An efficient method for thioacetalization of carbonyl compounds in the presence of a catalytic amount of benzyltriphenylphosphonium tribromide under solvent-free conditions

Article abstract of DOI:10.1080/10426500601088739

A variety of carbonyl compounds have been successfully converted to the corresponding thioacetal derivatives in good to excellent yields on the reaction of carbonyl compounds with 1,2-ethanedithiole, 1,3-propanedithiol, and ethanethiol in the presence of

Full text of DOI:10.1080/10426500601088739

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Phosphorus, Sulfur, and Silicon
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An Efficient Method for
Thioacetalization of Carbonyl
Compounds in the Presence
of a Catalytic Amount of
Benzyltriphenylphosphonium
Tribromide Under Solvent-Free
Conditions
Abdol R. Hajipour a b , Seied A. Pourmousavi a
Arnold E. Ruoho b
&
a Pharmaceutical Research Laboratory, Department
of Chemistry , Isfahan University of Technology ,
Isfahan, Iran
b Department of Pharmacology , University of
Wisconsin , Medical School, Madison, Wisconsin, USA
Published online: 19 Apr 2007.
To cite this article: Abdol R. Hajipour , Seied A. Pourmousavi & Arnold E. Ruoho
(2007) An Efficient Method for Thioacetalization of Carbonyl Compounds in the
Presence of a Catalytic Amount of Benzyltriphenylphosphonium Tribromide Under
Solvent-Free Conditions, Phosphorus, Sulfur, and Silicon and the Related Elements,
182:5, 921-937, DOI: 10.1080/10426500601088739
To link to this article: http://dx.doi.org/10.1080/10426500601088739
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Phosphorus, Sulfur, and Silicon, 182:921–937, 2007
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500601088739
An Efficient Method for Thioacetalization of Carbonyl
Compounds in the Presence of a Catalytic Amount of
Benzyltriphenylphosphonium Tribromide Under
Solvent-Free Conditions
Abdol R. Hajipour
Pharmaceutical Research Laboratory, Department of Chemistry,
Isfahan University of Technology, Isfahan, Iran, and Department
of Pharmacology, University of Wisconsin, Medical School, Madison,
Wisconsin, USA
Seied A. Pourmousavi
Pharmaceutical Research Laboratory, Department of Chemistry,
Isfahan University of Technology, Isfahan, Iran
Arnold E. Ruoho
Department of Pharmacology, University of Wisconsin, Medical School,
Madison, Wisconsin, USA
A variety of carbonyl compounds have been successfully converted to the correspond-
ing thioacetal derivatives in good to excellent yields on the reaction of carbonyl com-
pounds with 1,2-ethanedithiole, 1,3-propanedithiol, and ethanethiol in the presence
of catalytic amount of benzyltriphenylphosphonium tribromide under solvent-free
conditions. Some of the major advantages of this method are mild reaction condi-
tions, high efficiency, and compatibility with other reported methods. In addition,
no bromination occurs at the double bond, or α to the keto position, or even in the
aromatic ring under these experimental conditions.
Keywords Aldehydes; solvent free; thioacetalization; tribromide
Received June 6, 2006; accepted October 5, 2006.
We gratefully acknowledge the funding support received for this project from the
Isfahan University of Technology (IUT) I. R. Iran (Abdol R. Hajipour); and Grants GM
033138, MH 065503, NS 033650 (Arnold E. Ruoho) from the National Institutes of Health,
USA. Further financial support from Center of Excellency in Chemistry Research (IUT)
is gratefully acknowledged.
Address correspondence to Abdol R. Hajipour, Pharmaceutical Research Laboratory,
College of Chemistry, Isfahan University of Technology, Isfahan, 84156 Iran. E-mail:
haji@cc.iut.ac.ir
921

922
A. R. Hajipour et al.
INTRODUCTION
One of the major challenging problems during multistep syntheses
is protection of carbonyl functional groups from nucleophilic attack
until its electrophilic nature is exploited. For this reason, the pro-
tection of carbonyl groups is essential for organic chemists. Among
carbonyl protecting groups, dithioacetals constitute an important class
of compounds as acyl anion equivalents1 or masked methylene func-
tions in carbon-carbon bond forming reactions. On the other hand,
these substrates are versatile2 due to their straightforward prepa-
ration and also to their stability under basic or mildly acidic condi-
tions. Different methods have been reported for protection of carbonyl
compounds,3−16 but many of these procedures are associated with cer-
tain limitations such as low yields, harsh reaction conditions, longer
reaction times, and expensive reagents. Therefore milder, simpler, and
more efficient alternatives are still desirable for protection of carbonyl
compounds.
Organic Ammonium Tribromides (OATB)17 are extremely use-
ful reagents in organic synthesis particularly for deprotection of
dithioacetals,18 natural product synthesis,19 deprotection of tButyldi-
methylsillyl ether (TBDMS)20 and protection/deprotection of terahy-
dropyran (THP) ethers.21 Several tribromides have been reported;22
however, their preparation mostly involves using bromine, which in
most cases causes an environmental problem.
RESULTS AND DISCUSSION
In the course of our studies on reaction under solvent-free conditions
and developing a new method for transformation of organic functional
groups,23−25 here we introduce a new and environmentally benign
method for the synthesis of Benzyltriphenylphosphonium Tribromide
(BTPTB) 1 and application of this reagent as a mild and efficient cata-
lyst for protection of the carbonyl functional group.
Reagent 1 has been synthesized by dropwise addition of a solu-
tion of inexpensive and commercially available OxoneꢀR (2KHSO5.
KHSO4.K2SO4) to a solution of benzyltriphenylphosphonium bromide
and NaBr in water at r.t. to afford a yellow precipitate in quantitative
yields that showed an intense electronic absorbtion at 279 nm typical of
tribromide (Scheme 1).18 Reagent 1 is a very stable compound and can
be stored at bench for months without losing its activity. This reagent
also is a highly chemoselective catalyst for the conversion of aldehy-
des in the presence of ketones to the corresponding dithioacetals under
solvent-free conditions.

Thioacetalization of Carbonyl Compounds
923
SCHEME 1
Initially we tried the protection of aldehydes 2 to the corre-
sponding dithioacetals 3 by 1,2-ethanedithiol, 1,3-propanedithiol, and
ethanethiol in a mortar in the presence of 5 mol % of BTPTB at r.t.
under solvent-free conditions. This reaction gave dithioacetal deriva-
tives in a 90–98% yield after 3–7 min. The reaction was tried us-
ing a wide variety of aldehydes containing electron-withdrawing and
electron-donating substituents. The protection of heteroaromatic and
α, β-unsaturated aldehydes also were carried out under similar reac-
tion conditions. (Scheme 2, Table I) The reaction proceeded efficiently
for aldehydes at ambient temperature in essentially mild and almost
neutral conditions. This has been further substantiated by protecting
an acid-sensitive substrate such as furfural as its dithioacetals deriva-
tive in an almost quantitative yield without the formation of any side
products. In addition, no bromination occurred at the double bond, or
α to the keto position, or even in the aromatic ring under these experi-
mental conditions.
SCHEME 2
The thioacetalization of ketone 4 with 1,2-ethanedithiol under
solvent-free conditions was carried out in the presence of 5 mol% of
BTPTB to afford product 5 (Scheme 3). As shown in Table II, in compar-
ison to aldehydes, the reaction times for protection of ketones are longer
(1–2 h).
Moreover, this procedure is highly chemoselective, providing selec-
tive protection of an aldehyde in the presence of a ketone. Treatment of
an equimolar mixture of benzaldehyde and acetophenone in the pres-
ence of 1,2-ethanedithiol and a catalytic amount of BTPTB (5 mol%)
under solvent-free conditions produced only 1,2-dithiolane derivative of

924
A. R. Hajipour et al.
TABLE I Thioacetalization of Aldehyde 2 with Thiols under
Solvent-Free Conditionsa
Protecting
Groups
Time
(min)
Yieldb
(%)
Substrate
R
2a
2b
2c
2d
2e
2f
2g
2h
2i
Ph
Ph
HS(CH2)3SH
HS(CH2)2SH
SEt
HS(CH2)2SH
SEt
5
7
7
5
5
3
7
3
4
3
4
4
3
3
3
3
4
6
5
4
3
4
5
7
6
5
97
95
95
90
90
90
98
98
98
97
98
98
95
93
98
90
90
90
94
98
97
98
94
91
94
92
4-(NO2)C6H4
4-(Cl)C6H4
4-(MeO)C6H4
4 (Me2N)C6H4
2-(MeO)C6H4
3-(MeO)C6H4
4-(TBSO)C6H4
4-(AllylO)C6H4
4-(Cyclohexyl)C6H4
4(BzO)C6H3
PhCH2
4-(OH)C6H4
2-Furyl
4-(O2N)C6H4
PhCH CH
SEt
HS(CH2)2SH
HS(CH2)2SH
HS(CH2)3SH
HS(CH2)3SH
HS(CH2)3SH
HS(CH2)3SH
HS(CH2)3SH
HS(CH2)3SH
HS(CH2)3SH
HS(CH2)2SH
HS(CH2)3SH
HS(CH2)2SH
HS(CH2)3SH
HS(CH2)2SH
HS(CH2)2SH
HS(CH2)2SH
HS(CH2)2SH
HS(CH2)2SH
HS(CH2)2SH
HS(CH2)3SH
2j
2k
2l
2m
2n
2o
2p
2q
2r
2s
2t
2u
2v
2w
2x
2y
2z
n-C6H13
TBDPSO-n-C4H8
4-(MeO)C6H4
4-(Me)C6H4
4-(OH)C6H4
4-(OH)-2-(MeO)C6H4
4 (Me2N)C6H4
3-Formyl-hexane
2,5-(MeO)2C6H3
aConfirmed by TLC, GC, IR, 1H, 13C NMR, and CHN analysis.
bYield of isolated pure product after purification.
benzaldehyde, while the acetophenone was completely recovered back;
this competitive reaction illustrates the chemoselectivity of the present
method (Eq. (1), Scheme 4). The other competition reactions are shown
in Eqs. (1)–(3).
SCHEME 3

Thioacetalization of Carbonyl Compounds
925
(1)
(2)
(3)
The possible mechanism is shown in Scheme 4; initially BTPTB re-
acted with 1,2-ethandithiol to generate HBr as a catalyst, and HBr ac-
tivated as the carbonyl group for further reaction with dithiol to formal
hemithioacetal-type intermediate, which by losing an H2O molecule af-
forded the corresponding dithioacetal derivatives and HBr (Scheme 4).
Another noteworthy aspect of this procedure is that BTPTB is recy-
clable. To recover BTPTB, after completing the reaction and isolating
the product by ether, the residue was dissolved in water and treated
with a new batch of OxoneꢀR and NaBr to produce the catalyst again.
This method therefore is also important from the point of view of green
chemistry.

926
A. R. Hajipour et al.
TABLE II Thioacetalization of Ketone 4 with 1,2-Ethanedithiol under
Solvent-Free Conditions at r.t.a
Subtrate
R1
R2
Time (h)
Yield (%)b
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
Ph
Me
Me
Ph
Me
Me
Me
Ph
Me
1.5
1.7
1.3
1.5
1.5
1.5
1.5
2.0
2.0
2.0
1.5
2.0
1.5
1.5
98
93
93
98
95
97
91
94
91
94
96
93
96
97
4-(Me)C6H4
4-(Me)C6H4
4-(OH)C6H4
4-(Cl)C6H4
C6H4CH2
Ph
4-(Br)C6H4
(CH2)4
n-Pen
Et
(CH2)6
(CH2)5
CH3(CH2)4
CH3(CH2)2
Me
CH3(CH2)2
aConfirmed by TLC, GC, IR, 1H, 13C NMR, and CHN analysis.
bYield of isolated pure product after purification.
SCHEME 4

Thioacetalization of Carbonyl Compounds
927
In summary, we report here an efficient method for protection of alde-
hydes and ketones with thiols to form the corresponding dithioacetals
under solvent-free conditions. This procedure is an efficient method for
protection of aliphatic and aromatic ketones and aldehydes since the
yields of the products are high and the reaction times are low. The
catlyst is stable and may be kept in laboratory for months without loss
of activity, which is reproducible and easy to handle.
EXPERIMENTAL
General
All yields refer to isolated products after purification. All of the prod-
1
ucts were characterized by comparison of their spectral (IR, H NMR,
TLC, and GC) and physical data (melting or boiling points) with those of
authentic samples.3−17,26−30 All 1H NMR spectra were recorded at 300
MHz in CDCl3 relative to TMS as an internal standard. All 13CNMR
spectra were recorded at 75 MHz in CDCl3 relative to TMS as an in-
ternal standard. All of the reactions were carried out in a mortar in a
hood with strong ventilation.
Procedure for the Preparation of BTPTB
To a solution of BTPTB (0.01 mol, 3.88 g) and sodium bromide (0.023
mol, 2.37 g) in water (100 mL) was add dropwise a solution of OxoneꢀR
(2KHSO5.KHSO4.K2SO4) (0.022 mol, 13.65 g) in water (20 mL) under
stirring at r.t. until a yellow precipitate was formed. After stirring for 30
min, the mixture was filtered and washed with water (3 × 30 mL). The
filter cake was dried and recrystallized from CHCl3 to afford BTPTB as
yellow crystals (4.15 g, 70% yield), m.p.: 136–137◦C. IR (KBr) υ: 3050
(m), 2950 (s), 1580 (s), 1115 (s), 900 (m) cm−11H NMR: δ = 7.22–7.98
(m, 20H) 4.90 (d, J = 18 Hz, 2H), UV (CH2Cl2) λmax: 279 nm. Anal calcd.
for C25H22Br3P: C, 50.84%; H, 3.72%. Founder C, 50.74%; H, 3.60%.
Thioacetalization Under Solvent-Free Conditions
In a mortar, a mixture of 1,2-ethanedithiol, 1,3-propanedithiol, or
ethanethiol (14 mmol), and BTPTB (0.5 mmol 0.3 g) was added to
aldehyde or ketone (10 mmol). The reaction mixture was ground by
pestle at r.t. under solvent-free conditions. After disappearance of the
starting material (monitored by TLC), the mixture was extracted with
diethyl ether (2 × 20 mL) and filtered. The filtrate was evaporated un-
der reduced pressure, and the resulting crude material was purified by

928
A. R. Hajipour et al.
column chromatography (EtOAc:n-hexane) to afford pure dithioacetal
(Tables I and II).
2-Phenyl-1,3-dithiane (3a)
White solid; m.p. 74◦C; IR (KBr): 3037, 2940, 2894, 2827, 1593, 1491,
1429, 1281, 1183, 1066, 912, 728, 697 cm−1. 1H NMR: δ = 1.85–1.96 (m,
1 H, SCH2CHaHbCH2S), 2.09–2.16 (m, 1 H, SCH2CHaHbCH2S), 2.85–
2.90 (m, 2 H, SCH2), 2.99–3.07 (m, 2 H, SCH2), 5.16 (S, 1 H, ArCH),
7.24–7.35 (m, 3 H, ArH), 7.45–7.47 (m, 2 H, ArH) ppm. 13C NMR (125
MHz, CDCl3): δ = 24.96, 31.95 (2 C), 51.34, 127.61 (2 C), 128.29, 128.59
(2 C), 138.99 ppm. Anal calcd. for C10H12S2 (196.34): C, 61.17; H, 6.16;
S, 32.66%. Found: C, 61.95, H, 6.14; S, 32.49%.
2-Phenyl 1,3-dithiolane (3b)
IR (neat): 3429, 3060, 3026, 2922, 1690, 1661, 1600, 1494, 1451, 1422,
1
1276 cm−1. H NMR: δ = 3.23–3.46 (m, 4 H), 5.61 (s, 1 H), 7.19–7.30
(m, 3 H), 7.49 (d, J = 7.10Hz, 2 H). 13C NMR: δ = 40.81 (2 CH2), 56.82,
128.52, 128.56, 129.02, 140.94.
3-Nitrobenzaldehyde Diethyldithioacetal (3c)
1
Light yellow oil. H NMR. δ = 8.28 (br d, J = 1.5 Hz, 1 H), 8.12 (br
dd, J = 8.0, 1.5 Hz, 1 H), 7.80 (br dd, J = 8.0, 1.5Hz, 1 H), 7.52 (t,
J = 8.0 Hz, 1 H), 4.92 (s, 1 H), 2.58–2.46 (m, 4 H), 1.22 (t, J = 7.0 Hz, 6
H). EIMS: m/z = 257 (M+), 196, 168, 121. Anal. calcd. for C11H15NO2S2:
C, 51.36; H, 7.55; N, 5.45; Found: C, 51.55; H, 7.72; N, 5.38.
2-(4-Chlorophenyl) 1,3-dithiolane (3d)
IR (neat): 3006, 2903, 1486, 1404, 1085, 1012, 754 cm−1. 1H NMR: δ =
3.20–3.70 (m, 4 H), 5.58 (s, 1 H), 7.31 (d, J = 8.4Hz, 2 H), 7.41 (d, J =
8.4Hz, 2 H). 13C NMR: δ = 40.27 (2 CH2), 55.44, 128.57, 129.30, 133.61,
139.02.
4ꢀ-Methoxyb Diethenzaldehyde Diethyldithioacetal (3e)
White solid; m.p. 43◦C; IR (KBr): 2965, 2928, 1609, 1510, 1447, 1301,
1261, 1174, 1106, 1025 cm−1. 1H NMR: δ = 1.22 (t, J = 7.3Hz, 6 H, 2 ×
SCH2CH3), 2.46–2.63 (m, 4 H, 2 × SCH2CH3), 3.80 (s, 3 H, OCH3), 4.91
(s, 1 H, ArCH), 6.85 (d, J = 8.6 Hz, 2 H, ArH), 7.37 (d, J = 8.5 Hz, 2 H,
ArH) ppm. 13C NMR: δ = 14.24 (2 C), 26.15 (2 C), 51.69, 55.22, 113.75

Thioacetalization of Carbonyl Compounds
929
(2 C), 128.77 (2 C), 132.37, 159.00 ppm. Anal. calcd. for C12H18OS2
(242.41): C, 59.46; H, 7.48; S, 26.46%. Found: C, 59.60; H, 7.50; S,
26.20%.
4-N,N-Dimethylbenzaldehyde Diethyldithioacetal (3f)
Light yellow oil. 1H NMR: δ = 7.30 (d, J = 8.0 Hz, 2 H), 6.68 (d,
J = 8.0 Hz, 2 H), 4.86 (s, 1 H), 2.98 (s, 6 H), 2.62–2.43 (m, 4 H), 1.16
(t, J = 7.0 Hz, 6 H). EIMS: m/z = 255 (M+), 240, 194, 179, 120. Anal.
calcd. for C13H21NS2: C, 61.18; H, 8.24; N, 5.49%. Found: C, 61.32; H,
8.17; N, 5.33%.
2-(2-Methoxyphenyl) 1,3-dithiolane (3g)
IR (neat): 3038, 2999, 2923, 2833, 1597, 1488, 1464, 1434, 1316, 1263,
1149, 1047, 862, 779, 749, 693 cm−1. 1H NMR: δ = 3.10–3.45 (m, 4 H),
3.73 (s, 3 H), 5.58 (s, 1 H), 6.76 (d, J = 7.32 Hz, 1 H), 7.05–7.21 (m, 3 H).
13C NMR: δ = 40.04 (2 CH2), 55.08, 56.04, 113.34 (2 C), 120.14, 129.32,
141.91, 159.45.
2-(2-Methoxyphenyl) 1,3-dithiolane (3h)
IR (neat): 3068, 2921, 2777, 1609, 1500, 1487, 1443, 1370, 1249, 1183,
1096, 1038, 927, 866, 750 cm−1. 1H NMR: δ = 3.25–3.53 (m, 4 H), 5.60
(s, 1 H), 5.94 (s, 2 H), 6.69 (d, J = 8 Hz, 1 H), 6.91–6.95 (dd, J = 8,
1.7Hz, 1 H), 7.10 (d, J = 1.7 Hz, 1 H). 13C NMR: δ = 40.24 (2 CH2),
56.35, 101.20, 107.73, 108.32, 121.35, 133.88, 147.46, 147.85.
2-(4-tert-Butyldimethylsilyloxyphenyl)-1,3-dithiane (3i)
1H NMR: δ = 0.19 (s, 6 H), 0.97 (s, 9 H), 3.26–3.35 (m, 2 H), 3.40–3.66
(m, 2 H), 6.76 (d, J = 8.5Hz, 2 H), 7.38 (d, J = 8.5Hz, 2 H). 13C: δ = −4.2,
19.5, 27.6, 40.5, 57.3, 120.8, 131.7, 134.5, 156.3. MS: m/z = 313 (M +
H+), Anal calcd. for C15H24OS2Si: C, 57.64; H, 7.74%. Found: C, 57.60;
H, 7.70%.
2-(4ꢀ-Allyloxyphenyl)-1,3-dithiane (3j)
White solid; m.p. 81◦C; IR (KBr): 2914, 1603, 1506, 1429, 1245, 1183,
1
1015, 779 cm−1. H NMR: δ = 1.84–1.97 (m, 1 H, SCH2CH HbCH2S),
a
2.11–2.17 (m, 1 H, SCH2CHa H CH2S), 2.86–2.91 (m, 2 H, SCH2), 3.00–
b
3.14 (m, 2 H, SCH2), 4.50–4.52 (m, 2 H, OCH CH CH2), 5.13 (s, 1 H,
2
ArCH), 5.27 (dd, J = 3.0, J = 10.6 Hz, 1 H, OCH2CH CH Hb), 5.39
a
(dd, J = 3.2, J = 17.1 Hz, 1 H, OCH2CH CHa H ), 5.98–6.08 (m, 1 H,
b
OCH2CH CHaHb), 6.87 (d, J = 8.8 Hz, 2 H, ArH), 7.38 (d, J = 8.8 Hz,
2 H, ArH) ppm. 13C NMR: δ = 24.97, 32.10 (2 C), 50.66, 68.81, 114.86
(2 C), 118.26, 128.86 (2 C), 131.34, 133.03, 158.49 ppm. Anal. calcd. for

930
A. R. Hajipour et al.
C13H16OS2 (252.40): C, 61.86; H, 6.39; S, 25.41%. Found: C, 61.60; H,
6.30; S, 25.20%.
2-(4ꢀ-(Cyclohexenyloxy)phenyl)-1,3-dithiane (3k)
White solid; m.p. 103–104◦C; IR (KBr): 2933, 1605, 1509, 1242, 1168
cm−1. 1H NMR: δ = 1.57–1.65 (m, 2 H, CH2), 1.76–1.89 (m, 2 H, CH2),
1.91–2.03 (m, 1 H, SCH2CH HbCH2S), 2.05–2.18 (m, 3 H, SCH2CHa H
a
b
CH2S and CH2), 2.84–2.92 (m, 2 H, SCH2), 3.01–3.15 (m, 2 H, SCH2),
3.54–3.55 (m, 1 H, CH CHCHO), 5.10 (s, 1 H, ArCH), 5.81 (dd, J = 2.0,
J = 10.0 Hz, 1 H, CH CHCHO), 6.03–6.08 (m, 1 H, CH2CH CHCHO),
6.87 (d, J = 8.8 Hz, 2 H, ArH), 7.37 (d, J = 8.8 Hz, 2 H, ArH) ppm. 13
C
NMR: δ = 21.37, 24.93, 25.04, 29.80, 32.24 (2 C), 38.08, 50.94, 116.38,
126.87, 128.95, 129.36, 131.00, 131.18 (2 C), 154.14 ppm. Anal. calcd.
for. C16H20OS2 (292.47): C, 65.71; H, 6.89; S, 21.93; Found: C, 65.52; H,
6.81; S, 21.79%.
2-(4ꢀ-(Benzoyloxy)phenyl)-1,3-dithiane (3l)
M.p. 163–164◦C; IR (KBr): 3068, 2955, 2894, 1731, 1593, 1506, 1424,
1
1265, 1204, 1168, 1071, 1020, 886, 769, 707 cm−1. H NMR: δ = 1.88–
1.98 (m, 1 H, SCH2CH HbCH2S), 2.15–2.18 (m, 1 H, SCH2CHa H CH2S),
a
b
2.89–2.93 (m, 2 H, SCH2), 3.03–3.09 (m, 2 H, SCH2), 5.20 (S, 1 H, ArCH),
7.20 (d, J = 8.8 Hz, 2 H, ArH), 7.51 (m, 2 H, ArH), 7.53 (d, J = 8.5 Hz,
2 H, ArH), 7.63 (m, 1 H, ArH), 8.18 (m, 2 H, ArH) ppm. 13C NMR:
δ = 25.04, 32.03 (2 C), 50.72, 121.95 (2 C), 128.57 (2 C), 129.03 (2 C),
129.43, 130.17 (2 C), 133.64, 136.74, 150.80, 164.95 ppm. Anal. calcd.
for C17H16O2S2 (316.44): C, 64.53; H, 5.10; S, 20.27%. Found: C, 64.40;
H, 5.00; S, 20.00%.
2-Benzyl-1,3-dithiane (3m)
Colorless liquid; IR (neat): 3037, 2925, 2843, 1598, 1501, 1424, 1286,
1132, 1030, 846, 738 cm−1
.
1H NMR: δ = 3.04 (d, J = 7.1 Hz, 2 H,
PhCH2), 3.08–3.21 (m, 4 H, 2 × SCH2), 4.66 (t, J = 7.1 Hz, 1 H,
PhCH2CH), 7.16–7.26 (m, 5 H, ArH) ppm. Anal. calcd. for C10H12S2
(196.34): C, 61.17; H, 6.16; S, 32.66%. Found: C, 61.30; H, 6.10; S,
32.40%.
2-(4ꢀ-Hydroxyphenyl)-1,3-dithiane (3n)
M.p. 158◦C; IR (KBr): 3370, 2940, 2894, 2807, 1609, 1516, 1450, 1363,
1250, 1173, 1112, 851, 774 cm−1
.
1H NMR: δ = 1.85–1.96 (m, 1 H,
SCH2CH HbCH2S), 2.12–2.19 (m, 1 H, SCH2CHa H CH2S), 2.86–2.92
a
b
(m, 2 H, SCH2), 3.01–3.08 (m, 2 H, SCH2), 5.12 (S, 1 H, ArCH), 6.77 (d,
J = 8.2 Hz, 2 H, ArH), 7.31 (d, J = 8.3 Hz, 2 H, ArH) ppm. 13C NMR:
δ = 25.06, 32.18 (2 C), 50.74, 115.58 (2 C), 129.18 (2 C), 131.45, 155.61

Thioacetalization of Carbonyl Compounds
931
ppm. Anal. calcd. for C10H12OS2 (212.34): C 56.56, H 5.70, S 32.20%.
Found: C, 56.30; H, 5.60; S, 32.00%.
2-Furfuryl-1,3-dithiane (3o)
Pale yellow liquid; IR (neat): 2899, 1495, 1424, 1275, 1163, 1014, 748
1
cm−1. H NMR: δ = 1.92–2.01 (m, 1 H, SCH2CH HbCH2S), 2.08–2.16
a
(m, 1 H, SCH2CHa H CH2S), 2.88–2.93 (m, 4 H, 2 × SCH2), 5.20 (s, 1
b
H, SCHS), 6.32 (dd, J = 2.0, J = 3.2 Hz, 1 H, H-4), 6.37 (d, J = 3.1 Hz,
1 H, H-3), 7.34 (d, J = 1.9 Hz, 1 H, H-5) ppm. 13C NMR: δ = 25.22,
30.24 (2 C), 41.99, 107.83, 110.56, 142.27, 151.66 ppm. Anal. calcd. for
C8H10OS2 (186.30): C, 51.58; H, 5.41; S, 34.42%. Found: C, 51.40; H,
5.30; S 34.20%.
2-(4ꢀ-Nitrophenyl)-1,3-dithiolane (3p)
Yellow low melting solid; IR (neat): 2930, 2853, 1603, 1521, 1424,
1352, 1317, 1291, 1245, 1112, 1015, 984, 876, 830, 784 cm−1. 1H NMR:
δ = 3.37–3.43 (m, 2 H, SCH2), 3.45–3.55 (m, 2 H, SCH2), 5.65 (s, 1 H,
ArCH), 7.66 (d, J = 8.6 Hz, 2 H, ArH), 8.17 (d,J = 8.7 Hz, 2 H, ArH)
ppm. Anal. calcd. for C9H9NO2S2 (227.31): C, 47.56; H, 3.99; N, 6.16; S,
28.21%. Found: C, 47.30; H, 3.90; N, 6.00; S, 28.00%.
2-Styrenyl-1,3-dithiane (3q)
IR (neat): 3083, 3057, 3028, 2963, 2924, 1599, 1576, 1497, 1447, 1434,
1
1421, 968, 763, 687 cm−1. H NMR: δ = 3.24–3.37 (m, 4 H), 5.21 (d,
J = 9.1 Hz, 1 H), 6.16–6.25 (dd, J = 9.1, 15.5 Hz, 1 H), 6.49 (d, J = 15.5
Hz, 1 H), 7.22–7.38 (m, 5 H). 13C NMR: δ = 39.59 (2 CH2), 54.47, 126.60,
127.81, 128.53, 129.02, 130.14, 136.04.
2-Hexyl-1,3-dithiane (3r)
Colorless liquid; IR (neat): 2960, 2929, 2852, 1465, 1429, 1383, 1275,
1102, 979, 855, 728 cm−1. 1H NMR: δ = 0.85 (t, J = 6.6 Hz, 3 H, CH3),
1.25-1.42 (m, 8 H, CH2), 1.76–1.82 (m, 2 H, CH CHS), 3.14–3.25 (m, 4
2
H, 2 × SCH2), 4.44 (t, J = 7.08 Hz, 1 H, SCHS) ppm. Anal. calcd. for
C9H18S2 (190.37): C, 56.78; H, 9.53; S, 33.69%. Found: C, 56.50; H, 9.50;
S, 33.50%.
2-(4ꢀ-(tert-Butyldiphenylsilyloxy)butyl)-1,3-dithiane (3s)
Colorless liquid; IR (neat): 3068, 2935, 2863, 1588, 1434, 1260, 1107,
1
835, 748, 707. H NMR: δ = 1.04 (s, 9 H, SiC(CH3)3), 1.57–1.59 (m, 2
H, CH2), 1.75–1.79 (m, 3 H, CH2 and SCH2CH HbCH2S), 1.83–1.93 (m,
a
1 H, SCH2CH HbCH2S), 2.58–2.69 (m, 4 H, SCH2 and CH2), 2.71–2.83
a
(m, 2 H, SCH2), 3.65 (t, J = 5.8 Hz, 2 H, OCH2), 4.00 (t, J = 7.1 Hz, 1
H, CH), 7.34–7.42 (m, 5 H, ArH), 7.64–7.67 (m, 5 H, ArH) ppm. Anal.

932
A. R. Hajipour et al.
calcd. for C24H34OS2Si (430.75): C, 66.92; H, 7.96; S, 14.89%. Found: C,
66.80; H, 7.80; S, 15.00%.
2-(4-Methoxyphenyl)-1,3-dithiolane (3t)
White solid; m.p. 65◦C; IR (KBr): 1608, 1520, 1256, 1180, 1028 cm−1. 1H
NMR (400 MHz, CDCl3): = 3.28–3.35 (m, 2 H, SCH2), 3.44–3.51 (m, 2
H, SCH2), 3.77 (s, 3 H, OCH3), 5.62 (S, 1 H, ArCH), 6.83 (d, J = 8.56 Hz,
2 H, ArH), 7.44 (d, J = 8.76 Hz, 2 H, ArH) ppm. 13C NMR (100 MHz,
CDCl3): δ = 40.02 (2 C), 55.19, 55.94, 113.74 (2 C), 129.04 (2 C), 131.69,
159.25 ppm. C10H12OS2 (212.33): Anal. calcd. for C, 56.57; H, 5.70; S,
30.20%; Found: C, 56.70; H, 5.58; S, 30.35%.
2-(4ꢀ-Methylphenyl)-1,3-dithiolane (3u)
IR (neat): 3004, 1510, 1437, 1411, 1277, 1177, 1165, 830, 777 cm−1. 1H
NMR: δ = 2.32 (s, 3 H), 3.29–3.52 (m, 4 H), 5.62 (s, 1 H), 7.10 (d, J = 6.5
Hz, 2 H), 7.40 (d, J = 6.5 Hz, 2 H). 13C NMR: δ = 21.11, 40.20 (2 CH2),
56.12, 127.80, 129.15, 137.10, 137.84.
2-(4ꢀ-hydroxyphenyl)-1,3-dithiolane (3v)
IR (neat): 3188 (br), 2919, 1595, 1509, 1448, 1237, 1173, 838 cm−1. 1H
NMR: δ = 3.30–3.51 (m, 4 H), 5.00 (s, 1 H), 5.62 (s, 1 H), 6.73–6.79 (m, 2
H), 7.37–7.43 (m, 2 H). 13C NMR: 40.20 (2 CH2), 56.01, 115.31, 129.41,
131.99, 155.31.
2-(4ꢀ-hydroxy-3-methoxyphenyl)-1,3-dithiolane (3w)
IR (thin film): 3434 (br), 2996, 2918, 1607, 1596, 1509, 1464, 1449, 1427,
1
1266, 1227, 1145, 1118, 1026 cm−1. H NMR: δ = 3.29–3.53 (m, 4 H),
3.88 (s, 3 H), 5.69 (s, 1 H), 6.81 (d, J = 8.1 Hz, 1 H), 6.90–7.00 (dd,
J = 8.1, 1.69Hz, 1 H), 7.09 (s, 1 H). 13C NMR: δ = 40.14 (2 CH2), 55.91,
56.69, 110.26, 113.97, 121.07, 131.22, 145.54, 146.47.
2-(4ꢀ-N,N-dimethylphenyl)-1,3-dithiolane (3x)
IR (neat): 757, 824, 949, 1069, 1171, 1230, 1247, 1359, 1443, 1482, 1523,
1609, 2807, 2904, 3054 cm−1. 1H NMR: δ = 2.95 (s, 6 H), 3.32–3.36 (m,
2 H), 3.48–3.54 (m, 2 H), 5.65 (s, 1 H), 6.81 (d, J = 6.8 Hz, 2 H), 7.42
(d, J = 6.8 Hz, 2 H). 13C NMR: δ = 40.09 (2 CH3), 40.80 (2 CH2), 56.40,
112.60, 125.90, 128.77, 149.88.

Thioacetalization of Carbonyl Compounds
933
2-(3-Formyl)-1,3-dithiolane (3y)
IR (neat): 2955, 2926, 2854, 1735, 1465, 1377, 1275, 851, 725 cm−1. 1H
NMR: δ = 0.87 (t, J = 7.2 Hz, 3 H), 1.1–1.47 (m, 8 H), 1.79 (br s, 2 H),
3.18 (br s, 4 H), 4.35–4.45 (m, 1 H). 13C NMR: δ = 14.07, 22.57, 28.89,
29.10, 31.47, 38.34 (2 CH2), 39.41, 53.81.
2-(2ꢀ,4ꢀ-Dimethoxyphenyl)-1,3-dithiane (3z)
White solid; m.p. 103◦C; IR (KBr): 2996, 2939, 2893, 2837, 1618, 1505,
1454, 1424, 1326, 1290, 1116, 1039, 992 cm−1. 1H NMR: = 1.85-1.92 (m,
1 H, SCH2CHaHbCH2S), 2.12–2.17 (m, 1 H, SCH2CHaHbCH2S), 2.84–
2.90 (m, 2 H, SCH2), 3.05–3.16 (m, 2 H, SCH2), 3.78 (s, 3 H, OCH3), 3.83
(s, 3 H, OCH3), 5.61 (S, 1 H, ArCH), 6.42 (d, J = 2.4Hz, 1 H, ArH), 6.48
(dd, J = 2.4, J = 8.5Hz, 1 H, ArH), 7.48 (d, J = 8.5Hz, 1 H, ArH) ppm.
13C NMR (75 MHz, CDCl3): = 25.20, 32.41 (2 C), 43.10, 55.30, 55.60,
98.50, 104.70, 119.80, 129.70, 156.40, 160.60 ppm. C12H16O2S2.
2-Methyl-2-phenyl-1,3-dithiolane (5a)
Gummy liquid; IR (neat): 2971, 2935, 1598, 1491, 1445, 1276, 1071,
1030, 774, 702 cm−1. 1H NMR: = 2.14 (s, 3 H, CH3), 3.31–3.47 (m, 4 H,
2 × SCH2), 7.19–7.23 (m, 1 H, ArH), 7.28–7.32 (m, 2 H, ArH); 7.72–7.75
(m, 2 H, ArH) ppm. 13C NMR: = 33.81, 40.22 (2 C), 68.52, 126.68 (2 C),
126.99, 127.90 (2 C), 145.82 ppm. C10H12S2 (196.34): Anal. calcd. for C,
61.17; H, 6.16; S, 32.66%; Found: C, 61.01; H, 6.09; S, 32.43%.
2-Methyl-2-p-Tolyl-1,3-dithiolane (5b)
IR (neat): 731, 819, 1018, 1072, 1126, 1185, 1275, 1371, 1443, 1508,
1
1610, 1654, 2861, 2921, 2965, 3022 cm−1. H NMR: δ = 2.14 (s, 3 H),
2.32 (s, 3 H), 3.30–3.52 (m, 4 H), 7.11 (d, J = 8 Hz, 2 H), 7.63 (d, J = 8 Hz,
2 H). 13C NMR: δ = 20.89, 33.87, 40.29 (2 CH2), 68.39, 126.67, 128.64,
136.74, 142.87.
2-Phenyl-2-p-Tolyl-1,3-dithiolane (5c)
IR (thin film): 696, 741, 1032, 1186, 1275, 1443, 1506, 1594, 2874, 2921,
1
3022, 3056 cm−1. H NMR: δ = 2.31 (s, 3 H), 3.39 (m, 4 H), 7.08 (d,
J = 8.1 Hz, 2 H), 7.23–7.27 (m, 3 H), 7.48 (d, J = 8 Hz, 2 H), 7.60 (m, 2
H). 13C NMR: δ = 20.96, 40.12 (2 CH2), 127.10, 127.73, 127.97, 128.17,
128.64, 136.95, 141.47, 144.77.

934
A. R. Hajipour et al.
2-Methyl-2-(4-hydoxyphenyl)-1,3-dithiolane (5d)
IR (neat): 687, 738, 831, 844, 1074, 1180, 1230, 1273, 1375, 1442, 1508,
1
1596, 1608, 2876, 2929, 2969, 3225 (br) cm−1. H NMR: δ = 2.13 (s, 3
H), 3.35–3.51 (m, 4 H), 5.60 (br s, 1 H), 6.75 (d, J = 7.7 Hz, 2 H), 7.63
(d, J = 7.7 Hz, 2 H). 13C NMR: δ = 33.91, 40.35 (2 CH2), 68.22, 114.71,
128.33, 137.73, 154.64.
2-Methyl-2-(4-chlorophenyl)-1,3-dithiolane (5e)
IR (neat): 734, 830, 1011, 1069, 1093, 1275, 1372, 1396, 1422, 1444,
1
1489, 1570, 1591, 2860, 2922, 2966, 3059 cm−1. H NMR: δ = 2.1 (s, 3
H), 3.30–3.45 (m, 4 H), 7.26 (d, J = 6.4 Hz, 2 H), 7.68 (d, J = 6.4 Hz, 2
H). 13C NMR: δ = 33.46, 40.31 (2 CH2), 67.82, 127.87, 128.24, 132.70,
144.55.
2-Benzyl-2-methyl-[1,3]dithiolane (5f)
B.p. 129–130/1.5◦C. IR (neat): 3083, 3060, 3027, 2959, 2919, 2856, 1602,
1494, 1452, 1372, 1276, 1083, 752, 698 cm–1. H NMR: δ = 1.71 (s, 3
1
H), 3.00–3.32 (m, 6 H), 7.15–7.36 (m, 5 H). 13C NMR: d = 31.78, 39.72
(2 CH2), 51.41, 66.59, 126.68, 127.66, 130.69, 137.74.
2,2-Diphenyl-[1,3]dithiolane (5g)
M.p. 105–106◦C. IR (thin film): 696, 741, 1032, 1186, 1275, 1443, 1506,
1
1594, 2874, 2921, 3022, 3056 cm–1. H NMR: δ = 3.39 (m, 4 H), 7.08
(d, J = 8.1 Hz, 4 H), 7.23–7.27 (m, 6 H). 13C NMR: δ = 40.12 (2 CH2),
127.10, 127.73, 127.97, 128.17, 128.64, 136.95, 141.47, 144.7
2-Methyl-2-(4-bromophenyl)-1,3-dithiolane (5h)
IR (neat): 731, 827, 1007, 1077, 1275, 1391, 1486, 1583, 2858, 2922,
2965, 3061 cm−1. 1H NMR: δ = 2.07 (s, 3 H), 3.30–3.45 (m, 4 H), 7.38 (d,
J = 6.8 Hz, 2 H), 7.60 (d, J = 6.8 Hz, 2 H). 13C NMR: δ = 34.10, 41.01
(2 CH2), 68.50, 114.03, 129.60, 131.50, 145.76.
1,4-Dithiaspiro(4.4)nonane (5i)
Colorless liquid; IR (neat): 2960, 2924, 2878, 1449, 1275, 1168, 1101,
1
978, 851, 692 cm−1. H NMR: δ = 1.74–1.77 (m, 4 H, CH2), 2.07–2.14
(m, 4 H, CH2), 3.30 (s, 4 H, 2 × SCH2) ppm. 13C NMR: δ = 24.48 (2 C),

Thioacetalization of Carbonyl Compounds
935
39.37 (2 C), 43.92 (2 C), 70.86 ppm. C7H12S2 (160.30): Anal. calcd. for
C, 52.45; H, 7.55; S, 40.00%; Found: C, 52.12; H, 7.50; S, 39.85%.
2-Ethyl-2-pentyl-1,3-dithiolane (5j)
Colorless liquid; IR (neat): 2960, 2930, 2853, 1465, 1373, 1276, 1148,
1
984, 892, 851, 810, 733, 692 cm−1. H NMR: δ = 0.85 (t, J = 7.0Hz, 3
H, CH3), 0.99 (t,J = 7.30 Hz, 3 H, CH3), 1.21–1.31 (m, 4 H, CH2), 1.38–
1.46 (m, 2 H, CH2), 1.84–1.93 (m, 4 H, CH2), 3.21 (br. s, 4 H, SCH2)
ppm. 13C NMR (100 MHz, CDCl3): = 11.16, 14.01, 22.53, 26.58, 31.95,
36.12, 39.37 (2 C), 42.88, 72.41 ppm. C10H20S2 (204.40): Anal. calcd. for
C, 58.76; H, 9.86; S, 31.38%; Found: C, 58.54; H, 9.79; S, 31.09.
1,4-Dithiaspiro(4.6)undecane (5k)
White solid; m.p. 56◦C; SiO2-TLC (hexane). IR (KBr): 2919, 2842, 1460,
1
1424, 1275, 1244, 1234, 1152, 1101, 963, 846, 692 cm−1. H NMR: δ =
1.57 (m, 8 H, CH2), 2.17–2.19 (m, 4 H, CH2), 3.26 (s, 4 H, SCH2) ppm. 13
C
NMR: δ = 25.62 (2 C), 28.55 (2 C), 38.84 (2 C), 46.11 (2 C), 71.88 ppm.
C9H16S2 (188.36): Anal. calcd. for C, 57.39; H, 8.56; S, 34.05; Found: C,
57.18; H, 8.48; S, 33.87%.
1,4-Dithiaspiro(5.5)decane (5l)
Colorless liquid; IR (neat): 2930, 2853, 1440, 1265, 1127, 1015, 907, 861,
1
764 cm−1. H NMR: δ = 1.43–1.49 (m, 2 H, CH2), 1.60–1.67 (m, 4 H,
CH2), 1.96–2.02 (m, 6 H, SCH2CH2CH2S and 2 × CH2), 2.79–2.83 (m, 4
H, 2 × SCH2) ppm. 13C NMR: δ = 21.97 (2 C), 25.79 (2 C), 25.87, 26.12,
37.86 (2 C), 50.32 ppm. C9H16S2 (188.36): Anal. calcd. for C, 57.39; H,
8.56; S, 34.05%; Found: C, 57.14; H, 8.50; S, 34.23%.
2-Butyl-2-methyl-1,3-dithiolane (5m)
IR (neat): 686, 733, 852, 972, 1056, 1139, 1276, 1374, 1448, 2859, 2927,
2957 cm−1. 1H NMR: δ = 0.92 (t, J = 7.1 Hz, 3 H), 1.30–1.38 (m, 2 H),
1.43–1.54 (m, 2 H), 1.75 (s, 3 H), 1.90–1.95 (m, 2 H), 3.30 (m, 4 H). 13
C
NMR: δ = 14.00, 22.90, 29.50, 32.30, 40.00 (2 CH2), 45.80, 66.80.
2, 2-Dipropyl-1,3-dithiolane (5n)
IR (neat): 2961, 2873, 1707, 1459, 1380, 1275 cm−1. 1H NMR: δ = 0.90
(t, J = 7.3 Hz, 6 H), 1.35–1.63 (m, 4 H), 2.73–2.76 (m, 1 H), 3.13–3.23

936
A. R. Hajipour et al.
(m, 4 H), 4.63 (d, J = 6.2 Hz, 1 H). 13C NMR: δ = 10.91 (2 CH3), 23.94
(2 CH2), 28.72, 38.42 (2 CH2), 58.22.
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