Ascorbic acid based ionic liquids: Recyclable and efficient catalytic systems for the huisgen cycloaddition

Article abstract of DOI:10.1055/s-0033-1338975

A new method for the Huisgen cycloaddition using an ascorbic acid based ionic liquid and a copper catalyst in an ionic liquid, under microwave irradiation, is described. The reaction times are short and a simple procedure for separation of the products is

Full text of DOI:10.1055/s-0033-1338975

LETTER
▌2305
lAettsercorbic Acid Based Ionic Liquids: Recyclable and Efficient Catalytic Systems
for the Huisgen Cycloaddition
Ascorbic Acid Based Ionic Liquids
Shinichi Koguchi,* Kaori Nakamura
Department of Chemistry, School of Science, Tokai University, 4-1-1 Kitakaname, Hiratsuka, Kanagawa 259-1292, Japan
Fax +81(463)502094; E-mail: koguchi@tokai-u.jp
Received: 07.08.2013 ; Accepted after revision: 02.09.2013
ployed.12 Furthermore, there are no examples of organic
Abstract: A new method for the Huisgen cycloaddition using an
reactions in which an ascorbic acid based ionic liquid is
ascorbic acid based ionic liquid and a copper catalyst in an ionic liq-
uid, under microwave irradiation, is described. The reaction times
are short and a simple procedure for separation of the products is es-
tablished. Good conversions are obtained and the ionic liquid based
catalytic system can be recycled.
N
N
N
N
KHCO3
R
R
Br–
HCO3
–
Key words: ionic liquids, microwave irradiation, supported cataly-
sis, heterocycles, oxidation
R = Et ([emim]HCO3–) 1a: 96%
R = n-Bu ([bmim]HCO3–) 1b: 97%
OH
HO
Ionic liquids have attracted considerable attention from
the scientific community. They have several advantages,
including non-volatility, good thermal and electrical con-
ductivities, and high polarities and thermal stabilities.1
Ionic liquids are known as designer solvents for which
various structural alternatives are possible. Different
types of ionic liquids have been developed, derivatives of
which include imidazolium, pyridinium,2 phosphonium,3
and ammonium salts.4 Moreover, high-polarity ionic liq-
uids can be heated very efficiently under microwave irra-
diation.
HO
N
N
R
–O
O
O
OH
HO
CO2
+
H2O
+
HO
MeOH
O
O
HO
R = Et ([emim] ascorbate) 2a: 88%
R = n-Bu ([bmim] ascorbate) 2b: 98%
Scheme 1 A novel and simple method for the synthesis of ascorbic
acid based ionic liquids
In this paper, we describe the preparation of ascorbic acid
based ionic liquids and their application, in combination
with a copper(I) catalyst, for the synthesis of 1,4-disubsti-
tuted 1,2,3-triazoles, via the Huisgen reaction, in various
ionic liquids under microwave irradiation.
Table 1 Investigation of the Huisgen Reaction Using Ascorbic Acid
Based Ionic Liquids 2a,b in Various Ionic Liquidsa
Ph
2a or 2b (0.25 equiv)
CuSO4 (0.15 equiv)
N3
+
N
N
Bn
Ph
Bn
ionic liquid–H2O
2:1
N
Triazoles are an important structural component in organ-
ic materials and show antibacterial,5 anti-allergic,6 anti-
HIV,7 and antineoplastic activities.8 They are used in var-
ious research fields, including materials chemistry9 and
synthetic organic chemistry.10 Numerous methods have
been developed to synthesize 1,2,3-triazoles from azides
and alkynes (the Huisgen reaction). The copper(I)-cata-
lyzed azide–alkyne cycloaddition between an organic
azide and a terminal alkyne has been established as a use-
ful and extensively applied method for the synthesis of
1,4-disubstituted 1,2,3-triazoles.11
MW, 80 °C, 1 min
Entry Ionic liquid
Reducing agent
Yield (%)b
1
2
3
4
5
6
7
8
9
[bmim]BF4
[emim]BF4
[emim]PF6
[bmim]BF4
[bmim]MeSO4
[bmim]PF6
[emim]BF4
[bmim]BF4
[bmim]BF4
[emim]ascorbate (2a)
[emim]ascorbate (2a)
[emim]ascorbate (2a)
93
75
24
96
88
5
[bmim]ascorbate (2b)
[bmim]ascorbate (2b)
[bmim]ascorbate (2b)
[bmim]ascorbate (2b)
sodium ascorbate
The first objective of this work was the synthesis of the
ascorbic acid based ionic liquids. There is only one previ-
ous report describing studies on the synthesis of an ascor-
bic acid based ionic liquid, which might be a consequence
of the fact that the synthetic method was very complicated
due to the necessity for an ion-exchange step to be em-
59
55
9
ascorbic acid
a Reaction conditions: benzyl azide (2.0 mmol), phenylacetylene (3.0
mmol), CuSO4 (0.3 mmol), ascorbic acid based ionic liquid (2a or 2b)
(or sodium ascorbate or ascorbic acid) (0.5 mmol), ionic liquid (2
mL), H2O (1 mL), microwave irradiation, 80 °C, 1 min.
b Yield of isolated product.
SYNLETT 2013, 24, 2305–2309
Advanced online publication: 27.09.2013
DOI: 10.1055/s-0033-1338975; Art ID: ST-2013-U0761-L
© Georg Thieme Verlag Stuttgart · New York
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6

2306
S. Koguchi, K. Nakamura
LETTER
used. Therefore, we have developed a new procedure for oped ascorbic acid based ionic liquids as the reducing
the synthesis of ascorbic acid based ionic liquids, and agent, in different types of ionic liquids. The results of
have utilized them for the preparation of 1,4-disubstituted these investigations showed that hydrophilic ionic liquids
1,2,3-triazoles.
([bmim]BF4, [emim]BF4, [bmim]CH3SO4) were far supe-
rior to hydrophobic ionic liquids ([emim]PF6, [bmim]
PF6,) in terms of the obtained yield of the corresponding
triazole (Table 1, entries 1–7). The highest yield (96%)
was observed when the length of the alkyl chain on the im-
idazolium ring of the ionic liquid and that of the ascorbic
acid based ionic liquid were equal (Table 1, entry 4). We
also used sodium ascorbate and ascorbic acid as the reduc-
ing agents, and the best-performing ionic liquid, 1-butyl-
3-methylimidazolium tetrafluoroborate ([bmim]BF4), in
We applied the method of Zhijun et al. to prepare imidaz-
olium hydrogencarbonates 1a,b in excellent yields.13–15
Next, the 1,3-disubstituted imidazolium hydrogencarbon-
ates were dissolved in methanol and treated with ascorbic
acid to give the ascorbic acid based ionic liquids,
[emim]ascorbate (2a) and [bmim]ascorbate (2b), in good
yields and high purities (Scheme 1).14,16
We next investigated the model Huisgen reaction between
phenylacetylene and benzyl azide, using the newly devel-
Table 2 Synthesis of 1,4-Disubstituted 1,2,3-Triazoles under Microwave Irradiationa
Entry
1
Alkyne
Azide
Product
Yield (%)a
Ph
N3
96
N
N
Bn
Bn
Ph
N
3a
Ph
N3
N
N
2
3
4
5
6
7
8
97
4-MeC6H4CH2
4-MeC6H4CH2
Ph
N
3b
Ph
N3
N
N
87
4-MeOC6H4CH2
4-MeOC6H4CH2
Ph
N
3c
Ph
N3
N
Ph(CH2)3
N
N
80
Ph(CH2)3
Ph
3d
c-Pr
N3
Bn
N
N
N
N
N
89
Bn
c-Pr
N
N
N
N
3e
C6H4-4-t-Bu
N3
Bn
N
quant.
99
Bn
4-t-BuC6H4
Ph(CH2)3
n-Bu
3f
(CH2)3Ph
N3
Bn
N
Bn
3g
n-Bu
N3
Bn
N
74
Bn
3h
a Reaction conditions: azide (2.0 mmol), acetylene (3.0 mmol), CuSO4 (0.3 mmol), ascorbic acid based ionic liquid 2b (0.5 mmol), [bmim]BF4
(2 mL), H2O (1 mL), microwave irradiation, 80 °C, 1 min.
b Yield of isolated product.
Synlett 2013, 24, 2305–2309
© Georg Thieme Verlag Stuttgart · New York

LETTER
Ascorbic Acid Based Ionic Liquids
2307
the model Huisgen reaction. However, the yields of the
corresponding triazole were much lower (55% and 9%,
respectively, Table 1, entries 8 and 9).
Acknowledgment
We thank Dr. Hironobu Hojo for the MALDI-MS data collection.
We would particularly like to thank Dr. Mikio Watanabe and Dr.
Taichi Nakano for his valuable support with this work. This study
was supported by Tokai University Supporters Association Re-
search.
These results indicated that the combination of ascorbic
acid based ionic liquid 2b ([bmim]ascorbate), and the hy-
drophilic ionic liquid, [bmim]BF4, represented the most
efficient system for performing the azide–alkyne cycload-
ditions. Next, we investigated the scope of the Huisgen
cycloaddition between various azides and alkynes by em-
ploying the optimized reaction conditions.14,17 In each
case, the reactions proceeded rapidly (1 min) to form the
expected triazoles in good to excellent yields (Table 2, en-
tries 1–8). Extending the reaction time did not result in
any improvement in the yield; a further increase in the re-
action time led to decomposition of the product.
References and Notes
(1) (a) Wasserscheid, P.; Welton, T. Ionic Liquids in Synthesis;
Wiley-VCH: Weinheim, 2007. (b) Welton, T. Chem. Rev.
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111, 3508. (d) Wasserscheid, P.; Wilhelm, K. Angew. Chem.
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(2) (a) Marra, A. ChiappeMele, A. Chimia 2011, 65, 76.
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K.; Nomura, M.; Kitagawa, Y.; Miyazaki, Y. Chem. Lett.
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(5) (a) Genin, M. J.; Allwine, D. A.; Anderson, D. J.;
Barbachyn, M. R.; Emmert, D. E.; Garmon, S. A.; Graber, D.
R.; Grega, K. C.; Hester, J. B.; Hutchinson, D. K.; Morris, J.;
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Poojary, B.; Akberali, P. M.; Kumari, N. S. Eur. J. Med.
Chem. 2005, 40, 1173.
Finally, we examined the recyclability of this reaction
system for the azide–alkyne cycloaddition between ben-
zyl azide and phenylacetylene. After completion of the re-
action, the triazole product was extracted from the ionic
liquid phase using diethyl ether. Fresh reagents were then
added to the ionic liquid phase and the same reaction was
run again under microwave irradiation. Excellent conver-
sions were obtained over five consecutive cycles (Table
3).
Table 3 Recovery and Reuse of the Ionic Liquid Phase Containing
Ascorbic Acid Based Ionic Liquid 2ba
(6) (a) Buckle, D. R.; Rockell, C. J. M.; Smith, H.; Spicer, B. A.
J. Med. Chem. 1986, 29, 2262. (b) Buckel, D. R.; Outred, D.
J.; Rockell, C. J. M.; Smith, H.; Spicer, B. A. J. Med. Chem.
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Clercq, E.; Perno, C.-F.; Karlsson, A.; Balzarini, J.;
Camarasa, M. J. J. Med. Chem. 1994, 37, 4194.
reuse
2b (0.25 equiv)
CuSO4 (0.15 equiv)
ionic liquid–H2O
(2:1)
Ph
N3
+
N
Bn
N
Ph
Bn
MW, 80 °C
N
(8) Al-Masoudim, N. A.; Al-Soud, Y. A. Tetrahedron Lett.
2002, 43, 4021.
Run
1
2
3
4
5
(9) (a) Wu, P.; Feldman, A. K.; Nugent, A. K.; Hawker, C. J.;
Scheel, A.; Voit, B.; Pyun, J.; Fréchet, J. M. J.; Sharpless, K.
B.; Fokin, V. V. Angew. Chem. Int. Ed. 2004, 43, 3928.
(b) Aucagne, V.; Hänni, K. D.; Leigh, D. A.; Lusby, P. J.;
Walker, D. B. J. Am. Chem. Soc. 2006, 128, 2186. (c) Ye, C.
F.; Gard, G. L.; Winter, R. W.; Syvret, R. G.; Twamley, B.;
Shreeve, J. M. Org. Lett. 2007, 9, 3841. (d) Liu, Q. C.; Zhao,
P.; Chen, Y. M. J. Polym. Sci. 2007, 45, 3330.
Yield (%)a
96
92
96
quant.
99
a Reaction conditions: benzyl azide (2.0 mmol), phenylacetylene (3.0
mmol), CuSO4 (0.3 mmol), ascorbic acid based ionic liquid 2b (0.5
mmol), [bmim]BF4 (2 mL), H2O (1 mL), microwave irradiation,
80 °C. Reaction time was 1 minute for run 1, and 5 minutes for runs
2–5.
b Yield of isolated product.
(e) Nandivada, H.; Jiang, X. W.; Lahann, J. Adv. Mater.
2007, 19, 2197. (f) Angelos, S.; Yang, Y. W.; Patel, K.;
Stoddart, J. F.; Zink, J. I. Angew. Chem. Int. Ed. 2008, 45,
1435.
In summary, we have reported the use of ascorbic acid
based ionic liquids in combination with a copper catalyst
for the rapid preparation of 1,4-disubstituted 1,2,3-tri-
azoles under microwave irradiation. The synthesis of the
novel ionic liquid catalysts and separation of the product
from the ionic liquid phase are easily accomplished. The
process is advantageous due its green credentials, short re-
action times and the good yields of the obtained products.
Moreover, the reaction system can be reused over five
consecutive runs.
(10) (a) Wacharasindhu, S.; Bardhan, S.; Wan, Z.-K.; Tabei, K.;
Mansour, T. S. J. Am. Chem. Soc. 2009, 131, 4174. (b) Liu,
Y.; Yan, W.; Chen, Y.; Petersen, J. L.; Shi, X. Org. Lett.
2008, 10, 5385. (c) Katritzky, A. R.; Bobrov, S.; Kirichenko,
K.; Ji, Y.; Steel, P. J. J. Org. Chem. 2003, 68, 5713. (d) Reid,
A. K.; McHugh, C. J.; Richie, G.; Graham, D. Tetrahedron
Lett. 2006, 47, 4201. (e) Verma, A. K.; Singh, J.; Chaudhary,
R. Tetrahedron Lett. 2007, 48, 7199. (f) Dai, Q.; Gao, W.;
Liu, D.; Kapzes, L. M.; Zhang, X. J. Org. Chem. 2006, 71,
3928.
(11) (a) Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless,
K. B. Angew. Chem. Int. Ed. 2002, 41, 2596. (b) Tornoe, C.
W.; Christensen, C.; Meldal, M. J. Org. Chem. 2002, 67,
3057. (c) Chan, T. R.; Hilgraf, R.; Sharpless, K. B.; Fokin,
© Georg Thieme Verlag Stuttgart · New York
Synlett 2013, 24, 2305–2309

2308
S. Koguchi, K. Nakamura
LETTER
(17) 1,4-Disubstituted 1,2,3-Triazoles 3a–h; General
V. V. Org. Lett. 2004, 6, 2853. (d) Rodionov, V. O.;
Presolski, S. I.; Diaz Diaz, D.; Fokin, V. V.; Finn, M. G. J.
Am. Chem. Soc. 2007, 129, 12705.
Procedure
A solution of azide (2.0 mmol), acetylene (3.0 mmol),
CuSO4 (0.3 mmol) and 3-butyl-1-methyl-1H-imidazol-3-
ium ascorbate (2b) (0.5 mmol) in [bmim]BF4 (2 mL) and
H2O (1 mL) was stirred for 1 min at 80 °C under microwave
irradiation. After the reaction was complete, the mixture was
extracted with Et2O and the organic phase evaporated. The
product was isolated by silica gel column chromatography.
1-Benzyl-4-phenyl-1H-1,2,3-triazole (3a)
Yield: 451 mg (1.90 mmol, 96%); white solid; mp 122–
124 °C. 1H NMR (500 MHz, CDCl3): δ = 5.59 (s, 2 H),
7.26–7.42 (m, 8 H), 7.66 (s, 1 H), 7.80 (m, 2 H). 13C NMR
(125 MHz, CDCl3): δ = 54.3, 119.5, 125.7 (2 C), 128.1 (2
C), 128.2, 128.6, 128.8 (2 C), 129.2 (2 C), 130.6, 134.7,
148.3. HRMS (APCI): m/z [M + H]+ calcd for C15H14N3:
236.11877; found: 236.11002.
1-(4-Methylbenzyl)-4-phenyl-1H-1,2,3-triazole (3b)
Yield: 481 mg (1.93 mmol, 97%); white solid; mp 108–
111 °C. 1H NMR (500 MHz, CDCl3): δ = 2.36 (s, 3 H), 5.54
(s, 2 H), 7.19–7.23 (m, 4 H), 7.30–7.32 (m, 1 H), 7.39–7.41
(m, 2 H), 7.63 (s, 1 H), 7.78–7.80 (m, 2 H). 13C NMR (125
MHz, CDCl3): δ = 21.2, 54.0, 119.4, 125.7, 128.1 (2 C),
128.8 (2 C), 129.8 (2 C), 130.6 (2 C), 131.7 (2 C), 138.7,
148.2. HRMS (APCI): m/z [M + H]+ calcd for C16H16N3:
250.13442; found: 250.12573.
(12) Dinda, E.; Si, S.; Kotal, A.; Mandal, T. Chem. Eur. J. 2008,
14, 5528.
(13) Zhijun, D.; Jiangna, G.; Lihua, Q.; Yinxia, Z.; Lin, X.; Feng,
Y. Polym. Chem. 2012, 3, 2439.
(14) All reagents and chemicals (reagent grade) were obtained
from commercial suppliers, and were used as received. TLC
was performed using Merck silica gel 60 F254 aluminum
sheets. Column chromatography was performed using Kanto
Chemical silica gel 60. Melting points were determined
using a Yamoto MP-21 melting point apparatus. 1H (500
MHz) and 13C (125 MHz) NMR spectra were recorded in
CDCl3 on a Bruker Avance DRX 500 spectrometer.
Chemical shifts (δ) are expressed in ppm and are referenced
to the residual peak of the solvent or TMS as an internal
standard; coupling constants (J) are quoted in Hz. Mass
analyses were performed using a JEOL AccuTOF LC-plus
JMS-T100LP spectrometer. MALDI-MS (TOF) spectra
were recorded on a Voyager DE-STR instrument; α-cyano-
4-hydroxycinnamic acid was used as the matrix. Microwave
irradiation was performed using a Shikoku Instrumentation
CO., Inc. μReacter EX.
(15) 1-Ethyl-3-methyl-1H-imidazol-3-ium hydrogencarbonate
(1a)
Yield: 825 mg (4.79 mmol, 96%); yellow liquid. 1H NMR
(500 MHz, CDCl3): δ = 1.38 (t, J = 7.5 Hz, 3 H), 2.50 (s, 3
H), 4.19 (q, J = 7.5 Hz, 2 H), 7.70 (s, 1 H), 7.79 (s, 1 H), 9.13
(s, 1 H). 13C NMR (125 MHz, CDCl3): δ = 15.6, 36.2, 44.6,
122.3, 123.9, 136.6. MALDI-MS (TOF): m/z [M]+ calcd for
C6H11N2: 111.0; found: 111.0.
1-(4-Methoxybenzyl)-4-phenyl-1H-1,2,3-triazole (3c)
Yield: 464 mg (1.75 mmol, 87%); white solid; mp 135 °C.
1H NMR (500 MHz, CDCl3): δ = 3.82 (s, 3 H), 5.52 (s, 2 H),
6.92 (d, J = 9 Hz, 2 H), 7.28–7.33 (m, 2 H), 7.38–7.40 (m, 3
H), 7.62 (s, 1 H), 7.79 (d, J = 9 Hz, 2 H). 13C NMR (125
MHz, CDCl3): δ = 53.8, 55.4, 114.2, 114.5 (2 C), 119.3,
120.0, 125.7, 126.7, 128.1, 128.8, 129.7 (2 C), 130.6 (2 C),
159.9. HRMS (APCI): m/z [M + H]+ calcd for C16H16N3O:
266.12934; found: 266.12823.
4-Phenyl-1-(3-phenylpropyl)-1H-1,2,3-triazole (3d)
Yield: 420 mg (1.59 mmol, 80%); white solid; mp 82–83 °C.
1H NMR (500 MHz, CDCl3): δ = 2.31 (q, J = 7.5 Hz, 2 H),
2.70 (t, J = 7.5 Hz, 2 H), 4.41 (t, J = 7.5 Hz, 2 H), 7.19–7.35
(m, 6 H), 7.41–7.46 (m, 2 H), 7.72 (s, 1 H), 7.80–7.83 (m, 2
H). 13C NMR (125 MHz, CDCl3): δ = 30.4, 32.5, 50.6,
119.5, 125.7, 126.4, 126.1, 126.5, 128.49 (2 C), 128.5,
128.6, 128.7, 128.9, 130.7, 140.2, 147.8. HRMS (APCI): m/z
[M + H]+ calcd for C17H18N3: 264.15007; found: 264.14639.
1-Benzyl-4-cyclopropyl-1H-1,2,3-triazole (3e)
Yield: 353 mg (1.77 mmol, 89%); white solid; mp 58–59 °C.
1H NMR (500 MHz, CDCl3): δ = 0.80–0.83 (m, 2 H), 0.90–
0.94 (m, 2 H), 1.89–1.94 (m, 1 H), 5.47 (s, 2 H), 7.13 (s, 1
H), 7.24–7.26 (m, 2 H), 7.33–7.38 (m, 3 H). 13C NMR (125
MHz, CDCl3): δ = 6.7, 7.7, 54.0, 119.6, 128.0, 128.2 (2 C),
128.6 (2 C), 129.0, 135.0, 150.7. HRMS (APCI): m/z [M +
H]+ calcd for C12H14N3: 200.11877; found: 200.11366.
1-Benzyl-4-[4-(tert-butyl)phenyl]-1H-1,2,3-triazole (3f)
Yield: 638 mg (2.19 mmol, quant.); white solid; mp 112–
114 °C. 1H NMR (500 MHz, CDCl3): δ = 1.33 (s, 9 H), 5.58
(s, 2 H), 7.27–7.42 (m, 7 H), 7.63 (s, 1 H), 7.70–7.75 (m, 2
H). 13C NMR (125 MHz, CDCl3): δ = 31.3, 34.7, 54.2,
119.3, 125.3, 125.4, 125.7, 127.7, 128.0, 128.7 (2 C), 129.1,
131.9, 132.2, 134.8, 148.2, 151.3. HRMS (APCI): m/z [M +
H]+ calcd for C19H22N3: 292.18137; found: 292.17627.
1-Benzyl-4-(3-phenylpropyl)-1H-1,2,3-triazole (3g)
Yield: 550 mg (1.99 mmol, 99%); white solid; mp 64–65 °C.
1H NMR (500 MHz, CDCl3): δ = 1.95–2.01 (m, 2 H), 2.66
(t, J = 7.75 Hz, 2 H), 2.72 (t, J = 7.75 Hz, 2 H), 5.49 (s, 2 H),
7.15–7.18 (m, 5 H), 7.24–7.27 (m, 2 H), 7.33–7.39 (m, 4 H).
1-Butyl-3-methyl-1H-imidazol-3-ium
hydrogencarbonate (1b)
Yield: 971 mg (4.85 mmol, 97%); yellow liquid. 1H NMR
(500 MHz, CDCl3): δ = 0.89 (t, J = 7.5 Hz, 3 H), 1.24 (m, 2
H), 1.75 (m, 2 H), 2.51 (s, 3 H), 4.16 (t, J = 7.5 Hz, 2 H), 7.70
(s, 1 H), 7.77 (s, 1 H), 9.13 (s, 1 H). 13C NMR (125 MHz,
CDCl3): δ = 13.7, 19.2, 31.9, 36.3, 48.8, 122.7, 123.9, 136.9.
HRMS (APCI): m/z [M + H]+ calcd for C8H15N2: 139.1235;
found: 139.1241.
(16) Ascorbic Acid Based Ionic Liquids 2a,b; General
Procedure
A solution of 1,3-disubstituted imidazolium
hydrogencarbonate 1a,b (20 mmol) in MeOH (8 mL) was
added to L-ascorbic acid (20 mmol). The resulting mixture
was stirred at r.t. for 24 h and then evaporated.
3-Ethyl-1-methyl-1H-imidazol-3-ium ascorbate (2a)
Yield: 5060.0 mg (17.2 mmol, 88%); orange liquid. 1H NMR
(500 MHz, CDCl3): δ = 0.42–1.39 (m, 3 H), 2.50 (s, 3 H),
3.47–3.48 (m, 3 H), 3.48–3.80 (m, 1 H), 4.18–4.21 (m, 2 H),
7.70 (s, 1 H), 7.79 (s, 1 H), 9.17 (s, 1 H). 13C NMR (125
MHz, CDCl3): δ = 15.6, 36.1, 44.6, 63.5, 77.1, 115.9, 122.4,
123.9, 136.8, 167.5, 172.8, 176.2. MALDI-MS (TOF): m/z
[M]+ calcd for C6H11N2: 111.0; found: 110.9.
3-Butyl-1-methyl-1H-imidazol-3-ium ascorbate (2b)
Yield: 6179.2 mg (19.2 mmol, 98%); orange liquid. 1H NMR
(500 MHz, CDCl3): δ = 0.95–0.98 (m, 3 H), 1.34–1.41 (m, 2
H), 1.84–1.90 (m, 2 H), 3.16–3.20 (m, 3 H), 3.76 (s, 3 H),
3.80–3.85 (m, 1 H), 4.15–4.17 (m, 2 H), 7.25 (s, 1 H), 7.27
(s, 1 H), 10.64 (s, 1 H). 13C NMR (125 MHz, CDCl3):
δ = 13.7, 19.2, 31.8, 36.1, 48.9, 63.7, 76.9, 115.8, 122.7,
124.0, 137.2, 163.2, 167.6, 176.5. HRMS (ACPI): m/z [M]+
calcd for C8H15N2: 139.1235; found: 139.1253.
Synlett 2013, 24, 2305–2309
© Georg Thieme Verlag Stuttgart · New York

LETTER
13C NMR (125 MHz, CDCl3): δ = 25.3, 31.1, 35.4, 54.0,
Ascorbic Acid Based Ionic Liquids
2309
1.33–1.40 (m, 2 H), 1.59–1.70 (m, 2 H), 2.69 (t, J = 7.75, 2
H), 5.49 (s, 2 H), 7.17 (s, 1 H), 7.24–7.26 (m, 2 H), 7.33–7.39
(m, 3 H). 13C NMR (125 MHz, CDCl3): δ = 13.8, 22.3, 25.4,
31.5, 53.9, 127.9, 128.2, 128.3, 128.6 (2 C), 128.8, 129.0,
135.1. HRMS (APCI): m/z [M + H]+ calcd for C13H18N3:
216.15007; found: 216.14352.
120.8, 125.8, 125.9, 127.9, 128.35, 128.39, 128.4 (2 C),
128.5, 128.6, 129.1, 135.0, 141.9, 148.4. HRMS (APCI): m/z
[M + H]+ calcd for C18H20N3: 278.16572; found: 278.16215.
1-Benzyl-4-butyl-1H-1,2,3-triazole (3h)
Yield: 319 mg (1.48 mmol, 74%); white solid; mp 60–62 °C.
1H NMR (500 MHz, CDCl3): δ = 0.91 (t, J = 7.25 Hz, 3 H),
© Georg Thieme Verlag Stuttgart · New York
Synlett 2013, 24, 2305–2309