Ytterbium(III) triflate-catalyzed conversion of carbonyl compounds into 1,3-oxathiolanes in ionic liquids

Article abstract of DOI:10.1055/s-2004-835642

The reaction of carbonyl compounds with 2-mercapto-ethanol to prepare 1,3-oxathiolanes has been successfully carried out in ionic liquids using ytterbium(III) triflate as a catalyst. Yields of the products are high and the catalyst can be easily recovered

Full text of DOI:10.1055/s-2004-835642

LETTER
2785
Ytterbium(III) Triflate-Catalyzed Conversion of Carbonyl Compounds into
1,3-Oxathiolanes in Ionic Liquids
Y
tterbium(III) Trif
n
late-Catalyz
il
KinIonic Liquids umar, Nidhi Jain, Sandeep Rana, Shive M. S. Chauhan*
Department of Chemistry, University of Delhi, Delhi 110 007, India
E-mail: smschauhan@chemistry.du.ac.in
Received 25 May 2004
Abstract: The reaction of carbonyl compounds with 2-mercapto-
ethanol to prepare 1,3-oxathiolanes has been successfully carried
out in ionic liquids using ytterbium(III) triflate as a catalyst. Yields
of the products are high and the catalyst can be easily recovered and
reused in this reaction.
Scheme 1
Key words: carbonyl compounds, 1,3-oxathiolanes, ionic liquid,
ytterbium(III) triflate
The reaction of various aliphatic, aromatic and heterocy-
clic carbonyl compounds (1.0 equiv) with 2-mercaptoeth-
anol (1.5 equiv) in the presence of Yb(OTf)3 (0.01–0.05
equiv) in [bmim][PF6] at room temperature gave the cor-
responding 1,3-oxathiolanes (Table 1). Carbonyl com-
pounds with electron-withdrawing groups such as fluoro
(entry 4, Table 1) and nitro (entry 5, Table 1) gave higher
yields of corresponding 1,3-oxathiolanes compared with
carbonyl compounds with electron-donating groups (en-
try 3, Table 1). The reaction of aldehydes was faster com-
pared with ketones and 95% of 2-phenyl-1,3-oxathiolane
was obtained as compared to 20% of 2-phenyl-2-methyl-
1,3-oxathiolane after one hour of reaction of 2-mercapto-
ethanol with benzaldehyde and acetophenone, respective-
ly. The reaction of 4-nitrobenzaldehyde (1.0 equiv) with
2-mercaptoethanol (1.5 equiv) in the presence of a catalyt-
ic amount of Yb(OTf)3 (0.01 equiv) was compared in
[bmim][Br], [bmim][BF4] and [bmim][PF6] and best ac-
tivity of catalyst was observed in [bmim][PF6] (entry 5,
Table 1). A very small amount of Yb(OTf)3 (0.01–0.05
equiv) is required for the preparation of 1,3-oxathiolanes
unlike other Lewis acid-catalyzed methods which utilize
stoichiometric amounts of catalyst and require higher
temperatures. Furthermore, no dehydrating agent is re-
quired under these conditions and the products can be eas-
ily separated by extraction with varying ratios of hexane–
EtOAc leaving behind the catalyst immobilized in the ion-
ic liquid. Recycling experiments of the recovered ionic
liquid containing catalyst were carried out for the reaction
of 4-nitrobenzaldehyde and 2-mercaptoethanol and it was
observed that the catalyst could be reused for four cycles
without noticeable reduction in activity.
The protection and deprotection of carbonyl compounds
is of great importance in organic synthesis.1 1,3-Oxathiol-
anes have been recognized as useful protecting groups of
carbonyls due to their easy introduction and more stability
towards acidic media as compared to O,O-acetals and
easier removal than the corresponding S,S-acetals and can
be utilized as acyl equivalents for C-C bond formation.2
Various methods have been reported for their
preparation3,4 but many of these methods have drawbacks
such as long reaction times,5 use of expensive catalysts,6
harsh reaction conditions,7 and relatively low yields of the
oxathiolanes.8 Furthermore in most of the methods the
catalyst cannot be recovered.
Lanthanide triflates are versatile Lewis acids and they
have been employed in a number of organic reactions.9
Ytterbium(III) triflate Yb(OTf)3 was first used by
Forsberg et al.10 and since then it has found a wide utility
in organic synthesis especially in deprotection of ace-
tates,11 Michael and Diels–Alder reactions,12 aldol-Grob
reaction,13 imino ene reaction,14 detritylation,15 electro-
philic substitution and cyclization,16 and isomerization of
glycidic esters.17
Ionic liquids, particularly those based on the 1,3-dialkyl-
imidazolium cation have gained considerable interest as
reaction media in recent years,18 often permitting easier
catalyst recycling.19 Recently, lanthanide triflates immo-
bilized in ionic liquids have been used as efficient and re-
cyclable catalysts for different organic reactions20 but, to
the best of our knowledge, there is no report on the forma-
tion of 1,3-oxathiolanes catalyzed by Yb(OTf)3 immobi-
lized in ionic liquids. In this letter we wish to report the
conversion of different carbonyl compounds to 1,3-ox-
athiolanes with 2-mercaptoethanol using Yb(OTf)3 in
ionic liquid at room temperature (Scheme 1).
In conclusion we have developed an efficient and mild
procedure for the preparation of 1,3-oxathiolanes by the
reaction of carbonyl compounds with 2-mercaptoethanol
catalyzed by ytterbium(III) triflate in ionic liquids. The
method offers advantages as compared to other Lewis
acid-catalyzed reactions as tedious procedures to remove
water from the solvent; substrates and catalyst are not
necessary. Furthermore, the catalyst immobilized in ionic
liquid can be recycled and reused several times without
any loss in activity.
SYNLETT 2004, No. 15, pp 2785–2787
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Advanced online publication: 08.11.2004
DOI: 10.1055/s-2004-835642; Art ID: D13504ST
© Georg Thieme Verlag Stuttgart · New York

2786
A. Kumar et al.
LETTER
Table 1 Yb(OTf)3-Catalyzed Conversion of Carbonyl Compounds into 1,3-Oxathiolanes in [bmim][PF6]21,22
Entry
R
R¢
Substrate/Yb(OTf)3/
HOCH2CH2SH
Time (h)
Yield (%)a
1
Ph
H
1:0.01:1.5
1:0.01:1.5
1:0.01:1.5
1:0.01:1.5
1:0.01:1.5
1:0.01:1.5
1:0.01:1.5
1:0.02:1.5
1:0.01:1.5
1:0.02:1.5
1:0.02:1.5
1:0.01:1.5
1:0.05:1.5
1:0.01:1.5
1:0.01:1.5
1:0.05:1.5
1:0.05:1.5
1
1
95
90
86
95
98
88
89
86
84
82
80
78
82
87
83
80
72
2
4-CH3C6H4
H
3
4-CH3OC6H4
4-FC6H4
H
1
4
H
1
5
4-NO2C6H4
H
1
6
CH=CHC6H5
Citronellal
H
1
7
–
2
8
CH3(CH2)8CH2
Piperonal
H
4
9
–
2
10
2-Furfuralcarboxaldehyde
3-Pyridinecarboxaldehyde
4-Methylmaino-3-nitrobenzaldehyde
C6H5
–
3
11
–
3
12
–
3
13
CH3
–
5
14
Cyclohexanone
Tetralone
1
15
–
1
16
CH3(CH2)5CH2
C6H5
CH3
C6H5
8
17
20
a Isolated yield.
b Yield of oxathiolane was 86% in [bmim][Br] and 88% in [bmim][BF4] after 1 h.
(9) (a) Kobayashi, S.; Hachiya, I.; Takahori, T. Synthesis 1993,
371. (b) Kawada, A.; Mitamura, S.; Kobayashi, S. J. Chem.
Soc., Chem. Commun. 1993, 1157. (c) Inanaga, J.;
Yokoyama, Y.; Hanamoto, T. Tetrahedron Lett. 1993, 34,
2791. (d) Yang, D.; Li, J.-H.; Gao, Q.; Yan, Y.-L. Org. Lett.
2003, 5, 2869.
Acknowledgment
AK thanks the University Grant Commission (UGC), New Delhi
for a Senior Research Fellowship; NJ and SR thank the Council for
Scientific and Industrial Research (CSIR), New Delhi for a Senior
Research Fellowship and Junior Research Fellowship, respectively.
(10) Forsberg, J. H.; Spaziano, V. T.; Balasubramanian, T. M.;
Liu, G. K.; Kinsley, S. A.; Duckworth, C. A.; Poteruca, J. J.;
Brown, P. S.; Miller, J. L. J. Org. Chem. 1987, 52, 1017.
(11) Sharma, G. V. M.; Ilangovan, A. Synlett 1999, 1963.
(12) Kobayashi, S.; Hachiya, I.; Takahori, T.; Araki, M.; Ishitani,
H. Tetrahedron Lett. 1992, 33, 6815.
(13) Curini, M.; Epifano, F.; Maltese, F.; Marcotullio, M. C. Eur.
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Chem. 2003, 68, 3112. (b) Yamanaka, M.; Nishida, A.;
Nakagawa, M. Org. Lett. 2000, 2, 159.
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Synlett 2004, No. 15, 2785–2787 © Thieme Stuttgart · New York

LETTER
Ytterbium(III) Triflate-Catalyzed 1,3-Oxathiolanes in Ionic Liquids
2787
(18) (a) Dupont, J.; DeSouza, R. F.; Suarez, P. A. Z. Chem. Rev.
2002, 102, 3667. (b) Wasserscheid, P.; Keim, W. Angew.
Chem. Int. Ed. 2000, 39, 3772.
(19) (a) Chauhan, S. M. S.; Kumar, A.; Srinivas, K. A. Chem.
Commun. 2003, 2348. (b) Srinivas, K. A.; Kumar, A.;
Chauhan, S. M. S. Chem. Commun. 2002, 2456.
(22) Data of Selected Oxathiolanes:
2-(4-Methylphenyl)-1,3-oxathiolane (2): Anal. Calcd for
C10H12OS: C, 66.66; H, 6.68; S, 17.77. Found: C, 66.48; H,
6.72; S, 17.54. 1H NMR (300 MHz, CDCl3, TMS): d = 7.17
(2 H, d, J = 8 Hz), 6.99 (2 H, d, J = 8 Hz), 5.17 (1 H, s), 4.26–
4.28 (1 H, m), 3.84–3.88 (1 H, m), 3.22–3.25 (1 H, m), 3.02–
3.06 (1 H, m), 2.13 (3 H, s).
2-(3,4-Methylenedeoxyphenyl)-1,3-oxathiolane(9):Anal.
Calcd for C10H10O3S: C, 57.14; H, 4.76; S, 15.23. Found: C,
57.45; H, 4.57; S, 15.37. 1H NMR (300 MHz, CDCl3):
d = 6.64 (1 H, d, J = 9 Hz), 6.59 (1 H, s,), 5.90 (2 H, s), 5.17
(1 H, s), 4.30–4.32 (1 H, m), 3.90–3.94 (1 H, m), 3.24–3.29
(1 H, m), 3.12–3.16 (1 H, m).
2-(2-Furyl)-1,3-oxathiolane (10): Anal. Calcd for
C7H8O2S: C, 53.80; H, 5.12; S, 20.50. Found: C, 53.61; H,
5.25; S, 20.68. 1H NMR (300 MHz, CDCl3): d = 7.30, (1 H,
d, J = 8 Hz), 6.25 (1 H, m), 6.19 (1 H, d, J = 8 Hz), 5.40 (1
H, s), 4.20–4.22 (1 H, m), 3.70–3.74 (1 H, m), 3.12–3.18 (1
H, m), 2.90–2.96 (1 H, m).
2-(3-Pyridyl)-1,3-oxathiolane (11): Anal. Calcd for
C8H9OSN: C, 57.48; H, 5.38; N, 8.30; S, 19.16. Found: C,
57.32; H, 5.18; N, 8.45; S, 19.05. 1H NMR (300 MHz,
CDCl3): d = 8.70 (1 H, s, J = 8, 7 Hz), 8.55 (1 H, dd, J = 8, 3
Hz), 7.90 (1 H, dd, J = 8, 3 Hz), 7.42 (1 H, dd, J = 8, 7 Hz),
5.17 (1 H, s), 4.40–4.42 (1 H, m), 3.92–3.96 (1 H, m), 3.30–
3.36 (1 H, m), 3.22–3.26 (1 H, m).
(20) (a) Song, C. S.; Shim, W. H.; Roh, E. J.; Choi, J. H. Chem.
Commun. 2000, 1695. (b) Lee, S.-g.; Park, J. W. Bull.
Korean Chem. Soc. 2002, 23, 1367. (c) Yadav, J. S.; Reddy,
B. V. S.; Uma Gayathri, K.; Prasad, A. R. Synthesis 2002,
2537. (d) Yadav, J. S.; Reddy, B. V. S.; Reddy, P. N.; Rao,
M. S. Synthesis 2003, 1387.
(21) Representative Experimental Procedure for the Reac-
tion of 4-Nitrobenzaldehyde with 2-Mercaptoethanol:
To a mixture of 4-nitrobenzaldehyde (151 mg, 1 mmol) and
Yb(OTf)3 (6.2 mg, 0.01 mmol) in [bmim][PF6] (3 mL) was
added 2-mercaptoethanol (117 mg, 1.5 mmol) and the
contents were stirred at r.t. for about 1 h. The product was
extracted with a mixture of hexane–EtOAc (1:1 v/v, 3 × 10
mL) and this organic extract was washed with 10% NaHCO3
solution and then with H2O. The organic layer was dried
over anhyd Na2SO4 and concentrated under reduced pressure
to yield 2-(4-nitrobenzyl)-1,3-oxathiolane in 98% yield. The
products were characterized by 1H NMR spectroscopic data
and CHN analysis.
2-(4-Methylamino-3-nitrophenyl)-1,3-oxathiolane (12):
Anal. Calcd for C10H12O3N2S: C, 50.12; H, 5.00; N, 11.66;
S, 13.33. Found: C, 50.38; H, 5.16; N, 11.48; S, 13.20. 1H
NMR (300 MHz, CDCl3): d = 7.98 (1 H, d, J = 3 Hz), 7.57
(1 H, dd, J = 9, 3 Hz), 7.52 (1 H, d, J = 9 Hz), 6.05 (1 H, s),
4.52 (1 H, m), 4.00 (1 H, m), 3.24 (2 H, m).
2-Methyl-2-phenyl-1,3-oxathiolane (13): Anal. Calcd for
C10H12OS: C, 66.66; H, 6.66; S, 17.77. Found: C, 66.45; H,
6.43; S, 17.90. 1H NMR (300 MHz, CDCl3): d = 7.08–7.18
(3 H, m), 7.21 (2 H, m), 4.10–4.14 (1 H, m), 3.82 (1 H, m),
3.10 (2 H, m), 1.83 (3 H, s).
Cyclohexyl-1,3-oxathiolane (14): Anal. Calcd for
C8H14OS: C, 60.75; H, 8.86; S, 20.25. Found: C, 60.58; H,
8.42; S, 20.45. 1H NMR (300 MHz, CDCl3): d = 4.42 (1 H,
m), 4.17 (2 H, t, J = 11.4 Hz), 3.80–3.86 (1 H, m), 3.24 (1 H,
m), 3.10 (1 H, m), 3.03 (2 H, t, J = 11.4 Hz), 1.82 (6 H, m),
1.50 (4 H, m).
2-Tetralonyl-1,3-oxathiolane (15): Anal. Calcd for
C12H14OS: C, 69.90; H, 6.79; S, 15.53. Found: C, 69.78; H,
6.64; S, 15.42. 1H NMR (300 MHz, CDCl3): d = 6.93–7.24
(4 H, m), 4.53–4.55 (1 H, m), 3.70–3.74 (1 H, m,), 3.29–3.34
(1 H, m), 3.18–3.20 (1 H, m), 2.85 (2 H, t, J = 11 Hz), 2.06
(2 H, t, J = 11 Hz), 1.60 (2 H, m).
2-Phenyl-2-phenyl-1,3-oxathiolane (17): Anal. Calcd for
C15H14OS: C, 74.38; H, 5.78; S, 13.22. Found: C, 74.1; H,
5.64; S, 13.12. 1H NMR (300 MHz, CDCl3): d = 7.19–7.28
(6 H, m), 7.30–7.38 (4 H, m), 4.42–4.44 (1 H, m), 3.80–3.84
(1 H, m), 3.34–3.39 (1 H, m), 3.16 (1 H, m).
Synlett 2004, No. 15, 2785–2787 © Thieme Stuttgart · New York