Copper(II) tetrafluoroborate as an extremely efficient catalyst for 1,3-dithiolane/dithiane formation from carbonyl compounds under solvent-free conditions at room temperature

Article abstract of DOI:10.1016/j.tetlet.2005.07.059

Copper(II) tetrafluoroborate hydrate is a new and extremely efficient catalyst for 1,3-dithiolane/dithiane formation from aromatic, heteroaromatic and aliphatic aldehydes and cyclic saturated ketones in 1-5 min under solvent-free conditions at room temper

Full text of DOI:10.1016/j.tetlet.2005.07.059

Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 6213–6217
Copper(II) tetrafluoroborate as an extremely efficient catalyst
for 1,3-dithiolane/dithiane formation from carbonyl
compounds under solvent-free conditions at room temperature
Ram C. Besra, Santosh Rudrawar and Asit K. Chakraborti*
Department of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research (NIPER),
Sector 67, S.A.S.Nagar, Punjab 160 062, India
Received 1 June 2005;revised 7 July 2005;accepted 14 July 2005
Dedicated to the memory of Professor Usha Ranjan Ghatak
Abstract—Copper(II) tetrafluoroborate hydrate is a new and extremely efficient catalyst for 1,3-dithiolane/dithiane formation from
aromatic, heteroaromatic and aliphatic aldehydes and cyclic saturated ketones in 1–5 min under solvent-free conditions at room
temperature. The reaction is compatible with other functionalities such as ether, ester, hydroxyl, halide, nitro and cyano groups
and exhibits excellent chemoselectivity. a,b-Unsaturated aldehydes/ketones lead to selective formation of 1,3-dithiolanes instead
of Michael addition products. For substrates bearing an aldehyde and a ketone carbonyl group, chemoselective dithiolane forma-
tion takes place with the aldehyde.
Ó 2005 Elsevier Ltd. All rights reserved.
The formation of 1,3-dithiolanes is a versatile organic
transformation as it (i) provides a means to protect car-
bonyl groups,1 (ii) serves to generate umpoled carbon-
yls,2 (iii) constitutes a key step for deoxygenation of
carbonyl groups leading to the corresponding methylene
derivatives,3 and (iv) gives entry to titanium-alkylidene
chemistry for carbonyl olefination.4 1,3-Dithiolane
formation also gains importance due to the versatile
biological activity of compounds containing this moiety.
For example, 1,3-dithiolane-containing compounds
have been reported to have in vitro and in vivo leish-
manicidal activity at different concentrations against
promastigotes and amastogotes of L.donovani .5 Nucleo-
sides bearing the 1,3-dithiolane moiety possess anti-HIV
activity6 and dithiolane analogs of lignans inhibit inter-
feron-gamma and lipopolysaccharide-induced nitric
oxide production in macrophages.7 Other significant
biological activities of 1,3-dithiolane-containing com-
pounds include anticonvulsant,8 radioprotective,8,9
anti-tumor,10 radical scavenging and hepatoprotective11
activities. 1,3-Dithiolane derivatives are used for the
synthesis of new antibacterial penem compounds.12
Dithiolanes also find application as process stabilisers
for polyolefins.13 These factors have generated signifi-
cant interest amongst organic and medicinal chemists
for the synthesis of 1,3-dithiolanes.
Dithiolane formation is generally carried out by the con-
densation of a carbonyl compound with 1,2-ethanedi-
thiol in the presence of various Lewis acid catalysts.1
Recent endeavors towards the development of newer
methods for conversion of carbonyl compounds to 1,3-
dithiolanes have witnessed the use of halides, perchlo-
rate, nitrates, acetylacetonate, tetrafluoroborate and
triflates derived from alkali, transition and lanthanide
metals,1,14 clays1 and supported reagents.1,15 However,
many of these methods have drawbacks such as moder-
ate yields, long reaction times, harsh reaction condi-
tions, tedious work-up, use of expensive reagents, use
of solvents and toxic agents, special efforts required to
prepare the catalyst, the requirement for special appara-
tus, etc. Thus, the development of more efficient meth-
ods is still in demand.
Keywords: Copper(II) tetrafluoroborate;Catalyst;Aldehyde;Ketone;
1,3-Dithiolane;1,3-Dithiane;Solvent-free.
*
Recently, we reported that Cu(BF4)2ÆxH2O induces
ꢀelectrophilic activationꢁ for heteroatom acylation,16
Corresponding author. Tel.: +91 172 2214683/86;fax: +91 172
2214692;e-mail: akchakraborti@niper.ac.in
0040-4039/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.07.059

6214
R.C.Besra et al./ Tetrahedron Letters 46 (2005) 6213–6217
1,1-diacetate formation,17 and thia Michael addition
reactions.18 We disclose herein our finding on the cata-
lytic effect of Cu(BF4)2ÆxH2O for 1,3-dithiolane forma-
tion from carbonyl compounds. To determine the
optimum reaction conditions, benzaldehyde (2.5 mmol)
was taken as the model substrate and was treated with
1,2-ethanedithiol in the presence of Cu(BF4)2ÆxH2O at
rt varying the amount of the catalyst and thiol used
and the reaction time. On each occasion, the progress
of the reaction was monitored by TLC and GC–MS.
The reaction was best carried out when a mixture of
benzaldehyde, 1,2-ethanedithiol (1.2 equiv) and Cu(B-
F4)2ÆxH2O (1 mol %) was stirred magnetically at 25 °C
for 1 min. 2-Phenyl-1,3-dithiolane was exothermically
produced and isolated in 99% yield.
compared to that of benzaldehyde (1 min) was due to
the steric hindrance offered by the peri hydrogen in 1-
naphthaldehyde towards nucleophilic attack by the thiol
on the aldehyde carbonyl group. The difference in the
rate of dithiolane formation from benzaldehyde (Table
1, entry 1) and acetophenone (Table 1, entry 28) encour-
aged us to test the efficiency of the catalyst for chemo-
selective dithiolane formation during a competition
reaction between an aldehyde and a ketone. Thus,
4-acetylbenzaldehyde (entry 29) was subjected to 1,3-
dithiolane formation. Excellent chemoselective dithio-
lane formation with the aldehyde carbonyl group was
observed.
To establish the generality with other dithiols, we car-
ried out the reaction of 4-methoxybenzaldehyde, 4-
nitrobenzaldehyde and cyclohexanone as representative
electron rich and electron deficient aldehyde and cyclic
ketone, respectively, with 1,3-propanedithiol in the
presence of Cu(BF4)2ÆxH2O (1 mol %) under solvent
free conditions. The corresponding dithanes were
obtained in 98%, 89% and 96% yields, respectively, in
1 min.
The generality of the Cu(BF4)2ÆxH2O catalysed 1,3-
dithiolane formation was established by subjecting var-
ious carbonyl compounds to reaction with 1,3-propane-
dithiol under similar conditions (Table 1). Aliphatic,
aromatic and heteroaromatic aldehydes were efficiently
and rapidly converted to the corresponding 1,3-dithio-
lanes in excellent yields in short times. Dithiolane
formation was not affected by the presence of other
functionalities such as, ether, ester, hydroxyl, halide,
nitro and cyano groups (entries 3–15) that could be
expected to compete with the carbonyl group for
complex formation with the catalyst. The acid sensitive
substrate furfural19 (entry 19) provided the correspond-
ing 1,3-dithiolane in excellent yield. Cyclic saturated and
unsaturated ketones afforded the desired products in
good to excellent yields (entries 24–27). Chemoselective
dithiolane formation took place with a,b-unsaturated
aldehydes (entries 17 and 18) and no competitive
Michael addition was observed (GC–MS).18 Surpris-
ingly, the conversion of crotonaldehyde (entry 18) to
the desired dithiolane could not be increased beyond
65% even after repeated attempts and the unreacted
starting material remained unchanged (GC–MS) on
each occasion. The desired dithiolane was obtained in
60% yield after subjecting the crude reaction mixture
to chromatographic purification.
The present method is superior to the reported proce-
dures with respect to the reaction time, yields, amount
of the catalyst used, necessity to use solvent, etc. This
claim is justified through the following examples in
which the efficiency of Cu(BF4)2ÆxH2O has been com-
pared with that of other recently reported catalysts for
the reaction of a representative unactivated (entry 1),
an electron rich (entry 5), and an electron deficient
(entry 13) aldehyde and a saturated ketone (entry 24).
The Cu(BF4)2ÆxH2O (1 mol %) catalysed reaction of
benzaldehyde with 1,2-ethanedithiol afforded 99% yield
after 1 min in the absence of solvent. The corresponding
reaction gave 97%, 89%, 95% and 78% yields in DCM,
MeCN, MeCN and THF after 30, 30, 90 and 300 min
in the presence of PPA–SiO2 (150 mg/mmol),15 Pr(OTf)3
(5 mol %),14g MoO2(acac)2 (10 mol %)14f and Bi(NO3)3
(0.1 mol %),14e respectively. A 78% yield was obtained
from the reaction of 4-hydroxybenzaldehyde with 1,2-
ethanedithiol in MeCN in the presence of Pr(OTf)3
(5 mol %) in 5 h14g whereas the Cu(BF4)2ÆxH2O
(1 mol %) catalysed reaction afforded a 95% yield in
1 min under solvent-free conditions. The Pr(OTf)3
(5 mol %) catalysed reaction of 4-nitrobenzaldehyde
with 1,2-ethanedithiol led to an 80% yield in MeCN in
4 h14g compared to an 84% yield obtained in 1 min using
Cu(BF4)2ÆxH2O (1 mol %) in the absence of solvent. We
chose cyclopentanone as a representative saturated
ketone as ketal/thioketal formation of a five-membered
cyclic ketone is retarded due to the eclipsing effect
involving the newly generated C–X bond and the adja-
cent hydrogen atoms of the cyclopentane ring.20 The
superiority of Cu(BF4)2ÆxH2O over the recently reported
PPA–SiO2 and MoO2(acac)2 was reflected during the
reaction of cyclopentanone with 1,2-ethanedithiol.
Thus, compared to the 85% yield obtained after 1 min
in the Cu(BF4)2ÆxH2O (1 mol %) catalysed reaction
under solvent-free conditions, the corresponding
dithiolane was obtained in 72% and 88% yields on car-
rying out the reaction in the presence of PPA–SiO2
The GC–MS of the product isolated from the reaction
of 3-methyl-2-cyclohexenone revealed the formation of
the corresponding dithiolane in 80% yield along with a
12% yield of the dithiolane of the Michael adduct. The
desired dithiolane was obtained in 66% yield after puri-
fication by column chromatography (entry 27). Steri-
cally hindered 2,4,6-trimethoxy benzaldehyde (entry 8)
provided an excellent yield of the dithiolane. The rate
of the reaction was found to be very fast and in most
cases, dithiolane formation was complete after 1–5 min
(TLC, GC–MS) with excellent yields. An exothermic
reaction (except for entry 12) took place after addition
of Cu(BF4)2ÆxH2O to the mixture of the substrate and
1,2-ethanedithiol, which indicated completion of the
reaction. The rate of dithiolane formation was influ-
enced by the electronic and steric factors of the carbonyl
substrates. Substrates with electron withdrawing groups
such as F, OCOPh, CF3 and CN (entries 11, 12, 14 and
15; Table 1) required longer times. The longer time
(30 min) needed for the reaction of 1-naphthaldehyde

R.C.Besra et al./ Tetrahedron Letters 46 (2005) 6213–6217
6215
Table 1. Cu(BF4)2ÆxH2O catalysed 1,3-dithiolane formation from different carbonyl compounds with 1,2-ethanedithiola
Entry
Substrate
CHO
Time (min)
Yield (%)b,c
R5
R1
R2
R4
R3
1
2
3
4
5
6
7
8
R1 = R2 = R3 = R4 = R5 = H
1
1
1
1
1
1
1
1
1
1
5
5
1
5
5
99
94
96
96
95
97d
93d
98
85d
83e
96d
89f
84
100d
84
R1 = R2 = R4 = R5 = H; R3 = Me
R1 = R2 = R4 = R5 = H; R3 = OMe
R1 = R2 = R4 = R5 = H; R3 = OCH2Ph
R1 = R2 = R4 = R5 = H; R3 = OH
R1 = R5 = H; R2 = R4 = OMe; R3 = OH
R1 = R2 = OMe; R3 = R4 = R5 = H
R1 = R3 = R5 = OMe; R2 = R4 = H
R1 = H; R2 = OEt;R 3 = OH;R 4 = R5 = H
R1 = R2 = R4 = R5 = H; R3 = Cl
R1 = R2 = R4 = R5 = H; R3 = F
9
10
11
12
13
14
15
R1 = R2 = R4 = R5 = H; R3 = OCOPh
R1 = R2 = R4 = R5 = H; R3 = NO2
R1 = R2 = R4 = R5 = H; R3 = CF3
R1 = R2 = R4 = R5 = H; R3 = CN
CHO
16
30
86
CHO
CHO
17
18
1
1
86
60
Ph
Me
CHO
X
19
20
21
X = O
X = S
1
1
5
93
92
80
CHO
CHO
CHO
Ph
Ph
22
1
80
O
23
1
99
n
24
25
26
n = 1
n = 2
n = 3
1
1
5
85
87
92d
O
27
1
66g
Me
28
29
60
1
90h,i
95j
COCH3
O
H
O
H3C
a The substrate was treated with 1,2-ethanedithiol (1.2 equiv) in the presence of Cu(BF4)2ÆxH2O (1 mol %) under neat conditions (except for entry 12)
at room temperature.
b Yield of the corresponding 1,3-dithiolane after purification.
c All compounds were characterised by IR, NMR (1H and 13C) and MS.
d Unknown compounds gave satisfactory spectral and elemental analyses.
e A 26% yield was obtained on carrying out the reaction under the catalytic influence of LiBF4(10 mol %) in MeCN for 5 min.
f The reaction was carried out in MeCN.
g GC–MS revealed 80% conversion to the desired dithiolane along with 12% of the dithiolane of the Michael adduct.
h The reaction was carried out at 80 °C.
i The dithiolane was formed in 36% and 39% yields on carrying out the reaction at room temperature for 1 h under neat conditions and for 2 h in
MeCN, respectively.
j The dithiolane formation took place exclusively with the aldehyde carbonyl.

6216
R.C.Besra et al./ Tetrahedron Letters 46 (2005) 6213–6217
(500 mg/mmol) in DCM after 30 min15 and MoO2-
(acac)2 (10 mol %) in MeCN after 3 h,14f respectively.
1 mol %) and the mixture was stirred at room tempera-
ture under a nitrogen atmosphere for 1 min (TLC). The
reaction mixture was dissolved in EtOAc and filtered
through a bed of anhydrous Na2SO4. The residue was
washed with EtOAc and the combined filtrates were
concentrated under vacuum to afford the product
(450 mg, 99%) as colourless liquid. IR (Neat): 3063,
3022, 2924, 1685, 1598, 1491, 1445, 1429, 1276, 1240,
After completion of this work, LiBF4 was reported for
1,3-dithiane formation under solvent-free conditions.21
Although this method avoided the handling of solvent
during the workup, the necessity of distillation for prod-
uct isolation limited its applicability for non-volatile
products. However, the efficiency of the Cu(BF4)2ÆxH2O
was proved to be better than that of LiBF4 as only a
26% yield was obtained in carrying out the reaction of
4-chlorobenzaldehyde with 1,2-ethanedithiol in the
presence of LiBF4 (10 mol %) for 5 min whereas the
Cu(BF4)2ÆxH2O (1 mol %) catalysed reaction afforded
an 83% yield in 1 min (entry 10). The superiority of
Cu(BF4)2ÆxH2O over the newly reported LiBF4 reac-
tion21 was further demonstrated on comparing the
results of dithiolane/dithiane formation with furfural
(entry 19) and cyclopentanone (entry 24). Thus, com-
pared to the 93% yield of 1,3-dithiolane obtained after
1 min at rt using Cu(BF4)2ÆxH2O (1 mol %), the corre-
sponding 1,3-dithiane was obtained in 100% yield under
the catalytic influence of LiBF4 (10 mol %) after 5 h at
0 °C21 during the reaction of furfural with 1,2-ethane-
dithiol. The LiBF4 (10 mol %) catalysed 1,3-dithiane
formation from cyclopentanone with 1,2-ethanedithiol
required 21 h21 to afford a comparable yield of the cor-
responding 1,3-dithiolane after 1 min in the presence of
Cu(BF4)2ÆxH2O (1 mol %).
1158, 1071, 845 cmÀ1 1H NMR (300 MHz, CDCl3):
.
d = 3.22–3.30 (m, 2H), 3.38–3.44 (m, 2H), 5.60 (s, 1H),
7.18–7.29 (m, 3H), 7.48 (d, J = 7.5 Hz, 2H). 13C NMR
(75 MHz, CDCl3): d = 40.0, 56.0, 127.7, 127.7, 128.2,
140.1. MS (ESI): m/z = 182 (M+), identical with the lit-
erature.23 The spectral data (IR, 1H and 13C NMR, MS)
of known compounds were identical with those of
authentic samples. The following compounds were not
reported previously.
2-(4-Hydroxy-3,5-dimethoxyphenyl)-1,3-dithiolane: Mp
68–70 °C;IR (KBr): 3428, 2928, 1621, 1517, 1459,
1428, 1375, 1328, 1296, 1252, 1224, 1195, 1112, 721,
1
665 cmÀ1. H NMR (300 MHz, CDCl3): d = 3.30–3.39
(m, 2H), 3.45–3.53 (m, 2H), 3.89 (s, 6H), 5.62 (s, 1H),
6.79 (s, 2H). 13C NMR (75 MHz, CDCl3): d = 40.1,
56.3, 57.1, 104.7, 130.4, 134.59, 146.8. MS (ESI):
m/z = 258 (M+). Anal. Calcd for C11H14O3S2: C,
51.14;H, 5.46%. Found: C, 51.10;H, 5.48%. 2-(2,3-Di-
methoxyphenyl)-1,3-dithiolane: Yellow oil;IR (neat):
2997, 2930, 2833, 1585, 1471, 1428, 1307, 1277, 1235,
1215, 1168, 1085, 1068, 1005, 813, 797, 751, 727,
1
The superiority of Cu(BF4)2ÆxH2O for dithiane forma-
607 cmÀ1. H NMR (300 MHz, CDCl3): d = 3.29–3.38
tion over the recently reported catalysts, for example,
(m, 2H), 3.41–3.49 (m, 2H), 3.84 (s, 3H), 3.89 (s, 3H),
6.08 (s, 1H), 6.81 (d, J = 8.1 Hz, 1H), 7.03 (t,
J = 8.0 Hz, 1H), 7.32 (d, J = 7.9 Hz, 1H). 13C NMR
(75 MHz, CDCl3): d = 39.8, 48.8, 55.7, 61.1, 111.7,
120.2, 123.9, 134.4, 146.6, 152.3. MS (ESI): m/z = 242
(M+). Anal. Calcd for C11H14O2S2: C, 54.51;H,
5.82%. Found: C, 54.54;H, 5.81%. 2-(3-Ethoxy-4-
hydroxyphenyl)-1,3-dithiolane: White gum (low melting
solid);IR (neat): 3436, 2979, 2926, 1602, 1511, 1476,
1437, 1395, 1269, 1221, 1121, 1041, 977, 952, 864, 826,
21
14g
LiBF4 and Pr(OTf)3 was evidenced by the reaction
of 4-methoxybenzaldehyde, 4-nitrobenzaldehyde and
cyclohexanone with 1,3-propanedithiol. The use of
Pr(OTf)3 (5 mol %) in MeCN afforded dithianes from
4-methoxybenzaldehyde and 4-nitrobenzaldehyde in
91% and 84% yields after 0.5 and 3 h, respectively.14g
Compared to these observations, the corresponding
dithianes were formed in 98% and 89% yields, respec-
tively, after 1 min under solvent-free conditions in the
presence of Cu(BF4)2ÆxH2O (1 mol %). The LiBF4
(10 mol %) catalysed reaction afforded an 86% yield of
the dithiane from cyclohexanone after 5 h compared to
96% yield obtained in 1 min from the Cu(BF4)2ÆxH2O
(1 mol %) catalysed reaction.
808, 752, 610 cmÀ1 1H NMR (300 MHz, CDCl3):
.
d = 1.41 (t, J = 6.9 Hz, 3H), 3.27–3.36 (m, 2H), 3.42–
3.50 (m, 2H), 4.10 (q, J = 6.9 Hz, 2H), 5.60 (s, 1H),
5.79 (br s, 1H), 6.81 (d, J = 8.1 Hz, 1H), 6.97 (d,
J = 8.1 Hz, 1H), 7.07 (s, 1H). 13C NMR (75 MHz,
CDCl3): d = 14.7, 40.0, 56.6, 64.4, 111.1, 113.8, 120.8,
131.0, 145.5, 145.7. MS (ESI): m/z = 242 (M+). Anal.
Calcd for C11H14O2S2: C, 54.51;H, 5.82%. Found: C,
54.53;H, 5.83%. 2-(4-Fluorophenyl)-1,3-dithiolane: col-
ourless oil;IR (neat): 1592, 1510, 1418, 1228, 1157, 850,
In conclusion, Cu(BF4)2ÆxH2O is a novel and highly effi-
cient catalyst for 1,3-dithiolane/dithiane formation from
carbonyl compounds. The advantages are chemoselec-
tivity, high yields, extremely fast reaction times, low cost
of the catalyst and operation at room temperature. With
increasingly tight legislation on the release of waste and
use of toxic substances, as a measure to control environ-
mental pollution,22 the solvent-free conditions employed
in the present method make it ꢀenvironmentally friendlyꢁ
and a practical approach for the synthesis of 1,3-dithio-
lanes/dithianes.
1
762, 691 cmÀ1. H NMR (300 MHz, CDCl3): d = 3.40–
3.49 (m, 2H), 3.40–3.49 (m, 2H), 5.60 (s, 1H), 6.94–
7.00 (m, 2H), 7.45–7.50 (m, 2H). 13C NMR (75 MHz,
CDCl3): d = 40.1, 55.4, 115.0, 115.3, 129.4, 129.5,
135.8, 160.5, 163.8. MS (ESI): m/z = 200 (M+). Anal.
Calcd for C9H9FS2: C, 53.97;H, 4.53%. Found: C,
53.94;H, 4.54%. 2-(4-Trifluoromethylphenyl)-1,3-
dithiolane: Mp 50–54 °C;IR (KBr): 3428, 2925, 1650,
1428, 1323, 1163, 1121, 1066, 1011, 838, 759, 699, 602,
Typical experimental procedure: 2-phenyl-1,3-dithio-
lane: To a magnetically stirred mixture of benzaldehyde
(0.26 g, 2.5 mmol) and 1,2-ethanedithiol (0.28 g,
3 mmol) was added Cu(BF4)2ÆxH2O (6 mg, 0.025 mmol,
1
503 cmÀ1. H NMR (300 MHz, CDCl3): d = 3.33–3.41
(m, 2H), 3.45–3.53 (m, 2H), 5.60 (s, 1H), 7.55 (d,
J = 7.9 Hz, 2H), 7.62 (d, J = 7.9 Hz, 2H). 13C NMR

R.C.Besra et al./ Tetrahedron Letters 46 (2005) 6213–6217
6217
´
9. Taroua, M.;Pe ra, M. H.;Taillandier, G.;Fatome, M.;
Laval, J. D.;Leclerc, G. Eur.J.Med.Chem. 1994, 29, 621–
625.
(75 MHz, CDCl3): d = 40.3, 55.3, 125.4, 128.3, 144.9.
MS (ESI): m/z = 250 (M+). Anal. Calcd for
C10H9F3S2: C, 47.98;H, 3.62%. Found: C, 47.94;H,
3.61%. 1,4-Dithia-spiro[4.6]undecane: Mp 47–49 °C;
10. Ashizawa, T.;Kawashima, K.;Kanda, Y.;Gomi, K.;
Okabe, M.;Ueda, K.;Tamaoki, T. Anticancer Drugs 1999,
10, 829–836.
11. Ram, V. J.;Haque, N.;Singh, S. K.;Nath, M.;Shoeb, A.;
Tripathi, S. C.;Patnaik, G. K. Bioorg.Med.Chem.Lett.
1994, 4, 1453–1456.
12. Tanaka, T.;Hashimoto, T.;Iino, K.;Sugimura, Y.;
Miyadera, T. Tetrahedron Lett. 1982, 23, 1075–1078.
13. Zenner, J. M.;Lee, R. E.;Malatesta, V. Poly.Degrad.
Stab. 2000, 67, 553–561.
14. (a) CdI2: Laskar, D. D.;Prajapati, D.;Sandhu, J. S. J.
Chem.Res.(S) 2001, 313–315;(b) LiOTf: Firouzabadi,
H.;Eslami, S.;Karimi, B. Bull.Chem.Soc.Jpn. 2001, 74,
2401–2406;(c) LiBF 4: Yadav, J. S.;Reddy, B. V. S.;
IR (KBr): 2917, 2845, 1433, 1276, 963, 841, 684 cmÀ1
.
1H NMR (300 MHz, CDCl3): d = 1.59 (s, 8H), 2.19 (d,
J = 8.1 Hz, 4H), 3.28 (s, 4H). 13C NMR (75 MHz,
CDCl3): d = 25.6, 28.5, 38.8, 46.0, 71.8. MS (ESI):
m/z = 187 (MÀ1)+. Anal. Calcd for C9H16S2: C, 57.39;
H, 8.56%. Found: C, 57.42;H, 8.58%.
Supplementary data
Supplementary data associated with this article can be
found, in the online version at doi:10.1016/j.tetlet.
2005.07.059.
Pandey, S. K. Synlett 2001, 238–239;(d) NiCl : Khan, A.
T.;Mondal, E.;Sahu, P. R.;Islam, S.
2
Tetrahedron Lett.
2003, 44, 919–922;(e) Bi(NO 3)3: Srivastava, N.;Dasgupta,
S. K.;Banik, B. K. Tetrahedron Lett. 2003, 44, 1191–1193;
(f) MoO2(acac)2: Rana, K. K.;Guin, C.;Jana, S.;Roy, S.
References and notes
C. Tetrahedron Lett. 2003, 44, 8597–8599;(g) Pr(OTf)
De, S. K. Synthesis 2004, 2837–2840, and references cited
therein.
:
1. Green, T. W.;Wuts, P. G. M. Protective Groups in Organic
Synthesis, 3rd ed.;John Wiley and Sons: New York, 1999,
p 329.
3
15. Aoyama, T.;Takido, T.;Kodomari, M.
2307–2310.
Synlett 2004,
2. Seebach, D. Angew.Chem,. Int.Ed.Engl.
1979, 18, 239–
258.
16. Chakraborti, A. K.;Gulhane, R.;Shivani Synthesis 2004,
111–115.
3. (a) Pettit, G. R.;van Tamelen, E. E. In Organic Reactions;
`
John Wiley: New York, 1962;Vol. 12, p 356;(b) Caube re,
17. Chakraborti, A. K.;Thilagavathi, R.;Kumar, R. Synthe-
sis 2004, 831–833.
18. Garg, S. K.;Kumar, R.;Chakraborti, A. K. Tetrahedron
Lett. 2005, 46, 1721–1724.
P.;Coutrot, P. In Comprehensive Organic Synthesis;Trost,
B. M., Fleming, I., Eds.;Pergamon Press: Oxford, 1991;
Vol. 8, p 835.
4. Breit, B. Angew.Chem,. Int.Ed. 1998, 37, 453–456.
5. Ram, V. J.;Goel, A.;Kandpal, M.;Mittal, N.;Goyal, N.;
Tekwani, B. L.;Guru, P. Y.;Rastogi, A. K. Bioorg.Med.
Chem.Lett. 1997, 7, 651–656.
6. Nguyen-Ba, N.;Brown, W. L.;Chan, L.;Lee, N.;Brasili,
L.;Lafleur, D.;Zacharie, B. Chem.Commun. 1999, 1245–
1246.
19. Gandini, A. Adv.Polym.Sci. 1977, 25, 47.
20. Carey, F. A.;Sundberg, R. J. Advanced Organic Chemistry
Part A, 2nd ed.;Plenum Press: New York, 1984, Chapter 8.
21. Kazahaya, K.;Tsuji, S.;Sato, T. Synlett 2004, 1640–1642.
22. (a) Garrett, R. L. In Designing Safer Chemicals;Garrett,
R. L., De Vito, S. C., Eds.;American Chemical Society
Symposium Series 640;American Chemical Society:
Washington, DC, 1996, Chapter 1;(b) Tanaka, K.
Solvent-free Organic Synthesis;Wiley-VCH: Weinheim,
2003.
7. Hussaini, I. M.;Zhang, Y. H.;Lysiak, J. J.;Shen, T. Y.
Acta Pharmacol.Sin. 2000, 21, 897–904.
´
8. Taroua, M.;Ribuot, C.;Pe ra, M. H.;Taillandier, G.;
Fatome, M.;Laval, J. D.;Demenge, P.;Leclerc, G. Eur.J.
Med.Chem. 1996, 31, 589–595.
23. Perio, B.;Hamelin, J. Green Chem. 2000, 2, 252–255.