1,3-Dipolar cycloaddition of sugar azides with benzyne: A novel synthesis of 1,2,3-benzotriazolyl glycoconjugates

Article abstract of DOI:10.1016/j.carres.2010.12.015

Glycosyl azides undergo smooth 1,3-dipolar cycloaddition with benzyne generated in situ from 2-(trimethylsilyl)phenyltrifluoromethanesulfonate and cesium fluoride under mild conditions to furnish 1,2,3-benzotriazole-linked glycoconjugates in excellent yie

Full text of DOI:10.1016/j.carres.2010.12.015

Carbohydrate Research 346 (2011) 995–998
Contents lists available at ScienceDirect
Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
1,3-Dipolar cycloaddition of sugar azides with benzyne: a novel synthesis
of 1,2,3-benzotriazolyl glycoconjugates
Basi V. Subba Reddy a, , Karanam Praneeth a,b, Jhillu S. Yadav a
⇑
a Division of Organic Chemistry, Indian Institute of Chemical Technology, Hyderabad 500 007, India
b IICT an Associate Institution of University of Hyderabad, Hyderabad 500 046, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Glycosyl azides undergo smooth 1,3-dipolar cycloaddition with benzyne generated in situ from 2-(tri-
methylsilyl)phenyltrifluoromethanesulfonate and cesium fluoride under mild conditions to furnish
1,2,3-benzotriazole-linked glycoconjugates in excellent yields and with high stereoselectivity. This
method provides a novel class of benzotriazole linked glycoconjugates in a single-step reaction. This is
the first example of a fluoride-triggered 1,3-dipolar cycloaddition of benzyne with glycosyl azides.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 9 November 2010
Received in revised form 11 December 2010
Accepted 14 December 2010
Available online 22 December 2010
Keywords:
Azide–aryne cycloaddition
Glycoconjugates
N-Benzotriazolyl sugars
‘Click’ type reaction
1. Introduction
2. Results and discussion
1,2,3-Benzotriazoles are important structural scaffolds in var-
ious biologically active molecules.1,2 They exhibit a wide spec-
trum of pharmacological properties and clinical applications
such as antiinflammatory, antinociceptive, antitumor, and anti-
tubercular activities.3–5 In addition to this, they are important
intermediates, protecting groups, and end products in organic
synthesis.6 Furthermore, glycosyl amines are of great impor-
tance in nucleoside chemistry.7–9 Recently, the synthesis of N-
triazolyl-bridged glycoconjugates have been reported via ‘Click’
chemistry.10 However, the synthesis of 1,2,3-benzotriazolyl gly-
cosides involves the Ferrier rearrangement of glycals with ben-
zotriazole using trifluoroacetic acid.11,12 This approach often
requires high temperature, prolonged reaction time (two days),
and a sealed tube to achieve satisfactory results. The alternative
method for the synthesis of benzotriazole is the cycloaddition of
azides with arynes.13–15 In recent years, benzyne was generated
in situ from 2-(trimethylsilyl)phenyl trifluoromethanesulfonate
using cesium fluoride under mild conditions and used in various
cycloaddition reactions.16–21 Since benzotriazole-linked glyco-
conjugates have become increasingly useful and important in
Following our interest on azide–alkyne cycloadditions,26,27 we
herein report a novel method for the synthesis of benzotriazolyl
glycosides via the 1,3-dipolar cycloaddition of glycosyl azides with
benzyne under mild conditions. Initially, we have prepared glyco-
syl azides from glycals and trimethylsilyl azide via the Ferrier
rearrangement.28 The azides thus formed were then subjected to
1,3-dipolar cycloaddition. 29Accordingly, treatment of 2,3-dideoxy-
glycosyl azide (1a) with 2-(trimethylsilyl)phenyltrifluoromethane-
sulfonate (2) and cesium fluoride in acetonitrile at room
temperature gave the corresponding benzotriazolyl-2,3-dideoxy
glycoside (3a) in 86% yield (Scheme 1).
This result provided the incentive for further study with various
sugar azides such as 4,6-di-O-benzyl- (1b) and 4,6-di-O-allyl-2,3-
dideoxy-a-D-glycosyl azides (1c). These glycosyl azides reacted
readily with benzyne under similar conditions to produce 1,2,3-
benzotriazole-linked 2,3-dideoxypyranosides in excellent yields
(Table 1, entries b and c). Next, we have attempted the cycloaddi-
glycobiology,22–25 the development of
a simple, convenient,
and efficient method for their synthesis in a single-step opera-
tion is desirable.
N
CsF
Si
OTf
O
N3
O
N
AcO
AcO
N
AcO
AcO
+
CH3CN, rt
2
3a
1a
⇑
Corresponding author. Tel.: +91 40 27193535; fax: +91 40 27160512.
E-mail address: basireddy@iict.res.in (B.V. Subba Reddy).
Scheme 1. Synthesis of the benzotriazolyl-2,3-dideoxy glycoside (3a).
0008-6215/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2010.12.015

996
B. V. Subba Reddy et al. / Carbohydrate Research 346 (2011) 995–998
Table 1
1,3-Dipolar cycloaddition of various azides with benzyne in the presence of cesium
fluoride
O
N3
Si
OTf
CsF
O
N
N
AcO
Producta
Time
(h)
Yieldb
(%)
+
Entry Sugar azide
N
AcO
AcO
CH3CN, rt
AcO
OAc
OAc
O
N3
1d
2
3d
AcO
AcO
Scheme 2. Synthesis of a 1,2,3-benzotriazolyl-D-ribonucleoside.
N
N
O
N
N
a
b
c
12.0
13.0
12.0
86
88
92
N
N
AcO
AcO
1a
various azido sugars such as
deoxy-D-ribose, and 5-azido-5-deoxy-D-xylose were successfully
D
-ribosfuranosyl azide, 3-azido-3-
3a
converted into their 1,2,3-benzotriazolyl derivatives by using this
procedure. Notably, a variety of protecting groups such as benzyl
and allyl ethers and ester derivatives like acetyl and pivolyl esters
were well tolerated under the reaction conditions. As solvent, aceto-
nitrile gave the best results. The cycloaddition was successfully car-
ried out with the azides derived from both hexose and pentose
sugars. The scope and generality of this reaction is illustrated with
respect to various primary and secondary azides, and the results
are presented in Table 1.
Mechanistically, the reaction proceeds via the formation of a
benzyne intermediate from 2-(trimethylsilyl)phenyltrifluorome-
thanesulfonate and CsF. The benzyne thus formed may undergo
simultaneously 1,3-dipolar cycloaddition with glycosyl azide to fur-
nish 1,2,3-benzotriazole linked glycoside as depicted in Scheme 3.
Although other fluoride ion sources such as KF and tetrabutyl-
ammonium fluoride (TBAF) have effectively been used to generate
benzyne, CsF is found to be the best fluoride ion source under the
given conditions in terms of yields.
O
N3
BnO
BnO
O
BnO
BnO
1b
3b
O
N3
AllylO
AllylO
N
O
N
N
AllylO
AllylO
1c
3c
O
N3
AcO
AcO
O
N
N
OAc
N
d
e
f
16.0
94
88
90
AcO
AcO
1d
OAc
3d
O
N
O
N
N3
N
O
O
HO
3. Conclusions
O
8.0
1e
O
HO
In conclusion, we have successfully developed a novel and effi-
cient method for the synthesis of 1,2,3-benzotriazole-linked glyco-
conjugates via azide–aryne cycloaddition. The method is mild and
convenient and provides easy access to a variety of benzotriazole-
linked glycoconjugates that may find application in nucleoside
synthesis.
3e
O
N
O
N
N3
N
O
O
BzO
O
9.0
O
1f
BzO
3f
4. Experimental
O
BnO
O
O
BnO
PivO
O
4.1. General methods and materials
O
N3
O
g
12.0
14.0
80
80
N
All the products were characterized by 1H and 13C NMR, IR spec-
troscopy and by high-resolution mass spectrometry (HRMS). Melt-
ing points recorded are uncorrected. Analytical TLC was performed
using 2.5 ꢀ 5-cm plates coated with a 0.25 mm thickness of silica
gel (60F-254), and visualization was accomplished with p-anisal-
dehyde solution and subsequent charring over a hot plate. 1H
NMR spectra were recorded at 300 MHz with TMS as the internal
reference. 13C NMR spectra are recorded at 75 MHz with CDCl3 as
the internal reference. Chemical shifts are given in parts per mil-
lion downfield from internal standard Me4Si and coupling con-
stants are given in Hertz. IR spectra were recorded on Perkin–
Elmer 881 and FTIR-8210 PC Shimadzu spectrophotometers. Mass
spectra were recorded on a JEOL JMS-600H high-resolution spec-
trometer using the ESI mode at 70 eV. Optical rotations were mea-
sured at ambient temperature (25 °C) in CHCl3 solutions with a
polarimeter using a 1-mL capacity cell with 100-mm path length,
and concentrations are in g/100 mL.
N
N
1g
3g
O
O
O
O
PivO
O
O
N3
N
h
N
N
1h
3h
a
All products were characterized by NMR, IR, and mass spectrometry.
Yield refers to pure products after chromatography.
b
tion of benzyne with an azide derived from
2,3,5-tri-O-acetyl-b- -ribfuranosyl azide (1d) participated well in
benzyne–azide cycloaddition to afford the 1,2,3-benzotriazolyl-D-
ribonucleoside (3d) in 94% yield (entry d, Scheme 2).
Encouraged by the above results, we turned our attention to ex-
tend this method for primary azides. Interestingly, primary azides
D-ribose. Interestingly,
D
4.2. General experimental procedure for the preparation of
triazole-linked glycoconjugates
such as 5-azido-5-deoxy-
cycloaddition with benzyne to furnish the corresponding benzotri-
azole-linked -xylose derivatives (Table 1, entries e and f). Similarly,
3-azido-3-deoxy- -ribose derivatives 1g and 1h also participated
effectively in this cycloaddition (Table 1, entries g and h). Thus
D-xylose (1e, 1f) also underwent smooth
D
To a stirred solution of aryne precursor (1.2 mmol) and azide
(1 mmol) in dry CH3CN (3 mL) was added CsF (2 mmol), and the
D

B. V. Subba Reddy et al. / Carbohydrate Research 346 (2011) 995–998
997
-
CsF
O
O
N
N
N
N
N
AcO
N
AcO
+
TfO
Si
AcO
OAc
AcO
OAc
2
3a
Scheme 3. A plausible reaction mechanism.
resulting mixture was stirred for an appropriate time (Table 1).
After complete conversion, as indicated by TLC, the mixture was
quenched with satd aq NaHCO3 and extracted with EtOAc
(3 ꢀ 5 mL). The combined organic layers were dried over anhyd
Na2SO4 and concentrated under vacuum. The resulting residue
was purified by column chromatography on silica gel using
EtOAc–hexane as eluent to afford the pure benzotriazole
derivative.
7.67 (d, 1H, J = 7.7 Hz), 7.50 (t, 1H, J = 7.7 Hz), 7.38 (t, 1H,
J = 6.7 Hz), 6.29 (d, 1H, J = 8.7 Hz), 5.86 (t, 1H, J = 2.9 Hz), 5.72
(dd, 1H, J = 2.9, 8.7 Hz), 5.30–5.26 (m, 2H), 5.08 (t, 1H, J = 6.7 Hz),
2.24 (s, 3H), 2.08 (s, 3H), 1.8 (s, 3H); 13C NMR (CDCl3, 75 MHz): d
169.2, 169.0, 168.2, 146.5, 127.9, 124.4, 120.5, 120.4, 110.5, 83.5,
68.2, 67.0, 66.0, 63.6, 20.7, 20.5, 20.1. ESIMS: m/z: 378 (M+H)+.
HRESIMS: Calcd for C17H20N3O7 m/z 378.1301; Found, m/z
378.1295.
4.2.1. [(2R,3S,6R)-3-(Acetyloxy)-6-(1H-1,2,3-benzotriazol-1-yl)-
3,6-dihydro-2H-2-pyranyl]methyl acetate (3a)
4.2.5. (3aR,5R,6S,6aR)-5-(1H-1,2,3-Benzotriazol-1-ylmethyl)-2,2-
dimethylperhydrofuro[2,3-d][1,3]dioxol-6-ol (3e)
Light-yellow solid, mp 132–134 °C; ½a D25
ꢁ
198 (c 1.15, CHCl3); IR
2925, 2854, 1735, 1647, 1453, 1227, 1161, 1068, 753 cm
Light-yellow solid, mp 146–148 °C; ½a D25
ꢂ52.7 (c 2.10, CHCl3);
ꢁ
(KBr):
m
IR (KBr): m 3467, 2983, 2941, 1706, 1498, 1440, 1381, 1221,
ꢂ1
;
1H NMR (CDCl3, 300 MHz): d 8.03 (d, 1H, J = 8.3 Hz), 7.51–
1074, 1012, 752 cmꢂ1 1H NMR (CDCl3, 300 MHz): d 7.94 (d, 1H,
;
7.38 (m, 2H), 7.31 (t, 1H, J = 6.7 Hz), 6.79 (d, 1H, J = 5.2 Hz), 5.70
(td, 1H, J = 1.5, 5.2 Hz), 5.32 (dd, 1H, J = 5.2, 10.5 Hz), 5.06 (t, 1H,
J = 5.2 Hz), 4.60–4.54 (m, 1H), 4.26–4.22 (m, 2H), 2.03 (s, 3H),
1.56 (s, 3H); 13C NMR (CDCl3, 75 MHz): d 170.4, 169.8, 148.1,
134.1, 127.4, 123.9, 120.1, 112.9, 109.7, 95.4, 70.5, 67.5, 61.5,
51.1, 20.6, 20.2. ESIMS: m/z: 332 (M+H)+. HRESIMS: Calcd for
J = 9.0 Hz), 7.60 (d, 1H, J = 8.3 Hz), 7.42 (t, 1H, J = 7.5 Hz), 7.30 (t,
1H, J = 7.5 Hz), 5.96 (d, 1H, J = 3.7 Hz), 5.01 (dd, 1H, J = 7.5,
14.3 Hz), 4.79 (dd, 1H, J = 6.0, 14.3 Hz), 4.59–4.50 (m, 2H), 4.28–
4.18 (m, 2H), 1.34 (s, 3H), 1.22 (s, 3H); 13C NMR (CDCl3, 75 MHz):
d 145.3, 133.4, 127.7, 124.2, 119.5, 111.8, 109.5, 105.0, 85.2, 79.2,
74.4, 46.1, 26.6, 26.0. ESIMS: m/z: 292 (M+H)+. HRESIMS: Calcd
for C14H18N3O4 m/z 292.1297; Found, m/z 292.1290.
C16H18N3O5 m/z 332.1246; Found, m/z 332.1232.
4.2.2. 1-5-(Benzyloxy)-6-[(benzyloxy)methyl]-5,6-dihydro-2H-
2-pyranyl-1H-1,2,3-benzotriazole (3b)
4.2.6. (3aR,5R,6S,6aR)-5-(1H-1,2,3-Benzotriazol-1-ylmethyl)-2,2
dimethylperhydrofuro[2,3-d][1,3]dioxol-6-yl benzoate (3f)
White solid, mp 162–164 °C; ½a D25
ꢁ
+99.7 (c 0.7, CHCl3); IR (neat):
3448, 3036, 2922, 2856, 1723, 1651, 1492, 1451, 1362, 1239,
White solid, mp 100–102 °C; ½a D25
ꢂ1.9 (c 2.30, CHCl3); IR (KBr):
ꢁ
m
m ;
2987, 2932, 1725, 1452, 1264, 1102, 1027, 750, 712, 675 cmꢂ1
1094, 745, 669 cmꢂ1
;
1H NMR (CDCl3, 300 MHz): d 7.95 (d, 1H,
1H NMR (CDCl3, 300 MHz): d 8.01–7.90 (m, 3H), 7.56–7.19 (m,
6H), 5.98 (d, 1H, J = 3.3 Hz), 5.46 (d, 1H, J = 1.8 Hz), 4.98 (dd, 1H,
J = 2.8, 13.4 Hz), 4.86–4.70 (m, 2H), 4.64 (d, 1H, J = 3.3 Hz), 1.36
(s, 3H), 1.20 (s, 3H); 13C NMR (CDCl3, 75 MHz): d 164.9, 145.7,
133.7, 133.2, 129.6, 128.5, 127.3, 123.7, 119.7, 112.3, 109.6,
104.8, 83.2, 77.9, 76.7, 76.5, 46.8, 26.4, 25.9. ESIMS: m/z: 396
(M+H)+. HRESIMS: Calcd for C21H22N3O5 m/z 396.1559; Found, m/
z 396.1550.
J = 7.3 Hz), 7.54–7.41 (m, 1H), 7.33–7.05 (m, 10H), 6.98–6.84 (m,
2H), 6.64–6.59 (m, 1H), 5.67–5.57 (m, 1H), 4.92 (t, 1H, J = 5.6 Hz),
4.75 (dd, 1H, J = 2.0, 6.1 Hz), 4.67–4.16 (m, 4H), 4.11–4.01 (m,
1H), 3.81–3.76 (m, 1H), 3.65–3.60 (m, 1H); 13C NMR (CDCl3,
75 MHz): d 148.0, 146.3, 136.7, 132.1, 128.3, 128.1, 128.0, 127.9,
127.8, 127.6, 126.9, 123.3, 119.6, 110.9, 110.2, 79.8, 78.0, 73.9,
72.2, 72.4, 68.0; ESIMS: m/z: 428 (M+H)+. HRESIMS: Calcd for
C26H26N3O3 m/z 428.1974; Found, m/z 428.1987.
4.2.7. [(3aR,5S,6R,6aR)-6-(1H-1,2,3-Benzotriazol-1-yl)-2,2-dime-
thylperhydrofuro[2,3-d][1,3]dioxol-5-yl]methyl benzyl ether (3g)
4.2.3. 1-5-(Allyloxy)-6-[(allyloxy)methyl]-5,6-dihydro-2H-2-
pyranyl-1H-1,2,3-benzotriazole (3c)
Colorless oil; ½a D25
ꢁ
ꢂ55.7 (c 0.35, CHCl3); IR (neat):
m 3447, 2956,
Yellow solid, mp 146–148 °C; ½a D25
ꢁ
ꢂ26.8 (c 1.50, CHCl3); IR
1646, 1497, 1454, 1377, 1218, 1162, 1076, 1027, 888, 746, 698 cm
ꢂ1; 1H NMR (CDCl3, 300 MHz): d 7.99 (d, 1H, J = 8.3 Hz), 7.54 (d, 1H,
J = 8.3 Hz), 7.42–7.23 (m, 7H), 5.94 (d, 1H, J = 3.7 Hz), 4.95–4.88 (m,
1H), 4.78–4.60 (m, 4H), 4.43 (d, 1H, J = 11.1 Hz), 3.95 (d, 1H,
J = 3.7 Hz), 1.34 (s, 3H), 1.23 (s, 3H); 13C NMR (CDCl3, 75 MHz): d
145.9, 136.4, 132.7, 128.5, 128.1, 127.8, 127.2, 123.8, 119.5,
112.0, 110.1, 105.1, 81.9, 87.6, 79.1, 71.9, 46.7, 26.6, 26.0; ESIMS:
m/z: 382 (M+H)+. HRESIMS: Calcd for C21H24N3O4 m/z 382.1766;
Found, m/z 382.1772.
(neat):
m
3448, 2924, 2854, 1651, 1459, 1086, 748, 569 cmꢂ1 1H
;
NMR (CDCl3, 300 MHz): d 8.04 (t, 1H, J = 8.3 Hz), 7.67–7.58 (m,
1H), 7.47–7.27 (m, 2H), 6.81–6.61 (m, 1H), 5.96–5.81 (m, 1H),
5.73–5.59 (m, 1H), 5.33–4.85 (m, 5H), 4.74–4.62 (m, 1H), 4.30–
3.93 (m, 5H), 3.85–3.60 (m, 2H), 3.40–3.31 (m, 1H); 13C NMR
(CDCl3, 75 MHz): d 148.0, 146.5, 134.1, 133.5, 127.1, 123.9, 120.0,
118.0, 117.5, 110.9, 110.4, 94.9, 78.1, 73.0, 72.7, 71.6, 67.9, 60.2;
ESIMS: m/z: 328 (M+H)+. HRESIMS: Calcd for C18H22N3O3 m/z
328.1661; Found, m/z 428.1654.
4.2.8. [(3aR,5S,6R,6aR)-6-(1H-1,2,3-Benzotriazol-1-yl)-2,2-dime-
thylperhydrofuro[2,3-d][1,3]dioxol-5-yl]methyl pivalate (3h)
4.2.4. (2R,3R,4R,5R)-4-(Acetyloxy)-2-[(acetyloxy)methyl]-5-(1H-
1,2,3-benzotriazol-1-yl)tetrahydro-3-furanyl acetate (3d)
White solid, mp 116–118 °C; ½a D25
ꢂ26.8 (c 1.50, CHCl3); IR
ꢁ
Light-yellow solid, mp 132–134 °C; ½a D25
ꢁ
ꢂ28.1 (c 1.80, CHCl3);
(neat): m 3449, 2974, 2931, 1737, 1455, 1377, 1276, 1143, 1067,
IR (KBr):
695 cmꢂ1
m
2926, 2853, 1746, 1516, 1454, 1240, 1045, 750,
888, 747, 630 cmꢂ1
;
1H NMR (CDCl3, 300 MHz): d 8.04 (d, 1H,
;
1H NMR (CDCl3, 500 MHz): d 8.05 (d,1H, J = 8.7 Hz),
J = 803 Hz), 7.61 (d, 1H, J = 8.3 Hz), 7.46 (t, 1H, J = 7.5 Hz), 7.34 (t,

998
B. V. Subba Reddy et al. / Carbohydrate Research 346 (2011) 995–998
10. Srinivas, C.; Xie, F.; Wang, Q. Tetrahedron Lett. 2005, 46, 2331–2336.
11. Fuertes, M.; Garcia-Muñoz, G.; DE LAS Heras, F. G.; Madroñero, R.; Stud, M.;
Rico, M. Tetrahedron 1972, 28, 4099–4112.
1H, J = 7.5 Hz), 5.92 (d, 1H, J = 3.5 Hz), 5.26 (d, 1H, J = 3.5 Hz), 4.98
(dd, 1H, J = 4.1, 14.1 Hz), 4.78–4.57 (m, 2H), 4.47 (d, 1H, J = 3.5 Hz),
1.41 (s, 3H), 1.33–1.23 (m, 12H); 13C NMR (CDCl3, 75 MHz): d
176.6, 145.5, 132.8, 127.7, 123.5, 119.4, 112.0, 109.3, 104.3, 82.8,
76.1, 75.5, 46.5, 38.6, 26.6, 26.1; ESIMS: m/z: 376 (M+H)+. HRE-
SIMS: Calcd for C19H26N3O5 m/z 376.1872; Found, m/z 376.1870.
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Acknowledgment
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