Efficient method for thioacetalization of carbonyl compounds in the presence of a catalytic amount of benzyltriphenylphosphonium tribromide (BTPTB) under solvent-free conditions

Article abstract of DOI:10.1080/00397910802219197

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

Full text of DOI:10.1080/00397910802219197

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Efficient Method for
Thioacetalization of Carbonyl
Compounds in the Presence
of a Catalytic Amount of
Benzyltriphenylphosphonium
Tribromide (BTPTB) under
Solvent-Free Conditions
Abdol Reza Hajipour a , 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 Science , Madison, Wisconsin, USA
Published online: 09 Sep 2008.
To cite this article: Abdol Reza Hajipour , Seied A. Pourmousavi & Arnold E. Ruoho
(2008) Efficient Method for Thioacetalization of Carbonyl Compounds in the Presence
of a Catalytic Amount of Benzyltriphenylphosphonium Tribromide (BTPTB) under
Solvent-Free Conditions, Synthetic Communications: An International Journal for
Rapid Communication of Synthetic Organic Chemistry, 38:15, 2548-2566, DOI:
10.1080/00397910802219197
To link to this article: http://dx.doi.org/10.1080/00397910802219197

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Synthetic Communications1, 38: 2548–2566, 2008
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910802219197
Efficient Method for Thioacetalization of
Carbonyl Compounds in the Presence
of a Catalytic Amount of
Benzyltriphenylphosphonium Tribromide
(BTPTB) under Solvent-Free Conditions
Abdol Reza Hajipour,1 Seied A. Pourmousavi,1
and Arnold E. Ruoho2
1Pharmaceutical Research Laboratory, Department of Chemistry,
Isfahan University of Technology, Isfahan, Iran
2Department of Pharmacology, University of Wisconsin Medical Science,
Madison, Wisconsin, USA
Abstract: A variety of carbonyl compounds have been successfully converted to the
corresponding thioacetal derivatives in good to excellent yields on reaction of car-
bonyl compounds with 1,2-ethanedithiole, 1,3-propanedithiol, and ethylthiol in the
presence of a catalytic amount of benzyltriphenylphosphonium tribromide (BTPTB)
under solvent-free conditions. Some of the major advantages of this method are mild
reaction conditions, high efficiency, and the compatibility with other reported meth-
ods. In addition, no bromination occurs at the double bond or a to the keto position
or even in the aromatic ring under these experimental conditions.
Keywords: Carbonyl compounds, solvent-free, thioacetalization
INTRODUCTION
One of the major challenging problems during multistep syntheses is
protection of carbonyl functional groups from nucleophilic attack until
their electrophilic nature is exploited. For this reason, the protection
of carbonyl groups is essential for organic chemists. Among carbonyl
Received in the U.K. September 10, 2007
Address correspondence to Abdol Reza Hajipour, Pharmaceutical Research
Laboratory, Department of Chemistry, Isfahan University of Technology,
Isfahan 84156, Iran. E-mail: haji@cc.iut.ac.ir
2548

Thioacetalization of Carbonyl Compounds
2549
protecting groups, dithioacetals constitute an important class of
compounds as acyl anion equivalents[1] or masked methylene functions
in carbon–carbon bond-forming reactions. On the other hand, these sub-
strates are versatile[2] as a result of their straightforward preparation and
also their stability under basic or mildly acidic conditions. Different meth-
ods have been reported for protection of carbonyl compounds,[3–17] but
many of these procedures are associated with certain limitations such
as low yields, harsh reaction conditions, longer reaction times, and
expensive reagents. Therefore milder, simpler, and more efficient alterna-
tives are still desirable for protection of carbonyl compounds.
Organic ammonium tribromide (OATB)[18] is an extremely useful
reagent in organic synthesis particularly for deprotection of dithioacetals,[19]
natural product synthesis,[20] deprotection of tert-butyldimethylsilyl
(TBDMS) ethers,[21] and protection=deprotection of tetrahydropyranyl
(THP) ethers.[22] Several tribromides have been reported;[23] however, their
preparation mostly involves using bromine, which in most cases causes an
environmental problem.
RESULTS AND DISCUSSION
In continuation of our studies on reactions under solvent-free conditions
and developing new methods for transformation of organic functional
groups,[24–26] 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 catalyst
for protection of the carbonyl functional group.
Reagent 1 has been synthesized by dropwise addition of a solution
of inexpensive and commercially available Oxone1 (2KHSO5 ꢀ
KHSO4 ꢀ K2SO4) to a solution of benzyltriphenylphosphonium bromide
and NaBr in water at room temperature 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 for months without losing its activity. This
reagent also is a highly chemoselective catalyst for the conversion of
aldehydes in the presence of ketones to the corresponding dithioacetals
under solvent-free conditions.
Scheme 1.

2550
A. R. Hajipour, S. A. Pourmousavi, and A. E. Ruoho
Scheme 2.
Initially we tried the protection of aldehydes 2 to the corresponding
dithioacetals 3 by 1,2-ethanedithiole, 1,3-propanedithiol, and ethylthiol l
in a mortar in the presence of 5 mol% of BTPTB at room temperature
under solvent-free conditions. This reaction gave dithioacetal derivatives
in 90–98% yield after 3–7 min. The reaction was tried using wide variety
of aldehydes containing electron-withdrawing and electron-donating
substituents. The protection of heteroaromatic and a,ß-unsaturated alde-
hydes also was carried out under similar reaction conditions (Scheme 2,
Table 1). The reaction proceeds efficiently for aldehydes at ambient tem-
perature in essentially mild and almost neutral conditions. The reaction
in the absence of BTPTB did not occurred at all even under heating con-
ditions at 60 ꢁC for 10 h. The reaction also has been employed for protec-
tion of aldehydes with acid-sensitive substrate such as furfural as its
dithioacetals derive in almost quantitative yield without the formation
of any side products. In addition, no bromination occurs at the double
bond or a to the keto position or even in the aromatic ring under these
experimental conditions.
The thoacetalization 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. As shown in Table 2, in comparison to
aldehydes, the reaction times for protection of ketones are longer
(1–2 h) (Table 2, Scheme 3).
Moreover, this procedure is highly chemoselective, providing
selective protection of an aldehyde in the presence of a ketone. Treat-
ment of an equimolar mixture of benzaldehyde and acetophenone in
the presence of 1,3-ethanedithiol and a catalytic amount of reagent
1 (5 mol%) under solvent-free conditions produced only 1,3-dithiolane
derivative of benzaldehyde with complete recovery of the acetophe-
none, thus illustrating the chemoselectivity of the present method
[Eq. (1), Scheme 4]. The other competition reactions are shown in
Eqs. (1–3).

Thioacetalization of Carbonyl Compounds
2551
Table 1. Thioacetalization of aldehyde 2 with reagent 1 under solvent-free
conditionsa,b
Entry
Substrate
Protecting group
Time (sec)
Yield (%)b
2a
2b
2c
2d
2e
2f
2g
2h
2i
2j
2k
2l
2m
2n
2o
2p
2q
2r
Ph
Ph
HS(CH2)3SH
HS(CH2)2SH
SEt
HS(CH2)2SH
SEt
SEt
50
70
70
50
50
40
70
40
60
50
45
40
50
50
40
45
60
50
50
60
45
60
50
80
50
45
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
n-C6H13
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
2s
2t
TBDPSO-n-C4H8
4-(MeO)C6H4
4-(Me)C6H4
2u
2v
2w
2x
2y
2z
4-(OH)C6H4
4-(OH)-2-(MeO)C6H4
4 (Me2N)C6H4
3-Formyl-hexane
2,5-(MeO)2C6H3
aConfirmed by comparison with authentic samples (TLC, GC, IR, and 1H NMR).
bYield of isolated pure product after purification.
ð1Þ

2552
A. R. Hajipour, S. A. Pourmousavi, and A. E. Ruoho
Table 2. Thioacetalization of ketones 4 with reagent 1 under solvent-free
conditions at room temperaturea,b
Subtrate
R1
R2
Time (h)
Yield (%)c
4a
4b
4c
4d
4e
4f
Ph
Me
Me
Ph
Me
Me
Me
Ph
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
4g
4h
4i
4-(Br)C6H4
Me
ꢂ(CH2)4ꢂ
4j
n-Pen
Et
4k
4l
ꢂ(CH2)6ꢂ
ꢂ(CH2)5ꢂ
4m
4n
CH3(CH2)4
CH3(CH2)2
Me
CH3(CH2)2
aConfirmed by comparison with authentic samples (TLC, GC, IR, and NMR).
bMolar ratio of 1:4 (1:1).
cYield of isolated pure product after purification.
ð2Þ
ð3Þ

Thioacetalization of Carbonyl Compounds
2553
Scheme 3.
The possible mechanism is shown in Scheme 4. Initially the reagent
1 reacts with the 1,2-ethandithiol to generate HBr as catalyst, and the
producing HBr activates the carbonyl group for further reaction with
dithiol to form a hemithioacetal-type intermediate, which by losing
the HOBr molecule affords the corresponding carbonyl derivatives
(Scheme 4), and HBr activates the carbonyl compounds again for
further reaction.
Another noteworthy aspect of this reagent is that this reagent is
reproducible. To recover the reagent, after finishing the reaction and
isolating the product by ether, the residue was dissolved in water and
treated with new bath of Oxone1 and NaBr to produce the reagent
again. Therefore this method is also important from the point of view
of green chemistry.
In summary, we report here an efficient method for protection of
aldehydes and ketones with 1,4-ethanedithol to the corresponding 1,3-
dithiolane under solvent-free conditions. This procedure is an efficient
method for protection of aliphatic and aromatic ketone; the yields of pro-
ducts are high, and the reaction time is low. The reagent is stable and may
be kept for months without losing its activity. This reagent is reproduc-
ible and also handles easily.
EXPERIMENTAL
General
All yields refer to isolated products after purification. All of the products
1
were characterized by comparison of their spectral (IR, H NMR, TLC,
and GC) and physical data (melting and boiling points) with those of
Scheme 4.

2554
A. R. Hajipour, S. A. Pourmousavi, and A. E. Ruoho
1
authentic samples. All H NMR spectra were recorded at 300 MHz in
CDCl3 relative to TMS as an internal standard. All 13C NMR spectra were
recorded at 75 MHz in CDCl3 relative to TMS as an internal standard. All of
the reactions were carried out in a mortar in a hood with strong ventilation.
Procedure for the Preparation of Benzyltriphenylphosphonium
Tribromide
To a solution of benzyltriphenylphosphonium bromide (0.01 mol, 3.88 g)
and sodium bromide (0.043 mol, 4.37 g) in water (100 ml), a solution of
Oxone1 (4KHSO5 ꢀ KHSO4 ꢀ K4SO4) (0.044 mol, 13.65 g) in water
(40 ml) was added dropwise under stirring at room temperature until a
yellow precipitate was formed. After stirring for 30 min, the mixture
was filtered and washed with water (3 ꢃ 30 ml). The filter cake was dried
and recrystallized from CHCl3 to afford BTPTB as yellow crystals
(4.15 g, 70% yield), mp: 136–137 ꢁC. IR (KBr) t: 3050 (m), 4950 (s),
1
1580 (s), 1115 (s), 900 (m) cmꢂ1. H NMR: d 7.44–7.98 (m, 40H) 4.90
(d, J ¼ 18 Hz, 4H), UV (CH2C2) kmax: 479 nm. Anal. calcd. for
C45H44Br3P: C, 50.84%; H, 3.74%. Found: C, 50.74%; H, 3.60%.
Thioacetalization under Solvent-Free Conditions
In a mortar, aldehyde or ketone (10 mmol) was added to a mixture of 1,2-
ethandithiol, 1,3-propandithiol, or ethylthiol (14 mmol) and BTPTB
(0.5 mmol 0.3 g). The reaction mixture was ground by pestle at room tem-
perature under solvent-free conditions. After disappearance of starting
material (monitored by thin-layer chromatography, TLC), the mixture
was washed with diethyl ether and filtered. The filtrate was evaporated
under reduced pressure, and the resulting crude material was purified
by column chroatography (EtoAc–n-hexane) to afford pure dithioactas
(Tables 1 and 2).
Data
2-Phenyl-1,3-dithiane (3a)[27]
White solid; mp 74 ꢁC; IR (KBr): 3037, 2940, 2894, 2827, 1593, 1491,
1
1429, 1281, 1183, 1066, 912, 728, 697 cmꢂ1. H NMR: d ¼ 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): d ¼ 24.96, 31.95 (2 C), 51.34, 127.61

Thioacetalization of Carbonyl Compounds
2555
(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)[17]
IR (neat): 3429, 3060, 3026, 2922, 1690, 1661, 1600, 1494, 1451, 1422,
1
1276 cmꢂ1. H NMR: d ¼ 3.23–3.46 (m, 4 H), 5.61 (s, 1 H), 7.19–7.30
(m, 3 H), 7.49 (d, J ¼ 7.10 Hz, 2 H). 13C NMR: d ¼ 40.81 (2 CH2),
56.82, 128.52, 128.56, 129.02, 140.94.
3-Nitrobenzaldehyde Dethylthioacetal (3c)[17]
Light yellow oil. 1H NMR : d ¼ 8.28 (br d, J ¼ 1.5 Hz, 1 H), 8.12 (br dd,
J ¼ 8.0, 1.5 Hz, 1 H), 7.80 (br dd, J ¼ 8.0, 1.5 Hz, 1 H), 7.52 (t, J ¼ 8.0 Hz,
1 H), 4.92 (s, 1 H), 2.58–2.46 (m, 4 H), 1.22 (t, J ¼ 7.0 Hz, 6 H).EIMS:
m=z ¼ 257 (Mþ), 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)[28]
IR (neat): 3006, 2903, 1486, 1404, 1085, 1012, 754 cmꢂ1 1H NMR:
.
d ¼ 3.20–3.70 (m, 4 H), 5.58 (s, 1 H), 7.31 (d, J ¼ 8.4 Hz, 2 H), 7.41
(d, J ¼ 8.4 Hz, 2 H). 13C NMR: d ¼ 40.27 (2 CH2), 55.44, 128.57,
129.30, 133.61, 139.02.
40-Methoxyphenyl Diethyl Dithioacetal (3e)[28]
White solid; mp 43 ꢁC; IR (KBr): 2965, 2928, 1609, 1510, 1447, 1301,
1
1261, 1174, 1106, 1025 cmꢂ1. H NMR: d ¼ 1.22 (t, J ¼ 7.3 Hz, 6 H,
2 ꢃ SCH2CH3), 2.46–2.63 (m, 4 H, 2 ꢃ SCH2CH3), 3.80 (s, 3 H,
OCH3), 4.91 (s, 1 H, ArCH), 6.85 (d, J ¼ 8.6 Hz, 2 H, ArH), 7.37 (d,
J ¼ 8.5 Hz, 2 H, ArH) ppm. 13C NMR: d ¼ 14.24 (2 C), 26.15 (2 C),
51.69, 55.22, 113.75 (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 Diethylthioacetal (3f)
Light yellow oil. 1H NMR: d ¼ 7.30 (d, J ¼ 8.0 Hz, 2 H), 6.68
(d, J ¼ 8.0 Hz, 2 H), 4.86 (s, 1 H), 2.98 (s, 6 H), 2.62–2.43 (m, 4 H),

2556
A. R. Hajipour, S. A. Pourmousavi, and A. E. Ruoho
1.16 (t, J ¼ 7.0 Hz, 6 H). EIMS: m=z ¼ 255 (Mþ), 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-Methoxypheny-1,3-dithiolane (3g)[17]
IR (neat): 3038, 2999, 2923, 2833, 1597, 1488, 1464, 1434, 1316, 1263,
1
1149, 1047, 862, 779, 749, 693 cmꢂ1. H NMR: d ¼ 3.10–3.45 (m, 4 H),
3.73 (s, 3 H), 5.58 (s, 1 H), 6.76 (d, J ¼ 7.32 Hz, 1 H), 7.05–7.21 (m, 3
H). 13C NMR: d ¼ 40.04 (2 CH2), 55.08, 56.04, 113.34 (2 C), 120.14,
129.32, 141.91, 159.45.
2-(2-Methoxypheny 1,3-Dithiolane (3h)[17]
IR (neat): 3068, 2921, 2777, 1609, 1500, 1487, 1443, 1370, 1249, 1183,
1
1096, 1038, 927, 866, 750 cmꢂ1. H NMR: d ¼ 3.25–3.53 (m, 4 H), 5.60
(s, 1 H), 5.94 (s, 2 H), 6.69 (d, J ¼ 8 Hz, 1 H), 6.91–6.95 (dd, J ¼ 8,
1.7 Hz, 1 H), 7.10 (d, J ¼ 1.7 Hz, 1 H). 13C NMR: d ¼ 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)[17]
1H NMR: d ¼ 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 ¼ 8.5 Hz, 2 H), 7.38 (d, J ¼ 8.5 Hz, 2 H).
13C: d ¼ ꢂ 4.2, 19.5, 27.6, 40.5, 57.3, 120.8, 131.7, 134.5, 156.3.
MS: m=z ¼ 313 (M þ Hþ). Anal. calcd. for C15H24OS2Si: C, 57.64;
H, 7.74%. Found: C, 57.60; H, 7.70%.
2-(40-Allyloxyphenyl)-1,3-dithiane (3j)[17]
White solid; mp 81 ꢁC; IR (KBr): 2914, 1603, 1506, 1429, 1245, 1183,
1
1015, 779 cmꢂ1. H NMR: d ¼ 1.84–1.97 (m, 1 H, SCH2CHaHbCH2S),
2.11–2.17 (m, 1 H, SCH2CHaHb CH2S), 2.86–2.91 (m, 2 H, SCH2),
=
3.00–3.14 (m, 2 H, SCH2), 4.50–4.52 (m, 2 H, OCH2CH CH2), 5.13 (s,
=
1 H, ArCH), 5.27 (dd, J ¼ 3.0, J ¼ 10.6 Hz, 1 H, OCH2CH CHaHb),
=
5.39 (dd, J ¼ 3.2, J ¼ 17.1 Hz, 1 H, OCH2CH CHaHb), 5.98–6.08
=
(m, 1 H, OCH2CH CHaHb), 6.87 (d, J ¼ 8.8 Hz, 2 H, ArH), 7.38
(d, J ¼ 8.8 Hz, 2 H, ArH) ppm. 13C NMR: d ¼ 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 C13H16OS2 (252.40): C, 61.86; H, 6.39; S,
25.41%. Found: C, 61.60; H, 6.30; S, 25.20%.

Thioacetalization of Carbonyl Compounds
2557
2-(40-(Cyclohexenyloxy)phenyl)-1,3-dithiane (3k)[17]
White solid; mp 103–104 ꢁC; IR (KBr): 2933, 1605, 1509, 1242,
1
1168 cmꢂ1. H NMR: d ¼ 1.57–1.65 (m, 2 H, CH2), 1.76–1.89 (m, 2 H,
CH2), 1.91–2.03 (m, 1 H, SCH2CHaHbCH2S), 2.05–2.18 (m, 3 H,
SCH2CHaHb 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 ¼ 2.0, J ¼ 10.0 Hz, 1 H, CH CHCHO), 6.03–6.08 (m, 1 H,
=
CH2CH CHCHO), 6.87 (d, J ¼ 8.8 Hz, 2 H, ArH), 7.37 (d, J ¼ 8.8 Hz,
Hz, 2 H, ArH) ppm. 13C NMR: d ¼ 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-(40-(Benzoyloxy)phenyl)-1,3-dithiane (3l)[17]
Mp 163–164 ꢁC; IR (KBr): 3068, 2955, 2894, 1731, 1593, 1506, 1424,
1
1265, 1204, 1168, 1071, 1020, 886, 769, 707 cmꢂ1. H NMR: d ¼ 1.88–
1.98 (m,
1
H, SCH2CHaHbCH2S), 2.15–2.18 (m,
1
H,
SCH2CHaHbCH2S), 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 ¼ 8.8 Hz, 2 H, ArH), 7.51 (m,
2 H, ArH), 7.53 (d, J ¼ 8.5 Hz, 2 H, ArH), 7.63 (m, 1 H, ArH), 8.18
(m, 2 H, ArH) ppm. 13C NMR: d ¼ 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-dithiolane (3m)
Colorless liquid; IR (neat): 3037, 2925, 2843, 1598, 1501, 1424, 1286, 1132,
1
1030, 846, 738 cmꢂ1. H NMR: d ¼ 3.04 (d, J ¼ 7.1 Hz, 2 H, PhCH2),
3.08–3.21 (m, 4 H, 2 ꢃ SCH2), 4.66 (t, J ¼ 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-(40-Hydroxyphenyl)-1,3-dithiane (3n)[14]
Mp 158 ꢁC; IR (KBr): 3370, 2940, 2894, 2807, 1609, 1516, 1450, 1363,
1250, 1173, 1112, 851, 774 cmꢂ1
SCH2CHaHbCH2S), 2.12–2.19 (m, 1 H, SCH2CHaHbCH2S), 2.86–2.92
.
1H NMR: d ¼ 1.85–1.96 (m, 1 H,
(m, 2 H, SCH2), 3.01–3.08 (m, 2 H, SCH2), 5.12 (S, 1 H, ArCH), 6.77

2558
A. R. Hajipour, S. A. Pourmousavi, and A. E. Ruoho
(d, J ¼ 8.2 Hz, 2 H, ArH), 7.31 (d, J ¼ 8.3 Hz, 2 H, ArH) ppm. 13C NMR:
d ¼ 25.06, 32.18 (2 C), 50.74, 115.58 (2 C), 129.18 (2 C), 131.45,
155.61 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)[29]
Pale yellow liquid; IR (neat): 2899, 1495, 1424, 1275, 1163, 1014,
1
748 cmꢂ1. H NMR: d ¼ 1.92–2.01 (m, 1 H, SCH2CHaHbCH2S), 2.08–
2.16 (m, 1 H, SCH2CHaHbCH2S), 2.88–2.93 (m, 4 H, 2 ꢃ SCH2), 5.20
(s, 1 H, SCHS), 6.32 (dd, J ¼ 2.0, J ¼ 3.2 Hz, 1 H, H-4), 6.37
(d, J ¼ 3.1 Hz, 1 H, H-3), 7.34 (d, J ¼ 1.9 Hz, 1 H, H-5) ppm.
13C NMR: d ¼ 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-(40-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 cmꢂ1 1H NMR:
.
d ¼ 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 ¼ 8.6 Hz, 2 H, ArH), 8.17 (d, J ¼ 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-Cinamaldehyde-1,3-dithiane (3q)[17]
IR (neat): 3083, 3057, 3028, 2963, 2924, 1599, 1576, 1497, 1447, 1434,
1421, 968, 763, 687 cmꢂ1
.
1H NMR: d ¼ 3.24–3.37 (m, 4 H), 5.21
(d, J ¼ 9.1 Hz, 1 H), 6.16–6.25 (dd, J ¼ 9.1, 15.5 Hz, 1 H), 6.49
(d, J ¼ 15.5 Hz, 1 H), 7.22–7.38 (m, 5 H). 13C NMR: d ¼ 39.59 (2 CH2),
54.47, 126.60, 127.81, 128.53, 129.02, 130.14, 136.04.
2-Hexyl-1,3-dithiane (3r)[14]
Colorless liquid; IR (neat): 2960, 2929, 2852, 1465, 1429, 1383, 1275,
1102, 979, 855, 728 cmꢂ1
.
1H NMR: d ¼ 0.85 (t, J ¼ 6.6 Hz, 3 H,
CH3), 1.25–1.42 (m, 8 H, CH2), 1.76–1.82 (m, 2 H, CH2CHS), 3.14–
3.25 (m, 4 H, 2 ꢃ SCH2), 4.44 (t, J ¼ 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.

Thioacetalization of Carbonyl Compounds
2559
2-(40-(tert-Butyldiphenylsilyloxy)butane)-1,3-dithiane (3s)[30]
Colorless liquid; IR (neat): 3068, 2935, 2863, 1588, 1434, 1260, 1107, 835,
1
748, 707. H NMR: d ¼ 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 SCH2CHaHbCH2S), 1.83–1.93 (m, 1
H, SCH2CHaHbCH2S), 2.58–2.69 (m, 4 H, SCH2 and CH2), 2.71–2.83
(m, 2 H, SCH2), 3.65 (t, J ¼ 5.8 Hz, 2 H, OCH2), 4.00 (t, J ¼ 7.1 Hz, 1
H, CH), 7.34–7.42 (m, 5 H, ArH), 7.64–7.67 (m, 5 H, ArH) ppm. Anal.
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-(40-Methoxyphenyl)-1,3-dithiolane (3t)[30]
White solid; mp 65 ꢁC; IR (KBr): 1608, 1520, 1256, 1180, 1028 cmꢂ1
.
1H NMR (400 MHz, CDCl3 ): d ¼ 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 ¼ 8.56 Hz, 2 H, ArH), 7.44 (d, J ¼ 8.76 Hz, 2 H, ArH) ppm. 13C
NMR (100 MHz, CDCl3): d ¼ 40.02 (2 C), 55.19, 55.94, 113.74 (2 C),
129.04 (2 C), 131.69, 159.25 ppm. Anal. calcd. for C10H12OS2 (212.33):
C, 56.57; H, 5.70; S, 30.20. Found: C, 56.70; H, 5.58; S, 30.35.
2-(40-Methylphenyl)-1,3-dithiane (3u)
IR (neat): 3004, 1510, 1437, 1411, 1277, 1177, 1165, 830, 777 cmꢂ1
.
1H NMR: d ¼ 2.32 (s, 3 H), 3.29–3.52 (m, 4 H), 5.62 (s, 1 H), 7.10
(d, J ¼ 6.5 Hz, 2 H), 7.40 (d, J ¼ 6.5 Hz, 2 H). 13C NMR: d ¼ 21.11,
40.20 (2 CH2), 56.12, 127.80, 129.15, 137.10, 137.84.
2-[40-Hydroxyphenyl)-1,3-dithiane (3v)[17]
1
IR (neat): 3188 (br), 2919, 1595, 1509, 1448, 1237, 1173, 838 cmꢂ1. H
NMR: d ¼ 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-(40-Hydroxy-3-methoxyphenyl)-1,3-dithiane (3w)
IR (thin film): 3434 (br), 2996, 2918, 1607, 1596, 1509, 1464, 1449, 1427,
1
1266, 1227, 1145, 1118, 1026 cmꢂ1. H NMR: d ¼ 3.29–3.53 (m, 4 H),
3.88 (s, 3 H), 5.69 (s, 1 H), 6.81 (d, J ¼ 8.1 Hz, 1 H), 6.90–7.00
(dd, J ¼ 8.1, 1.69 Hz, 1 H), 7.09 (s, 1 H). 13C NMR: d ¼ 40.14 (2 CH2),
55.91, 56.69, 110.26, 113.97, 121.07, 131.22, 145.54, 146.47.

2560
A. R. Hajipour, S. A. Pourmousavi, and A. E. Ruoho
2-(40-N,N-dimethylphenyl)-1,3-dithiane (3x)[31]
IR (neat): 757, 824, 949, 1069, 1171, 1230, 1247, 1359, 1443, 1482, 1523,
1609, 2807, 2904, 3054 cmꢂ1. 1H NMR: d ¼ 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 ¼ 6.8 Hz, 2 H), 7.42
(d, J ¼ 6.8 Hz, 2 H). 13C NMR: d ¼ 40.09 (2 CH3), 40.80 (2 CH2),
56.40, 112.60, 125.90, 128.77, 149.88.
2-(3-Formyl)-1,3-dithiane (3y)[32]
IR (neat): 2955, 2926, 2854, 1735, 1465, 1377, 1275, 851, 725 cmꢂ1
.
1H NMR: d ¼ 0.87 (t, J ¼ 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: d ¼ 14.07, 22.57,
28.89, 29.10, 31.47, 38.34 (2 CH2), 39.41, 53.81.
2-(20,40-Dimethoxyphenyl)-1,3-dithiane (3z)
White solid; mp 103 ꢁC; IR (KBr): 2996, 2939, 2893, 2837, 1618, 1505,
1
1454, 1424, 1326, 1290, 1116, 1039, 992 cmꢂ1. H NMR: d ¼ 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 ¼ 2.4 Hz,
1 H, ArH), 6.48 (dd, J ¼ 2.4, J ¼ 8.5 Hz, 1 H, ArH), 7.48 (d, J ¼ 8.5 Hz,
Hz, 1 H, ArH) ppm. 13C NMR (75 MHz, CDCl3): d ¼ 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. Anal. calcd. for C12H16O2S2 (257.05): C, 56.22; H, 6.29; S,
25.01. Found: C, 56.40; H, 6.10; S, 25.30.
2-Methyl-2-phenyl-1,3-dithiolane (5a)[30]
Gummy liquid; IR (neat): 2971, 2935, 1598, 1491, 1445, 1276, 1071, 1030,
1
774, 702 cmꢂ1. H NMR: d ¼ 2.14 (s, 3 H, CH3), 3.31–3.47 (m, 4 H,
2 ꢃ 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: d ¼ 33.81, 40.22 (2 C), 68.52,
126.68 (2 C), 126.99, 127.90 (2 C), 145.82 ppm. Anal. calcd. for
C10H12S2 (196.34): C, 61.17; H, 6.16; S, 32.66. Found: C, 61.01; H,
6.09; S, 32.43.
2-Methyl-2-tolyl-1,3-dithiane (5b)
IR (neat): 731, 819, 1018, 1072, 1126, 1185, 1275, 1371, 1443, 1508, 1610,
1
1654, 2861, 2921, 2965, 3022 cmꢂ1. H NMR: d ¼ 2.14 (s, 3 H), 2.32

Thioacetalization of Carbonyl Compounds
2561
(s, 3 H), 3.30–3.52 (m, 4 H), 7.11 (d, J ¼ 8 Hz, 2 H), 7.63 (d, J ¼ 8 Hz, 2
H). 13C NMR: d ¼ 20.89, 33.87, 40.29 (2 CH2), 68.39, 126.67, 128.64,
136.74, 142.87.
2-Phenyl-2-tolyl-1,3-dithiane (5c)[33]
IR (thin film): 696, 741, 1032, 1186, 1275, 1443, 1506, 1594, 2874, 2921,
3022, 3056 cmꢂ1
.
1H NMR: d ¼ 2.31 (s, 3 H), 3.39 (m, 4 H), 7.08
(d, J ¼ 8.1 Hz, 2 H), 7.23–7.27 (m, 3 H), 7.48 (d, J ¼ 8 Hz, 2 H), 7.60
(m, 2 H). 13C NMR: d ¼ 20.96, 40.12 (2 CH2), 127.10, 127.73, 127.97,
128.17, 128.64, 136.95, 141.47, 144.77.
2-Methyl-2-(4-hydoxyphenyl)-1,3-dithiane (5d)[30]
IR (neat): 687, 738, 831, 844, 1074, 1180, 1230, 1273, 1375, 1442, 1508,
1
1596, 1608, 2876, 2929, 2969, 3225 (br) cmꢂ1. H NMR: d ¼ 2.13 (s, 3
H), 3.35–3.51 (m, 4 H), 5.60 (br s, 1 H), 6.75 (d, J ¼ 7.7 Hz, 2 H), 7.63
(d, J ¼ 7.7 Hz, 2 H). 13C NMR: d ¼ 33.91, 40.35 (2 CH2), 68.22,
114.71, 128.33, 137.73, 154.64.
2-Methyl-2-(4-chlorophenyl)-1,3-dithiane (5e)[34]
IR (neat): 734, 830, 1011, 1069, 1093, 1275, 1372, 1396, 1422, 1444, 1489,
1570, 1591, 2860, 2922, 2966, 3059 cmꢂ1. 1H NMR: d ¼ 2.1 (s, 3 H), 3.30–
3.45 (m, 4 H), 7.26 (d, J ¼ 6.4 Hz, 2 H), 7.68 (d, J ¼ 6.4 Hz, 2 H).
13C NMR: d ¼ 33.46, 40.31 (2 CH2), 67.82, 127.87, 128.24, 132.70, 144.55.
2-Benzyl-2-methyl-[1,3]dithiolane (5f)[34]
Bp 129–130=1.5 ꢁC. IR (neat): 3083, 3060, 3027, 2959, 2919, 2856, 1602,
1
1494, 1452,1372, 1276, 1083, 752, 698 cmꢂ1. H NMR: d ¼ 1.71 (s, 3
H), 3.00–3.32 (m, 6 H), 7.15–7.36 (m, 5 H). 13C NMR: d ¼ 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)
Mp 105–106 ꢁC. IR (thin film): 696, 741, 1032, 1186, 1275, 1443, 1506,
1
1594, 2874, 2921, 3022, 3056 cmꢂ1. H NMR: d ¼ 3.39 (m, 4 H), 7.08
(d, J ¼ 8.1 Hz, 4 H), 7.23–7.27 (m, 6 H). 13C NMR: d ¼ 40.12 (2 CH2),
127.10, 127.73, 127.97, 128.17, 128.64, 136.95, 141.47, 144.7.

2562
A. R. Hajipour, S. A. Pourmousavi, and A. E. Ruoho
2-Methyl-2-(4-bromophenyl)-1,3-dithiolane (5h)[35]
IR (neat): 731, 827, 1007, 1077, 1275, 1391, 1486, 1583, 2858, 2922, 2965,
3061 cmꢂ1
.
1H NMR: d ¼ 2.07 (s, 3 H), 3.30–3.45 (m, 4 H), 7.38
(d, J ¼ 6.8 Hz, 2 H), 7.60 (d, J ¼ 6.8 Hz, 2 H). 13C NMR: d ¼ 34.10,
41.01 (2 CH2), 68.50, 114.03, 129.60, 131.50, 145.76.
1,4-Dithiaspiro(4.4)nonane (5i)[35]
Colorless liquid; IR (neat): 2960, 2924, 2878, 1449, 1275, 1168, 1101, 978,
1
851, 692 cmꢂ1. H NMR: d ¼ 1.74–1.77 (m, 4 H, CH2), 2.07–2.14 (m, 4
H, CH2), 3.30 (s, 4 H, 2 ꢃ SCH2) ppm. 13C NMR: d ¼ 24.48 (2 C),
39.37 (2 C), 43.92 (2 C), 70.86 ppm. Anal. calcd. for C7H12S2 (160.30):
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)[35]
Colorless liquid; IR (neat): 2960, 2930, 2853, 1465, 1373, 1276, 1148, 984,
1
892, 851, 810, 733, 692 cmꢂ1. H NMR: d ¼ 0.85 (t, J ¼ 7.0 Hz, 3 H,
CH3), 0.99 (t, J ¼ 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): d ¼ 11.16, 14.01, 22.53, 26.58,
31.95, 36.12, 39.37 (2 C), 42.88, 72.41 ppm. Anal. calcd. for C10H20S2
(204.40): 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)[36]
While solid; mp 56 ꢁC; SiO2–TLC (hexane). IR (KBr): 2919, 2842, 1460,
.
1424, 1275, 1244, 1234, 1152, 1101, 963, 846, 692 cmꢂ1 1H NMR:
d ¼ 1.57 (m, 8 H, CH2), 2.17–2.19 (m, 4 H, CH2), 3.26 (s, 4 H, SCH2)
ppm. 13C NMR: d ¼ 25.62 (2 C), 28.55 (2 C), 38.84 (2 C), 46.11 (2 C),
71.88 ppm. Anal. calcd. for C9H16S2 (188.36): C, 57.39; H, 8.56; S,
34.05. Found: C, 57.18; H, 8.48; S, 33.87.
[35]
1,4-Dithiaspiro(5.5)decane (5l)
Colorless liquid; IR (neat): 2930, 2853, 1440, 1265, 1127, 1015, 907, 861,
1
764 cmꢂ1. H NMR: d ¼ 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 ꢃ CH2), 2.79–2.83 (m, 4
H, 2 ꢃ SCH2) ppm. 13C NMR: d ¼ 21.97 (2 C), 25.79 (2 C), 25.87, 26.12,
37.86 (2 C), 50.32 ppm. Anal. calcd. for C9H16S2 (188.36): C, 57.39;
H, 8.56; S, 34.05. Found: C, 57.14; H, 8.50; S, 34.23.

Thioacetalization of Carbonyl Compounds
2563
2-Butyl-2-methyl-1,3-dithiolane (5m)[35]
IR (neat): 686, 733, 852, 972, 1056, 1139, 1276, 1374, 1448, 2859, 2927,
1
2957 cmꢂ1. H NMR: d ¼ 0.92 (t, J ¼ 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).
13C NMR: d ¼ 14.00, 22.90, 29.50, 32.30, 40.00 (2 CH2), 45.80, 66.80.
2, 2-Dipropyl-1,3-dithiolane (5n)[36]
1
IR (neat): 2961, 2873, 1707, 1459, 1380, 1275 cmꢂ1. H NMR: d ¼ 0.90
(t, J ¼ 7.3 Hz, 6 H), 1.35–1.63 (m, 4 H), 2.73–2.76 (m, 1 H), 3.13–3.23
(m, 4 H), 4.63 (d, J ¼ 6.2 Hz, 1 H). 13C NMR: d ¼ 10.91 (2 CH3),
23.94 (2 CH2), 28.72, 38.42 (2 CH2), 58.22.
ACKNOWLEDGMENTS
We gratefully acknowledge the funding support received for this project
from the Isfahan University of Technology (IUT), I.R. Iran (A. R. H.),
and Grants GM 033138, MH 065503, and NS 033650 (A. E. R.)
from the National Institutes of Health, USA. Further financial support
from Center of Excellency in Sensor Research (IUT) is gratefully
acknowledged.
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