 (s, 2H), 4.62 (s, 2H), 5.40 (s, 2H), 6.77 (s, 1H), 6.79–6.85 (m,
2H), 7.20–7.26 (m, 2H), 7.28–7.30 (m, 3H), 7.47 (s, 1H); 13C NMR
(100 MHz, CDCl3) d 53.6, 54.9, 63.3, 72.1, 113.4, 113.7, 119.9,
122.3, 127.4, 127.5, 128.0, 135.8, 137.5, 145.1, 159.7.
Resorcin[4]arene glycoconjugate (RG). Acetylated sugar
resorcin[4]arene 6 (1 g) was dissolved in (0.1 M) sodium
methoxide solution. The reaction mixture was allowed to stir
at room temperature for 4 h. Aer completion, the reaction
mixture was neutralized using Dowex 50W-X8. This was fol-
lowed by ltration and concentration of methanol with no
further purication to afford RG as a pale yellow solid in 92%;
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4-Butyl-1-(3-methoxybenzyl)-1H-1,2,3-triazole (11c). Brown
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13C NMR (100 MHz, CDCl3) d 18.9, 52.3, 62.0, 102.1, 107.5,
126.6, 129.1, 129.4, 129.9, 130.9, 132.3, 136.8, 159.3.
1,3-Bis((1-(3-methoxybenzyl)-1H-1,2,3-triazol-4-yl)methoxy)
benzene (28c). White solid (91%); H NMR (400 MHz, CDCl3)
d 3.73 (s, 6H), 5.11 (s, 4H), 5.46 (s, 4H), 6.54 (m, 3H), 6.76 (s, 2H),
6.83 (t, J ¼ 7.5 Hz, 1H), 7.25 (m, 2H) 7.58 (bs, 2H); 13C NMR (100
MHz, CDCl3) d 54.1, 55.2, 61.8, 101.9, 107.5, 113.6, 114.1, 120.1,
129.9, 130.1, 135.8, 159.3, 159.9.
1,3-Bis((1-(4-bromobenzyl)-1H-1,2,3-triazol-4-yl)methoxy)
benzene (29c). Yellow solid (96%); H NMR (400 MHz, DMSO-
d6) d 5.07 (s, 4H), 5.56 (s, 4H), 6.57 (d, J ¼ 2.3 Hz, 1H), 6.59 (d, J ¼
2.3 Hz, 1H), 6.67 (t, J ¼ 2.5 Hz, 1H), 7.14 (t, J ¼ 7.9 Hz, 1H), 7.22–
7.26 (m, 4H), 7.51–7.55 (m, 4H), 8.28 (s, 2H); 13C NMR (100 MHz,
DMSO-d6) d 52.5, 61.5, 102.1, 107.8, 121.9, 125.2, 130.6, 132.1,
135.8, 143.5, 159.7.
oil (91%) yield; 1H NMR (400 MHz, CDCl3) d 0.78 (t, J ¼ 7.3 Hz,
3H), 1.19–1.28 (m, 2H), 1.46–1.54 (m, 2H), 2.56 (t, J ¼ 7.7 Hz,
2H), 3.61 (s, 3H), 5.31 (s, 2H), 6.66 (s, 1H), 6.71 (t, J ¼ 9.0 Hz,
2H), 7.12 (t, J ¼ 7.9 Hz, 1H), 7.19 (s, 1H); 13C NMR (100 MHz,
CDCl3) d 13.3, 21.8, 24.9, 31.0, 53.2, 54.7, 113.0, 113.4, 119.6,
120.3, 129.5, 136.2, 148.2, 159.5.
1
1-(2-Ethoxyphenyl)-4-phenyl-1H-1,2,3-triazole (19c). White
solid (98%); 1H NMR (400 MHz, CDCl3) d 1.37 (t, J ¼ 6.9 Hz, 3H),
4.08 (q, J ¼ 6.9 Hz, 2H), 7.04 (m, 2H), 7.34 (m, 2H), 7.43 (t, J ¼
7.5 Hz, 2H), 7.81 (d, J ¼ 7.8 Hz, 1H), 7.89 (d, J ¼ 7.6 Hz, 2H), 8.38
(s, 1H); 13C NMR (100 MHz, CDCl3) d 14.5, 64.6, 113.2, 121.0,
121.6, 125.0, 125.6, 126.3, 127.9, 128.7, 129.8, 130.7, 147.0,
150.1.
1
1-(2-Butoxyphenyl)-4-phenyl-1H-1,2,3-triazole (20c). White
solid (98%); 1H NMR (400 MHz, CDCl3) d 0.93 (t, J ¼ 6.8 Hz, 3H),
1.40–1.47 (m, 2H), 1.72–1.78 (m, 2H), 4.05 (t, J ¼ 6.3 Hz, 2H),
7.08 (t, J ¼ 8.9 Hz, 2H), 7.32–7.39 (m, 2H), 7.44 (t, J ¼ 8.0 Hz, 2H),
1,4-Bis((1-benzyl-1H-1,2,3-triazol-4-yl)methoxy)
benzene
1
(30c). Yellow solid (92%); H NMR (400 MHz, CDCl3) d 5.06 (s,
4H), 5.60 (s, 4H), 6.95 (s, 4H), 7.30 (m, 2H), 7.32–7.33 (m, 3H),
7.34 (d, J ¼ 1.8 Hz, 1H), 7.35–7.36 (m, 2H), 7.37–7.40 (m, 2H),
8.25 (s, 2H); 13C NMR (100 MHz, CDCl3) d 52.8, 61.6, 115.6,
124.5, 127.9, 128.1, 128.73, 135.9, 143.2, 152.3.
7.83 (d, J ¼ 7.8 Hz, 1H) 7.88 (d, J ¼ 8.1 Hz, 2H), 8.36 (s, 1H); 13
C
NMR (100 MHz, CDCl3) d 13.7, 19.2, 31.0, 68.7, 113.2, 121.0,
121.7, 125.2, 125.7, 126.4, 128.0, 128.8, 129.9, 130.7, 147.0,
150.4.
1,4-Bis((1-(2-methylbenzyl)-1H-1,2,3-triazol-4-yl)methoxy)
benzene (31c). White solid (93%); H NMR (400 MHz, CDCl3)
1
1,2-Bis((1-benzyl-1H-1,2,3-triazol-4-yl)methoxy)
benzene
1
d 2.24 (s, 6H), 5.06 (s, 4H), 5.49 (s, 4H), 6.83 (s, 4H), 7.10–7.11
(22c). White solid (95%); H NMR (400 MHz, CDCl3) d 5.15 (s,
4H), 5.44 (s, 4H), 6.85–6.90 (m, 2H), 6.95–7.00 (m, 2H), 7.19 (d, J
¼ 1.9 Hz, 2H), 7.20 (d, J ¼ 3.8 Hz, 2H), 7.30 (d, J ¼ 1.9 Hz, 3H),
7.31 (d, J ¼ 1.7 Hz, 2H), 7.58 (s, 2H); 13C NMR (100 MHz, CDCl3)
d 54.1, 63.5, 115.7, 122.2, 128.0, 128.7, 129.0, 134.5, 148.4.
1,2-Bis((1-(2-methylbenzyl)-1H-1,2,3-triazol-4-yl)methoxy)
(m, 2H), 7.16–7.19 (m, 4H), 7.23–7.27 (m, 2H), 7.41 (bs, 2H); 13
C
NMR (100 MHz, CDCl3) d 18.9, 52.4, 62.6, 115.8, 126.6, 129.1,
129.3, 130.9, 132.3, 136.8, 152.7.
1,4-Bis((1-(3-methoxybenzyl)-1H-1,2,3-triazol-4-yl)methoxy)
benzene (32c). White solid (92%); H NMR (400 MHz, CDCl3)
d 3.74 (s, 6H), 5.09 (bs, 4H), 5.46 (s, 4H), 6.75 (s, 2H), 6.81–6.86
(m, 8H), 7.24 (m, 2H), 7.67 (bs, 2H); 13C NMR (100 MHz, CDCl3)
d 54.3, 55.2, 62.4, 113.6, 114.1, 115.7, 120.1, 130.0, 135.7, 152.6,
159.9.
1,4-Bis((1-(4-bromobenzyl)-1H-1,2,3-triazol-4-yl)methoxy)
benzene (33c). Yellow solid (92%); H NMR (400 MHz, DMSO-
d6) d 5.07 (s, 4H), 5.60 (s, 4H), 6.95 (s, 4H), 7.26 (d, J ¼ 8.6 Hz,
4H), 7.57 (d, J ¼ 8.6 Hz, 4H), 8.26 (s, 2H); 13C NMR (100 MHz,
DMSO-d6) d 52.1, 61.5, 115.6, 121.4, 124.6, 130.2, 131.7, 135.4,
143.3, 152.3.
1-Phenyl-2-(4-phenyl-1H-1,2,3-triazol-1-yl)ethan-1-one (35c).
Pale yellow solid (92%) yield; 1H NMR (400 MHz, DMSO-d6)
d 6.26 (s, 2H), 7.35 (m, 1H), 7.47 (t, J ¼ 7.5 Hz, 2H), 7.63 (t, J ¼
7.5 Hz, 2H), 7.75 (m, 1H), 7.87 (d, J ¼ 7.6 Hz, 2H), 8.09 (d, J ¼
7.8 Hz, 2H), 8.52 (s, 1H); 13C NMR (100 MHz, DMSO-d6) d 56.0,
123.0, 125.2, 128.2, 127.9, 128.2, 128.9, 130.7, 134.3, 146.3,
192.2.
1
1
benzene (23c). White solid (94%); H NMR (400 MHz, CDCl3)
d 2.21 (s, 6H), 5.12 (s, 4H), 5.43 (s, 4H), 6.83–6.87 (m, 2H), 6.93–
6.98 (m, 2H), 7.03 (d, J ¼ 7.6 Hz, 2H), 7.11–7.16 (m, 4H), 7.20–
7.24 (m, 2H), 7.47 (bs, 2H); 13C NMR (100 MHz, CDCl3) d 18.8,
63.4, 115.6, 122.0, 126.4, 128.9, 129.1, 130.8, 132.4, 136.6, 148.3.
1,2-Bis((1-(3-methoxybenzyl)-1H-1,2,3-triazol-4-yl)methoxy)
1
1
benzene (24c). White solid (94%); H NMR (400 MHz, CDCl3)
d 3.72 (s, 6H), 5.12 (s, 4H), 5.41 (s, 4H), 6.74 (s, 2H), 6.78 (m, 4H),
6.88 (bs, 2H), 6.98 (bs, 4H), 7.22 (t, J ¼ 8.4 Hz, 2H), 7.71 (bs, 2H);
13C NMR (100 MHz, CDCl3) d 54.3, 55.1, 63.5, 113.5, 113.9,
115.4, 120.1, 121.9, 129.9, 135.7, 148.2, 159.7.
1,2-Bis((1-(4-bromobenzyl)-1H-1,2,3-triazol-4-yl)methoxy)
1
benzene (25c). Yellow solid (96%); H NMR (400 MHz, CDCl3)
d 5.16 (s, 4H), 5.45 (s, 4H), 6.90–6.93 (m, 2H), 6.99–7.02 (m, 2H),
7.09 (d, J ¼ 8.7 Hz, 4H), 7.44 (d, J ¼ 7.7 Hz, 4H), 7.70 (bs, 2H); 13
C
NMR (100 MHz, CDCl3) d 53.5, 115.6, 122.2, 122.7, 129.6, 132.1,
133.5, 148.4.
1-(4-Methoxyphenyl)-2-(4-phenyl-1H-1,2,3-triazol-1-yl)ethan-
1-one (36c). Pale yellow solid (95%) yield; H NMR (400 MHz,
CDCl3) d 3.84 (s, 3H), 5.77 (s, 2H), 6.93 (d, J ¼ 6.9 Hz, 2H), 7.28 (t,
J ¼ 7.3 Hz, 1H), 7.37 (t, J ¼ 7.8 Hz, 2H), 7.90 (s, 1H), 7.92 (d, J ¼
7.8 Hz, 2H); 13C NMR (100 MHz, CDCl3) d 55.2, 114.4, 125.8,
126.9, 128.8, 130.6, 164.6, 188.6.
1,3-Bis((1-benzyl-1H-1,2,3-triazol-4-yl)methoxy)
benzene
1
(26c). Yellow solid (94%) yield; 1H NMR (400 MHz, CDCl3) d 5.11
(s, 4H), 5.61 (s, 4H), 6.61 (d, J ¼ 2.2 Hz, 1H), 6.63 (d, J ¼ 2.2 Hz,
1H), 6.71 (t, J ¼ 2.3 Hz, 1H), 7.18 (t, J ¼ 8.2 Hz, 1H), 7.30–7.40 (m,
10H), 8.28 (s, 2H);13C NMR (100 MHz, CDCl3) d 52.8, 61.1, 101.6,
107.3, 124.6, 127.9, 128.1, 128.7, 135.9, 159.2.
1,3-Bis((1-(2-methylbenzyl)-1H-1,2,3-triazol-4-yl)methoxy)
1
benzene (27c). White solid (92%); H NMR (400 MHz, CDCl3)
d 2.24 (s, 6H), 5.08 (s, 4H), 5.49 (4H), 6.52–6.55 (m, 3H), 7.09–
7.13 (m, 3H), 7.16–7.20 (m, 4H), 7.23–7.27 (m, 2H), 7.40 (s, 2H);
Conflicts of interest
There are no conicts to declare.
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2007, 129, 12696–12704; V. O. Rodionov, S. I. Presolski,
D. D. Diaz, V. V. Fokin and M. G. Finn, J. Am. Chem. Soc.,
2007, 129, 12705; Q. Wang, T. R. Chan, R. Hilgraf,
V. V. Fokin, K. B. Sharpless and M. G. Finn, J. Am. Chem.
Soc., 2003, 125, 3192–3193.
6 N. Sun, Z. Yu, H. Yi, X. Zhu, L. Jin, B. Hu, Z. Shen and X. Hu,
New J. Chem., 2018, 42, 1612; S. Chassaing, V. Beneteau and
P. Pale, Catal. Sci. Technol., 2016, 6, 923–957; J. Albadi and
M. Keshavarz, Synth. Commun., 2013, 43, 2019–2030.
7 C. Girard, E. Onen, M. Aufort, S. Beauviere, E. Samson and
J. Herscovici, Org. Lett., 2006, 8, 1689–1693.
Acknowledgements
We are grateful to the Department of Chemistry and the
Department of Sponsored research at the University of South
Florida. The authors acknowledge the support of the Depart-
ment of Chemistry NMR and Peptide core facilities directors, Dr
Edwin Rivera and Dr Mohanraja Kumar, in acquisition of the
NMR and HRMS spectral data.
Notes and references
1 R. Huisgen, G. Szeimies and L. Mobius, Chem. Ber., 1967,
100, 2494–2507.
8 U. Sirion, Y. J. Bae, B. S. Lee and D. Y. Chi, Synlett, 2008, 15,
2326–2330.
2 V. V. Rostovtsev, L. G. Green, V. V. Folkin and K. B. Sharpless,
Angew. Chem., Int. Ed., 2002, 41, 2596–2599.
3 C. W. TornØe, C. Christensen and M. Meldal, J. Org. Chem.,
2002, 67, 3057–3064.
9 C. Spiteri and J. E. Moses, Angew. Chem., Int. Ed., 2010, 49,
31–33; S. Chassaing, M. Kumarraja, A. S. S. Sido, P. Pale
and J. Sommer, Org. Lett., 2007, 9, 883–886.
10 E. Tasca, G. La Sorella, L. Sperni, G. Strukul and A. Scarso,
Green Chem., 2015, 17, 1414; J.-A. Shin, Y.-G. Lim and
K.-H. Lee, J. Org. Chem., 2012, 77, 4117; J.-A. Shin,
S.-J. Oh, H.-Y. Lee and Y.-G. Lim, Catal. Sci. Technol.,
2017, 7, 2450.
11 A. D. Moorhouse and J. E. Moses, Synlett, 2008, 14, 2089–
2092; P. Appukkuttan, W. Dehaen, V. V. Fokin and E. Van
der Eycken, Org. Lett., 2004, 6, 4223–4225.
12 G. Cravotto, V. V. Fokin, D. Garella, A. Binello, L. Boffa and
A. Barge, J. Comb. Chem., 2010, 12, 13–15; P. Cintas,
K. Martina, B. Robaldo, D. Garella, L. Boffa and
G. Cravotto, Collect. Czech. Chem. Commun., 2007, 72,
1014–1024.
4 Selected reviews: C. J. Pickens, S. N. Johnson,
M. M. Pressnall, M. A. Leon and C. J. Berkland,
Bioconjugate Chem., 2018, 29, 686–701; A. D. Pehere,
X. Zhang and A. D. Abell, Aust. J. Chem., 2017, 70, 138–
151; V. K. Tiwari, B. B. Mishra, K. B. Mishra, N. Mishra,
A. S. Singh and X. Chen, Chem. Rev., 2016, 116, 3086–
3240; C. Wang, D. Ikhlef, S. Kahlal, J.-Y. Saillard and
D. Astruc, Coord. Chem. Rev., 2016, 316, 1; X. Wang,
B. Huang, X. Liu and P. Zhan, Drug Discovery Today, 2016,
21, 118; M. S. Singh, S. Chowdhury and S. Koley,
Tetrahedron, 2016, 72, 5257–5283; M. Arseneault, C. Wafer
and J. F. Morin, Molecules, 2015, 20, 9263–9294;
P. Thirumurugan, D. Matosiuk and K. Jozwiak, Chem.
Rev., 2013, 113, 4905–4979; M. V. Walter and M. Malkoch,
Chem. Soc. Rev., 2012, 41, 4593; L. Liang and D. Astruc,
Coord. Chem. Rev., 2011, 255, 2933; G. Franc and
A. K. Kakkar, Chem. Soc. Rev., 2010, 39, 1536; K. D. Hanni
and D. A. Leigh, Chem. Soc. Rev., 2010, 39, 1240; A. H. El-
Sagheer and T. Brown, Chem. Soc. Rev., 2010, 39, 1388–
1405; J. M. Holub and K. Kirshenbaum, Chem. Soc. Rev.,
2010, 39, 1325–1337.
5 N. Touj, A. Chakchouk-Mtibaa, L. Mansour, A. H. Harrath,
J. H. Al-Tamimi, I. Ozdemir, L. Mellouli, S. Yasar and
N. Hamdi, J. Organomet. Chem., 2017, 853, 49; A. Keivanloo,
M. Bakherad and M. Lot, Tetrahedron, 2017, 73, 5872–
5882; A. A. Ali, M. Chetia, P. J. Saikiab and D. Sarma, RSC
Adv., 2014, 4, 64388; H. A. Michaels and L. Zhu, Chem.–
Asian J., 2011, 6, 2825; S. I. Presolski, V. Hong, S. H. Cho
and M. Finn, J. Am. Chem. Soc., 2010, 132, 14570;
G. C. Kuang, H. A. Michaels, J. T. Simmons, R. J. Clark and
L. Zhu, J. Org. Chem., 2010, 75, 6540; P. S. Donnelly,
S. D. Zanatta, S. C. Zammit, J. M. White and S. J. Williams,
Chem. Commun., 2008, 2459; V. O. Rodionov, S. I. Presolski,
S. Gardinier, Y. H. Lim and M. G. Finn, J. Am. Chem. Soc.,
13 A. Barge, S. Tagliapietra, A. Binello and G. Cravotto, Curr.
Org. Chem., 2011, 15, 189–203.
14 A. A. Husain, A. Maknenko and K. S. Bisht, Chem.–Eur. J.,
2016, 22, 6223.
15 S. N. Parulekar, K. Muppalla, F. R. Fronczek and K. S. Bisht,
Chem. Commun., 2007, 4901; S. N. Parulekar, K. Muppalla,
A. A. Husain and K. S. Bisht, RSC Adv., 2015, 5, 25477;
E. E. Dueno and K. S. Bisht, Tetrahedron, 2004, 60, 10859;
E. E. Dueno and K. S. Bisht, Chem. Commun., 2004, 954;
R. Wu, T. F. Al-Azemi and K. S. Bisht, Chem. Commun.,
2009, 1822; R. Wu, T. F. Al-Azemi and K. S. Bisht, RSC Adv.,
2014, 4, 16864.
16 R. Singh and A. Varma, Green Chem., 2012, 14, 348–356;
P. Chong and P. Petillo, Org. Lett., 2000, 2, 1093–1096.
17 J. Garcia-Alvarez, J. Gimeno and A. J. L. Pombeiro, Adv.
Organomet. Chem. Catal., 2014, 199–206.
18 S. Hassana and T. J. Muller, Adv. Synth. Catal., 2015, 357,
617–666.
19 B. T. Worrell, J. A. Malik and V. V. Fokin, Science, 2013, 340,
457–460.
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