A new convenient procedure for the thionation of carbonyl compounds utilizing tetrachlorosilane-sodium sulfide

Article abstract of DOI:10.1016/j.tetlet.2009.08.039

A combination of tetrachlorosilane (TCS) and sodium sulfide in acetonitrile is found to be an efficient thionating reagent for aromatic aldehydes in the absence of catalysis to give the corresponding thioaldehydes as trimers in good yields. Under cobalt(I

Full text of DOI:10.1016/j.tetlet.2009.08.039

Tetrahedron Letters 50 (2009) 5933–5936
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A new convenient procedure for the thionation of carbonyl compounds
utilizing tetrachlorosilane–sodium sulfide
a
a
a
a,c
Tarek A. Salama a,b, , Abdel-Aziz S. El-Ahl , Saad S. Elmorsy , Abdel-Galil M. Khalil , Mohamed A. Ismail
*
a Chemistry Department, Faculty of Science, Mansoura University, 35516 Mansoura, Egypt
b Chemistry Department, Faculty of Education, Amran University, Amran, Yemen
c Chemistry Department, College of Science, King Faisal University, PO Box 380, Hofuf 31982, Saudi Arabia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 19 June 2009
Revised 29 July 2009
Accepted 14 August 2009
Available online 20 August 2009
A combination of tetrachlorosilane (TCS) and sodium sulfide in acetonitrile is found to be an efficient thi-
onating reagent for aromatic aldehydes in the absence of catalysis to give the corresponding thioaldehy-
des as trimers in good yields. Under cobalt(II) chloride catalysis, a,b-unsaturated ketones react with TCS–
Na2S to give the respective disulfides in good yields via the intermediacy of b-mercaptoketones at ambi-
ent temperature.
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Tetrachlorosilane–sodium sulfide
Thionation
Trithioaldehydes
b-Mercaptoketones
Synthesis
Organosulfur compounds are important intermediates for the
synthesis of various biologically active molecules as well as in
industry.1 Thionation of carbonyl compounds is widely applied
for the synthesis of organosulfur compounds.2 A variety of thionat-
temperature but, in the presence of cyanide, thiolate, or fluoride
ions, the addition process occurs very efficiently to afford 1,4-ad-
ducts.11 The development of novel synthetic strategies for thiona-
tion, which have advantages with respect to mild reaction
conditions, cleaner reactions, and simple isolation of the product,
is of interest. In this context, and in conjunction with our interest12
in exploring the utility of in situ reagents based on tetrachlorosi-
lane (TCS)13 in organic synthesis, we report herein a new in situ
thiosilane system derived from cheap and readily available tetra-
chlorosilane and sodium sulfide that converts aromatic aldehydes
into their corresponding thioaldehydes, which are obtained as tri-
mers, in good yield at room temperature using acetonitrile as a sol-
vent without any catalyst. Also, under these exceptionally mild
ing reagents have been described in the literature.3 Synthetically,
5a
Lawesson’s reagent (LR)4 and P4S10
,
either alone or with addi-
tives,5b–d are the most effective sulfurating reagents. However,
aside from its high cost, LR has the major disadvantage of being ex-
tremely sensitive to moisture and it is very difficult to prepare and
handle it in pure form,6 and the by-products derived from the re-
agent itself cannot, in general, be removed by any extractive proce-
dure and must be separated by column chromatography.
Thiosilanes, particularly hexamethyldisilathiane (HMDST),7 have
been used as thionating reagents, often under catalysis. They exhi-
bit specific reactivity due to the unique and complementary prop-
erties of sulfur and silicon, and have thus emerged as very useful
reagents in synthetic organic chemistry.8 However, organothiosil-
anes are good reagents for carbonyl functionalization9 as they react
with activated carbonyl compounds through cleavage of the Si–S
bond and addition to the C@O group; the uncatalyzed thiosilane
addition is still not a facile process, and requires high temperatures
and long reaction times.10 On the other hand, silyl sulfides were
conditions,
a,b-unsaturated ketones react with the SiCl4–Na2S re-
agent in the presence of a catalytic amount of CoCl2ꢀ6H2O to give
b-mercaptoketone derivatives that subsequently auto-oxidize to
give the respective disulfides. However, no reaction was observed
with aryl methyl ketones.
The reaction of aldehydes with SiCl4–Na2S proceeds without
further addition of any catalyst giving good yields of the corre-
sponding thioaldehydes which were obtained as trimers (Scheme
1, Table 1). The structures of the isolated trithioaldehydes were as-
signed based on their spectral analyses as well as by comparison of
their melting points with reported values.14
found to react slowly with
a,b-unsaturated ketones at elevated
The driving force for the present reaction is the net formation of
the stronger Si–O bond, where the difference in Si–O and Si–S bond
energies is ꢁ34 kcal,15 and therefore promotes the easy addition of
* Corresponding author at present address: Chemistry Department, Faculty of
Education, Amran University, Amran, Yemen. Tel.: +967 733411626.
E-mail address: tasalama@yahoo.com (T.A. Salama).
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.08.039

5934
T. A. Salama et al. / Tetrahedron Letters 50 (2009) 5933–5936
R'
R'
R
R
O
S
S
R
H
H
SiCl4, Na2S
MeCN, r.t.
3
S
S
R
R
R'
R'
1a-f
2a-f
R'
1a, 2a; R' = R = H
1b, 2b;
R' =H, R = Me
1c, 2c; R' = H, R = OMe
1d, 2d;
R' = H, R = Cl
1e, 2e; R' = H, R = Br
1f, 2f;
R' = Br, R = H
Scheme 1.
Table 1
The structure of disulfides 4 was supported by analytical and
spectral data. In the IR spectra of 4, the absorption at 1670–
1680 cmꢂ1 attributed to the carbonyl stretching of the saturated
system showed a clear shift compared to the corresponding start-
Reaction of aryl aldehydes with the TCS–Na2S reagent
Entry
Substrate
Time (h)
Product
Yielda (%)
1
2
3
4
5
6
Benzaldehyde
9
10
8
12
14
18
2a
2b
2c
2d
2e
2f
82
77
79
68
72
63
4-Methylbenzaldehyde
4-Methoxybenzaldehyde
4-Chlorobenzaldehyde
4-Bromobenzaldehyde
3-Bromobenzaldehyde
ing a
,b-unsaturated ketone. The 1H NMR spectrum of 4f, for exam-
ple, showed two doublets at d 3.46 and d 3.29 as well as two
triplets at d 4.42 and d 4.16. These were assigned to the C-2 and
C-3 protons, respectively.
a
Plausible mechanisms for the present reactions may proceed as
depicted in Scheme 3. 1,2-Addition of stoichiometric thiosilane,
generated in situ from the reaction of TCS and Na2S in 2:1 molar
ratio, in a similar manner to HMDST preparation17 (proposed hexa-
chlorodisilathiane A; HCDST) to the carbonyl group of the aldehyde
1 yields the transient thioaldehyde B which undergoes trimeriza-
tion to form 2. By analogy, the proposed hexachlorodisilathiane A
Yield of isolated product.
thiosilane to the carbonyl group of the aldehyde with formation of
the thermodynamically controlled products.
Applying the present reaction to aryl methyl ketones failed to
yield the corresponding thioketones even with the use of a catalyst
and/or by heating. This led us to attempt the reaction with
unsaturated ketones, the reason being that the 1,4-addition might
be a favorable process (Scheme 2). Thus, ,b-unsaturated ketones
were found to react with TCS–Na2S in the presence of a catalytic
amount of CoCl2ꢀ6H2O to give the 1,4-adducts (presumably the thi-
ols C, Scheme 3) but, as is well known, such thiols undergo auto-
oxidative dimerization easily to give disulfides 4.16 It is noteworthy
to mention that no reaction was observed in the absence of either
the catalyst or SiCl4. The generality of the process was examined by
reacts with
a,b-unsaturated ketones 3 only in the presence of
a,b-
CoCl2ꢀ6H2O catalysis via a 1,4-addition mechanism to give the thiol
C which subsequently undergoes autooxidative dimerization to
form disulfides 4.
In conclusion, we have developed a new thiosilane reagent
which is generated in situ from readily available and inexpensive
tetrachlorosilane and sodium sulfide.18 The thiosilane reagent acts
as a mild and potent thionating reagent for aromatic aldehydes in
acetonitrile at room temperature without catalysis giving the cor-
responding trithioaldehydes in good yields. Under these mild con-
a
applying the reaction to various examples of
a,b-unsaturated ke-
ditions,
a,b-unsaturated ketones react with SiCl4–Na2S using a
tones; however, bischalcones gave a complex mixture with no pre-
parative value. For example, dibenzalacetone and 2,6-bis(4-
methoxybenzal)cyclohexanone gave no distinct products (Scheme
2, Table 2).
catalytic amount of CoCl2ꢀ6H2O to give the respective disulfides
via a 1,4-conjugate addition mechanism. This new in situ reagent
may find additional applications as a substitute for HMDST, poten-
Ar
Ar
Ar'
Ar'
O
SH
Ar'
O
SiCl4, Na2S
Autooxidative-
Dimerization
O
O
S
S
Ar
Ar
Ar'
CoCl2.6H2O
r.t.
3a-f
4a-f
3a, 4a;
Ar = Ar' = Ph
3b, 4b; Ar = Ph, Ar' = 4-BrC6H4-
3c, 4c;
Ar = Ph, Ar' = 4-MeC6H4-
3d, 4d; Ar = 4-MeC6H4-, Ar' = 4-BrC6H4-
3e, 4e; Ar = Ar' = 4-MeC6H4-
3f, 4f;
Ar 2-thienyl, Ar' = Ph
Scheme 2.

T. A. Salama et al. / Tetrahedron Letters 50 (2009) 5933–5936
5935
2 SiCl4 + Na2S
O
H
S
Ar
S
Ar
OSiCl3
S
SiCl3
Ar
R'
H
Cl3Si-O-SiCl3
-
1
Cl3Si-S-SiCl3
Ar
Ar
H
S
S
B
A
Ar
2
O
R
3
OH SH
R'
CoCl2.6H2O
R
R
R
R'
R'
OSiCl3
H2O
O
O
S
S
SSiCl3
R'
R
O
SH
R'
R
4
C
Scheme 3. Plausible mechanisms for the formation of 2 and 4.
Table 2
Reaction of
a,b-unsaturated ketones with the TCS–Na2S reagent in the presence of CoCl2ꢀ6H2O
Entry
Substrate
Time (h)
Product
Yielda (%)
1
2
3
4
5
6
7
8
Benzalacetophenone
12
14
12
14
12
11
17
18
4a
4b
4c
4d
4e
4f
—
71
63
72
66
74
61
—
4-Bromobenzalacetophenone
4-Methylbenzal-acetophenone
4-Bromobenzal-40-methylacetophenone
4-Methylbenzal-40-methylacetophenone
2-Benzal-2-acetylthiophene
Dibenzalacetone
2,6-Bis(4-methoxybenzal)cyclohexanone
—
—
a
Yield of isolated product.
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K. A. M. Synlett 1995, 655–658.
4. (a) Curphey, T. J. Tetrahedron Lett. 2002, 43, 371–373; (b) Curphey, T. J.
Tetrahedron Lett. 2000, 41, 9963–9966; (c) Curphey, T. J. J. Org. Chem. 2002, 67,
6461–6473.
5. (a) Polshettiwar, V. Synlett 2004, 2245–2246. and references cited therein; (b)
Kaleta, Z.; Tarkanyi, G.; Gomory, A.; Kalman, F.; Nagy, T.; Soos, T. Org. Lett. 2006,
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Pedersen, B. S.; Lawesson, S. O. Tetrahedron 1979, 35, 2433–2437.
6. (a) Colvin, E. W. In Chemistry of Organic Silicon Compounds; Rappoport, Z.,
Apeloig, Y., Eds.; Wiley: Chichester, 1998; Vol. 2, Part 2, p 1667; (b) Lecher, H.
Z.; Greenwood, R. A.; Whitehouse, K. C.; Chao, T. H. J. Am. Chem. Soc. 1956, 78,
5018–5022.
7. (a) Degl’Innocenti, A.; Capperucci, A.; Castagnoli, G.; Malesci, I. Synlett 2005,
1965–1983; (b) Matulenko, M. A.. In Encyclopedia of Reagents for Organic
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1981, 37, 3899–3910.
15. Eaborn, C. J. Chem. Soc. 1950, 3077–3089.
16. (a) Choi, S. S.-M.; Kirby, G. W. J. Chem. Soc., Perkin Trans. 1 1991, 3225–3233; (b)
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T. A. Salama et al. / Tetrahedron Letters 50 (2009) 5933–5936
17. So, J.-H.; Boudjouk, P.. In Inorganic Syntheses; Russell, N. G., Ed.; Wiley: New
York, 1992; Vol. 29, p 30.
18. A typical procedure for the thionation of carbonyl compounds: A mixture of
anhydrous Na2S (10 mmol) and SiCl4 (20 mmol) in MeCN (15 ml) was stirred
for 15 min at ambient temperature. To this mixture, a solution of carbonyl
compound (5 mmol) in MeCN (10 ml) was added as well as a catalytic amount
44.12, 21.1; EI-MS (m/z, %): 510 (M+, 7), 255 (13), 223 (25), 119 (100), 77 (91).
Anal. Calcd for C32H30O2S2 (510.892): C, 75.26; H, 5.92; S, 12.56. Found: C,
75.18; H, 6.02; S, 12.67.
Bis-[1,3-bis(4-methylphenyl)-3-oxopropyl]disulfide 4e: Yield 74%; Purification by
recrystallization from diethyl ether; mp 113–115 °C.; IR (KBr plate)
2918, 2859, 1677 (CO), 1605, 1512, 1410, 1367, 1263, 1182, 1116, 810,
726 cmꢂ1 1H NMR (200 MHz, CDCl3) d 7.71–7.65 (m, 4H), 7.24–7.12 (m, 10H),
m 3027,
of CoCl2ꢀ6H2O (in the case of
a
,b-unsaturated ketones), and the reaction
;
mixture was stirred at room temperature. On completion (TLC), the mixture
was quenched with cold water, extracted with ethyl acetate (for aldehydes) or
7.05 (d, 2H, J = 7.4 Hz), 4.39 (t, 1H, J = 7.3 Hz), 4.11 (t, 1H, J = 7.3 Hz), 3.46 (d,
2H, J = 7.2 Hz), 3.34–3.27 (m, 2H), 2.36 (s, 6H, 2 ꢃ CH3), 2.28 (s, 6H, 2 ꢃ CH3);
13C NMR (50 MHz, CDCl3) d 196.15, 142.18, 138.69, 137.07, 136.13, 128.91,
128.35, 127.19, 46.12, 44.57, 23.19, 21.34; EI-MS (m/z, %): 538 (M+, 5), 269
(15), 237 (32), 119 (100), 91 (82). Anal. Calcd for C34H34O2S2 (538.76): C, 75.79;
H, 6.36; S, 11.90. Found: C, 75.84; H, 6.28; S, 11.65.
with CHCl3 (for
a,b-unsaturated ketones), dried over anhydrous MgSO4, and
the solvent was evaporated under vacuum and the residue was recrystallized
to give compound 2 or chromatographed using petroleum ether–ethyl acetate
(20:1) as eluent (in most cases) to give pure 4. Note: Sodium sulfide
nonahydrate (Na2Sꢀ9H2O) was dried by refluxing using dry benzene and a
Dean–Stark apparatus for three days. All the prepared trithioaldehydes 2 are
known.14 Disulfides 4 are novel except for 4a.19 Data for some representative
examples are provided.
Bis-[1-phenyl)-3-oxo-3-thienylpropyl]disulfide 4f: Yield 61%; mp 97 °C; IR (KBr
plate, cmꢂ1
) m 3094, 3027, 2920, 1659 (CO), 1599, 1515, 1451, 1413, 1357,
1329, 1237, 1063, 856, 753, 726, 699; 1H NMR (200 MHz, CDCl3) d 7.60–7.54
(m, 2H), 7.27–7.15 (m, 10H), 7.10–7.05 (m, 4H), 4.42 (t, 1H, J = 7.0 Hz), 4.16 (t,
1H, J = 7.0 Hz), 3.46 (d, 2H, J = 7.4 Hz), 3.29 (d, 2H, J = 7.4 Hz); 13C NMR
(50 MHz, CDCl3) d 191.05, 142.10, 141.56, 133,72, 131.53, 128.69, 127.53,
127.29, 127.12, 45.16, 43.88; EI-MS (m/z, %): 494 (M+, 9), 247 (10), 246 (12),
215 (27), 105 (100). Anal. Calcd for C26H22O2S4 (494.71): C, 63.12; H, 4.48; S,
25.93. Found: C, 63.02; H, 4.29; S, 26.02.
Bis-[1-(4-methylphenyl)-3-oxo-3-phenylpropyl]disulfide 4c: Yield 72%; mp
105 °C; IR (KBr plate)
m
3054, 3027, 2918, 1677 (CO), 1597, 1513, 1447,
1367, 1257, 1208, 819, 760, 687 cmꢂ1
;
1H NMR (300 MHz, CDCl3) d 7.78 (m,
4H), 7.58 (m, 2H), 7.53–7.06 (m, 12H), 4.14 (m, 2H), 3.44 (dd, J = 16.76, 7.93 Hz,
2H), 3.38 (dd, J = 16.76, 7.93 Hz, 2H), 2.28 (s, 6H, 2 ꢃ CH3); 13C NMR (75 MHz,
CDCl3) d 196.66, 138.56, 136.87, 136.66, 132.98, 129.12, 128.00, 127.97, 45.52,
19. Tanaka, H.; Yokoyama, A. Chem. Pharm. Bull. 1960, 8, 275–279.