Tungsten hexachloride (WCl6) in the presence of dimethylsulfoxide promoted facile and efficient one-pot ring expansion-chlorination reactions of 1,3-dithiolanes and 1,3-dithianes

Article abstract of DOI:10.1055/s-1999-2628

Tungsten hexachloride (WCl₆) in the presence of DMSO could be efficiently used for the conversion of 1,3-dithiolanes and 1,3-dithianes to their corresponding chlorinated derivatives of dihydro-1,4-dithiin and dihydro-1,4-dithiepine in high yiel

Full text of DOI:10.1055/s-1999-2628

LETTER
413
Tungsten Hexachloride (WCl6) in the Presence of Dimethylsulfoxide Promoted
Facile and Efficient One-Pot Ring Expansion-Chlorination Reactions of 1,3-
Dithiolanes and 1,3-Dithianes
Habib Firouzabadi*, Nasser Iranpoor*, Babak Karimi
Department of Chemistry, College of Sciences, Shiraz University, Shiraz 71454, Iran.
Fax +98 (071) 20027
Received 19 November 1999
Abstract: Tungsten hexachloride (WCl6) in the presence of DMSO
could be efficiently used for the conversion of 1,3-dithiolanes and
1,3-dithianes to their corresponding chlorinated derivatives of dihy-
dro-1,4-dithiin and dihydro-1,4-dithiepine in high yield, respective-
ly.
Key words: 1,3-dithiolanes, tungsten hexachloride, 1,3-dithianes,
ring-enlargement, dimethylsulfoxide
The annelation reactions of 1,3-dithiolane and 1,3-
dithianes for the construction of larger rings containing
hetero-sulfur atoms have been of interest from different
point of views.1-7 Nevertheless, less attention has been
paid to the development of new improved methodologies
based on rearrangement reactions. In recent years we
have been exploring new applications for tungsten hexa-
chloride (WCl6). In this regard halode-hydroxylation and
dihalo-oxo-bissubstitution reactions,8 thioacetalization of
carbonyl compounds, transthioacetalization and deprotec-
tion of acetals9, 10 have been reported. In continuation of
these studies we now report an efficient and highly regio-
selective ring expansion-chlorination reaction of 2-aryl-2-
methyl-1,3-dithiolanes 1a,b and 1,3-dithianes 2a,b with
electron-donating substituent on aromatic rings to pro-
duce the corresponding chlorinated dihydro-1,4-dithiin
3a,b and 1,4-dithiepines 4a,b by using WCl6/DMSO in
CH2Cl2 (Scheme1, Table).
Scheme 1
1H-NMR, 13C-NMR, and mass spectra of the isolated
dimethyl sulfide was also detected, therefore, we propose
products clearly showed the formation of the chlorinated
products.11 However, the presence of a nitro group as an
electron withdrawing group on aromatic ring (1c, 2c)
strongly retards the chlorination reaction, and only the re-
arrangement product 3c, 4c were formed in excellent
yields (Table).11 This observation indicates that the for-
mation of the chlorinated products probably goes through
cationic intermediates. In all reactions fast liberation of
here a potential mechanism, which indicates the role of
DMSO, cationic character of reaction intermediates, and
the formation of the chlorinated products (Scheme 2). The
reactions proceeded cleanly without formation of poly-
meric material and the analytical data were also in accord
with the proposed structures. This method is not suitable
for aliphatic substrates that produce a mixture of uniden-
tified products.
Synlett 1999, No. 4, 413–414 ISSN 0936-5214 © Thieme Stuttgart · New York

414
H. Firouzabadi et al.
LETTER
(8) Firouzabadi, H.; Shiriny, F. Tetrahedron 1996, 52, 14929.
(9) Firouzabadi, H.; Iranpoor, N.; Karimi, B. Synlett 1998, 739.
(10) Firouzabadi, H.; Iranpoor, N.; Karimi, B. J. Chem. Res., (Syn-
op.) accepted for publication.
(11) A typical experimental procedure is as follows: To a solution
of 2-phenyl-2-methyl-1,3-dithiolane 1a (393 mg, 2mmol), and
dry DMSO (469 mg, 6 mmol), in dry CH2Cl2 (20 mL) was ad-
ded WCl6 (634 mg, 1.6 mmol) and the resulting solution was
stirred at room temperature. The progress of the reaction was
monitored by TLC (CCl4 as eluent). After completion (30
min), the reaction was quenched with an aqueous solution of
NaOH (10%, 25 mL), and extracted with CH2Cl2 (3 × 25 mL).
The organic extracts were washed successively brine (15 mL),
and water (2 × 10 mL). The organic layer was separated and
dried over anhydrous Na2SO4 and the solvent was evaporated
under reduced pressure to afford the crude product. Further
purification was performed using chromatography over a
short column of silica gel (CCl4 as eluent) which after evapo-
ration of the solvent afforded the desired oily pure product 3a
(412 mg, 90% yield).
3a: 1H-NMR (CDCl3, 250 MHz) δ = 3.10 (m, 4H), 7.18 (m,
5H); 13C-NMR (CDCl3, 63 MHz) δ = 30.21, 32.20, 113.14,
126.28, 128.36, 128.46, 129.67, 145.75; MS (20 eV) m/z (re-
lative intensity) 228 (M+, 74.0), 200 (M+ - CH2=CH2, 26.3),
165 (36.3), 121 (100), 77 (15.9).
Scheme 2
To the best of our knowledge this method is the first ex-
ample of one-pot ring expansion-chlorination of 1,3-
dithianes and 1,3-dithiolanes derived from the corre-
sponding substituted acetophenones.
4a : 1H-NMR (CDCl3, 250 MHz) δ = 2.18 (m, 2H), 3.50-3.75
(m, 4H), 7.24-7.48 (m, 5H); 13C-NMR (CDCl3, 63 MHz) δ =
30.38, 31.97, 33.40, 120.58, 128.42, 129.67, 134.56, 140.01;
MS (20 eV) m/z (relative intensity) 242 (55.1), 168 (16.7), 136
(9.4), 121 (M/2, 12.0), 89 (25.7), 73 (100).
Further investigations about the new synthetic applica-
tions of WCl6 and its related compounds are under study
in our laboratories.
4b: 1H-NMR (CDCl3, 250 MHz) δ = 2.10-2.20 (m, 2H), 3.45-
3.50 (m, 4H), 7.24-7.36 (m, 4H); 13C-NMR (CDCl3, 63 MHz)
δ = 29.47, 33.12, 33.55, 121.29, 128.84, 131.44, 133.17,
134.54, 138.59; MS (20 eV) m/z (relative intensity) 276 (M+,
30.2), 202 (10.7), 170 (8.4), 138 (M/2, 12.2), 123 (20.2), 73
(100).
Acknowledgement
The authors appreciate the partial support of this work through a
grant from Shiraz University Research Council.
3b: 1H-NMR (CDCl3, 250 MHz) δ = 3.15 (m, 4H), 7.35-7.50
(m, 9H); 13C-NMR (CDCl3, 63 MHz) δ = 29.72, 31.83,
112.95, 125.40-129.70 (8 carbon atoms), 138,93; MS (20 eV)
m/z (relative intensity) 304 (M+, 65.7), 276 (M+ - CH2=CH2,
29.3), 241 (18.0), 197 (100.0), 153 (12.0).
References and Notes
3c: 1H-NMR (CDCl3, 250 MHz) δ = 3.27-3.33 (m, 4H), 6.64
(s, 1H), 7.82-8.30 (dd, 4H); 13C-NMR (CDCl3, 63 MHz) δ =
27.11, 27.17, 117.52, 123.85, 123.86, 125.67, 126.12, 146.15;
MS (20 eV) m/z (relative intensity) 240 (M+, 100), 211 (M+ -
CH2=CH2, 4.0), 166 (26.1), 121 (26.2), 89 (11.5).
(1) Chen, C. H. Tetrahedron Lett.1976, 25.
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(4) Bulman-Page, P. C.; Ley, S. V.; Morton,J. A. J. Chem. Soc.,
Perkin Trans. 1 1981, 457.
4d: 1H-NMR (CDCl3, 250 MHz) δ = 2.20-2.29 (m, 2H), 3.30-
3.70 (m, 4H), 6.28 (s, 1H), 7.61-8.15 (dd, 4H); 13C-NMR
(CDCl3, 63 MHz) δ = 29.9, 30.74, 32.95, 121.28, 122.87,
123.57, 127.72, 127.75, 146.67; MS (20 eV) m/z (relative in-
tensity) 254(M+, 88.6), 166 (12.4), 150 (11.9), 106 (39.5), 89
(37.3).
(5) Francisco, C. G.; Freire, R.; Hernandez, R.; Salazar, J. A.;
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1990, 1323.
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H.; Suzuki, H. Phosphorous, Sulfur, and Silicon 1992, 67,
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Synlett 1999, No. 4, 413–414 ISSN 0936-5214 © Thieme Stuttgart · New York