Nitrosyl tetrafluoroborate catalyzed preparation of 2,3-unsaturated glycosides and 2-deoxyglycosides of hindered alcohols, thiols, and sulfonamides

Article abstract of DOI:10.1055/s-0032-1318406

Nitrosyl tetrafluoroborate (NOBF₄) has been successfully applied as an efficient organocatalyst for the preparation of 2,3-unsaturated and 2-deoxyglycosides of hindered alcohols, aryl thiols, and aryl sulfonamides from glycal derivatives under

Full text of DOI:10.1055/s-0032-1318406

LETTER
▌581
lNettiertrosyl Tetrafluoroborate Catalyzed Preparation of 2,3-Unsaturated Glyco-
sides and 2-Deoxyglycosides of Hindered Alcohols, Thiols, and Sulfonamides
2,3-Unsaturated Glycosides and 2-Deoxyglycosides
Abhishek Santra, Goutam Guchhait, Anup Kumar Misra*
Division of Molecular Medicine, Bose Institute, P-1/12, C. I. T. Scheme VII M, Kolkata 700054, India
Fax +91(33)23553886; E-mail: akmisra69@gmail.com
Received: 25.01.2013; Accepted: 17.02.2013
is pertinent. Recently, we have used nitrosyl tetrafluorob-
Abstract: Nitrosyl tetrafluoroborate (NOBF4) has been successful-
orate (NOBF4) as an efficient organocatalyst in the activa-
ly applied as an efficient organocatalyst for the preparation of 2,3-
tion of glycosyl trichloroacetimidate derivatives in the
unsaturated and 2-deoxyglycosides of hindered alcohols, aryl thiols,
and aryl sulfonamides from glycal derivatives under the Ferrier re-
stereoselective glycosylations.31 Since the application of
arrangement conditions. Product yields and stereo-outcomes were nonmetallic catalysts in the glycosylation reactions is lim-
very good.
ited, we sought to explore the catalytic potential of
NOBF4 in the Ferrier rearrangement of glycal derivatives.
Therefore, a series of hindered alcohols (e.g., 2° and 3° al-
cohols), thiols, and aryl sulfonamides were allowed to re-
act with D-glucal, D-galactal, and L-rhamnal derivatives in
the presence of NOBF4 as a nonmetallic organocatalyst.
We report herein our findings on these reactions (Scheme
1). To the best of our knowledge NOBF4 has not been
used earlier in this area.
Key words: glycal, Ferrier rearrangement, NOBF4, 2,3-unsaturated
glycoside, 2-deoxyglycoside
2,3-Unsaturated glycosides (pseudoglycals) and 2-deoxy-
glycoside derivatives are useful intermediates in the syn-
thesis of diversity-oriented small-molecule libraries with
definite stereochemistry having immense biological im-
portance.1–3 Acid-catalyzed Ferrier rearrangement4 of gly-
cal derivatives is the best route to achieve 2,3-unsaturated
glycosides. 2,3-Unsaturated glycosides or pseudoglycals
and 2-deoxyglycosides have been used as important inter-
mediates for the synthesis of a number of antibiotics,5 oli-
gosaccharides,6 natural product7 derivatives, and many
bioactive molecules.8 The unsaturated part of the pseudo-
glycal derivative offers the scope of its further modifica-
tions such as aminohydroxylation,9 epoxidation,10
dihydroxylation,11 hydrogenation,12 etc. Although a large
number of reports have appeared in the literature for the
preparation of 2,3-unsaturated or 2-deoxyalkyl- or thio-
glycosides,13–22 but the preparations of sulfonamido
glycosides23–27 are scarce in the literature. Due to its wide
range of synthetic applicability, the Ferrier rearrangement
of glycal derivatives has been carried out using a variety
of metallic and nonmetallic acidic and Lewis acid cata-
lysts.13–27 A number of heterogeneous catalysts28,29 and
special reaction conditions30 have also been used in the
Ferrier rearrangement of glycal derivatives. However,
many of the metal catalysts used in this transformation are
highly expensive, and most of the other catalysts have
several shortcomings such as air- and moisture- sensitivi-
ty, toxicity, oxidizing nature, requirement of stoichiomet-
ric quantity, requirement of catalyst preparation, longer
reaction time, lack of generality, formation of unwanted
side products, etc. Hence the development of a mild, inex-
pensive, and metal-free catalyst for the exclusive prepara-
tion of 2,3-unsaturated glycosides and/or 2-
deoxyglycosides with high anomeric selectivity and yield
OR1
R2XH (1.5 equiv)
NOBF4 (0.1 equiv)
MeCN, r.t.
OR1
O
R1O
O
R1O
R1O
XR2
4–14, 22, 23
30–45 min
R1O
R1O
OR1
O
R1O
R1O
OR1
O
R1 = acyl, alkyl
R2XH = 2°, 3° alcohol, aryl thiol, aryl sulfonamide
XR2
15–21
Scheme 1 Reaction of hindered alcohol, aryl thiol, and aryl sulfon-
amide with glycal derivatives in the presence of NOBF4
During the course of our investigations, tri-O-acetyl-D-
glucal (1) was treated with 5-methyl-2-hexanol (2.0
equiv) in MeCN in the presence of a varied quantity of
NOBF4 at variable temperatures and at room temperature.
It was observed that the reaction of compound 1 with 1.5
equivalents of alcohol in the presence of NOBF4 (0.2
equiv) at room temperature could furnish excellent yield
of 2,3-unsaturated glycoside 4 in 30 minutes. A variety of
2° and 3° alcohols were allowed to react with compound
1 under similar reaction conditions to give good yield of
2,3-unsaturated alkyl glycosides. Other commonly used
organic solvents (e.g., CH2Cl2, THF, and Et2O) were
found inferior to MeCN in terms of the reaction time and
yield. The reaction was further extended by reacting com-
pound 1 with aryl thiols and aryl sulfonamides using sim-
ilar reaction conditions, and to our interest 2,3-
unsaturated thio- and sulfonamido glycosides were ob-
tained in excellent yield. No trace of the formation of fur-
ther rearranged product was observed using thiols, which
was evident in earlier reports.32,33 Since sulfonamide de-
SYNLETT 2013, 24, 0581–0586
Advanced online publication: 01.03.2013
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
DOI: 10.1055/s-0032-1318406; Art ID: ST-2013-D0084-L
© Georg Thieme Verlag Stuttgart · New York

582
A. Santra et al.
LETTER
rivatives play an important role in a wide range of chemo- ic major product has been explained earlier by Colinas et
therapeutic agents used for the treatment of cancers,34,35 al.37 In another set of experiments, the reaction of 3,4-di-
the preparation of 2,3-unsaturated sulfonamido glyco- O-acetyl-L-rhamnal (3) with aryl sulfonamides furnished
sides could add value to the preparation of novel chemo- 2,3-unsaturated sulfonamido glycosides in excellent
therapeutic agents. Inspired by the NOBF4-catalyzed yield. In most of the D-glucal- and L-rhamnal-derived 2,3-
reactions of tri-O-acetyl-D-glucal (1) with a variety of nu- unsaturated glycosides a mixture of two anomers (α and β)
cleophiles, tri-O-acetyl-D-galactal (2) was allowed to re- were formed, the ratio was determined from the integra-
act with a series of hindered alcohols, thiols, and tion values of the peaks in the 1H NMR spectra. The ste-
sulfonamides under similar reaction conditions. To our reochemical assignment of the anomeric centers of the
surprise, exclusive formation of 2-deoxy alkyl-, thio-, and products were carried out considering the position of the
sulfonamido glycosides was observed instead of 2,3-un- anomeric peaks and also by using NOE experiments. The
saturated glycosides. Formation of 2-deoxyglycosides observations on the treatment of compounds 1–3 with hin-
from the acid-catalyzed reaction of tri-O-acetyl-D-galactal dered alcohols, aryl thiols, and aryl sulfonamides are pre-
(2) with different nucleophiles has been documented in sented in Table 1. Other available acid catalysts were also
some earlier instances.36 The reaction of compound 2 with tested to establish a comparative catalytic potential in the
benzenesulfonamide furnished a mixture (2:1) of the α- Ferrier rearrangement, and it was found that NOBF4 has
and β-isomers of the products whereas reaction of com- several advantages to be considered as an efficient or-
pound 2 with p-toluenesulfonamide resulted in the forma- ganocatalyst for the preparation of 2,3-dideoxy- and 2-de-
tion of the β-isomer as the major product (α/β = 1:7). oxyglycosides from glycals (Table 2).
Formation of the thermodynamically controlled β-isomer-
Table 1 Preparation of 2,3-Unsaturated and 2-Deoxyglycosides of Secondary and Tertiary Alcohols, Thiols, and Sulfonamidesa
Entry
Glycal
Alcohol, thiol, or sulfonamide
5-methyl-2-hexanol
Product
Time
(min)
Yield (%)b
(α/βc)
OAc
OAc
O
AcO
O
AcO
AcO
78
(4:1)
O
1
30
1
4
OAc
AcO
O
80
2
3
1
t-BuOH
30
30
O
(5:1)38
5
OAc
AcO
O
76
O
1
1
2-methyl-2-butanol
(α)39
6
OAc
O
AcO
74
4
5
cholesterol
30
40
O-cholesteryl
(12:1)17
7
OAc
O
AcO
OH
O
O
72
BnO
1
O
BnO
(10:1)28
BnO
BnO
BnO
OMe
BnO
OMe
8
Synlett 2013, 24, 581–586
© Georg Thieme Verlag Stuttgart · New York

LETTER
2,3-Unsaturated Glycosides and 2-Deoxyglycosides
583
Table 1 Preparation of 2,3-Unsaturated and 2-Deoxyglycosides of Secondary and Tertiary Alcohols, Thiols, and Sulfonamidesa (continued)
Entry
Glycal
Alcohol, thiol, or sulfonamide
Product
Time
(min)
Yield (%)b
(α/βc)
OAc
O
AcO
HO
BnO
OBn
O
O
74
OBn
O
6
1
40
(11:1)40
BnO
BnO
BnO
OMe
OMe
9
OAc
O
AcO
76
7
8
1
1
PhSO2NH2
40
40
(6:1)21
NHSO2Ph
NHSO2Tol
10
OAc
O
AcO
78
TolSO2NH2
(α)22
11
OAc
HS
AcO
O
77
9
1
1
30
30
(12:1)41
S
S
12
OAc
HS
HS
AcO
O
74
10
(10:1)28
13
OAc
AcO
O
72
11
1
30
(α)42
S
14
AcO
OAc
AcO
OAc
O
O
AcO
76
12
13
t-BuOH
30
30
AcO
(α)43
O
2
15
AcO
OAc
O
AcO
74
(α)
2
cholesterol
O-cholesteryl
NHSO2Ph
16
AcO
OAc
O
AcO
76
(2:1)
14
15
2
2
PhSO2NH2
TolSO2NH2
45
45
17
AcO
OAc
O
AcO
74
(1:7)
NHSO2Tol
18
© Georg Thieme Verlag Stuttgart · New York
Synlett 2013, 24, 581–586

584
A. Santra et al.
LETTER
Table 1 Preparation of 2,3-Unsaturated and 2-Deoxyglycosides of Secondary and Tertiary Alcohols, Thiols, and Sulfonamidesa (continued)
Entry
Glycal
Alcohol, thiol, or sulfonamide
Product
Time
(min)
Yield (%)b
(α/βc)
AcO
AcO
OAc
O
HS
70
(9:1)
16
2
30
S
19
AcO
OAc
O
HS
AcO
74
(10:1)
17
18
2
2
30
30
S
OMe
OMe
20
AcO
OAc
O
HS
AcO
70
(α)
S
Br
Br
21
O
O
O
AcO
22
72
(5:1)
AcO
NHSO2Ph
NHSO2Tol
19
20
PhSO2NH2
TolSO2NH2
30
30
OAc
3
AcO
23
75
3
(9:1)44
a All reactions were carried out at r.t.
b Isolated yield.
c The α/β ratio was determined from the integration values of the peaks in the 1H NMR spectrum.
Table 2 Comparative Catalytic Potential of Different Catalysts in the Reaction of tri-O-Acetyl-D-glucal (1) with tert-Butanol in MeCN at
Room Temperature
Entry
Substrate
Product
Catalyst (equiv)
Time (h)
Yield (%)
1
2
NOBF4 (0.2)
0.5
5
80
72
camphorsulfonic acid (0.3)
OAc
OAc
O
AcO
O
AcO
AcO
3
HClO4–SiO2 (0.2)
0.5
20
O
1
5
4
5
ZnCl2 (0.2)
6
1
65
70
HBr·Ph3P (0.2)
In conclusion, NOBF4 has been used as an efficient or- glycosides was observed without formation of a trace of
ganocatalyst to prepare 2,3-unsaturated sterically hin- 2,3-unsaturated glycosides. The reaction conditions are
dered alkyl, thio, and sulfonamido glycosides from D- reasonably fast, clean, high-yielding, and thus may be
glucal and L-rhamnal derivatives and 2-deoxy alkyl, thio, considered as a suitable alternative to the existing method-
and sulfonamido galactosides from D-galactal derivatives. ologies in this area.
In the case of D-galactal exclusive formation of 2-deoxy-
Synlett 2013, 24, 581–586
© Georg Thieme Verlag Stuttgart · New York

LETTER
2,3-Unsaturated Glycosides and 2-Deoxyglycosides
585
General Experimental Conditions
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To a solution of 3,4,6-tri-O-acetyl-D-glucal (1; 1.0 mmol) and 2°, 3°
aliphatic alcohol, aryl thiol, or aryl sulfonamide (1.5 mmol) in
MeCN (5 mL) was added NOBF4 (0.2 mmol), and the reaction mix-
ture was allowed to stir at r.t. for the appropriate time as mentioned
in Table 1. The reaction mixture was filtered and washed with
CH2Cl2 (25 mL). The combined filtrate was concentrated under re-
duced pressure to give the crude product, which was purified over
SiO2 using hexane–EtOAc as eluant to give pure 2,3-unsaturated or
2-deoxyglycoside. All known compounds gave NMR spectra that
matched the data reported in the cited references.45
Acknowledgment
A.S. thanks CSIR, New Delhi for providing a Senior Research Fel-
lowship. This project was funded by the CSIR, New Delhi [Project
No. 02 (0038)/11/EMR-II].
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(45) Spectral data of the products those are not reported earlier
are as follows.
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5-Methyl-2-hexyl 4,6-Di-O-acetyl-2,3-dideoxy-α-D-
erythro-hex-2-enopyranoside (4)
(6) Bussolo, V. D.; Kim, Y. J.; Gin, D. Y. J. Am. Chem. Soc.
1998, 120, 13515.
1H NMR (500 MHz, CDCl3):  = 5.78–5.71 (m, 1 H, H-2),
5.69–5.66 (m, 1 H, H-3), 5.23–5.20 (m, 1 H, H-4), 5.05 (br
s, 1 H, H-1), 4.19–4.10 (m, 2 H, H-6ab), 4.02–3.98 (m, 1 H),
1.99, 1.96 (2 s, 6 H, 2 COCH3), 1.72–1.58 (m, 1 H), 1.48–
1.38 (m, 2 H), 1.18 (br s, 3 H), 1.13–1.07 (m, 2 H), 0.89, 0.84
(2 s, 6 H). 13C NMR (125 MHz, CDCl3): δ = 170.7, 170.2,
129.0, 128.4, 91.2, 67.1, 65.2, 63.4, 47.5, 25.0, 23.1, 23.0,
22.9, 22.5, 21.0, 20.8, 20.1. ESI-MS: m/z = 351.1 [M + Na]+.
Anal. Calcd for C17H28O6 (328.18): C, 62.17; H, 8.59.
Found: C, 62.02; H, 8.80.
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Tetrahedron Lett. 2001, 42, 4053.
(19) Yadav, J. S.; Reddy, B. V. S. Synthesis 2002, 511.
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and references cited therein.
(22) Yadav, J. S.; Reddy, B. V. S.; Reddy, K. B.; Satyanarayana,
M. Tetrahedron Lett. 2002, 43, 7009.
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Tetrahedron Lett. 2004, 45, 6481.
(24) Colinas, P. A.; Bravo, R. D. Carbohydr. Res. 2007, 342,
2297.
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Lett. 2010, 51, 5372.
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1154.
Cholesteryl 3,4,6-Tri-O-acetyl-2-deoxy-α-D-
galactopyranoside (16)
1H NMR (500 MHz, CDCl3): δ = 5.28–5.23 (m, 2 H, H-1, H-
3), 5.08 (br s, 1 H, H-4), 4.17–4.15 (m, 1 H, H-5), 4.04–3.97
(m, 2 H, H-6ab), 3.40–3.30 (m, 1 H), 2.26–2.21 (m, 1 H), 2.16
(s, 3 H, COCH3), 2.03–1.98 (m, 1 H, H-2e), 1.97, 1.90 (2 s,
6 H, 2 COCH3), 1.92–1.86 (m, 1 H, H-2a), 1.80–0.60 (m, 43
H, cholesterol). 13C NMR (125 MHz, CDCl3): δ = 170.4,
170.1, 170.0, 140.7, 121.9, 95.7, 77.3, 66.9, 66.7, 66.4, 62.7,
56.7, 56.1, 50.2, 42.3, 40.0, 39.8, 39.5, 37.1, 36.7, 36.2, 35.8,
31.9, 31.8, 30.7, 28.2, 28.0, 27.9, 24.3, 23.8, 22.8, 22.6, 21.0,
20.9, 20.8, 20.7, 19.3, 18.7, 11.8. ESI-MS: m/z = 681.4 [M +
Na]+. Anal. Calcd for C39H62O8 (658.44): C, 71.09; H, 9.48.
Found: C, 70.91; H, 9.66.
Benzenesulfonamido 3,4,6-Tri-O-acetyl-2-deoxy-α-D-
galactopyranoside (17)
1H NMR (500 MHz, CDCl3): δ = 7.86–7.82 (m, 2 H, ArH),
7.51–7.40 (m, 2 H, ArH), 6.70 (d, J = 7.5 Hz, 1 H, NH),
5.45–5.43 (m, 1 H, H-1), 5.19–5.15 (m, 1 H, H-3), 5.11 (br
s, 1 H, H-4), 3.71–3.67 (m, 1 H, H-6a), 3.62–3.59 (m, 1 H,
H-6b), 3.14–3.12 (m, 1 H, H-5), 2.25–2.19 (m, 1 H, H-2e),
2.00, 1.98, 1.78 (3 s, 9 H, 3 COCH3), 1.80–1.74 (m, 1 H, H-
2a). 13C NMR (125 MHz, CDCl3): δ = 171.2, 170.2, 170.1,
141.1-126.7 (ArC), 79.1, 66.7, 65.7, 65.5, 60.8, 29.3, 20.8,
20.7, 20.6. ESI-MS: m/z = 452.1 [M + Na]+. Anal. Calcd for
C18H23NO6S (429.11): C, 50.34; H, 5.40. Found: C, 50.26;
H, 5.57.
p-Toluenesulfonamido 3,4,6-Tri-O-acetyl-2-deoxy-β-D-
© Georg Thieme Verlag Stuttgart · New York
Synlett 2013, 24, 581–586

586
A. Santra et al.
LETTER
galactopyranoside (18)
CDCl3):  = 170.3, 170.1, 169.8, 159.9, 134.9 (2 C), 124.0,
114.7 (2 C), 84.7, 67.4, 66.8 (2 C), 62.4, 55.3, 30.6, 20.9,
20.0 (2 C). ESI-MS: m/z = 435.1 [M + Na]+. Anal. Calcd for
C19H24O8S (412.12): C, 55.33; H, 5.87. Found: C, 55.20; H,
6.0.
1H NMR (500 MHz, CDCl3): δ = 7.71–7.69 (m, 2 H, ArH),
7.21–7.17 (m, 2 H, ArH), 6.28 (d, J = 7.6 Hz, 1 H, NH), 5.12
(d, J = 3.0 Hz, 1 H, H-4), 4.94–4.89 (m, 1 H, H-3), 4.86–4.81
(m, 1 H, H-1), 3.84–3.80 (m, 1 H, H-5), 3.71–3.63 (m, 1 H,
H-6ab), 2.32 (s, 3 H, CH3), 1.99, 1.94, 1.91 (3 s, 9 H, 3
COCH3), 1.98–1.95 (m, 1 H, H-2e), 1.79–1.72 (m, J = 12.0
Hz each, 1 H, H-2a). 13C NMR (125 MHz, CDCl3): δ = 170.3,
170.2, 169.8, 143.8–127.2 (ArC), 80.6, 72.3, 68.5, 64.9,
61.3, 31.9, 21.5, 20.8, 20.7, 20.5. ESI-MS: m/z = 466.1 [M +
Na]+. Anal. Calcd for C19H25NO9S (443.12): C, 51.46; H,
5.68. Found: C, 51.32; H, 5.87.
p-Bromophenyl 3,4,6-Tri-O-acetyl-2-deoxy-1-thio-α-D-
galactopyranoside (21)
1H NMR (200 MHz, CDCl3):  = 7.44–7.31 (m, 4 H, ArH),
5.73–5.70 (m, 1 H, H-1), 5.35 (br s, 1 H, H-4), 5.28–5.19 (m,
1 H, H-3), 4.66–4.60 (m, 1 H, H-5), 4.10–4.06 (m, 2 H, H-
6ab), 2.56–2.40 (m, 1 H, H-2e), 2.14 (s, 3 H, COCH3), 2.13–
2.07 (m, 1 H, H-2a), 2.00, 1.99 (2 s, 6 H, 2 COCH3). 13
C
2-Naphthyl 3,4,6-Tri-O-acetyl-2-deoxy-1-thio-α-D-
galactopyranoside (19)
NMR (125 MHz, CDCl3):  = 170.1, 169.9, 169.6, 133.0–
121.7 (ArC), 83.4, 67.7, 66.5 (2 C), 62.2, 30.5, 20.7, 20.6 (2
C). ESI-MS: m/z = 483.0 [M + Na]+. Anal. Calcd for
C18H21BrO7S (460.02): C, 46.86; H, 4.59. Found: C, 46.70;
H, 4.80.
1H NMR (200 MHz, CDCl3):  = 7.96–7.42 (m, 7 H, ArH),
5.91–5.88 (m, 1 H, H-1), 5.39 (br s, 1 H, H-4), 5.36–5.29 (m,
1 H, H-3), 4.74–4.70 (m, 1 H, H-5), 4.15–4.04 (m, 2 H, H-
6ab), 2.58–2.47 (m, 1 H, H-2e), 2.13 (s, 3 H, COCH3), 2.11–
2.07 (m, 1 H, H-2a), 2.01, 1.79 (2 s, 6 H, 2 COCH3). ESI-MS:
m/z = 455.1 [M + Na]+. Anal. Calcd for C22H24O7S (432.12):
C, 61.10; H, 5.59. Found: C, 61.0; H, 5.77.
Benzenesulfonamido 2,3,6-Tri-deoxy-α-L-erythro-hex-2-
enopyranoside (22)
1H NMR (500 MHz, CDCl3):  = 7.87–7.40 (m, 5 H, ArH),
6.56 (d, J = 7.9 Hz, 1 H, NH), 5.79–5.76 (m, 1 H, H-2),
5.72–5.70 (m, 1 H, H-3), 5.48–5.46 (m, 1 H, H-1), 4.83–4.80
(m, 1 H, H-4), 3.33–3.29 (m, 1 H, H-5), 1.97 (s, 3 H,
COCH3), 0.57 (d, J = 6.0 Hz, 3 H, CCH3). 13C NMR (125
MHz, CDCl3): δ = 170.3, 141.8–126.7 (m, ArC, C-2, C-3),
76.8, 69.9, 64.9, 20.9, 17.1. ESI-MS: m/z = 334.0 [M + Na]+.
Anal. Calcd for C14H17NO5S (311.08): C, 54.01; H, 5.50.
Found: C, 53.85; H, 5.69.
p-Methoxyphenyl 3,4,6-Tri-O-acetyl-2-deoxy-1-thio-α-D-
galactopyranoside (20)
1H NMR (200 MHz, CDCl3):  = 7.36–7.22 (m, 2 H, ArH),
6.79–6.75 (m, 2 H, ArH), 5.51–5.48 (m, 1 H, H-1), 5.29 (br
s, 1 H, H-4), 5.24–5.14 (m, 1 H, H-3), 4.68–4.62 (m, 1 H, H-
5), 4.07–4.00 (m, 2 H, H-6ab), 3.73 (s, 3 H, OCH3), 2.45–2.29
(m, 1 H, H-2e), 2.07 (s, 3 H, COCH3), 2.01–1.86 (m, 1 H, H-
2a), 1.96, 1.94 (2 s, 6 H, 2 COCH3). 13C NMR (125 MHz,
Synlett 2013, 24, 581–586
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