Preparation of 1,3-dithiol-2-ones from 1,2-bis-triisopropylsilanylsulfanyl alkenes under mild acidic conditions

Article abstract of DOI:10.1080/10426500307851

1,2-Bis-triisopropylsilanylsulfanyl alkenes are readily converted to 1,3-dithiol-2-ones with phosgene under very mild acidic conditions at room temperature.

Full text of DOI:10.1080/10426500307851

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Phosphorus, Sulfur, and Silicon and the Related
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Preparation of 1,3-Dithiol-2-ones from 1,2-Bis-
triisopropylsilanylsulfanyl Alkenes Under Mild Acidic
Conditions
Yves Gareau a & Hélène Juteau a
a Merck Frosst Canada & Cie , Quebec, Canada
Published online: 27 Oct 2010.
To cite this article: Yves Gareau & Hélène Juteau (2003) Preparation of 1,3-Dithiol-2-ones from 1,2-Bis-
triisopropylsilanylsulfanyl Alkenes Under Mild Acidic Conditions, Phosphorus, Sulfur, and Silicon and the Related Elements,
178:5, 1021-1026, DOI: 10.1080/10426500307851
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Phosphorus, Sulfur and Silicon, 2003, Vol. 178:1021–1026
C
Copyright 2003 Taylor & Francis
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DOI: 10.1080/10426500390208857
PREPARATION OF 1,3-DITHIOL-2-ONES FROM
1,2-BIS-TRIISOPROPYLSILANYLSULFANYL ALKENES
UNDER MILD ACIDIC CONDITIONS
Yves Gareau and He´le`ne Juteau
Merck Frosst Canada & Cie, Quebec, Canada
(Received August 12, 2002; accepted October 15, 2002)
1,2-Bis-triisopropylsilanylsulfanyl alkenes are readily converted to 1,3-
dithiol-2-ones with phosgene under very mild acidic conditions at room
temperature.
Keywords: 1,3-Dithiol-2-one; Lewis acid; phosgene; silyl; sulfide; zinc
chloride
Recently we have described the preparation of a series of 1,2-bis-
triisopropylsilanylsulfanyl alkenes 2 via a palladium cross-coupling re-
action between disulfide 1 and several alkynes.1,2 These compounds
subsequently were treated with tetrabutylammonium fluoride (TBAF)
to remove the silyl protecting groups and to allow both of the resulting
mercaptides to react with various electrophiles. These electrophiles in-
cluded alkyl halides, epoxides, acyl chlorides, thiophosgene, and chloro-
formates (Scheme 1). The last two electrophiles provided cyclic adducts
namely 1,3-dithiol-2-thiones and 1,3-dithiol-2-ones. We previously ex-
perienced problems in the preparation of 1,3-dithiol-2-ones using phos-
gene. We found that phosgene was much too reactive under the ba-
sic conditions (TBAF) used to furnish the cycloadduct 3 in reasonable
yield, so instead we looked at much less reactive species such as chloro-
formates to produce the 1,3-dithio-2-ones. The chloroformates had just
the right balance between stability toward TBAF and reactivity with
mercaptides. In our search to find a practicable way to circumvent the
problem of high reactivity of phosgene toward TBAF, we sought differ-
ent conditions to resolve this.
Address correspondence to Yves Gareau, Department of Chemistry, Merck-Frost
Canada & Cie, 16711 Autoroute Transcanada, Kirkland, Quebec, Canada H9H 3L1.
E-mail: yves gareau@merck.com
1021

1022
Y. Gareau and H. Juteau
SCHEME 1
RESULTS
The action of phosgene onto trimethylsilyl ethylsulfide already has been
reported.3 This gives the corresponding dithiocarbonic acid S,S0-diethyl
ester in 88% yield. In our hands, treatment of 2 and phosgene under
the same conditions (pyridine/0 C) provided only starting material. It
seems that the triisopropylsilanyl groups completely inhibit the spon-
taneous reaction with phosgene due to their bulkiness. We also have
reacted 2 and phosgene at room temperature and up to 110 C with no
success, yielding only the unreacted alkene.
Since mildly basic and neutral conditions were not successful, we
then turned our attention to mildly acidic conditions. To achieve this,
a number of Lewis acids were tested to convert 2 into 3 using 2 equiv-
alents of phosgene (1.9 M in toluene) in dichloromethane at room
temperature for 18 h. Table I shows the results of our study with 1,2-
bis-triisopropylsilanylsulfanyl-dec-1-ene as a model substrate. We en-
countered no success with phosgene alone nor with our first two Lewis
acids, BF3 OEt2 and FeCl3. We only recovered the starting material
along with some decomposition product. Our first positive result came
using SnCl4 where we isolated a 38% yield of the desired adduct.
The yield of the reaction was improved considerably when zinc
derivatives were used. For example, a 25% solution of zinc chloride

Preparation of 1,3-Dithiol-2-ones
1023
TABLE I Lewis Acid Catalyzed Formation of 1,3-Dithiol-2-ones 3
Entry
Lewis acid
Yield (%)
1
2
3
4
5
6
7
8
9
None
nra
0b
BF3 OEt2
FeCl3
SnCl4
SnCl2
ZnCl2
Znl2
0b
38c
nr
75d
74
57
71
ZnOTf2
InCl3
aNo reaction even at 110 C.
bSlight decomposition.
cComplete conversion after 24 h.
d11% conversion at 0 C with 50% of ZnCl2.
(1.0 M in ether) gave an isolated yield of 75% of 3. In a similar way, a
suspension of zinc iodide in dichloromethane gave essentially the same
result yielding 74% of 3. Not all zinc catalysts were equally good. For
example, zinc triflate was not as effective as the previous two catalysts
and only a 57% yield of the 1,3-dithiol-2-one was isolated. Two other dis-
tinct catalysts were investigated to conclude this study. The first one
was FeCl3, which only gave decomposition products. The second one
surprisingly gave better results then expected. A suspension of InCl3
in dichloromethane gave an isolated yield of 71% of the desired product
comparable to the results obtained with the zinc halides. This certainly
is not a systematic list of catalysts but gives rather a general idea of
the kind of catalyst one can use. Based on these results the conditions
of entry 6 were selected as standard for the subsequent reactions.
The next step was to prepare a series of 1,2-bis-triisopropylsil-
anylsulfanyl alkenes, according to the reported procedure1 in order to
study the scope and limitations of this reaction. All of the examples in
Table II previously were described except for entry 8. We also have com-
pared this approach to the one using phenyl chlorothionoformate1 in the
first four cases (Table II). We already have seen that when R1 = octyl one
The compounds not described in the Experimental section already have been re-
ported.

1024
Y. Gareau and H. Juteau
TABLE II Preparation of 1,3-Dithiol-2-ones from Phosgene and
1,2-Bis-triisopropylsilanylsulfanyl-alkenes. Comparison with Phenyl
Chlorothionoformate
Yield (%)
(COCl2)
Yield (%)
(ClCOSPh)
Entry
1
Substrate
Product
75
82
63
67
2
3
72
40
4
5
64
53
63
—
6
7
8
71
73
—
—
—
64
(3 days)

Preparation of 1,3-Dithiol-2-ones
1025
can isolate 3 in 75% yield. When compared to the chloroformate/TBAF
methodology, we did in fact increase the yield of 3 by 12%. A simi-
lar improvement was seen with R1 = propyl, R2 = methyl (entry 2) and
R1 = R2 = ethyl (entry 3) giving 15% and 32%, respectively, more of
the cyclic adducts. The superiority of ZnCl2 over chloroformate/TBAF
was not general but at least was comparable. This was observed with
R1 = cyclohexenyl of entry 4. Both methods basically gave the same
result.
A number of functionalities were well tolerated under these condi-
tions. For instance, both the acetate group (entry 6) and the methyl
ester (entry 7) gave good yields of the corresponding 1,3-dithiol-2-one,
whereas the terminal chloride (entry 5) was less successful yielding 55%
of the desired product. We have observed something slightly different in
the course of the reaction when an aromatic group was placed in conju-
gation with the 1,2-bis-triisopropylsilanylsulfanyl alkene (entry 8). In
fact the tolyl group greatly slowed down the rate of reaction and what
would have normally taken 18 h required 3 days to go to completion.
The conjugation also diminished the yield of final product to 64%, a
situation we have seen with the cyclohexenyl group (entry 4).
CONCLUSIONS
We have shown that 1,3-dithiol-2-ones can be prepared readily under
mild acidic conditions from 1,2-bis-triisopropylsilanylsulfanyl alkenes
and phosgene with a catalytic amount of ZnCl2 or several other Lewis
acids. Also, this method is at least equal to or superior to the one using
phenyl chlorothionoformate.
Experimental
1-(1,2-Bis-triisopropylsilanylsulfanyl-vinyl)-4-methyl
Benzene
A solution of 4-ethynyltoluene (3.6 mmol), disulfide 1 (3.9 mmol), and
tetrakistriphenylphosphine palladium (0.18 mmol) in 1.8 mL of toluene
was heated to 140 C in a sealed tube for 16 h. The solution was cooled
and the solvent was removed. Purification on a short pad of silica gel
using hexane/toluene (9-1) gave 0.75 g (42%) of the desired compound.
1H NMR (CDCl3, 400 MHz) 1.05 (s, 18H), 1.15 (d, 18H, J = 7.3 Hz),
1.35 (1H, m), 2.34 (s, 3H), 6.67 (s, 1H), 7.08 (d, 2H, J = 7.7 Hz), and
7.37 (2H, d, J = 7.7 Hz); 13C NMR (CDCl3, 125 MHz) 12.7, 13.5, 18.3,
18.4, 21.0, 126.8, 127.0, 128.4, 131.6, 136.5, and 141.2; HRMS calcd for
C27H50S2Si2 + K+: 533.2530. Found: 533.2529.

1026
Y. Gareau and H. Juteau
General procedure for the preparation of 1,3-dithiol-2-ones. To
a 0.3 M solution of 1,2-bis-triisopropylsilanylsulfanyl alkenes in
dichloromethane was added phosgene (2 equivalents, 1.9 M in toluene)
and 25% of a 1.0 M solution of ZnCl2 in ether. The solution was stirred
16–18 h, quenched with an ammonium chloride solution, and diluted
with ethyl acetate. The organic phase was separated, dired, and the
solvent removed. Purification by flash chromatography using hexane-
ethyl acetate gave the desired product.
1
4-(3-chloropropyl)-1,3-dithiol-2-one. H NMR (CDCl3, 400 MHz) 2.0
(m, 2H), 2.76 (t, 2H, J = 7.4 Hz), 3.55 (t, 2H, J = 6.2 Hz), and 6.4 (s, 1H);
13C NMR (CDCl3, 125 MHz) 29.7, 31.5, 43.2, 112.5, 134.3, and 193.3;
HRMS calcd for C6H7OS2Cl + H+: 194.97051. Found: 194.97050.
1
9-(2-Oxo-1,3-dithiol-4-yl) nonyl acetate. H NMR (CDCl3, 400 MHz)
1.31 (m, 10H), 1.60 (m, 4H), 2.04 (s, 3H), 2.57 (t, 2H, J = 8.0 Hz), 4.05
(t, 2H, J = 6.8 Hz), and 6.33 (s, 1H); 13C NMR (CDCl3, 125 MHz) 20.8,
25.7, 28.6, 28.9, 29.0, 29.1, 32.7, 64.4, 110.8, 136.5, 171.0, and 193.7;
HRMS calcd for C14H22O3S2 + H+: 303.10886. Found: 303.10882.
1
Methyl 9-(2-oxo-1,3-dithiol-4-yl) nonanoate. H NMR (CDCl3, 400
MHz)
1.31 (m, 8H), 1.61 (m, 4H), 2.30 (t, 2H, J = 7.5 Hz), 2.57
(t, 2H, J = 7.2 Hz), 3.66 (s, 3H), and 6.32 (s, 1H); 13C NMR (CDCl3,
125 MHz) 24.7, 28.5, 28.8, 28.9, 29.1, 32.7, 33.9, 51.2, 110.9, 136.5,
174.0, and 193.6; Elemental analysis calcd for C13H20O3S2: C, 54.14; H,
6.99; S, 22.23. Found: C, 54.06; H, 7.14, S, 22.35.
1
4-(4-Methylphenyl)-1,3-dithiol-2-one. H NMR (CDCl3, 400 MHz)
2.36 (s, 3H), 6.75 (s, 1H), 7.19 (d, 2H, J = 7.4 Hz), and 7.29 (d, 2H, J = 7.4
Hz); 13C NMR (CDCl3, 125 MHz) 21.2, 110.7, 126.1, 129.7, 129.8, 135.0,
139.3, and 192.7; m.p: 80–81 C (hexane/dichloromethane); HRMS calcd
for C10H8OS2 + H+: 209.0095. Found: 209.0095.
REFERENCES
[1] Y. Gareau, M. Tremblay, D. Gauvreau, and H. Juteau, Tetrahedron, 57, 5739 (2001).
[2] Y. Gareau and A. Orellana, Syn. Lett., 803 (1997).
[3] M. D. Mizhiritskii and V. O. Reikhsfel’d, J. Gen. Chem. USSR, 56, 1373 (1986).