A rapid and efficient method of thioacetalization of carbonyl compounds catalysed by POCl3-montmorillnite

Article abstract of DOI:10.1081/SCC-100103985

Aldehydes and ketones were thioactalized with 1,2-ethanedithiol in the presence POCl₃-montmorillonite at room temperature in excellent yields.

Full text of DOI:10.1081/SCC-100103985

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A RAPID AND
EFFICIENT METHOD OF
THIOACETALIZATION OF
CARBONYL COMPOUNDS
CATALYSED BY POCl3-
MONTMORILLNITE
Tong-Shou Jin a , Xu Sun a , Yan-Ran Ma a & Tong-
Shuang Li a
a Department of Chemistry, Hebei University,
Baoding, 071002, P.R. China
Version of record first published: 09 Nov 2006.
To cite this article: Tong-Shou Jin , Xu Sun , Yan-Ran Ma & Tong-Shuang Li (2001): A
RAPID AND EFFICIENT METHOD OF THIOACETALIZATION OF CARBONYL COMPOUNDS
CATALYSED BY POCl3-MONTMORILLNITE, Synthetic Communications: An International
Journal for Rapid Communication of Synthetic Organic Chemistry, 31:11, 1669-1673
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SYNTHETIC COMMUNICATIONS, 31(11), 1669–1673 (2001)
A RAPID AND EFFICIENT METHOD
OF THIOACETALIZATION OF
CARBONYL COMPOUNDS CATALYSED
BY POCl3-MONTMORILLNITE
Tong-Shou Jin,* Xu Sun, Yan-Ran Ma, and
Tong-Shuang Li
Department of Chemistry, Hebei University,
Baoding 071002, P.R. China
ABSTRACT
Aldehydes and ketones were thioactalized with 1,2-
ethanedithiol in the presence POCl3-montmorillonite at room
temperature in excellent yields.
1,3-Dithiolanes are widely employed for protection of carbonyl com-
pounds in multistep synthesis.1 In general, these compounds are prepared by
protic or Lewis acid catalyzed condensation of carbonyl compounds with
thiols. Several types of Lewis acid catalysts were introduced previously for
this purpose, such as BF3-Et2O,2 ZnCl2,3 LnCl3,4 AlCl3,5 TiCl4,6 TeCl4,7
SiCl4,8 (CH3)3-SiCl,9 Zn(OTf )2 and Mg(OTf )2,10 MgI2-Et2O complex,11
SnCl2-2H2O,12 BiCl3 and Bi2(SO4)3,13 as well as some supported reagent
systems including FeCl3-SiO2,14 ZrCl4-SiO2,15 SOCl2-SiO2,16 Cu(OTf )2-
SiO2 and solid protic acids such as Nafion-H18 and acidic ion exchange19
17
* Corresponding author. E-mail: orgsyn@mail.hbu.edu.cn
1669
Copyright & 2001 by Marcel Dekker, Inc.
www.dekker.com

1670
JIN ET AL.
have also been developed. However, many of these methods have not been
entirely satisfactory, owing to such drawbacks as low yields, long reaction
time, stoichiometric use of expensive reagent and tedious workup.
Consequently, it is necessary to develop alternative methods for the syn-
thesis of ethylene dithioacetals and dithioketals. Herein we report a rapid
and efficient procedure for the synthesis of ethylene dithioacetals and dithio-
ketals by condensation of aldehydes and ketones with 1,2-ethanedithiol
catalysed by POCl3-montmorillonite clays at room temperature in excellent
yields.
Scheme 1.
As shown in Table 1, various types of aromatic aldehydes and ketones
in the presence of POCl3-montmorillonite were treated with 1,2-ethane-
dithiol could be converted into ethylene dithioacetals and dithioketals at
room temperature in good to excellent yields.
We found that ketones show less reactivity than aldehydes for this
reaction, for example, cinnamaldithioacetal(3n) was obtained in 98% yield
for 5 min whereas the conversion rate of cyclohexanone(1o) was 75% for 1 h
in the presence of POCl3-montmorillonite at room temperature.
The selectivity of the present method is demonstrated by competition
experiments using structurally differing carbonyl compounds. The
results are shown in Table 2. Benzaldehyde and cinnamaldehyde both
were cleanly thioacetalized nearly quantitation in the presence of aceto-
phenone.
In conclusion, we have provided a facile and efficient method for the
synthesis 1,3-dithiolanes of aldehydes and ketones catalysed by POCl3-mon-
tmorillonite, because of its operational simplicity, high yields, short reaction
time. This procedure can also be utilized in the selective conversion of
aromatic and a,b-unsaturated aldehydes to their corresponding dithio-
acetals in the presence other carbonyl moieties under very mild conditions.
EXPERIMENTAL
The POCl3-montmorillonite catalyst was obtained by mixing POCl3
and montmorillonite clays in CH2Cl2, then the solvent was removed under

THIOACETALIZATION OF CARBONYL COMPOUNDS
1671
Table 1. Synthesis of 1,3-Dithiolanes Catalysed by POCl3-Montmorillonite
Time
(min)
Products
Yield (%)a
Entry
Carbonyl Compounds
Solvent
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
C6H5CHO(1a)
None
None
None
CH2Cl2
CH2Cl2
CH2Cl2
None
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
None
None
None
CH2Cl2
2
3
3
2
2
5
5
5
2
96
96
95
94
94
95
98
90
98
92
92
98
98
75
80
80
4-MeC6H4CHO(1b)
4-MeOC6H4CHO(1c)
3,4-(OCH2O)C6H3(1d)
2-HOC6H4CHO(1e)
4-HOC6H4CHO(1f )
3-ClC6H4CHO(1g)
4-ClC6H4CHO(1h)
2,4-Cl2C6H4CHO(1I)
3-O2NC6H4CHO(1k)
4-O2NC6H4CHO(1l)
3-MeO-4-HOC6H3CHO(1m)
C6H5CH=CHCHO(1n)
Cyclohexanone(1o)
Cycloheptanone(1p)
(C6H5)2CO(1q)
10
10
5
5
1 h
1 h
3 h
a Isolated yields
Table 2. Selectivity Dithioacetalization of Aromatic and a,b-Unsaturated
Aldehydes vs Other Carbonyl Compounds with POCl3-montmorillonite as Catalyst
Entry
18
Substrate
Solvent
CH2Cl2
Time (min)
10
Yield (%)
98
C6H5CHO
+
C6H5COCH3
0
C6H5CH=CHCHO
+
C6H5COCH3
98
19
20
21
CH2Cl2
CH2Cl2
CH2Cl2
5
20
5
0
C6H5CHO
+
Cyclohexanone
98
70
96
C6H5CHO
+
C6H5CH=CHCHO
96

1672
JIN ET AL.
reduced pressure, and finally stored in a desiccator until use. The products
were characterised by 1H NMR spectra and comparison of their melting or
boiling points with literature values.
General Procedure for Thioacetalization Reactions
Amixture of a carbonyl compound ( 1, 3 mmol) and 1,2-ethanedithiol
(2, 3.6 mmol) and POCl3-montmorillonite (300 mg) in CH2Cl2(5 mL) was
stirred at room temperature (Table 1). The progress of the reaction was
followed by TLC. After completion of the reaction, the catalyst was
removed by filtration and washed with CH2Cl2 (5 mL Â 2). The filtrate
was washed successively with 5% sodium hydroxide solution (25 mL Â 2)
to remove the excess 1,2-ethanedithiol, brine (15 mL), H2O (15 mL), and
dried over anhydrous Na2SO4. Evaporation of the solvent under reduced
pressure gave the almost pure dithioacetal. Further purification was per-
formed by column chromatography on silica gel using petroleum ether as
eluent or recrystallization from appropriate solvent desired products.
Typical Procedure for Selective Dithioacetalization of Benzaldehyde
vs Acetophenone with 1,2-Ethanedithiol
To a stirred mixture of benzaldehyde (3 mmol), acetophenone
(3 mmol), 1,2-ethanedithiol (3.6 mmol) and POCl3-mont. (300 mg) in
CH2Cl2 (5 mL) was stirred at room temperature in 10 min. After completion
of the reaction, the catalyst was removed by filtration and washed with
CH2Cl2 (5 mL Â 2). The filtrate was washed successively with 5% sodium
hydroxide solution (25 mL Â 2), brine (20 mL), H2O (20 mL). The organic
layer was separated and dried (Na2SO4) and concentrated under reduced
pressure. The mixture was separated by silica gel column chromatography
to afford 2-phenyl-1,3-dithiolane in 98% yield and the acetophenone
was quantitatively recovered. 3c: dH(300 MHz)/ppm 5.6429(1H, s, -HC-),
3.7799(3H, s, -OCH3), 3.4393(4H ,m, -CHS2 (CH2)2), 7.4419(2H, d, J 8.68 Hz
3,5-ArH), 6.8299(2H, d, J 8.68 Hz 2,6-ArH); 3l: dH(300 MHz)/ppm
5.6434(1H,s,-HC-), 3.4678(4H, m, -CHS2CH2)2), 8.1571(2H, d, J 8.67 Hz
3,5-ArH), 7.6672(2H, d, J 8.67 Hz 2,6-ArH).
ACKNOWLEDGMENTS
The project was supported by NSFC (29872011), Education
Committee of China and Education Committee of Hebei Province (99014).

THIOACETALIZATION OF CARBONYL COMPOUNDS
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Accepted in the Netherlands August 3, 2000