A convenient preparation of sulfines (R2C=S=O) from thioketones

Full text of DOI:10.1021/jo990967p

J . Org. Chem. 1999, 64, 6935-6936
6935
Ta ble 1. Yield s of Su lfin es P r ep a r ed by Differ en t
Meth od s of Th ion e Oxid a tion
A Con ven ien t P r ep a r a tion of Su lfin es
(R2CdSdO) fr om Th iok eton es
sulfine yield
(%)
oxidizing reagent
conditions
rt, <5 min
rta
Ruili Huang and J ames H. Espenson*
MTO/H2O2
>90
Department of Chemistry, Iowa State University,
Ames, Iowa 50011
perbenzoic acid1
80-90b
38-89
50-90
0-71
monoperoxyphthalic acid2,3 0 °C, 30-45 minc
m-CPBA4-6
0 °C, 30-40 mind
-70 to -78 °C, N2
hν, 0.5-48 h
e
ozone7-9
Received J une 17, 1999
10
1O2
2-25
70-90
N-sulfonyloxaziridines11
0 °C, N2, 0.5-1.5 hf
In tr od u ction
a
b
A kinetics investigation. Conversion of the thione to sulfine
Hydrogen peroxide is able to oxidize thiobenzophe-
nones and thiocamphor to their sulfines, when catalyzed
by methyltrioxorhenium, CH3ReO3 or MTO, according to
this general reaction:
monitored by UV-vis, not the isolated yield. c 1:2 ratio of peracid
d
to thione. m-CPBA was the limiting reagent. e 1:1 ratio of ozone
and thione. f Only two sulfines, (1R)-(+)-thiocamphor S-oxide and
(1S)-(-)-thiofenchone S-oxide, were prepared by this method.
a 1 mmol scale, only the requisite quantity of hydrogen
peroxide was used. This method succeeds because the
subsequent oxidation of the sulfines occurs <103 times
as rapidly as the rate of reaction 1. With a 1:1 ratio of
R2CS/H2O2, no further oxidation or side products were
obtained, as judged by 1H NMR. The reaction was carried
out at room temperature in organic solvents (acetonitrile,
chloroform, etc.) or in aqueous mixtures.
R2CdS + H2O2 cat. MTO8 R2CdSdO + H2O (1)
This method has provided a new route to sulfines that is
superior to known methods. Peracids are traditionally
used, such as perbenzoic acid,1 monoperoxyphthalic
acid,2,3 and m-CPBA.4-6 Even with a limited peracid
concentration to prevent overoxidation, yields were not
entirely satisfactory. On the basis of the peracids con-
sumed, conversions were in the range 9-99%, but
expressed as the conversion of thione, it was much less
satisfactory, even at 0 °C. Ozonation is another common
method,7,8 often carried out at -70 °C under nitrogen.
With a 1:1 ratio of thione/O3 at room temperature, the
yield was still quite low, about 3-6% of sulfine, with most
of the thione remaining unoxidized or overoxidized to the
Some of these reactions have now been carried out on
a larger scale, starting with 0.7-1.0 g of the thione
dissolved in 1:4 aqueous acetonitrile. The solution also
contained 0.1 M trifluoromethanesulfonic acid to stabilize
MTO. This catalyst was added at 1-10% (usually 1-2%)
relative to the thione, followed by hydrogen peroxide (1.0
equiv). The color of solution changed from the dark blue
of the thiobenzophenone to light yellow in less than 2
min, signaling the completion of the reaction. The
conversion was checked at this point by 1H NMR; the
reactions were found to be completed within 5 min.
Acetonitrile was removed from the product solution by
rotary evaporation. Hexane and water were added,
followed by excess sodium bicarbonate to neutralize the
triflic acid and decompose MTO to perrhenate ions.15 The
sulfine appeared in the hexane layer; the aqueous layer
contained sodium triflate, excess sodium bicarbonate, and
the perrhenate salt. The yellow hexane layer was washed
with water several times and then rotary evaporated to
remove the solvent. Higher purity material could be
obtained by column or thin-layer chromatography on
silica gel, eluting with ethyl acetate-hexane. Recrystal-
lization from hexane-isooctane or hexane alone gave the
sulfine as light yellow crystals.
1
10
ketone.9 The use of O2 proved unsatisfactory, as did
other oxidizing reagents.11 The conditions used in these
reactions and the yields of sulfines thus obtained are
summarized in Table 1.
Aside from oxidative methods, one should note the
alkylidenation of sulfur dioxide with R-silyl carbanions
at -78 °C12 and the base-induced elimination of alkane-
sulfinyl derivatives.13,14
In this work, reaction 1 was carried out for several
thiobenzophenones, with these para substituents: NMe2,
OMe, Me, H, F, Cl, Br, m-CF3, and m-NO2. Thiocamphor
was used as well. To obtain the sulfines in high yield on
(1) Battaglia, A.; Dondoni, A.; Giorgianni, P.; Maccagnani, G.;
Mazzanti, G. J . Chem. Soc. B)1971, 1547.
(2) Zwanenburg, B.; Thijs, L.; Strating, J . Rec. Trav. Chim. Pays-
Bas 1967, 86, 577.
(3) Saito, T.; Takekawa, K.; Nishimura, J .-I.; Kawamara, M. J .
Chem. Soc., Perkin Trans. 1 1997, 2957.
(4) Carlsen, L.; Snyder, J . P.; Holm, A.; Pederson, E. Tetrahedron
1981, 37, 1257.
(5) Adiwidjaja, G.; Sawluk, A.; Volz, W.; Voss, J . Phosphorus, Sulfur,
Silicon 1973, 74, 451.
(6) Cerreta, F. Bull. Soc. Chim. Fr. 1995, 67, 132.
(7) Zwanenburg, B.; J anssen, W. A. J . Synthesis 1973, 617.
(8) Tabuchi, T.; Nojima, M.; Kusabayashi, S. J . Chem. Soc., Perkin
Trans. 1 1991, 12, 3043.
(9) Ramnath, N.; Ramesh, V.; Ramamurthy, V. J . Chem. Soc., Chem.
Commun. 1981, 112.
(10) Ramnath, N.; Ramesh, V.; Ramamurthy, V. J . Org. Chem. 1983,
48, 214.
The products from 4,4′-dimethoxythiobenzophenone
and thiocamphor were isolated in 95-99% isolated yield.
The crude sulfines were further purified by column
chromatography on silica gel. Elution was with 15% ethyl
acetate-hexane. 4,4-Dimethoxythiobenzophenone sul-
foxide was recrystallized from hexane, yielding greenish-
yellow needles.16 Thiocamphor sulfine was obtained as a
light yellow solid; spectroscopic data for it are given in
Table 1.
(11) Maccagnani, G.; Innocenti, A.; Zani, P.; Battaglia, A. J . Chem.
Soc., Perkin Trans. 2 1987, 1113.
(12) Van der Leij, M.; Porskamp, P. A. T. W.; Lammerink, B. H.
M.; Zwangenburg, B. Tetrahedron Lett. 1978, 811.
(13) Kice, J . L.; Rudzinski, J . J . J . Am. Chem. Soc. 1987, 109, 2414.
(14) Kice, J . L.; Kupczyk-Subotkowska, L. J . Org. Chem. 1991, 56,
1424.
(15) Abu-Omar, M.; Hansen, P. J .; Espenson, J . H. J . Am. Chem.
Soc. 1996, 118, 4966-4974.
(16) 1H NMR: δ/ppm 0.80 (d, 2H), 7.29 (d, 2H), 7.00 (m, 4H), 3.82
(s, 3H), 3.80 (s, 3H). MS m/z: 274 (M+, 67), 258 (M+ - O, 11), 226 (M+
- SO, 8.5), 211 (M+ - SO - CH3, 10), 196 (M+ - SO - OCH3, 2.4),
183 (M+ - OCH3 - CSO, 7), 151 (M+ - CSO - 2MeO, 6), 135 (M+
S - MeOC6H4, 100), 107 (M+ - CSO - MeOC6H4, 33).
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10.1021/jo990967p CCC: $18.00 © 1999 American Chemical Society
Published on Web 08/11/1999

6936 J . Org. Chem., Vol. 64, No. 18, 1999
Ta ble 2. Sp ectr oscop ic a n d An a lytica l Da ta for P r eviou sly-Un r ep or ted Su lfin esa
Notes
method
(p-FC6H4)2CSO
(m-CF3C6H4)2CSO
1H NMR (CDCl3)
7.66 (m, 2H), 7.13 (m, 2H), 6.90 (m, 4H)
8.09 (s, 1H), 8.02 (d, 1H), 7.83 (d, 1H), 7.76 (d, 1H),
7.67-7.56 (m, 4H)
13C NMR (CDCl3)
185.26 (CSO), 165.21 (d, J (F, C) ) 296),
185.51 (CSO), 134.36, 132.66, 132.16, 131.83, 131.68,
1
1
3
162.70 (d, J (F, C) ) 307), 131.53, 131.44,
131.60, 130.01, 129.55, 128.08 (q, J (F, C) ) 14),
4
3
3
130.84 (d, J (F, C) ) 15), 126.91 (d,
127.87 (q, J (F, C) ) 14), 125.98 (q, J (F, C) ) 15),
2
3
4J (F, C)) 14), 116.10 (d, J (F, C) ) 88),
125.73 (q, J (F, C) ) 15), 124.82 (CF3, q,
2
1
115.64 (d, J (F, C) ) 88)
1J (F, C) ) 35),122.11 (CF3, q, J (F, C) ) 35)
MS
250 (M+, 75), 234 (M+ - O, 18), 202
350 (M+, 66), 334 (M+ - O, 17), 331 (M+ - F, 2),
301 (M+ - SO, 30), 281 (M+ - CF3, 100),
233 (M+ - CF3 - SO, 43)
(M+ - SO, 100), 183 (M+ - SO - F, 16)
λmax (ꢀ) (ethyl acetate)b
elemental analysis,
found (calcd)
327 (12 100); 260 (9260)
C 62.24 (62.38); H 3.15 (3.22); S 12.46 (12.81)
320 (19 400)
C 51.92 (51.43); H 2.32 (2.30); S 9.18 (9.15)
habit
yellow crystals, mp 75-76 °C
pale yellow, mp 53-55 °C
a
Thiocamphor sulfine, previously reported,11 has this 1H spectrum [2.94 (d of m, 1H), 2.45 (d, 1H), 2.02 (t, 1H), 1.86 (m, 2H), 1.39 (m,
1H), 1.24 (m, 1H), 1.06 (s, 3H), 0.90 (s, 3H), 0.77 (s, 3H)] and this MS: 184 (M+, 59), 167 (M+ - OH, 4), 135 (M+ - SOH, 3), 125 (5), 107
(45), 105 (43), 93 (72), 91 (100). UV spectra determined at four concentrations; Beer’s law was exactly obeyed.
b
Sch em e 1. In itia l Sta ge of Oxid a tion
Most sulfines were obtained as yellow or yellowish
crystalline materials. They are mildly photosensitive to
room light and to oxygen, but are much more stable than
the parent thioketones. Even if exposed to air and light,
sulfines can be kept unchanged for days and are stable
enough to be isolated and characterized. Some of the
sulfines are stable for months when stored in the dark
under argon. The melting points, colors, and isolated
yields of the other materials have also been noted.17
reviewed.25,26 The essence of this chemistry is captured
in Scheme 1.
The sulfines with the para substituents NMe2, OMe,
Me, H, Cl, Br, and m-NO2 were previously known. They
were identified by comparing their 1H and 13C NMR
spectra, mass spectra, and IR spectra with data previ-
ously reported.8,10,11,18-24
The second stage of oxidation, in which the sulfine, in
>1 step, is converted to the ketone, occurs rather more
slowly. Under conditions at which a thioketone is oxidized
in ca. 10 min, the sulfine required 100-600 h. This
timing difference is quite reasonable in that the addition
of an oxygen atom to the sulfur will certainly reduce
sharply the rate of a subsequent oxidation step by the
same reagent. It is just this difference that enables the
present procedure to give a high yield of the sulfine with
so little loss to the ketone. In the case of thiocamphor,
the oxidation stops at the sulfine, even with excess
peroxide.
The CdS bond in thioketones is known to be strongly
polarized,2 unlike a CdO bond. A negative charge resides
on the carbon atom. The sulfine is formed by the
nucleophilic attack of the sulfur atom on the electron-
deficient oxygen atom of the peroxorhenium complexes
that are the active intermediates in the reaction.
Two new sulfines were prepared, with p-F and m-CF3
substituents. They were obtained by the same procedure
in >90% yields and purified by thin-layer chromatogra-
phy on silica gel, eluting with 5% ethyl acetate-hexane.
Yellow crystals were grown from hexane-isooctane. The
spectroscopic data and elemental analyses for the new
compounds are given in Table 2.
The success of the method rests, first, on the MTO-
catalyzed reaction converting the thioketone to a sulfine.
This type of transformation has been verified for a
considerable number of substrates, as has recently been
(17) For (p-XC6H4)2CSO, the melting points, colors, and yields are
as follows: NMe2, 181-183 °C, gold 88%; MeO, 84-85, greenish-yellow,
95%; Me, 89-91 °C, yellow, 98%; H, 33-35 °C, greenish yellow, 92%;
F, 75-76 °C; yellow, 95%; Cl, 87.5-88 °C; yellow, 95%; Br, 106-108
°C; yellow, 90%. For these meta isomers, CF3, 53-55 °C, light yellow,
92%; NO2, 162-164 °C, light yellow, 90%. The sulfine from thiocam-
phor is a light yellow oily solid, mp 118-120 °C, obtained in 97% yield.
(18) Dahn, H.; Pechy, P.; Toan, V. V.; Bonini, B. F.; Lunazzi, L. J .
Chem. Soc., Perkin Trans. 2 1993, 10, 1881.
(19) Zwanenburg, B. Tetrahedron 1971, 27, 1731.
(20) Tangerman, A.; Zwanenburg, B. J . Chem. Soc., Perkin Trans.
2 1973, 458.
(21) Tangerman, A.; Zwanenburg, B. J . Chem. Soc., Perkin Trans.
2 1974, 1141.
(22) Veenstra, G. E.; Zwanenburg, B. Rec. Trav. Chim. Pays-Bas
1976, 95, 37.
Ack n ow led gm en t. This research was supported by
a grant from the National Science Foundation (CHE-
9007283). Some experiments were conducted with the
use of the facilities of the Ames Laboratory. We grate-
fully acknowledge helpful conversations with Professor
W. S. J enks.
J O990967P
(23) Huisgen, R.; Mloston, G.; Polborn, K.; Palacios-Gambra, F.
Liebigs Ann. Org. Bioorg. Chem. 1997, 1, 187.
(24) Kuipers, J . A. M.; Lammerink, B. H. M.; Still, K. W. J .;
Zwanenburg, B. Synthesis 1981, 4, 295.
(25) Espenson, J . H.; Abu-Omar, M. M. Adv. Chem. Ser. 1997, 253,
99-134.
(26) Espenson, J . H. J . Chem. Soc., Chem. Commun. 1999, 479-
488.