Indium triflate: A mild Lewis acid catalyst for thioacetalization and transthioacetalization

Article abstract of DOI:10.1016/S0040-4020(02)00897-9

Protection of a variety of carbonyl compounds as thioacetals using indium triflate, a mild Lewis acid catalyst, was achieved at ambient temperature in very good yield. Transthioacetalization of oxyacetals into thioacetals was also achieved in an excellent

Full text of DOI:10.1016/S0040-4020(02)00897-9

Tetrahedron 58 (2002) 7897–7901
Indium triflate: a mild Lewis acid catalyst for thioacetalization
and transthioacetalization
*
Sengodagounder Muthusamy, Srinivasarao Arulananda Babu and Chidambaram Gunanathan
Silicates and Catalysis Discipline, Central Salt and Marine Chemicals Research Institute, Bhavnagar 364 002, India
Received 26 April 2002; revised 1 July 2002; accepted 25 July 2002
Abstract—Protection of a variety of carbonyl compounds as thioacetals using indium triflate, a mild Lewis acid catalyst, was achieved at
ambient temperature in very good yield. Transthioacetalization of oxyacetals into thioacetals was also achieved in an excellent yield. A
mixture of carbonyl compound and its respective oxyacetal was also completely converted into thioacetal in the presence of indium
triflate. q 2002 Elsevier Science Ltd. All rights reserved.
1. Introduction
tion. We herein report an efficient and mild method for
thioacetalization and transthioacetalization at ambient
temperature using indium triflate as a catalyst.
Protection and deprotection of reactive functional groups
are essential steps in the synthesis of polyfunctional
compounds.1 The protection of carbonyl compounds as
thioacetals is a frequently encountered synthetic step for the
preparation of many important natural/unnatural organic
compounds including multifunctional complex molecules.2
The recognition of thioacetals is due in part to their inbuilt
stability over usual acidic or basic conditions and also
because of their behavior as masked acyl anions or
methylene functions.3 Further, the use of thioacetals as
blocking groups has enabled a new strategy for the
electrophilic substitution on the carbonyl compound. In
this view, there have been continued improvements in the
methods of synthesis of thioacetals. Commonly, these
compounds are prepared by protic or Lewis acid-catalyzed
condensation of carbonyl compounds with thiols.1 Lewis
acid catalysts such as, ZnCl2,4 LnCl3,5 FeCl3/SiO2,6 AlCl3,7
2. Results and discussion
The protection of a variety of aldehydes and ketones with
ethane-1,2-dithiol in the presence of indium triflate was
carried out at ambient temperature. Additionally, we carried
out the transthioacetalization of oxyacetals and thioaceta-
lization of a mixture of an oxyacetal and its parent carbonyl
compound. The details are presented in the following
sections.
CHO
S
S
ZrCl4/SiO2,8 TeCl4,9 SnCl2,10 SiCl4,11 TiCl4,12 BF3·OEt2
13
In(OTf)3
DCM/r.t.
+
etc. have been used for this purpose. Reagents such as I2/
alumina,14 Cu(OTf)2/SiO2,15 magnesium or zinc triflate,16
InCl3,17a amberlyst-15,18a thionyl chloride18b adsorbed on
silica gel, lithium perchlorate,19a bis(diisobutylaluminium)-
1,2-ethanedithiolate19b and ceric ammonium nitrate20 have
also found favor.
HS
SH
R2
R2
R1
1a-f
R1
3a-f
2
Scheme 1.
Indium triflate21 is a mild Lewis acid, which has attracted
little attention as a catalyst. Recently, we have shown that
the O–H insertion reaction of a-diazo carbonyl compounds
to various alcohols is facilitated in the presence of
In(OTf)3.21a To the best of our knowledge, indium triflate
has not been used for thioacetalization or transthioacetaliza-
Table 1. Thioacetalization of aldehydes in the presence of In(OTf)3
Aldehyde Thioacetal
R1
R2
Time (min) Yielda of 3 (%)
1a
1b
1c
1d
1e
1f
3ab
3bb
3c
3d
3e
OH
OH
OMe
Me
H
OMe
H
H
H
H
8
9
6
8
8
35
84
85
95
93
89
86
Keywords: carbonyl compounds; indium triflate; thioacetalization;
transthioacetalization.
3f
NO2
H
a
*
Corresponding author. Tel.: þ91-278-567760; fax: þ91-278-567562;
Yields (unoptimized) based on the starting aldehydes.
Reaction was carried out using methanol as a solvent.
b
e-mail: salt@csir.res.in
0040–4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(02)00897-9

7898
S. Muthusamy et al. / Tetrahedron 58 (2002) 7897–7901
S
R1O
OR1
S
S
X
CHO
X
In(OTf)3
S
In(OTf)3
2, DCM/r.t.
5a; X = O (87%)
5b; X = S (89%)
4a; X = O
4b; X = S
2, DCM/r.t.
R
R
H
H
S
S
12a; R = Me, R1 = (CH2)2
12b; R = H, R1 = (CH2)2
12c; R = H, R1 = Me
In(OTf)3
3d; R = Me
3e; R = H
CHO
2, DCM/r.t.
H
H
7 (90%)
6
Scheme 2.
O
O
S
S
R1
R2
R1
R2
In(OTf)3
2.1. Thioacetalization of aldehydes
2, DCM/r.t.
( )n
13a-d
( )n
To a mixture of an equimolar amount of the aldehyde 1a
and ethane-1,2-dithiol was added 8 mol% of indium triflate
and stirred at room temperature for 8 min. Concentration
followed by column chromatographic purification of the
crude reaction mixture afforded product 3a in 84% yield.
The reaction was repeated with various aldehydes 1b–f
containing electron-withdrawing and electron-donating
substituents (Scheme 1, Table 1). The protection of
heteroaromatic (4a,b) and a,b-unsaturated (6) aldehydes
was also carried out under similar reaction conditions and
the results are summarized in Scheme 2. In each case the
corresponding thioacetals were obtained in good yield.
9a; R1 = CH2COOEt, R2 = H, n = 1
9b; R1 = (CH2)2COOEt, R2 = H, n = 1
9d; R1, R2 = H, n = 1
9e; R1, R2 = H, n = 2
Scheme 4.
Table 3. Transthioacetalization of oxyacetals
Oxyacetal
Thioacetal
Time (min)
Yielda (%)
12a
12b
12c
13a
13b
13c
13d
3d
3e
3e
9a
9b
9d
9e
10
8
5
240
270
150
150
90
89
92
92
90
88
93
2.2. Thioacetalization of ketones
The reaction of an equimolar amount of ketone 8a with
O
S
S
a
R1
R2
R1
R2
In(OTf)3
Yields (unoptimized) based on the starting oxyacetals.
2, DCM/r.t.
( )n
( )n
9a-e
ethane-1,2-dithiol in dry DCM was carried out in the
presence of 10 mol% of indium triflate as described earlier
to afford product 9a in 91% yield. This reaction was
generalized using various mono- and disubstituted cyclo-
alkanones to afford the corresponding thioacetals 9a–e in
very good yield (Scheme 3, Table 2). This reaction was
extended to other cyclic ketones such as a-tetralones under
similar experimental conditions to afford the respective
thioacetals 11a,b in good yield (Scheme 3, Table 2).
8a-e
a; R1= CH2COOEt, R2 = H, n = 1
b; R1= (CH2)2COOEt, R2 = H, n =1
c; R1= CH3, R2 = COOEt, n=0
d; R1, R2 = H, n = 1
e; R1, R2 = H, n = 2
O
S
S
In(OTf)3
2.3. Transthioacetalization of oxyacetals
2, DCM/r.t.
R
R
A mixture of the oxyacetal 12a and ethane-1,2-dithiol was
allowed to react in the presence of indium triflate (15 mol%)
for 10 min at room temperature. The reaction mixture was
worked-up and purification of the crude reaction mixture
afforded product 3d in 90% yield (Scheme 4, Table 3). This
reaction revealed that transthioacetalization of the oxyacetal
12a into 3d occurred swiftly in a clean manner without any
side product. Similarly, transthioacetalization of the oxy-
acetal 12b and the hemiacetal 12c derived from aromatic
aldehydes was also performed to furnish thioacetal 3e in
very good yield. Consequently, we were interested to
execute a similar reaction using oxyacetals prepared from
ketones. For this purpose, we carried out the reaction of 13a
with 2 in the presence of indium triflate for 4 h to afford
product 9a in 92% yield (Scheme 4, Table 3). This reaction
exposed that an oxyacetal of ketone can also be converted
10a; R = H
10b; R = OMe
11a; R = H
11b; R = OMe
Scheme 3.
Table 2. Thioacetalization of ketones in the presence of In(OTf)3
Ketone
Thioacetal
Time (h)
Yielda (%)
8a
8b
8c
8d
8e
10a
10b
9a
9b
9c
9d
9e
11a
11b
2.5
2.5
3.5
1.5
1.5
4.5
4.0
91
93
87
92
90
89
94
a
Yields (unoptimized) based on the starting ketones.

S. Muthusamy et al. / Tetrahedron 58 (2002) 7897–7901
7899
and carbonyl compounds, which also yielded good con-
version into thioacetals; the results are summarized in
Scheme 5.
25 mol% In(OTf)3
9b (96%)
9e (94%)
13b
8b
+
2, DCM/8h/r.t.
25 mol% In(OTf)3
2.5. Competitive thioacetalization of aldehydes and
ketones
8e
1d
13d
12a
+
+
2, DCM/6 h/r.t.
In order to check the chemoselectivity of the thioacetaliza-
tion reaction, equimolar quantities of aldehyde 1a, ketone
8e and ethane-1,2-dithiol were allowed to react in the
presence of 10 mol% of indium triflate for 7 min at ambient
temperature. Immediate work-up and purification of the
crude reaction mixture afforded products 3a and 9e,
respectively. In a similar manner, the reaction of aldehyde
1d and ketone 10a with ethane-1,2-dithiol was carried out to
afford products 3d and 11a, respectively (Scheme 6). These
reactions provided the thioacetals from aldehydes
preferentially.
15 mol% In(OTf)3
3d (97%)
2, DCM/0.5 h/r.t.
S
S
COOEt
S
S
In(OTf)3
+
13b + 12a
2, DCM
3 h/ r.t.
Me
3d (94%)
9b (87%)
Scheme 5.
In summary, we have shown that In(OTf)3 can be effectively
employed for the protection of carbonyl compounds as their
thioacetals in good yield at ambient temperature in a mild
manner. Moreover, transthioacetalization of oxyacetals in
the presence or absence of their parent carbonyl compounds
was also achieved in an excellent yield using indium triflate.
efficiently into a thioacetal in the presence of indium triflate.
In order to generalize this transthioacetalization reaction,
we carried out the reactions of various oxyacetals derived
from ketones 13b–d with 2 in the presence of indium triflate
(25 mol%) to afford the respective products in good yield.
Use of five or less mol% of indium triflate catalyst for
transthioacetalization of oxyacetals derived from ketone
required long reaction times (,35 h).
3. Experimental
2.4. Transthioacetalization of a mixture of an oxyacetal
and its parent carbonyl compound
Melting points are uncorrected. IR spectra were recorded on
a Perkin–Elmer Spectrum GX FT-IR spectrophotometer.
1H NMR, 13C NMR spectra were recorded on a Bruker
Avance DPX 200 (200 and 50.3 MHz, respectively)
spectrometer and referenced to TMS. Carbon types were
determined from DEPT 13C NMR experiments. Elemental
analyses were performed on a Perkin–Elmer Model 2400
analyzer. Thin layer chromatography was performed on
silica/alumina plates and components were visualized by
observation under iodine or by sulfuric acid charring.
Column chromatography was performed on neutral alumina/
silica gel. Preparation of oxyacetals of carbonyl compounds
were carried out according to the general procedure using
ethylene glycol in the presence of catalytic amount of
4-toluenesulfonic acid.1a
It has been reported19 that a mixture of an oxyacetal and
ketone with 2 afforded only the transthioacetalization
product. To test this theory, we carried out the reaction of
the oxyacetal 13b (1 equiv.) and ketone 8b (1 equiv.) with
an excess amount of thiol 2 (2.1 equiv.) in the presence of
indium triflate (25 mol%). Purification of the reaction
mixture afforded product 9b in 96% yield and no detectable
amount of the starting materials remaining in the reaction
mixture. This reaction revealed that the oxyacetal 13b as
well as its parent ketone 8b were converted simultaneously
into thioacetal 9b in good yield. Subsequently, we per-
formed further experiments on the mixture of oxyacetals
3.1. General procedure for the indium triflate-catalyzed
conversion of carbonyl compounds or oxyacetals into
thioacetals
S
S
S
S
In(OTf)3
1a
8e
+
+
To a solution of carbonyl compound or an oxyacetal
(1 mmol) and ethane-1,2-dithiol (1.1 mmol) in dry DCM
(5 mL) was added 8–10 mol% of indium triflate. The
reaction mixture was stirred at room temperature under an
inert atmosphere and monitored by TLC until the dis-
appearance of starting carbonyl compound or an oxyacetal.
After the appropriate period, the reaction mixture was
diluted with DCM (10 mL) and water (15 mL) was added.
The organic phase was separated and the aqueous layer was
washed with DCM (10 mL). Concentration of the combined
organic layer under reduced pressure afforded the crude
product, which was purified by neutral alumina/silica gel
column chromatography to afford the corresponding
product.
2, DCM
OMe
7 min/ r.t.
OH
3a (83%)
9e (9%)
S
S
S
S
In(OTf)3
1d + 10e
+
2, DCM
7 min/ r.t.
Me
3d (90%)
11a (7%)
Scheme 6.

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S. Muthusamy et al. / Tetrahedron 58 (2002) 7897–7901
3.2. General procedure for the indium triflate-catalyzed
thioacetalization of a mixture of an oxyacetal and its
parent carbonyl compound
J¼8.6 Hz, arom-H ), 6.78 (2H, d, J¼8.6 Hz, arom-H ), 5.59
(1H, s, CH ), 3.66 (3H, s, OCH3), 3.42–3.14 (4H, m); dC
(50.3 MHz, CDCl3) 159.3 (quat-C), 131.9 (quat-C), 129.2
(vC H), 113.8 (vC H), 56.1 (C H), 55.3 (OC H3), 40.3
(C H2).
To a solution of carbonyl compound (1 mmol), oxyacetal
(1 mmol) and ethane-1,2-dithiol (2.1 mmol) in dry DCM
(15 mL) was added 10–25 mol% of indium triflate. The
reaction mixture was stirred at room temperature under an
inert atmosphere. The reaction was monitored by TLC,
which showed initially the formation of the respective
carbonyl compound as well as dithiol. The reaction was
continued until the disappearance of starting material and
carbonyl compound was indicated. After the appropriate
period, the reaction mixture was diluted with dichloro-
methane (15 mL) and washed with water (15 mL). The
organic phase was separated and the aqueous layer was
washed with DCM (15 mL). Concentration of the organic
fractions under reduced pressure afforded the crude product,
which was further purified by neutral alumina/silica gel
column chromatography to afford the respective thioacetal.
3.3.4. 4-Methylphenyl-1,3-dithiolane 3d.14a,15,18b Color-
less solid, mp 55–578C (CHCl3/petroleum ether, lit.14a mp
56–588C); dH (200 MHz, CDCl3) 7.37 (2H, d, J¼7.2 Hz,
arom-H), 7.06 (2H, d, J¼7.2 Hz, arom-H ), 5.58 (1H, s,
CH ), 3.40–3.17 (4H, m), 2.27 (3H, s, CH3); dC (50.3 MHz,
CDCl3) 138.2 (quat-C), 137.8 (quat-C), 129.7 (vC H),
128.4 (vC H), 56.7 (C H), 40.8 (C H2), 24.6 (CH3).
3.3.5. Phenyl-1.3-dithiolane 3e.18a,19a Thick oil; dH
(200 MHz, CDCl3) 7.37–7.33 (5H, m, arom-H ), 5.56
(1H, s, CH), 3.41–3.37 (4H, m); dC (50.3 MHz, CDCl3)
138.4 (quat-C), 128.8 (vC H), 128.3 (vC H), 126.9
(vC H), 56.1 (C H), 40.4 (C H2).
3.3.6. 2-(4-Nitrophenyl)-1,3-dithiolane 3f.14b,22b Pale
yellow solid, mp 70–728C (CHCl3/petroleum ether, lit.22a
mp 67–698C); 8.15 (2H, d, J¼8.7 Hz, arom-H ), 7.67 (2H,
d, J¼8.7 Hz, arom-H ), 5.65 (1H, s, CH ), 3.57–3.37 (4H,
m); dC (50.3 MHz, CDCl3) 149.1 (quat-C), 147.8 (quat-C),
129.2 (vC H), 124.1 (vCH), 55.3 (C H), 40.9 (C H2).
3.3. Procedure for the competitive thioacetalization of
aldehydes and ketones
To a mixture of aldehyde 1a (1 mmol), ketone 8e (1 mmol)
and ethane-1,2-dithiol (1 mmol) in analytical grade metha-
nol (8 mL) was added 10 mol% of indium triflate. The
reaction mixture was stirred at ambient temperature for
7 min. Concentration in vacuum furnished the crude
mixture which was then dissolved in dry dichloromethane
and worked-up as described above to afford thioacetals 3a,
9e in 83 and 9% yields, respectively. Similarly, the reaction
of an aldehyde 1d and ketone 10a in dichloromethane was
carried out to afford the thioacetals 3d, 11a in 90 and 7%
yields, respectively.
3.3.7. 2-(1,3-Dithiolan-2-yl)furan 5a.18a,b Thick oil; dH
(200 MHz, CDCl3) 7.32 (1H, t, J¼4 Hz, vCH ), 6.26 (2H,
d, J¼4 Hz, vCH ), 5.60 (1H, s, CH ), 3.40–3.18 (4H, m); dC
(50.3 MHz, CDCl3) 154.6 (quat-C), 142.6 (vC H), 110.6
(vC H), 107.2 (vC H), 47.7 (C H), 39.3 (C H2).
3.3.8. 2-Thien-2-yl-1,3-dithiolane 5b. Thick oil; [Found:
C, 44.79; H, 4.34; S, 51.19. C7H8S3 requires C, 44.64; H,
4.28; S, 51.07%]; nmax (neat) 3100, 2964, 2921, 1651, 1429,
1269 cm21; dH (200 MHz, CDCl3) 7.17 (1H, d, J¼4 Hz,
vCH ), 7.00 (1H, d, J¼4 Hz, vCH ), 6.84 (1H, t, J¼4 Hz,
vCH ), 5.88 (1H, s, CH ), 3.41–3.24 (4H, m); dC
(50.3 MHz, CDCl3) 147.8 (quat-C), 127.1 (vC H), 126.2
(vC H), 126.1 (vC H), 51.3 (C H), 40.5 (C H2).
All new compounds gave satisfactory spectral data in
accordance to their proposed structures and known
compounds gave consistent data with the literature report.
3.3.1. 4-(1,3-Dithiolan-2-yl)-2-methoxyphenol 3a. Color-
less solid, mp 100–1028C (CHCl3/petroleum ether);
[Found: C, 52.80; H, 5.21; S, 28.15. C10H12S2O2 requires
C, 52.60; H, 5.29; S, 28.09%]; nmax (KBr) 3400, 1597, 1509,
1449, 1425, 1268, 1227 cm21; dH (200 MHz, CD3CN) 7.07
(1H, s, arom-H ), 6.98 (1H, d, J¼8.0 Hz, arom-H ), 6.81 (1H,
d, J¼8.0 Hz, arom-H ), 5.89 (1H, s, OH ), 5.60 (1H, s, CH ),
3.81 (3H, s, OCH3), 3.50–3.23 (4H, m); dC (50.3 MHz,
CD3CN) 147.0 (quat-C), 146.0 (quat-C), 131.8 (quat-C),
121.6 (vC H), 114.6 (vC H), 110.9 (vC H), 57.2 (C H),
56.4 (OCH3), 40.6 (CH2).
3.3.9. (E ) 2-(2-Phenylethenyl)-1,3-dithiolane 7.14b,19a
Pale yellow solid, mp 57–598C (CHCl3/petroleum ether,
lit.19a mp 58–598C); dH (200 MHz, CDCl3) 7.45–7.19 (5H,
m, arom-H ), 6.50 (1H, d, J¼15.5 Hz, vCH ), 6.20 (1H, dd,
J1¼15.5 Hz, J2¼8.9 Hz, vCH ), 5.22 (1H, d, J¼8.9 Hz,
vCH ), 3.60–3.20 (4H, m); dC (50.3 MHz, CDCl3) 136.2
(quat-C), 130.1 (vCH), 129.4 (vC H), 128.7 (vC H),
128.0 (vC H), 126.8 (vCH), 52.0 (C H), 39.8 (C H2).
3.3.2. 4-(1,3-Dithiolan-2-yl)phenol 3b.18b Colorless solid,
mp 115–1178C (CHCl3/petroleum ether, lit.18b mp 1168C);
dH (200 MHz, CD3CN) 7.54 (1H, s, OH ), 7.34 (2H, d,
J¼8.4 Hz, arom-H ), 6.75 (2H, d, J¼8.4 Hz, arom-H ), 5.63
(1H, s, CH ), 3.49–3.24 (4H, m); dC (50.3 MHz, CD3CN)
155.8 (quat-C), 130.4 (quat-C), 128.2 (vC H), 114.1
(vCH), 54.6 (C H), 38.9 (C H2).
3.3.10. Ethyl 1,4-dithiaspiro[4.5]dec-6-ylacetate 9a.
Thick oil; [Found: C, 55.48; H, 7.70; S, 24.80.
C12H20S2O2 requires C, 55.35; H, 7.74; S, 24.63%]; nmax
(neat) 2978, 2929, 2856, 1730, 1443, 1373, 1287,
1172 cm21; dH (200 MHz, CDCl3) 4.12 (2H, q, J¼7.0 Hz,
OCH2), 3.24–3.18 (4H, m), 3.09–2.99 (1H, m), 2.34–1.50
(8H, m), 1.35–1.15 (2H, m), 1.25 (3H, t, J¼7.0 Hz, CH3);
dC (50.3 MHz, CDCl3) 173.3 (COO), 74.0 (quat-C), 60.6
(OC H2), 45.8 (CH2), 44.9 (CH), 39.6 (C H2), 39.3 (C H2),
38.4 (C H2), 32.6 (CH2), 26.2 (C H2), 25.4 (C H2), 14.6
(C H3).
3.3.3. 4-Methoxyphenyl-1,3-dithiolane 3c.18b,19a,22a
Colorless solid, mp 60–628C (CHCl3/petroleum ether,
lit.19a mp 59–608C); dH (200 MHz, CDCl3) 7.40 (2H, d,

S. Muthusamy et al. / Tetrahedron 58 (2002) 7897–7901
7901
3.3.11. Ethyl 3-(1,4-dithiaspiro[4.5]dec-6-yl)propionate
9b. Colorless oil; [Found: C, 56.82; H, 8.15; S, 23.19.
C13H22S2O2 requires C, 56.89; H, 8.08; S, 23.37%]; nmax
(neat) 2929, 2855, 1734, 1445, 1333, 1170 cm21; dH
(200 MHz, CDCl3) 4.05 (2H, q, J¼7.0 Hz, OCH2),
3.21–3.08 (4H, m), 2.41–2.09 (4H, m), 1.89–1.76 (2H,
m), 1.56–1.35 (5H, m), 1.22–0.97 (2H, m), 1.18 (3H, t,
J¼7.0 Hz, CH3); dC (50.3 MHz, CDCl3) 173.9 (COO), 74.8
(quat-C), 60.5 (OC H2), 47.7 (CH), 45.5 (C H2), 39.5 (CH2),
39.3 (CH2), 32.9 (C H2), 31.2 (C H2), 27.7 (CH2), 26.2
(CH2), 25.1 (C H2), 14.6 (C H3).
and Dr R. V. Jasra, Head of the Discipline, for their
encouragement shown in this work. S. A. B. and C. G. thank
CSIR, New Delhi for a fellowship.
References
1. (a) Greene, T. W. Protective Groups in Organic Synthesis.
Wiley: New York, 1981. (b) Loewenthal, H. J. E. In Protective
Groups in Organic Chemistry. McOmie, J. F. W., Ed.;
Plenum: New York, 1973; pp 323–402.
3.3.12. Ethyl 6-methyl-1,4-dithiaspiro[4.4]nonane-6-car-
boxylate 9c. Thick oil; [Found: C, 53.77; H, 7.45; S, 26.11.
C11H18S2O2 requires C, 53.62; H, 7.36; S, 26.03%]; nmax
(neat) 2970, 2928, 1727, 1461, 1371, 1282 cm21; dH
(200 MHz, CDCl3) 4.14 (2H, q, J¼7.0 Hz, OCH2), 3.26–
3.24 (4H, m), 2.54–2.36 (3H, m), 1.80–1.55 (3H, m),
1.41 (3H, s, CH3), 1.27 (3H, t, J¼7.0 Hz, CH2CH3); dC
(50.3 MHz, CDCl3) 175.5 (COO), 77.9 (quat-C), 60.8
(OC H2), 58.0 (quat-C), 44.7 (C H2), 40.2 (C H2), 39.7
(CH2), 35.9 (C H2), 22.8 (C H2), 20.4 (C H2), 14.5 (CH3).
2. Kunz, H.; Waldmann, H. Comprehensive Organic Synthesis,
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3.3.13. 1,4-Dithiaspiro[4.5]decane 9d.14b,22c Thick oil; dH
(200 MHz, CDCl3) 3.29–3.25 (4H, m), 2.02–1.96 (4H, m),
1.68–1.57 (4H, m), 1.44–1.41 (2H, m); dC (50.3 MHz,
CDCl3) 69.2 (quat-C), 43.3 (C H2), 38.8 (C H2), 26.6 (CH2),
25.4 (CH2).
8. Patney, H. K.; Margan, S. Tetrahedron Lett. 1996, 37, 4621.
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242.
3.3.14. 1,4-Dithia-spiro[4.6]undecane 9e.18a,22d Thick oil;
dH (200 MHz, CDCl3) 3.29–3.25 (4H, m), 2.20–2.16
(4H, m), 1.60–1.57 (8H, m); dC (50.3 MHz, CDCl3) 72.3
(quat-C), 46.5 (CH2), 39.3 (C H2), 29.0 (C H2), 26.1 (CH2).
11. Ku, B.; Oh, D. Y. Synth. Commun. 1989, 19, 433.
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2001, 749 and references cited therein.
3.3.15. 30,40-Dihydro-20H-spiro[1,3-dithiolane-2,10-
naphthalene] 11a.15 Thick oil; dH (200 MHz, CDCl3)
7.95–7.90 (1H, m, arom-H), 7.15–6.94 (3H, m, arom-H ),
3.60–3.35 (4H, m), 2.80–2.71 (2H, m), 2.40–2.35 (2H, m),
2.04–1.95 (2H, m); dC (50.3 MHz, CDCl3) 139.5 (quat-C),
137.7 (quat-C), 131.3 (vC H), 129.1 (vCH), 127.7
(vC H), 126.5 (vC H), 69.2 (quat-C), 44.3 (CH2), 41.3
(CH2), 29.9 (C H2), 23.3 (C H2).
15. Anand, R. V.; Saravanan, P.; Singh, V. K. Synlett 1999, 415.
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T.; Hojo, K.; Masuda, R.; Kimura, T.; Yoshida, T. J. Org.
Chem. 1986, 51, 1427.
3.3.16. 60-Methoxy-30,40-dihydro-20H-spiro[1,3-dithio-
lane-2,10-naphthalene] 11b.14b Colorless solid, mp
85–878C (petroleum ether); dH (200 MHz, CDCl3) 7.85
(1H, d, J¼8.8 Hz, arom-H ), 7.74 (1H, dd, J1¼8.8 and
J2¼2.2 Hz, arom-H ), 6.47 (1H, s, arom-H), 3.73 (3H, s,
OCH3), 3.58–3.33 (4H, m), 2.77–2.70 (2H, m), 2.38–2.33
(2H, m), 2.02–1.94 (2H, m); dC (50.3 MHz, CDCl3) 158.9
(quat-C), 139.2 (quat-C), 132.7 (vC H), 131.2 (quat-C),
113.5 (vC H), 112.8 (vC H), 69.2 (quat-C), 55.7 (OCH3),
44.5 (CH2), 41.2 (CH2), 30.4 (C H2), 23.3 (C H2).
19. (a) Saraswathy, V. G.; Sankararaman, S. J. Org. Chem. 1994,
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Acknowledgements
This research was supported by CSIR (Young Scientist
Scheme), New Delhi. We thank Dr P. K. Ghosh, Director