1,2-Cyclic sulfite and sulfate furanoside diesters: improved syntheses and stability

Article abstract of DOI:10.1016/j.tet.2009.06.013

The facile syntheses of 1,2- and 3,5-cyclic sulfite and sulfate furanoside diesters were conducted in molecular solvents and ionic liquids in the presence of immobilised morpholine. Molecular solvents and ionic liquids performed similarly with regards to overall yields. However, the use of ILs allowed for the reactions to be carried out under atmospheric conditions and showed good recyclability. Additionally, increases in product stability was achieved in ILs over organic solvents, in particular, in bis{(trifluoromethanesulfonyl)imide} and trispentafluoro-ethyltrifluorophosphate-based ionic liquids, which were also excellent media to control the hydrolysis of thionyl chloride and sulfuryl chloride.

Full text of DOI:10.1016/j.tet.2009.06.013

Tetrahedron 65 (2009) 6341–6347
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
1,2-Cyclic sulfite and sulfate furanoside diesters: improved syntheses and stability
*
*
Christopher Hardacre , Ivano Messina, Marie E. Migaud , Kerry A. Ness, Sarah E. Norman
School of Chemistry and Chemical Engineering, David Keir Building, Stranmillis Road, Queen’s University, Belfast BT9 5AG, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 1 April 2009
Received in revised form 20 May 2009
Accepted 4 June 2009
Available online 10 June 2009
The facile syntheses of 1,2- and 3,5-cyclic sulfite and sulfate furanoside diesters were conducted in
molecular solvents and ionic liquids in the presence of immobilised morpholine. Molecular solvents and
ionic liquids performed similarly with regards to overall yields. However, the use of ILs allowed for the
reactions to be carried out under atmospheric conditions and showed good recyclability. Additionally,
increases in product stability was achieved in ILs over organic solvents, in particular, in bis{(tri-
fluoromethanesulfonyl)imide} and trispentafluoro-ethyltrifluorophosphate-based ionic liquids, which
were also excellent media to control the hydrolysis of thionyl chloride and sulfuryl chloride.
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Cyclic-sulfite
Cyclic-sulfate
Carbohydrates
Ionic liquids
1. Introduction
sulfate derivatives of carbohydrates have the potential to be ver-
satile synthetic precursors to modified nucleosides, C-nucleosides
Thionyl chloride (SOCl2) and sulfuryl chloride (SO2Cl2) are ex-
tensively used in industry for the manufacture of materials ranging
from herbicides, drugs and dyestuffs to thermoplastics, surfactants
and electrolytes.1,2 In organic synthesis; they are primarily used as
chlorination reagents,2,3 while the reactivity of their respective
cyclic sulfodiester derivatives is often compared with that of ep-
oxides.4,5 One limitation to the use of SOCl2 and SO2Cl2 arises from
their high reactivity towards moisture. Similarly, cyclic sulfite/sul-
fate esters have had limited applications due to problems associ-
ated with their syntheses4,6,7 (e.g., difficulties in controlling
cyclisation vs chlorination), as well as their variable reactivity to-
wards nucleophiles.8,9 For example, there are currently only two
reported procedures used to prepare 1,2-cyclic sulfites from 1,2-
diols. These involve thionyl chloride or N,N0-thionyl diimidazole in
pyridine under anhydrous and temperature controlled condi-
tions.8,10 Similarly, this chemistry is not applicable to cyclic sulfates
which are prepared from the cyclic sulfite precursors, via oxidation
with ruthenium tetroxide, thus limiting their potential usage es-
pecially within an industrial setting.5 These issues are further ex-
acerbated in the case of partially protected sugar 1,2-diols which do
not behave as standard diols, as the stereochemistry of anomeric
position (alpha and beta configuration at C-1 of the sugar) controls
the sulfite/sulfate formation, reactivity and stability, especially to-
wards water.11 This is particularly relevant as 1,2-cyclic sulfite and
and any derivatives where a ring opening via a nucleophilic sub-
stitution at the C-1 position of the sugar results in the regio- and
stereo-selective introduction of the aglycon unit. Therefore, if the
synthetic and stability problems related to these sulfur-containing
reagents could be overcome, cyclic sulfites and sulfates would find
a wider range of applications in organic synthesis and large scale
productions, in particular in C-nucleoside chemistry. Herein, we
report a simple procedure for which reaction and work-up condi-
tions have been optimised in order to maximise conversion and
minimise furanosyl cyclic sulfoester decomposition. Additionally,
we have investigated the possibility of using non-molecular sol-
vents in order to achieve higher conversions/yields by providing
a stabilising media.
2. Results and discussion
2.1. Synthesis of cyclic sulfites and sulfates in ILs
and molecular solvents
To date, the syntheses of cyclic sulfites from diols has to be
carried out under strictly anhydrous conditions, with or without
the use of triethylamine or pyridine as base4,6 and this has resulted
in varied success. Cyclic sulfates are commonly obtained by mild
oxidation of the sulfite parents using Sharpless’ conditions re-
quiring the use of heavy metals.12–14 In general, direct syntheses of
cyclic sulfates from diols and SO2Cl2 generate several side products
(competition between chlorination, multiple sulfurylation and cy-
clic sulfate formation) and average yields.11 Only one report
* Corresponding authors. Tel.: þ44 2890 974339/4592; fax: þ44 2890 974687.
E-mail addresses: c.hardacre@qub.ac.uk (C. Hardacre), m.migaud@qub.ac.uk
(M.E. Migaud).
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.06.013

6342
C. Hardacre et al. / Tetrahedron 65 (2009) 6341–6347
Table 1
Synthesis of cyclic sulfites from 1,2- and 3,5-partially protected furanose derivatives
Diols
Cyclic sulfites
Conditions
Isolated yields
O
O
O
OH
SOCl2 NEt3, DCM
SOCl2 NEt3, [C4mpyrr][NTf2]
SOCl2 PS-Morp, DCM
50
67
57
75
BnO
BnO
*
S
O
O
OH
SOCl2 PS-Morp, [C4mpyrr][NTf2]
BnO
BnO
HO
1
5
O
O
O
O
SOCl2 NEt3, DCM
SOCl2 NEt3, [C4mpyrr][NTf2]
SOCl2 PS-Morp, DCM
62
83
55
83
HO
O
O
S
O
O
O
SOCl2 PS-Morp, [C4mpyrr][NTf2]
*
2
6
O
O
O
OH
PivO
PivO
SOCl2 NEt3, DCM
SOCl2 NEt3, [C4mpyrr][NTf2]
SOCl2 PS-Morp, DCM
50
38
57
43
*
S
S
O
O
O
SOCl2 PS-Morp, [C4mpyrr][NTf2]
PivO
BnO
PivO
OH
3
7
SOCl2 NEt3, DCM
SOCl2 NEt3, [C4mpyrr][NTf2]
SOCl2 PS-Morp, DCM
74
O
O
O
OH
a
PivO
PivO
*
78
a
SOCl2 PS-Morp, [C4mpyrr][NTf2]
O
BnO
OH
4
8
a
Product not extractable from the IL.
describes the direct formation of cyclic sulfates from diols but the
procedure requires controlled conditions such as 0 ꢀC, anhydrous
atmosphere and slow reagent addition.11
with low recovery yields in the case of molecular solvents, but re-
duced hydrolysis was observed in the case of the IL. Further opti-
misation of the work-up conditions eliminated the need for an
aqueous treatment. In this case, filtration, to remove solid sup-
ported morpholine, followed by flushing through a short pad of
silica provided a method whereby high isolated yields could be
achieved. Whilst the arabinose and ribose derivatives gave similar
isolated yields in DCM, it was not possible to extract the riboside
product 8 from the IL using diethyl ether, nor to perform an
aqueous/DCM work-up due to rapid hydrolysis.
Humenik reported that the formation of a-cyclic sulfites from
1,2-deprotected sugars of the type 5, 7 and 8 (Table 1) was pre-
vented through anomeric destabilisation of the C1–O-bond.15
However Beaupere reported that such cyclic sulfites could be
obtained for the pyranose form of arabinose.8 In order to establish
whether direct access to cyclic sulfites and sulfates species could be
formed from 1,2- and 3,5-deprotected sugars (Scheme 1), the re-
actions of a series of sugar-diols (Table 1, 1–4) and bases with thi-
onyl chloride were investigated.
All reactions proceeded with the formation of a mixture of
diastereoisomers. Initial spectroscopic analysis revealed that this
The synthesis of cyclic sulfite diester sugars was carried out at
room temperature using triethylamine or immobilised morpholine
in either anhydrous DCM under an atmosphere of argon, or in non-
dried [C4mpyrr][NTf2] in air. The isolated yields of the reaction
products are summarised in Table 1. In both molecular and ionic
solvents, the use of immobilised morpholine led to a reduction in
side-product formation and allowed for an easier reaction workup.
Upon aqueous work-up, rapid product hydrolysis could be observed
was not a mixture of a and b isomers, but diastereoisomers due to
the inherent chirality of tetrahedral sulfur (Fig. 1). The diastere-
oisomeric ratio being independent of the reaction conditions
used.
Initial attempts to access the cyclic sulfates from the sulfite de-
rived from 3,5-di-O-benzyl xylofuranose 1 using the standard
Sharpless oxidation reaction conditions proved unsuccessful.3 This
was due to the rapid hydrolysis of the cyclic sulfate product which
RO
O
O
O
O
*
OR'
S
*
O
RO
S
O
O
O
O
RO
OR'
SO Cl2
x
OR'
OR'
SO Cl2
x
x = 1
x = 1
or
O
Base
Base
Solvent
or
O
RO
Solvent
O
RO
O
OR'
R=H, Piv or Bn
R'=H or isopropylidene
O
S
O
O
S
O
OR'
x = 2
O
RO
O
x = 2
Scheme 1. Preparation of the 1,2-cyclic sulfite and sulfate diester furanosides.

C. Hardacre et al. / Tetrahedron 65 (2009) 6341–6347
6343
observed in the presence of solid supported morpholine. This base
then negates the use of an aqueous work-up thus preventing loss of
material due to hydrolysis of these very sensitive functionalities.
Filtration through a pad of silica, rather than purification by column
chromatography also improved the isolated yields.
Given that the cyclic sulfite/sulfate formation in non-dried ILs
(in the absence of an inert atmosphere) shows enhanced yields and
stability over the anhydrous DCM counterparts, a stability study of
the moisture sensitive SOCl2/SO2Cl2 reagents in a range of solvents
was initiated. The stabilities were analysed over time using Raman
spectroscopy in air and moisture equilibrated ILs. The stability was
assessed by dissolving 10 mol % SOCl2 and SO2Cl2 in a range of ILs
and compared with a range of organic solvents. The results are
summarised in Table 3 which shows the percentage of SOCl2 and
SO2Cl2 remaining after a 12 h and 72 h period.
PGO
PGO
O
O
O
O
PGO
O
PGO
O
O
S*
O
S
*
Figure 1. Structure illustrating the chiral configurations of the sulfur moiety.
occurs under the aqueous conditions required for this salt-catalysed
oxidation.16 This result was independent of the nature of the solvent
and was attributed to the increased reactivity of the C-1–O–S linkage
towards water once the sulfur center had been oxidised. Direct
synthesis of the cyclic sulfate derived from 3,5-di-O-benzyl xylo-
furanose, 1, was obtained with SO2Cl2 in the presence of base, and to
the best of our knowledge, this is the first time SO2Cl2 has been used
in one step procedure to form 1,2-carbohydrate cyclic sulfates. Again,
the combined use of immobilised morpholine and [C4mpyrr][NTf2]
further increased the yields compared with DCM, as shown in Table
2. A similar trend was also observed for the more robust cyclic sulfate
As expected, hydrophilic solvents, THF and [C4mpyrr][OTf],
showed low ability to stabilise both SOCl2 and SO2Cl2 with either
Table 3
Stability of SOCl2 and SO2Cl2 in a range of wet ILs and organic solvents stirred in air at
20 ꢀC monitored by Raman spectroscopy. The composition for each reagent in the
mixture is a percentage compared with the Raman taken after initial addition of the
reagent to the solvent at time¼0 h, normalised to the spectral features of the solvent
derivative of 1,2-O-isopropylidene-a-xylofuranose, 2. In the case of
the arabinose derivative 3, the synthesis of cyclic sulfate was lower
yielding in both organic solvents and ILs compared with the other
furanosides. The lower yields of the arabinose reactions may be at-
Solvent
Solvent/H2O Mol ratioa
Time (h)
SOCl2 (%)
SO2Cl2 (%)
[C4mpyrr][NTf2]
107:1
12
72
100
100
100
15
tributed in part to the 60:40
a
/b
ratio of starting materials and the
iso-
preferred cis configuration of the product, which favours the
b
[C4mim][NTf2]
[C4dmim][NTf2]
[C4mpyrr][FAP]
61:1
48:1
12
72
95
15
92
8
mer. In addition, the increased reactivity of the highly strained
trans-cyclic sulfate, would increase the likelihood of product de-
composition, resulting in lower yields. Reactions to form the cyclic
sulfate from 3-O-benzyl-5-O-pivaloyl-D-ribofuranoside 4 resulted in
no product being formed in either the organic solvent or ionic liquid.
The benzyl protecting group at C-3 may be responsible for this lack of
12
72
84
25
90
20
307:1
12
72
100
98
100
100
reaction since it hinders the a-face.
[C4mpyrr][OTf]
THF
1.5:1
12
0
0
Unlike the reactions with SOCl2 which formed only one
anomeric species, the reactions with SO2Cl2 resulted in the for-
mation of an anomeric mixture, leading to the formation of both cis
and trans cyclic sulfates. However, in agreement with the synthesis
of the cyclic sulfite, regardless of the reaction conditions used, the
ratio of cis/trans ring systems remained independent of the fu-
ranoside stereochemistry.
Whilst both DCM and ILs offer a medium in which to perform
the reactions of SOCl2 and SO2Cl2 with partially protected furano-
sides to form cyclic sulfites and sulfates, a marked improvement is
<1453:1
12
72
70
0
48
0
Hexane
<1072:1
<461:1
12
72
90
50
84
30
Benzene
12
72
94
32
92
5
DCM
<1046:1
12
72
100
0
100
0
a
Water content determined at t¼0 h.
Table 2
Synthesis of cyclic sulfates from 1,2- and 3,5-partially protected furanose derivatives
Diols
Cyclic sulfates
Conditions
Isolated yields
O
O
O
OH
SO2Cl2 NEt3, DCM
SO2Cl2 NEt3, [C4mpyrr][NTf2]
SO2Cl2 PS-Morp, DCM
43
62
47
67
O
BnO
BnO
S
O
O
SO2Cl2 PS-Morp, [C4mpyrr][NTf2]
OH
BnO
BnO
HO
1
9
O
O
O
O
SO2Cl2 NEt3, DCM
SO2Cl2 NEt3, [C4mpyrr][NTf2]
SO2Cl2 PS-Morp, DCM
61
73
55
69
O
HO
O
S
O
SO2Cl2 PS-Morp, [C4mpyrr][NTf2]
O
O
10
2
O
SO2Cl2 NEt3, DCM
SO2Cl2 NEt3, [C4mpyrr][NTf2]
SO2Cl2 PS-Morp, DCM
27
30
35
9
O
O
OH
O
PivO
PivO
O
S
SO2Cl2 PS-Morp, [C4mpyrr][NTf2]
O
O
OH
PivO
PivO
11
3

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C. Hardacre et al. / Tetrahedron 65 (2009) 6341–6347
hydrolysis of the reagent or, in the case of the triflate anion, nu-
cleophilic attack on the electron deficient sulfur centre being ob-
served. Higher stability was displayed in more hydrophobic
solvents with the [FAP]ꢁ based ionic liquid showing the highest
degree stabilization of both reagents. In this case, only 2% degra-
dation was observed over 72 h. Interestingly, despite the high levels
of water found in the [NTf2]ꢁ based ionic liquids compared with the
organic solvents, similar stability of the SOCl2 and SO2Cl2 was ob-
served. Although both [C4mpyrr][NTf2] and [C4mpyrr][FAP] were
able to stabilize SOCl2, only the [FAP]ꢁ based ionic liquids were able
to stabilise SO2Cl2 reflecting the increased reactivity of the latter
reagent. Even though the [FAP]ꢁ based ionic liquid clearly stabilise
SOCl2 and SO2Cl2 far better than the other solvents, due to the in-
solubility of the partially protected carbohydrates, the subsequent
preparation of the cyclic sulfite/sulfates was not possible in this
medium. Importantly, although DCM is the most commonly used
solvent for cyclic sulfite/sulfate formation, this solvent showed very
limited ability for the stabilisation of the reagents over time in air.
Similar effects have been observed previously for PCl3 and POCl3
where higher stability was observed in ionic liquids when com-
pared with commonly used organic solvents. No hydrolysis was
found in wet [C4mpyrr][NTf2] for PCl3 and [C5mim][FAP] for POCl3
over one week open to air and this behaviour was attributed to the
distribution of water molecules in the ILs.17 In the present study
only [FAP]ꢁ based ionic liquids provided the enhanced stability for
both sulfur containing electrophiles (SOCl2, SO2Cl2). This may re-
flect the increased hydrolytic instability of the sulfur reagents
compared with the phosphorus based reagents. It was, therefore,
informative to examine the kinetics of the hydrolysis. For the or-
ganic solvents, a gradual degradation of the solute is observed,
whereas in the [NTf2]ꢁ based ionic liquids, the solutes remained
stable for a period of time before rapid hydrolytic reaction occurred
(see the Supplementary data). This reflected the need for a critical
amount of water to be present in the IL before hydrolysis became
significant. During hydrolysis, chloride is released into the solution
which creates a binary ionic liquid consisting of both hydrophilic,
Clꢁ, and hydrophobic, [NTf2]ꢁ, anions. This increases the hydro-
philicity of the media raising the water content further which, in
turn, results in more hydrolysis and rapid decomposition.
4. Experimental
4.1. General
1-Butyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}imide
([C4mim][NTf2]), 1-butyl-2,3-dimethylimidazolium bis{(trifluorome-
thyl)sulfonyl}imide ([C4dmim][NTf2]),1-butyl-1-methyl-pyrrolidinium
bis{(trifluoromethyl)sulfonyl}imide ([C4mpyrr][NTf2]) and 1-butyl-1-
methyl-pyrrolidinium trifluoromethanesulfonate ([C4mpyrr][OTf])
were prepared in house using standard literature methods18,19 from the
appropriate halide salt. 1-Butyl-1-methyl-pyrrolidinium tris(penta-
fluoroethyl)trifluorophosphate ([C4mpyrr][FAP]) was obtained from
Merck. Bromide content was measured for each ionic liquid using ion
chromatography. In each case, the bromide levels were below 5 ppm.
The ionic liquids were used without drying and their water content was
analysed via Karl Fischer titration. All organic solvents for the stability
studies were HPLC grade solvents which were further distilled either
over sodium/benzophenone or calcium hydride.
4.2. Spectroscopic details
All the Raman data was collected on an Avalon 785 instrument
at 25 ꢀC and normalised to the solvent features. SOCl2 frequencies-
346 cmꢁ1, SO wag, 490 cmꢁ1, SCl2 stretch, 286 cmꢁ1, SCl2 rock,
444 cmꢁ1, SCl2 stretch, 1230 cmꢁ1, SO stretch. SO2Cl2 frequencies-
346 cmꢁ1, SO wag, 490 cmꢁ1, SCl2 stretch, 286 cmꢁ1, SCl2 rock,
444 cmꢁ1, SCl2 stretch, 1230 cmꢁ1, SO stretch. All 1H and 13C NMR
spectra were been recorded on a Bruker Avance 300 or 500 at 25 ꢀC
in CDCl3 referenced to 0.00 ppm using TMS for the 1H NMR and
77.00 ppm using CDCl3 for the 13C NMR unless otherwise stated.
The chemical shifts are reported in parts per million (ppm).
4.3. 3,5-Di-O-benzyl-D
-xylofuranose (1)20
Xylose (1 equiv) was dissolved in acetone (100 cm3) and to this
was added copper sulfate (2 equiv) and sulfuric acid (0.1 equiv) the
reaction mixture was stirred at room temperature for 12 h. The
copper sulfate was then filtered and the filtrate neutralised with
ammonia and passed through a pad of Celite. The acetone was then
removed in vacuo to give yellow syrup. To the syrup was added 0.1 M
HCl (50 cm3) and the solution stirred overnight. The resulting mix-
turewas extractedwith chloroform, and the combined extracts were
washed with saturated NaHCO3 solution (50 cm3). The aqueous was
further extracted with ethyl acetate and the organic phases com-
bined, dried and concentrated and used in the next reaction with no
further purification. The material was dissolved in DMF (100 cm3)
and to this was added sodium hydride (3.5 equiv), benzyl bromide
(2.5 equiv) and tetrabutylammonium iodide (0.1 equiv). The re-
action mixture was then stirred at room temperature for 12 h.
Workup was then carried out by addition of water and extraction
with DCM. The organic phase was then concentrated and purified by
column chromatography. After purification the material was stirred
inTFA/water(4:1) until nostartingmaterialremainedas determined
by TLC analysis. The solutionwas then diluted with ethyl acetate and
potassium carbonate solution added. The pH was adjusted to 7 and
extraction with ethyl acetate was carried out. The organic phase was
then dried and concentrated to yield (1) as a mixture of anomers. 1H
3. Conclusions
This study has shown that hydrophobic ILs offer a means to
stabilise SOCl2 (in particular [C4mpyrr][NTf2] and [C4mpyrr][FAP])
and SO2Cl2 (in particular [C4mpyrr][FAP]) while maintaining the
reactivity of these reagents towards nucleophiles such as diols. The
stabilisation of these highly reactive species could find application
in large scale synthesis allowing more widespread use. Both SOCl2
and SO2Cl2 showed excellent reactivity at room temperature in
ionic liquid media when compared to the same reactions in organic
solvent. The syntheses of cyclic sulfites and sulfates have also been
improved upon when carried out in ILs, due to improved stability
and use of simple reaction conditions (room temperature in air).
For the first time, direct access to cyclic sulfates of highly reactive
modified furanosides has been achieved and the synthetic medium,
i.e., the hydrophobic ILs, provided a stabilising environment that
limited product decomposition. Further improvements were
obtained by the introduction of an immobilised base (which can be
recycled by simple NEt3/DBU/DCM wash), which resulted in higher
yields of cyclic sulfite and sulfate formation. Owing to the solubility
of the diols and relative stability of SOCl2 and SO2Cl2 in organic
solvents, only DCM could be used. In this case the ILs, which can be
recycled, provide a green alternative for this procedure. These
highly reactive cyclic sulfite/sulfates are ideal intermediates for
further elaboration towards substituted nucleosides and work is
currently ongoing in this area.
NMR (500 MHz, MeOD)
J¼7.0 Hz, H-1 ), 5.10 (d, 1H, J¼2.5 Hz, H-1
CH2Ph), 4.67 (d,1H, J¼6.1 Hz, CH2Ph), 4.57–4.50 (m, 6H, CH2Ph), 4.42
(d, 1H, J¼10.3 Hz, H-3 ), 4.38 (d, 1H, J¼8.6 Hz, H-4 ), 4.13 (d, 1H,
J¼14.7 Hz, H-2 ), 4.04 (t, 1H, J¼6.3 Hz, H-2 ), 3.91 (dd, 1H, J¼3.7,
8.5 Hz, H-3 ), 3.80–3.59 (m, 2H, H-5b
), 3.54 (d, 1H, J¼10.0 Hz, H-
). 13C NMR (125 MHz, MeOD)
141.3, 141.2, 141.0, 140.9 (PhØ),
130.0, 129.8, 29.6, 129.2, 128.6, 128.5, 128.3, 128.1, 128.0, 127.8 (Ph),
105.3 (C-1 ), 98.2 (C-1 ), 85.4 (C-2 ), 85.2 (C-2 ), 82.0 (C-3 ), 81.6
d
7.33–7.29 (m, 10H, Ph), 5.33 (d, 1H,
a
b
), 4.72 (d, 1H, J¼5.3 Hz,
b
a
a
b
a
a/b
4b
d
a
b
b
a
a

C. Hardacre et al. / Tetrahedron 65 (2009) 6341–6347
6345
(C-3
b
), 78.6 (C-5
b
), 76.2 (C-4
a
), 75.0 (CH2Ph), 74.8 (CH2Ph), 73.5
THF (20 cm3). The reaction was stirred at room temperature for
12 h under argon. Water (5 cm3) was then added and some of the
THF removed under reduced pressure prior to addition of EtOAc
(100 cm3) and an aq NH4Cl solution (100 cm3). The aqueous layer
was extracted with EtOAc (2ꢂ100 cm3) and the combined organic
fractions were washed with brine and dried (MgSO4). The crude
was then dissolved in THF (200 cm3) and TBAF (1 M in THF,
23.5 cm3, 23.5 mmol) was added. The resulting solution was stirred
overnight then concentrated to 20 cm3. After addition of EtOAc
(100 cm3), the organic layer was washed with an aq NH4Cl solution
(100 cm3), dried (MgSO4) filtered and concentrated in vacuo. The
residue was purified by column chromatography (hexane/ethyl
(CH2Ph), 73.2 (CH2Ph), 71.8 (C-5a), 70.9 (C-4b). HRMS (ES) m/z
(MþHþ) calculated for C19H23O5 353.1365, found 353.1374. IR nmax
(thin film, CHCl3) 3398, 2927, 751, 697.
4.4. 1,2-O-Isopropylidene-a-D-xylofuranose (2)
Xylose (1 equiv) was dissolved in acetone (100 cm3) and to this
was added copper sulfate (2 equiv) and sulfuric acid (0.1 equiv) the
reaction mixture was stirred at room temperature for 12 h. The
copper sulfate was then filtered and the filtrate neutralised with
ammonia and passed through a pad of Celite. The acetone was then
removed in vacuo to give yellowsyrup. Tothe syrup was added 0.1 M
HCl (50 cm3) and the solution stirred overnight. The resulting mix-
ture was washed with chloroform until the pH was raised to 8. The
aqueous phase was extracted with ethyl acetate and the organic
phases combined, dried and concentrated to yield (2) as a colourless
acetate (4:1)). 1,2-O-Isopropylidene-3-O-benzyl-D-ribofuranoside
(4.60 g, 16.4 mmol) was dissolved in DCM (150 cm3) under argon
and stirred at 0 ꢀC. Triethylamine (6.90 cm3, 49.3 mmol), dime-
thylaminopyridine (0.2 g, cat) and pivaloyl chloride (2.43 ml,
19.7 mmol) were added successively to the solution. After 24 h,
a 0.5 M HCl solution was added. The organic layer was then washed
with a saturated NH4Cl solution and brine, then dried (MgSO4) and
concentrated in vacuo. The residue was then dissolved in a TFA/
water (4:1) mixture (40 cm3) and stirred at room temperature for
3 h. The TFA was partially removed under reduced pressure (re-
sidual volume w5 cm3) and EtOAc (100 cm3) was added. The or-
ganic layer was washed with saturated NaHCO3 and brine then
dried (MgSO4), and concentrated in vacuo. The residue was purified
by column chromatography (hexane/ethyl acetate (1:1)) to yield (4)
(3.21 g, 9.9 mmol) as a 1:1 mixture of anomers (46% overall yield
oil. 1H NMR (500 MHz, MeOD)
d
5.22 (d,1H, J¼6.15 Hz, H-1), 3.81 (d,
1H, J¼6.15 Hz, H-2), 3.51 (dt, 1H, J¼4.75, 10.65 Hz, H-4), 3.45 (d, 1H,
J¼4.75 Hz, H-3), 3.11 (m, 2H, H-5a,b), 0.79 (s, 3H, CH3), 0.64 (s, 3H,
CH3). 13C NMR (125 MHz, MeOD)
d 107.2 (C-1), 87.6 (C-2), 82.8 (C-4),
76.7 (C-3), 61.5 (C-5), 27.7 (CH3), 26.7 (CH3). HRMS (ES) m/z (MꢁHþ)
calculated for C8H13O5 189.0763, found 189.0790. IR nmax (thin film,
CHCl3) 3451, 2979, 1374. [
4.5. 3,5-Di-O-pivaloyl-
a]
D ꢁ19.7 (c 1.1, H2O) [lit.21 ꢁ18.9 (H2O)].
D-arabinofuranose (3)
1,2-O-Isopropylidene-
b
-D
-arabinofuranoside was prepared as
-arabino-
over four steps). 1H NMR (500 MHz, CDCl3)
5.32 (s, 1H, H-1 ), 5.28 (br s, 1H, H-1
d 7.39–7.32 (m, 5H, Ph),
), 4.68 (d, 1H, J¼11.9 Hz,
per literature procedures.22,23 1,2-O-isopropylidene-
b
-D
a
b
furanoside (750 mg, 3.9 mmol) was dissolved in dry pyridine/dry
dichloromethane (50 cm3/50 cm3). To this solution was added
dropwise at0 ꢀC asolution ofpivaloyl chloride(1.1 cm3, 8.7 mmol) in
DCM (10 cm3). The resulting solution was warmed up at room
temperature and was stirred overnight. The solvent was then con-
centrated in vacuo. The white residue was dissolved in chloroform
(100 cm3), washed with a solution of saturated sodium hydrogen
carbonate, brine, and water then dried, filtered and concentrated in
vacuo to afford the crude as an oil. Purification by flash chroma-
tography (hexane/ethyl acetate (9:1)) yielded 3,5-di-O-pivaloyl-1,2-
CH2Ph), 4.65 (d, 1H, J¼11.8 Hz, CH2Ph), 4.62 (d, 1H, J¼12.0 Hz,
CH2Ph), 4.57 (d, 1H, J¼11.7 Hz, CH2Ph), 4.31 (dd, J¼4.2, 12.0 Hz, H-
4
a
), 4.11–4.21 (m, 6H, H-2
a
, H-3
b
, H-4
b
, H-5b
a
, H-5a,b
), 3.86 (dd,
), 3.22 (br s, 1H, OH), 3.00 (br s, 2H, OH), 2.68 (br
s, 1H, OH), 1.18 (s, 9H, Piv-CH3). 13C NMR (125 MHz, CDCl3)
178.9
(Piv-CO), 178.5 (Piv-CO), 137.0 (PhØ), 129.1, 128.9, 128.4 (Ph), 102.6
b), 4.06 (d,
1H, J¼4.6 Hz, H-2
b
), 4.00 (dd, 1H, J¼4.3, 12.0 Hz, H-5a
a
J¼4.4, 5.6 Hz, H-3
a
d
(C-1
73.9 (C-4
64.1 (C-5
a
), 97.4 (C-1
b
), 79.8 (C-2
b
), 79.2 (C-2
a
), 79.0 (C-3
b
), 78.2 (C-3
a
a
),
),
a
), 73.7 (CH2Ph), 73.5 (CH2Ph), 70.9 (C-4
b), 65.3 (C-5
b), 39.3, 39.2 (C-qPiv), 27.6 (MePiv). HRMS (ES) m/z
O-isopropylidene-
b
-D-arabinofuranoside as
a
yellow oil. This
(MþNaþ) calculated C17H24O6Na 347.1471, found 347.1475. IR nmax
intermediate was then treated with a mixture TFA/water (4:1) at
0 ꢀC. The resulting solution was stirred for 3 h and then diluted with
DCM (25 cm3). A saturated solution of NaHCO3 was added and solid
NaHCO3 was added until the pH was neutral. The aqueous layer was
extracted with DCM and the combined organic layers were washed
with brine and water then dried, and concentrated in vacuo. Puri-
fication by flash chromatography (chloroform to chloroform/etha-
(thin film, CHCl3) 3401, 2967, 1728, 738, 696.
4.7. Synthesis of cyclic sulfites and sulfates in organic solvent
or ILs using triethylamine
To DCM or IL (2 cm3) stirred under argon, was added diol
(0.30 mmol) and triethylamine (0.90 mmol). To the resulting sus-
pension were added thionyl or sulfuryl chloride (0.36 mmol) and
the reaction mixture allowed to stir gently at room temperature
overnight. Workup was then carried by extraction with water to
remove the triethylamine. The organic fraction was then passed
through a pad of silica and concentrated to yield the sulfite or
sulfate. Those carried out in IL were extracted from the IL using
diethyl ether prior to extraction with water then filtration through
silica. (For yields see Tables 1 and 2.)
nol (95:5)) gave (3) (1.0 g, 88%) as an
CDCl3)
5.40 (d, J¼4.2 Hz, 2H, H-1
(dd, 1H, J¼2.5, 5.6 Hz, H-3 ), 4.45–4.22 (m, 5H, H-5a,b
), 4.16 (d,1H, J¼4.7 Hz, H-2 ), 4.13–4.06 (m, 2H, H-2
3.83 (m, 1H, H-3
), 3.26 (br, 1H, OH), 1.24 (s, 18H, CH3). 13C NMR
(125 MHz, CDCl3) 179.7, 178.6 (C-OPiv), 103.2 (C-1 ), 97.4 (C-1 ),
81.7 (C-3 ), 81.4 (C-3 ), 80.4 (C-4 ), 80.1 (C-4 ), 79.5 (C-2 ), 76.8 (C-
), 65.3 (C-5 ), 63.8 (C-5
a
a
/b
mixture.1H NMR (500 MHz,
, H-1 ), 4.94 (t, 1H, H-3 ), 4.70
, H-5a,b , H-
, H-4 ), 3.84–
d
b
a
b
a
b
b
4
b
a
a
a
d
a
b
a
b
a
b
a
2
b
b
a), 39.3, 39.1 (C-qPiv), 27.5, 27.4 (C-MePiv).
HRMS (ES) m/z (MþNaþ) calculated for C15H26O7Na 341.1576, found
341.1575. IR nmax (thin film, CHCl3) 3448, 2973, 1734.
4.8. Synthesis of cyclic sulfites and sulfates in organic solvent
or ILs using immobilised base
4.6. 3-O-Benzyl 5-O-pivaloyl-D-ribofuranose (4)
To DCM or IL (2 cm3) stirred under argon was added diol
(0.30 mmol) and immobilised morpholine (StratospheresÒ PL-
MPH) (0.90 mmol). To the resulting suspension was added thionyl
or sulfuryl chloride (0.36 mmol) and the reaction mixture was
allowed to stir gently at room temperature overnight. For reactions
in DCM, workup was then carried by filtration to remove the
immobilised morpholine, followed by washing through with DCM.
1,2-O-Isopropylidene-5-O-(tert-butyldimethylsilyl)-
D-ribofur-
anoside was prepared from (2) as per literature procedure.24 1,2-O-
Isopropylidene-5-O-(tert-butyldimethylsilyl)-D-ribofuranoside
(6.58 g, 21.4 mmol), was dissolved in dry THF (300 cm3), cooled to
0 ꢀC and benzyl bromide (5.48 g, 32 mmol) was added. To this so-
lution was added slowly a suspension of NaH (0.77 g, 32 mmol) in

6346
C. Hardacre et al. / Tetrahedron 65 (2009) 6341–6347
The filtrate was then passed through a pad of silica and concen-
trated to yield the sulfite or sulfate. For reactions in ILs reaction
product was extracted form the IL using diethyl ether prior to fil-
tration through silica. (For yields see Tables 1 and 2.)
126.5 (Ph), 91.5 (C-1), 90.8 (C-10), 78.7 (C-4), 78.3 (C-40), 73.9
(CH2Ph), 72.4 (CH2Ph), 72.3 (CH2Ph), 71.8 (CH2Ph), 69.5 (C-3), 69.1
(C-30), 66.7 (C-5), 66.3 (C-50). HRMS (ES) m/z (MꢁHþ) calculated for
C19H19O7S 391.0869, found 391.0852. IR nmax (thin film, CHCl3)
2927, 2862, 1212 (S]O), 1092 (S]O), 756, 698.
4.9. 3,5-Di-O-benzyl-1,2-O-sulfinyl-a-D
-xylofuranose (5)8
4.14. 1,2-Isopropylidene-3,5-O-sulfanyl-
D
-xylofuranose (10)25
Mixture of two diastereoisomers at the sulfur centre obtained in
a 5:2 ratio. 1H NMR (500 MHz, CDCl3)
7.33–7.26 (m, 10H, Ph), 5.94
d
Mixture of two diastereoisomers obtained in a 10:1 ratio. 1H
(d,1H, J¼6.4 Hz, H-1), 4.70–4.51 (m, 5H, 2ꢂCH2Ph, H-2), 4.48 (dt,1H,
NMR (500 MHz, CDCl3)
d
6.05 (d, 1H, J¼3.7 Hz, H-1), 6.00 (d, 1H,
J¼5.4, J¼10.0 Hz, H-4), 3.96 (d, 1H, J¼5.3 Hz, H-3), 3.75 (dd, 2H,
J¼3.7 Hz, H-10), 5.28 (d, 1H, J¼2.7 Hz, H-3), 5.18 (d, 1H, J¼2.0 Hz, H-
40), 4.98 (d, 1H J¼12.9 Hz, H-5a0), 4.95 (d, 1H, J¼3.5 Hz, H-20), 4.83
(d, 1H, J¼12.9 Hz, H-5b0), 4.73 (d, 1H, J¼3.7 Hz, H-2), 4.57 (dt, 1H,
J¼2.7, 5.6 Hz, H-4), 4.26 (s, 1H, H-40), 3.76 (dd, 1H, J¼5.5, 11.2 Hz, H-
5a), 3.66 (dd, 1H, J¼8.6, 11.2 Hz, H-5b), 1.55 (s, 3H, CH3), 1.51 (s, 1H,
J¼3.5 Hz, 10.2 Hz, H-5a,b). 13C NMR (125 MHz, CDCl3)
d 138.1 (CØ),
137.5 (CØ),128.5,128.4,128.0,127.9,127.5 (Ph), 99.9 (C-1), 81.2 (C-3),
79.7 (C-4), 79.3 (C-2), 73.6 (CH2Ph), 72.1 (CH2Ph), 68.0 (C-5). HRMS
(ES) m/z (MþNaþ) calculated for C19H20O6SNa 399.0878, found
399.0870. IR nmax (thin film, CHCl3) 2924, 2868,1216 (S]O), 740, 697.
CH3). 13C NMR (125 MHz, CDCl3)
d 113.7 (CØ), 113.3 (CØ), 104.9 (C-
10), 104.8 (C-1), 89.8 (C-3), 86.5 (C-40), 82.8 (C-2), 82.2 (C-20), 78.8
(C-4), 72.4 (C-30), 70.4 (C-50), 64.8 (C-3), 38.1 (C-5), 26.þ5 (CH3), 26.2
4.10. 1,2-Isopropylidene-3,5-O-sulfinyl-
1H NMR (500 MHz, CDCl3)
1H, J¼11.9 Hz, H-5a), 4.91 (d, 1H, J¼2.3 Hz, H-4), 4.62 (d, 1H,
J¼3.7 Hz, H-2), 4.18 (d, 1H, J¼3.5 Hz, H-3), 4.17 (d, 1H, J¼13.1 Hz, H-
5b), 1.49 (s, 3H, CH3), 1.44 (s, 3H, CH3). 13C NMR (125 MHz, CDCl3)
a-D
-xylofuranose (6)25
0
0
(CH3), 26.1 (CH3 ), 25.8 (CH3 ). HRMS (ES) m/z (MþH ) calculated
for C8H13O7S 270.0647, found 270.0652. IR nmax (thin film, CHCl3)
2989, 1375, 1262 (S]O), 1192 (S]O).
d
6.03 (d, 1H, J¼3.7 Hz, H-1), 4.95 (d,
4.15. 3,5-O-Pivaloyl-1,2-O-sulfanyl-D-arabinofuranose (11)
d
112.6 (CØ),104.9 (C-1), 83.6 (C-2), 71.2 (C-3), 69.3 (C-4), 55.7 (C-5),
26.6 (CH3), 26.2 (CH3). HRMS (ES) m/z (MþNHþ4 ) calculated for
Mixture of two diastereoisomers at the anomeric centre
obtained in a 3:2 ratio. 1H NMR (500 MHz, CDCl3)
6.42 (d,
J¼4.7 Hz, 1H, H-1 ), 6.38 (d, 1H, J¼5.1 Hz, H-1 ), 5.73 (t, 1H,
J¼4.1 Hz H-2 ), 5.43 (m, 2H, H-2 , H-3 ), 5.33 (dd,1H, J¼4.4, 2.7 Hz,
H-3 ), 4.58–4.3 (m, 6H, H-4 , H-4 , H-5a,b , H-5a,b ), 1.24 (s, 18H,
CH3). 13C NMR (125 MHz, CDCl3)
177.7, 176.6 (C-OPiv), 92.1 (C-1 ),
), 42.4 (C-2 ), 79.4 (C-4 ), 79.2 (C-4 ), 74.3
), 60.7 (C-5
C8H16NO6S 254.0687, found 254.0698. IR nmax (thin film, CHCl3)
2923, 1380, 1190 (S]O). [
(CHCl3)].
d
a
]
D
þ37.6 (c 0.065, CHCl3) [lit.25 þ47
a
b
a
b
a
b
a
b
a
b
4.11. 3,5-Di-O-pivaloyl-1,2-O-sulfinyl-
D
-arabinofuranose (7)
d
a
89.8 (C-1
b
), 83.7 (C-2
a
b
a
b
Mixture of two diastereoisomers at the sulfur centre obtained in
a 7:3 ratio. 1H NMR (500 MHz, CDCl3)
(C-3 ), 71.3 (C-3
a
b
), 62.7 (C-5
a
b), 37.9, 37.6 (C-qPiv), 26.1,
d
6.65 (d, 1H, J¼4.1 Hz, H-1),
26.0 (C-MePiv). HRMS (ES) m/z (MþOHþ) calculated for C15H25O10
S
6.38 (d, 1H, J¼5.1 Hz, H-10), 5.33 (d, 1H, J¼4.1 Hz, H-2), 5.12 (dd, 1H,
J¼5.1 Hz, H-20), 4.53–4.43 (m, 2H, H-3, H-30), 4.38–4.35 (m, 2H, H-4,
H-40), 4.25–4.20 (m, 3H, H-5a,b, H-2), 4.08 (dd, 2H, J¼7.1 J¼11.7 Hz,
397.1174, found 397.1168. IR nmax (thin film, CHCl3) 2977, 1745, 1281
(S]O), 1193 (S]O).
H-5a0,b0), 1.24 (s, 18H, CH3). 13C NMR (125 MHz, CDCl3)
d
179.7, 178.6
4.16. Preparation of non-dried IL solutions
(C-OPiv), 111.2 (C-1), 110.1 (C-10), 90.7 (C-2), 86.7 (C-20), 85.5 (C-4),
85.4 (C-40), 77.9 (C-3), 76.8 (C-30), 63.9 (C-5), 62.9 (C-50), 39.3, 39.1
(C-qPiv), 27.5, 27.4 (C-MePiv). HRMS (ES) m/z (MþNaþ) calculated
for C15H24O8SNa 387.1090, found 387.1091. IR nmax (thin film, CHCl3)
2974, 1734, 1159 (S]O).
For the study of the stability of SOCl2 and SO2Cl2 in non-dried
ILs, all the ILs were left open to the air prior to use to allow air
equilibration. A sample of each IL was removed for water content
analysis via Karl Fischer titration.
4.12. 3-O-Benzyl-5-O-pivaloyl 1,2-O-sulfinyl-
ribofuranose (8)
D-
4.17. Stability of SOCl2 and SO2Cl2 in non-dried ILs and organic
solvents
Mixture of two diastereoisomers at the sulfur centre obtained in
a 1:1 ratio. 1H NMR (300 MHz, CDCl3)
7.40–7.32 (m, 5H, Ph), 6.45
All experiments carried out in non-dried ILs and organic sol-
vents were carried out in oven dried glassware with a headspace of
air. In each case the storage vessels were sealed to avoid evapora-
tion of either the SOCl2/SO2Cl2 or the organic solvent. To 1 cm3 of
d
(d, 1H, J¼3.9 Hz, H-1), 6.32 (d, 1H, J¼4.8 Hz, H-10), 5.24 (dd, 1H,
J¼4.2, 4.5 Hz, H-2), 4.92 (dd, 1H, J¼5.3, 4.9 Hz, H-20), 4.90–4.10 (m,
2ꢂCH2Ph, H-4, H-40, H-5a,b, H-5a0,b0), 3.91 (dd, 1H, J¼4.5, 8.1 Hz, H-
3), 3.83 (dd, 1H, J¼5.4, 9.3 Hz, H-30). 13C NMR (70 MHz, CDCl3)
solvent was added 29 mL of SOCl2 or 33 mL of SO2Cl2 to obtain
a 10 mol % solution. After 15 min stirring the samples were placed
in a quartz cuvette and a Raman spectrum taken. For the kinetic
experiments the solution was stirred in the quartz cuvette and
spectra taken every 30 min.
d
178.3 (C-OPiv), 136.6, 129.2, 129.1, 129.0, 128.7, 128.6 (Ph), 110.1 (C-
10), 108.5 (C-1), 83.1 (C-20), 79.5 (C-2), 78.1 (C-4), 77.7 (C-40), 73.1 (C-
3), 72.8 (C-30), 61.8 (CH2Ph), 39.3, 27.5 (C-MePiv). HRMS (ES) m/z
(MþNaþ) calculated for C17H22NaO7S 393.0984, found 393.0989. IR
nmax (thin film, CHCl3) 2395, 1728, 1215 (S]O), 757, 669.
Acknowledgements
4.13. 3,5-Di-O-benzyl-1,2-O-sulfanyl-
D
-xylofuranose (9)
We would like to thank QUILL, Merck KGaA for the donation of
ionic liquids and an EPSRC (Portfolio Partnership), and EC-Marie
Curie FP6 EST program (MEST-CT-2005-020351) for funding.
Mixture of two diastereoisomers at the anomeric centre
obtained in a 5:2 ratio. 1H NMR (500 MHz, CDCl3)
7.24–7.18 (m,
20H, Ph), 6.37 (d, 1H, J¼4.5 Hz, H-1 ), 6.23 (s, 1H, H-1 ), 5.51 (t, 1H,
H-2 ), 4.60–4.50 (m, 9H, H-4
, J¼4.5 Hz), 5.2 (d, 1H, J¼5.7 Hz, H-2
2ꢂCH2Ph), 4.36 (dt, 1H, J¼10.6, 5.4 Hz, H-4
). 13C NMR (125 MHz,
CDCl3) 138.3, 138.0, 137.5, 137.2 (CØ), 127.6, 127.4, 127.2, 126.9,
d
a
b
Supplementary data
a
b
a,
b
Supplementary data associated with this article can be found in
the online version, at doi:10.1016/j.tet.2009.06.013.
d

C. Hardacre et al. / Tetrahedron 65 (2009) 6341–6347
6347
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16. Batoux, N.; Migaud, M. Unpublished Data, 2004.
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