Bi(OTf)3 as novel and efficient catalyst for the stereoselective synthesis of C-pseudoglycals

Article abstract of DOI:10.1055/s-2004-831187

D-Glycals undergo smoothly allylic rearrangement with allyltrimethylsilane and trimethylsilyl cyanide in the presence of catalytic amount of bismuth triflate to afford the corresponding 2,3-unsaturated allyl glycosides and glycosyl cyanides in excellent y

Full text of DOI:10.1055/s-2004-831187

PAPER
2523
Bi(OTf)3 as Novel and Efficient Catalyst for the Stereoselective Synthesis of
C-Pseudoglycals
B
i(OTf)
a
.
s
N
ovel and
S
E
fficient Cata
.
lyst Yadav,* B. V. S. Reddy, K. Srinivasa Reddy, L. Chandraiah, V. Sunitha
3
Division of Organic Chemistry, Indian Institute of Chemical Technology, Hyderabad–500 007, India
Fax +91(40)27160512; E-mail: yadav@iict.res.in
Received 26 April 2004; revised 23 June 2004
Abstract: D-Glycals undergo smoothly allylic rearrangement with
allyltrimethylsilane and trimethylsilyl cyanide in the presence of
catalytic amount of bismuth triflate to afford the corresponding 2,3-
unsaturated allyl glycosides and glycosyl cyanides in excellent
yields with high a-selectivity.
Key words: bismuth reagents, glycals, pseudoglycals, C-glyco-
sides
Scheme 1
Thus, treatment of 3,4,6-tri-O-acetyl-D-glucal with allyl-
trimethylsilane in the presence of 2 mol% Bi(OTf)3 in
MeCN at ambient temperature resulted in the formation of
2,3-unsaturated allyl glycoside in 95% yield with high a-
selectivity. In a similar fashion, various derivatives of D-
glucal react smoothly with allyltrimethylsilane to give the
corresponding allyl C-pseudoglycals in excellent yields.
These results prompted us to investigate the C-glycosyla-
tion reactions with trimethylsilyl cyanide to produce gly-
cosyl cyanides. 3,4,6-Trisubstituted-D-glucal derivatives
reacted smoothly with TMSCN in the presence of bismuth
triflate to afford the corresponding glycosyl cyanides in
high yields. D-Galactal also underwent allylic rearrange-
ment with carbon nucleophiles under bismuth triflate ca-
talysis to afford the corresponding pseudoglycal C-
glycosides. This method is applicable for both ester and
ether derivatives of D-glucal. There are several advantag-
es in the use of bismuth triflate as catalyst for this trans-
formation, which include high yields of products, cleaner
reaction profiles, short reaction times, operational sim-
plicity and high a-selectivity. All products were charac-
C-Glycosides are versatile chiral intermediates for the
synthesis of many biologically active macromolecules
such as palytoxin, spongistatin, halichondrin and many
others.1 In addition, C-glycosides are potential inhibitors
of carbohydrate processing enzymes and they are stable
analogs of glycals involved in important intra- and inter-
cellular processes.2 In particular, allyl glycosides are at-
tractive due to the presence of a terminal double bond that
can be easily converted into other chiral molecules and
carbohydrate derivatives.3 Among these C-glycosides,
glycosyl cyanides are used as chiral intermediates for the
synthesis of naturally occurring C-nucleoside antibiotics.4
Lewis acids such as titanium tetrachloride, boron trifluo-
ride etherate and TMSOTf are required for the C-glycosi-
lation of glycals with carbon nucleophiles.5 Other
reagents including montmorillonite K10, DDQ and lan-
thanide triflates are also reported to effect this transforma-
tion.6,7 High catalytic activity, low toxicity, moisture and
air tolerance and their recyclability make use of lan-
thanide triflates attractive alternatives to conventional
Lewis acids. However, unfortunately lanthanide triflates
are rather expensive and thus their use in large-scale syn-
thesis is limited. Therefore, cheaper and efficient catalysts
are desirable for glycosidation reactions. In this direction,
bismuth triflate has evolved as remarkable Lewis acid cat-
alyst for effecting various organic transformations.8 Com-
pared to lanthanide triflates, bismuth triflate is an
inexpensive and easy to prepare even on multi-gram scale
in laboratory from commercially available bismuth oxide
and triflic acid.9
1
terized by H, 13C NMR and IR spectra and also by
comparison with authentic samples.10 The ratio of a and
b-isomers was determined by 1H NMR spectrum of crude
product. The spectroscopic data of the products was iden-
tical with the data reported in the literature. The scope and
generality of this method is illustrated with respect to var-
ious glycals and silylated carbon nucleophiles and the re-
sults are presented in the Table 1.
In summary, bismuth triflate is proved to be a remarkable
and highly efficient catalyst for the activation of glycals
under mild conditions. The use of inexpensive and readily
accessible bismuth triflate together with high yields and
good stereoselectivity makes it useful and attractive alter-
native to the more expensive lanthanide triflates or stoi-
chiometric conventional Lewis acids promoted C-
glycosidation procedures.
In this report, we wish to highlight our results on bismuth
triflate catalyzed C-glycosilation of glycals with carbon
nucleophiles (Scheme 1).
SYNTHESIS 2004, No. 15, pp 2523–2526
x
x.
x
x
.
2
0
0
4
Advanced online publication: 19.08.2004
DOI: 10.1055/s-2004-831187; Art ID: Z08204SS
© Georg Thieme Verlag Stuttgart · New York

2524
J. S. Yadav et al.
PAPER
tracted with EtOAc (2 × 10 mL). The combined organic layers were
dried over anhyd Na2SO4 and purified by column chromatography
on silica gel (Merck, 100–200 mesh, EtOAc–hexane, 2:8) to afford
pure glycoside.
Table 1 Bi(OTf)3-Catalyzed Syntheses of C-Pseudoglycals from
Glycols
Entry Substrate (1)
Product (3)
Time Yield Ratio
(min) (%)a (a:b)b
3-(4,6-Di-O-acetyl-2,3-dideoxy-a-D-erythro-hex-2-enopyrano-
syl)-1-propene (3a)
a
15
20
10
20
95
92
89
95
9.5:1
Liquid; [a]D25 +79.9 (c = 1.0, CHCl3).
1H NMR (CDCl3): d = 2.08 (s, 6 H), 2.25 (ddd, J = 5.5, 8.7, 14.5 Hz,
1 H), 2.40 (ddd, J = 6.5, 7.8, 14.7 Hz, 1 H), 3.75 (ddd, J = 3.5, 6.5,
10.0 Hz, 1 H), 4.15 (dd, J = 3.5, 12.0 Hz, 1 H), 4.20 (dd, J = 6.5,
12.0 Hz, 1 H), 4.35 (ddd, J = 2.5, 5.0, 8.7 Hz, 1 H), 5.05 (dd, J = 1.7,
17.3 Hz, 1 H), 5.08 (dd, J = 1.8, 17.3, Hz, 1 H), 5.20 (dd, J = 2.4,
10.0 Hz, 1 H), 5.75 (dd, J = 2.4, 10.5 Hz, 1 H), 5.80 (dd, J = 2.5,
10.5 Hz, 1 H), 5.95 (ddt, J = 6.8, 10.3, 17.3 Hz, 1 H).
13C NMR (1H-decoupled, CDCl3; a-isomer): d = 20.5, 20.8, 37.7,
62.8, 64.9, 69.8, 71.3, 117.4, 123.5, 132.5, 134.0, 169.7, 170.2.
13C NMR (1H-decoupled, CDCl3; b-isomer): d = 20.5, 20.8, 39.8,
63.7, 65.4, 73.9, 74.2, 117.4, 125.0, 132.2, 133.5, 169.7, 170.4.
b
c
7:3
10:1
d
9.5:1
e
f
10
20
25
10
15
88
92
90
89
91
10:1
4,6-Di-O-acetyl 2,3-dideoxy-a-D-erythro-hex-2-enopyranosyl
Cyanide (3b)
a-Isomer: Solid; mp 81.5 °C; [a]D25 –14.8 (c = 1.0, CHCl3).
b-Isomer: Liquid; [a]D25 214° (c = 1.0, CHCl3).
9.5:1
6:4
IR (neat): 2950, 2362, 1732, 1436, 1371, 1221, 1108, 1046, 890,
769 cm–1.
1H NMR (CDCl3): d = 2.15 (s, 3 H), 2.25 (s, 3 H), 4.05 (dt, J = 4.0,
9.0 Hz, 1 H), 4.25 (dd, J = 4.0, 11.8 Hz, 2 H), 5.10 (dt, J = 3.5, 2.5
Hz, 1 H), 5.35 (dq, J = 2.5, 9.0 Hz, 1 H), 5.90 (dt, J = 3.5, 10.5 Hz,
1 H), 6.05 (dt, J = 2.5, 10.5 Hz, 1 H).
13C NMR (1H-decoupled, CDCl3; a-isomer): d = 20.5, 20.6, 62.0,
62.4, 63.5, 71.8, 115.5, 123.4, 129.4, 169.8, 169.9.
g
h
i
9.5:1
9:1
13C NMR (1H-decoupled, CDCl3; b-isomer): d = 20.5, 20.6, 62.3,
62.7, 63.3, 74.2, 115.3, 124.0, 128.5, 169.8, 169.9.
3-(4,6-Di-O-allyl-2,3-dideoxy-a-D-erythro-hex-2-enopyrano-
syl)-1-propene (3c)
Liquid; [a]D25 +36.5 (c = 1.0, CHCl3).
j
25
87
7:3
1H NMR (CDCl3): d = 2.25 (ddd, J = 5.5, 8.5, 14.3 Hz, 1 H), 2.45
(ddd, J = 6.0, 7.5, 14.3 Hz, 1 H), 3.60 (dd, J = 4.0, 12.0 Hz, 2 H),
3.65 (ddd, J = 3.5, 6.5, 9.8 Hz, 1 H), 3.93 (dd, J = 3.5, 12.0 Hz, 1
H), 4.05 (m, 4 H), 4.20 (dt, J = 1.8, 6.0, 8.5 Hz, 1 H), 5.10 (dd, J =
1.3, 17.3 Hz, 3 H), 5.20 (dd, J = 1.5, 17.3 Hz, 3 H), 5.80–6.0 (m, 5
H).
a Isolated yields as pure products after purification.
b Anomeric ratio was determined on the basis of the integrated ratios
of the anomeric hydrogens in 1H NMR spectroscopy.
13C NMR (1H-decoupled, CDCl3): d = 37.9, 62.6, 65.6, 70.2, 71.3,
71.9, 72.5, 117.3, 126.0, 128.0, 130.3, 130.5, 134.2, 134.3, 134.5.
Anal. Calcd for C15H22O3 (250.34): C, 71.97; H, 8.86. Found: C,
71.3; H, 8.28.
Melting points were recorded on Buchi R-535 apparatus and are un-
corrected. IR spectra were recorded on a Perkin-Elmer FT-IR
240-c spectrophotometer using KBr optics. H NMR spectra were
recorded on Gemini-200 spectrometer in CDCl3 using TMS as in-
ternal standard. Mass spectra were recorded on a Finnigan MAT
1020 mass spectrometer operating at 70 eV. CHN analyses were re-
corded on a Vario EL analyzer. The optical rotations were measured
on a Jasco Dip 360 Digital polarimeter.
1
3-(4,6-Di-O-benzoyl-2,3-dideoxy-a-D-erythro-hex-2-enopyra-
nosyl)-1-propene (3d)
Solid; mp 74–76 °C; [a]D25 +105.1 (c = 1.0, CHCl3).
1H NMR (CDCl3): d = 2.30 (ddd, J = 5.5, 8.7, 14.3 Hz, 1 H), 2.53
(ddd, J = 6.0, 7.8, 14.3 Hz, 1 H), 4.31 (ddd, J = 3.5, 6.5, 9.8 Hz, 1
H), 4.39 (dd, J = 3.5, 12.0 Hz, 1 H), 4.52 (dq, J = 4.0, 11.8 Hz, 2 H),
5.08 (dd, J = 1.3, 17.3 Hz, 1 H), 5.15 (dd, J = 1.7, 17.3 Hz, 1 H),
5.48 (ddd, J = 2.1, 5.8, 8.5 Hz, 1 H), 5.88 (ddt, J = 7.3, 10.3, 17.2
Hz, 1 H), 5.97 (dt, J = 2.1, 2.4, 10.3 Hz, 1 H), 6.01 (dt, J = 1.2, 2.1,
10.3 Hz, 1 H), 7.45–7.55 (m, 6 H), 8.05–8.15 (m, 4 H).
13C NMR (1H-decoupled, CDCl3): d = 37.8, 63.7, 65.8, 69.9, 71.3,
117.6, 123.7, 128.2, 128.3, 129.7, 129.7, 129.7, 133.0, 133.1, 133.2,
134.0, 165.9, 166.3.
Stereoselective Synthesis of C-Pseudoglycals; General Proce-
dure
A mixture of D-glucal or D-galactal derivative (2 mmol) and allyl-
trimethylsilane or cyanotrimethylsilane (2.5 mmol) and bismuth tri-
flate (2 mol%) in MeCN (10 mL) was stirred at ambient temperature
for an appropriate time. After complete conversion, as indicated by
TLC, the reaction mixture was diluted with water (10 mL) and ex-
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Bi(OTf)3 as Novel and Efficient Catalyst
2525
3-(4,6-Di-O-benzyl-2,3-dideoxy-a-D-erythro-hex-2-enopyrano-
syl)-1-propene (3e)
J = 2.4, 10.0 Hz, 1 H), 5.80 (ddt, J = 6.8, 10.3, 17.3 Hz, 1 H), 5.95
(dd, J = 2.5, 10.3 Hz, 1 H), 6.03 (dd, J = 2.4, 10.3 Hz, 1 H).
13C NMR (1H-decoupled, CDCl3): d = 20.7, 20.8, 36.8, 62.8, 63.7,
68.0, 72.1, 117.5, 122.0, 133.8, 134.7, 170.3, 170.5.
Liquid; [a]D25 +40.1 (c = 1.5, CHCl3).
1H NMR (CDCl3): d = 2.25 (ddd, J = 5.7, 8.5, 14.3 Hz, 1 H), 2.45
(ddd, J = 6.0, 7.5, 14.3 Hz, 1 H), 3.65 (dq, J = 4.0, 12.0 Hz, 2 H),
3.78 (ddd, J = 3.5, 6.5, 9.8 Hz, 1 H), 3.97 (dd, J = 3.5, 12.0 Hz, 1
H), 4.20 (dt, J = 2.0, 6.0, 8.5 Hz, 1 H), 4.50 (dd, J = 8.5, 14.7 Hz, 2
H), 4.58 (dd, J = 6.5, 14.7 Hz, 2 H), 5.05 (dd, J = 1.3, 17.3 Hz, 1 H),
5.10 (dd, J = 1.5, 17.3 Hz, 1 H), 5.79 (ddt, J = 7.3, 10.3, 17.2 Hz, 1
H), 5.83 (dt, J = 2.0, 2.4, 10.3 Hz, 1 H), 5.85 (dt, J = 1.2, 2.0, 10.3
Hz, 1 H), 7.23–7.35 (m, 10 H).
Anal. Calcd for C13H18O5 (254.28): C, 61.41; H, 7.13. Found: C,
61.05; H, 7.65.
4,6-Di-O-acetyl-2,3-dideoxy-a-D-threo-hex-2-enopyranosyl Cy-
anide (3j)
Solid; mp 115 °C [a]D25 –353 (c = 1.0, CHCl3).
IR (neat): 2927, 2359, 1746, 1436, 1372, 1228, 1048, 1010, 915,
765 cm–1.
1H NMR (CDCl3): d = 2.08 (s, 6 H), 4.19 (dt, J = 4.0, 9.0 Hz, 1 H),
4.25 (dd, J = 4.0, 11.8 Hz, 2 H), 5.15 (dd, J = 2.5, 9.0 Hz, 2 H), 6.05
(dd, J = 3.5, 10.3 Hz, 1 H), 6.25 (dd, J = 2.5, 10.3 Hz, 1 H).
13C NMR (1H-decoupled, CDCl3; a-isomer): d = 20.5, 20.6, 62.0,
62.4, 63.5, 71.8, 115.5, 123.4, 129.4, 169.8, 169.9.
13C NMR (1H-decoupled, CDCl3): d = 38.0, 69.3, 69.9, 70.7, 71.4,
71.9, 73.2, 96.1, 117.1, 125.7, 127.3, 127.4, 127.5, 127.7, 128.1,
128.2, 130.9, 134.4, 138.2.
3-(4,6-Di-O-pivolyl-2,3-dideoxy-a-D-erythro-hex-2-enopyrano-
syl)-1-propene (3f)
Liquid; [a]D25 +82.2 (c = 1.0, CHCl3).
1H NMR (CDCl3): d = 1.20 (s, 18 H), 2.30 (ddd, J = 5.5, 8.7, 14.2
Hz, 1 H), 2.45 (ddd, J = 6.0, 7.9 14.2 Hz, 1 H), 3.97 (ddd, J = 3.3,
6.5, 9.8 Hz, 1 H), 4.18 (dd, J = 3.3, 12.0 Hz, 2 H), 4.28 (dd, J = 6.2,
12.0 Hz, 1 H), 5.07 (ddd, J = 2.4, 5.5, 8.7 Hz, 1 H), 5.10 (dd, J = 1.3,
17.2 Hz, 1 H), 5.13 (dd, J = 1.5, 17.2 Hz, 1 H), 5.78 (dt, J = 2.4, 10.5
Hz, 1 H), 5.85 (ddt, J = 7.0, 10.3, 17.2 Hz, 1 H), 5.91 (dt, J = 2.3,
10.5 Hz, 1 H).
13C NMR (1H-decoupled, CDCl3; b-isomer): d = 20.5, 20.6, 62.3,
62.7, 63.3, 74.2, 115.3, 124.0, 128.5, 169.8, 169.9.
Anal. Calcd for C11H13NO5 (239.23): C, 55.23; H, 5.48, N, 5.86.
Found: C, 55.61; H, 5.50, N, 5.37.
Acknowledgements
13C NMR (1H-decoupled, CDCl3): d = 27.0, 27.1, 38.0, 38.7, 38.8,
62.9, 64.7, 70.4, 71.2, 117.3, 123.9, 132.7, 134.1, 177.8, 178.1.
BVS, KSR, LC and VS thank CSIR, New Delhi for the award of fel-
lowships.
4,6-Di-O-pivolyl-2,3-dideoxy-a-D-erythro-hex-2-enopyranosyl
Cyanide (3g)
References
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3-(4,6-Di-O-methyl-2,3-dideoxy-a-D-erythro-hex-2-enopyrano-
syl)-1-propene (3h)
Liquid; [a]D25 +34.5 (c = 3.0, CHCl3).
1H NMR (CDCl3): d = 2.25 (ddd, J = 5.7, 8.5, 14.3 Hz, 1 H), 2.45
(ddd, J = 6.0, 7.5, 14.3 Hz, 1 H), 3.40 (s, 6 H), 3.53–3.65 (m, 4 H),
4.20 (dt, J = 2.0, 6.0, 8.3 Hz, 1 H), 5.05 (dd, J = 1.5, 17.3 Hz, 1 H),
5.10 (dd, J = 1.5, 17.3 Hz, 1 H), 5.79–5.98 (m, 3 H).
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Anal. Calcd for C11H18O3 (198.26): C, 66.64; H, 9.15. Found: C,
66.05; H, 9.87.
3-(4,6-Di-O-acetyl-2,3-dideoxy-a-D-threo-hex-2-enopyranosyl)-
1-propene (3i)
Liquid; [a]D25 –293 (c = 1.0, CHCl3).
1H NMR (CDCl3): d = 2.07 (s, 3 H), 2.15 (s, 3 H), 2.24 (ddd, J = 5.6,
8.5, 14.3 Hz, 1 H), 2.43 (ddd, J = 6.3, 7.7, 14.5 Hz, 1 H), 4.09 (ddd,
J = 3.5, 6.3, 10.3 Hz, 1 H), 4.18 (dd, J = 3.5, 12.0 Hz, 1 H), 4.20 (dd,
J = 6.3, 12.0 Hz, 1 H), 4.33 (ddd, J = 2.5, 5.0, 8.5 Hz, 1 H), 5.03 (dd,
J = 1.7, 17.3 Hz, 1 H), 5.10 (dd, J = 1.8, 17.3 Hz, 1 H), 5.15 (dd,
Synthesis 2004, No. 15, 2523–2526 © Thieme Stuttgart · New York

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J. S. Yadav et al.
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