Properties of Triflic Anhydride. Oxidation of Alcohols and Sulfides

Article abstract of DOI:10.1021/jo9620270

The reaction of dimethyl sulfide with triflic anhydride leads to the formation of the corresponding dimethyl(trifluoromethanesulfonyl)sulfonium salt. The latter can be used in the mild oxidation of primary and secondary alcohols including unsaturated and natural ones to the corresponding carbonyl compounds in 34-75% yield. The reaction of various sulfides with triflic anhydride was studied. It was found that the reactions give rise to the corresponding dialky(trifluoromethane- sulfonyl)sulfonium salts. Succeeding treatment with water leads to the formation of sulfoxides in 25-73% yield. Formation of sulfones does not proceed.

Full text of DOI:10.1021/jo9620270

J . Org. Chem. 1997, 62, 2483-2486
2483
Oxid a tive P r op er ties of Tr iflic An h yd r id e. Oxid a tion of Alcoh ols
a n d Su lfid es
Valentine G. Nenajdenko, Pavel V. Vertelezkij, Andrej B. Koldobskij,† Igor V. Alabugin,‡ and
Elizabeth S. Balenkova*
Department of Chemistry, Moscow State University, Moscow 119899, Russia,
A. N. Nesmeyanov Institute of Elementorganic Chemistry, Academy of Sciences, Moscow, Russia, and
Institute of Physiologically Active Compounds, Academy of Sciences, Chernogolovka, Russia
Received October 29, 1996X
The reaction of dimethyl sulfide with triflic anhydride leads to the formation of the corresponding
dimethyl(trifluoromethanesulfonyl)sulfonium salt. The latter can be used in the mild oxidation of
primary and secondary alcohols including unsaturated and natural ones to the corresponding
carbonyl compounds in 34-75% yield. The reaction of various sulfides with triflic anhydride was
studied. It was found that the reactions give rise to the corresponding dialkyl(trifluoromethane-
sulfonyl)sulfonium salts. Succeeding treatment with water leads to the formation of sulfoxides in
25-73% yield. Formation of sulfones does not proceed.
Sch em e 1
In tr od u ction
Recently, we have found that dimethyl sulfide reacts
with acylium salts to form dimethylacylsulfonium salts.1
These sulfonium salts are mild acylating reagents for
different unsaturated hydrocarbonssalkenes, acetylenes,
and conjugated dienes. This method of acylation was
found to be particularly important for labile dienes
having the propensity to cationic polymerization. Fur-
thermore, using this approach, we have proposed a novel
method of direct electrophilic perfluoroacylation of un-
saturated hydrocarbons that is based on utilization of
trifluoroacetic anhydride in the presence of the dimethyl
sulfide-boron trifluoride complex.2-4
Some properties of anhydrides of carboxylic acids are
similar to those of anhydrides of sulfonic acids. In this
research, we have studied interaction of trifluoromethane-
sulfonic acid anhydride (triflic anhydride) with different
sulfides. Triflic anhydride has found wide application
in organic synthesis.5 However, little is known about
oxidative properties of this reagent.6,7 Reactions of triflic
anhydride with sulfides have not yet been described.
We have attempted to establish the structure of the
dimethyl sulfide/triflic anhydride complex on the basis
of NMR spectra. The 1H and 13C NMR spectra show
singlets at 3.13 and 24.24 ppm correspondingly (-20 °C,
in CD2Cl2/CH3NO2 2/1), both of which are shifted to low
field in comparison to the signals of dimethyl sulfide (2.08
and 19.5 ppm). The downfield shift indicates a consider-
able positive charge at the sulfonium sulfur atom and is
characteristic for sulfonium methyls.
Chemistry of similar sulfonium salts can be considered
as nearly unexplored. Only one example of dimethyl-
sulfonylsulfonium salt was previously described.8 Di-
methyltosylsulfonium triflate (obtained by reaction of
methyl (toluenethio)sulfonate with methyl triflate) dis-
plays in the 1H NMR spectrum a singlet of sulfonium
methyls at 3.12 ppm. Our spectral data are very close
(3.13 ppm), i.e., the structure of triflic anhydride/dimethyl
sulfide complex is very likely to be dimethyl(trifluo-
romethanesulfonyl)sulfonium salt (1a ). It should be
mentioned that compounds 1a and 1c have two electro-
philic centers, sulfonium sulfur (path A) and sulfonate
sulfur (path B) (Figure 1), and a nucleophile can attack
both of them. Previously reported dimethyltosylsulfo-
nium triflate (1c) (Scheme 2) was found to undergo
nucleophilic attack by anisole and diethylamine on the
S(VI) atom (path B).8
Resu lts a n d Discu ssion
We have found that dimethyl sulfide reacts with triflic
anhydride in methylene chloride at -60 °C to form a
white solid. It is worthy of note that the reaction of
dimethyl sulfide with less electrophilic methanesulfonic
anhydride does not take place during 1 week under room
temperature. It would be reasonable to assume that the
formation of dimethyl(trifluoromethanesulfonyl)sulfonium
salt (1a ) takes place. The other possible structure having
an S-O instead of an S-S bond could be sulfonium salt
1b formed via isomerization of 1a (Scheme 1).
In contrast, we have found that the reaction of the
dimethyl sulfide/triflic anhydride complex with primary
and secondary alcohols proceeded exclusively at sulfo-
nium sulfur (path A) with formation of the corresponding
alkoxysulfonium salts. Treatment of the alkoxysulfo-
nium salts with triethylamine leads to effective formation
of the corresponding carbonyl compounds in 34-75%
yield (Scheme 3).
† A. N. Nesmeyanov Institute of Elementorganic Chemistry.
‡ Institute of Physiologically Active Compounds.
X Abstract published in Advance ACS Abstracts, March 1, 1997.
(1) Vertelezkij, P. V.; Balenkova, E. S. Zh. Org. Khim. 1990, 26,
2446.
(2) Nenajdenko, V. G.; Balenkova E. S. Tetrahedron 1994, 50, 775.
(3) Nenajdenko, V. G.; Balenkova, E. S. Tetrahedron 1994, 50,
11023.
(4) Nenajdenko, V. G.; Balenkova, E. S. Tetrahedron 1994, 50,
12407.
(5) Stang, P. J .; Hanack, M.; Subramanian, L. R. Synthesis 1982,
2, 85.
(6) Maas, G.; Stang, P. J . J . Org. Chem. 1981, 46, 1606.
(7) Creary, X. J . Org. Chem. 1980, 45, 2727.
(8) Minato, H.; Yamaguchi, K.; Miura, T.; Kobayashi, M. Chem. Lett.
1976, 593.
S0022-3263(96)02027-0 CCC: $14.00 © 1997 American Chemical Society

2484 J . Org. Chem., Vol. 62, No. 8, 1997
Nenajdenko et al.
Sch em e 4
time, it can be seen from Figure 1, representing the
LUMO of the new reagent, that orbital factors favor SN2-
like nucleophilic attack on the S(II) atom, followed by
S(II)-S(VI) bond cleavage. It should be mentioned that
the frontier orbital interactions are expected to be
important in this case because the LUMO has very low
energy (-8.0 eV). Thus, consideration of both charge and
orbital factors leads one to expect nucleophilic attack on
the S(II) atom in full accord with the experiment. We
believe that the dramatic distinction in the reaction path
for 1c and 1a is connected with the electron-withdrawing
influence of the CF3 group.
F igu r e 1. LUMO of 1a (dashed and solid lines correspond to
different signs of wave function) and two possible paths of
reaction of 1a with nucleophiles.
Sch em e 2
The behavior of 1a in the reaction with alcohols
permitted us to suggest the possibility of selective oxida-
tion of sulfides to sulfoxides by reaction of triflic anhy-
dride with sulfides followed by hydrolysis.
In spite of the fact that there are numerous reagents
for oxidation of sulfides to the corresponding sulfoxides,14
some of the methods give rise to competitive formation
of sulfones. Therefore, elaboration of new selective
methods for oxidation of sulfides is a desirable goal.
We have found that reaction of triflic anhydride with
various sulfides leads to formation of the complexes,
which are possibly dialkyl(trifluoromethanesulfonyl)-
sulfonium salts. Succeeding treatment of the reaction
mixture with aqueous sodium acetate results in the
corresponding sulfoxides without sulfone formation
(Scheme 4).
In order to determine the scope and limitations of this
method, we have applied it to a number of sulfides (Table
2) and found that the reaction is sensitive to electronic
and steric factors. The yields of the sulfoxides are better
in the case of aliphatic sulfides. The presence of func-
tional groups in the original sulfide does not prevent the
oxidation, but the reaction requires higher temperature
and yields of the corresponding sulfoxides are lower.
Oxidation of diphenyl sulfide, methyl 4-nitrophenyl
sulfide, (cyclohexylthio)methyl cyanide, and 1-adamantyl
ethyl sulfide does not take place even at room tempera-
ture; the formation of complexes with triflic anhydride
does not proceed, and sulfides are recovered.
In the case of thioanisole (4f), the corresponding
sulfoxide was isolated in low yield (25%). We have found
that a competing electrophilic substitution reaction takes
place to form diarylmethylsulfonium salt 5g. We believe
that the sulfonylsulfonium salt reacts as a sulfonium
electrophile toward the electron-rich aromatic nucleus of
thioanisole. Raising the reaction temperature changes
the reaction selectivity. In this case, only sulfonium salt
5g was isolated in 67% yield. For 4-methylthioanisole
(4h ), similar to the reaction with 4f, the corresponding
sulfonium salt 5h was isolated in 73% yield. In this case,
electrophilic substitution at the ortho position to the
methylthio group takes place.
Sch em e 3
Ta ble 1. Oxid a tion of Alcoh ols w ith Dim eth yl Su lfid e/
Tr iflic An h yd r id e Com p lex
isolated
yields
entry
alcohol
product
(%)
1
2
3
4
5
6
7
2-phenylethanol (2a )
benzyl alcohol (2b)
phenylacetaldehyde (3a )
benzaldehyde (3b)
2-(2-thienyl)ethanol (2c) (2-thienyl)acetaldehyde (3c)
45a
60a
34b
55a
75a
75
cinnamyl alcohol (2d )
cyclohexanol (2e)
menthol (2f)
cinnamaldehyde (3d )
cyclohexanone (3e)
menthone (3f)
cholesterol (2g)
5-cholesten-3-one (3g)
50
a
b
Isolated as the semicarbazone. Isolated as the diethyl acetal.
Thus, the overall result of this one-pot procedure is
mild oxidation of alcohols to carbonyl compounds (Table
1). Although this method is similar to other methods
based on dimethyl sulfoxide-derived reagents,9 it proceeds
under mild conditions and is suitable for unsaturated and
natural substrates. Thus, in some cases, it could con-
stitute a useful addition to known methods.
In order to rationalize the observed difference between
our data and the data in the literature8 and get insight
into the electronic structure of the new electrophilic
reagent, we have performed molecular orbital calcula-
tions on compound 1a . For this purpose, we have applied
a recently developed semiempirical PM310 method that
had been reported to give satisfactory results for sulfur
organic compounds including hypervalent ones.11
In accord with molecular orbital perturbation theory,12
the selectivity of the reaction appears to arise from the
interplay between charge and orbital interactions. Both
sulfur atoms bear high positive charge.13 At the same
(13) Unfortunately, it is impossible to judge on the basis of PM3
data which sulfur atom (S(II) or S(VI)) is more positive because the
PM3 method is known to overestimate Mulliken net charges on sulfur-
(VI) atoms. Nevertheless, it is obvious that both of the sulfur atoms
are positively charged.
(14) Houben-Weyl. Methoden der Organishen Chemie; Klamann, D.,
Ed.; Verlag: Stuttgart, 1985; B. E11, p 702.
(9) Houben-Weyl. Methoden der Organishen Chemie; Klamann, D.,
Ed.; Verlag: Stuttgart, 1985; B. E11, p 365.
(10) Stewart, J . P. J . Comput. Chem. 1989, 10, 221.
(11) Stewart, J . P. J . Comput. Chem. 1990, 11, 543.
(12) Chemical reactivity and reactions paths; Klopman, G., Ed.;
Wiley: New York, 1974.

Oxidative Properties of Triflic Anhydride
J . Org. Chem., Vol. 62, No. 8, 1997 2485
Ta ble 2. Oxid a tion of Su lfid es w ith Tr iflic An h yd r id e16
silica gel (63-200 mesh, Merck). All solvents were dried and
distilled according to the standard procedure. Triflic anhy-
dride was prepared according to literature procedure5 from
trifluoromethanesulfonic acid (Merck).
Sch em e 5
Gen er a l P r oced u r e for Alcoh ol Oxid a tion . A solution
of 1.7 g (6 mmol) of triflic anhydride in 30 mL of anhydrous
CH2Cl2 was cooled to -70 °C. A solution of 0.31 g (6 mmol) of
dimethyl sulfide in 10 mL of CH2Cl2 was added dropwise. A
white precipitate formed. After 5 min, 5 mmol of the alcohol
was added dropwise, the reaction mixture was stirred for 15
min, and 1.3 g (13 mmol) of triethylamine was added. The
reaction mixture was allowed to warm to rt, and 20 mL of
water was then added. The organic layer was separated and
washed with water (2 × 20 mL). The solution was diluted
with 30 mL of ether and filtered. The filtrate was dried with
Na2SO4, and solvents were removed in vacuo. The isolated
carbonyl derivative gave spectroscopic data and physical
constants in accord with the literature.15,16
Gen er a l P r oced u r e for Su lfid e Oxid a tion . A solution
of 1.7 g (6 mmol) of triflic anhydride in 30 mL of anhydrous
CH2Cl2 was cooled to -40 °C. Over a period of 10 min, 5 mmol
of the corresponding sulfide in 10 mL of CH2Cl2 was added
dropwise. The reaction mixture was allowed to warm (Table
2) followed by addition of an aqueous solution of sodium
acetate. The resulting mixture was stirred for an additional
15 min. The organic layer was separated, and the aqueous
layer was extracted with CH2Cl2 (3 × 20 mL). The organic
fraction was dried with Na2SO4, and solvents were removed
in vacuo. The product was purified by column chromatography
(silica gel, benzene-CHCl3 10/1). Isolated sulfoxides 5a ,d -f
gave spectroscopic data and physical constant in accord with
the literature.15,17,18
Reaction of methyl benzyl sulfide (4i) with triflic
anhydride does not result in formation of the correspond-
ing sulfoxide, but gives only dibenzylmethylsulfonium
triflate (5i). We assume that the anomalous reaction
path is due to enhanced propensity of the benzyl group
to nucleophilic substitution resulting in transbenzylation
(Scheme 5).
Con clu sion
Thus, the reaction of dimethyl sulfide with triflic
anhydride leads to formation of a complex. This complex
was investigated as an oxidant of alcohols, and it was
found that formation of the corresponding carbonyl
compounds could be achieved in 34-75% yields. The
structure of the reagent was studied by NMR spectro-
scopy and semiempirical quantum chemical PM3 calcula-
tions. The computational data were found to be in good
accord with the experimental results. Various sulfides
can be converted to sulfoxides, without overoxidation to
sulfones, under mild conditions using treatment with
triflic anhydride followed by hydrolysis. Yields are in the
range of 25-73%. The reaction is sensitive to electronic
and steric factors.
Eth yl 3-(eth ylsu lfin yl)p r op a n oa te (5b): yield 62%; oil;
1
IR (neat) 1030, 1050, 1740 cm-1; H NMR (CD2Cl2) δ 4.12 (q,
2H, J ) 7.0 Hz), 3.16 -2.63 (m, 6H), 2.52 (q, 2H, J ) 7.0 Hz),
(15) Dictionary of Organic Compounds; Heilbron, I., Bunbury, H.
M., Eds.; Eyze & Spottiswoode (Publishers) Ltd.: London, 1934; Vols.
1-3.
(16) Brandsma, L.; Verkruijsse, H. D. Preparative Polar Organo-
metallic Chemistry; Springer-Verlag: Berlin, 1987; Vol. 1, p 126.
(17) Carlson, R. M.; Helquist, P. M. J . Org. Chem. 1968, 33(6), 2596.
(18) Cornelis, R. M.; de Longe, I.; Hageman, H. J .; Huysmans, W.
J . B.; Mijs, W. J . J . Chem. Soc., Perkin Trans. 2 1973, 9, 1276.
Exp er im en ta l Section
Melting points were determined in sealed capillaries and
are uncorrected. Column chromatography was performed on

2486 J . Org. Chem., Vol. 62, No. 8, 1997
Nenajdenko et al.
mp 129-130 °C; IR (Nujol) 1300-1100, 1040, 990 cm-1 1H
NMR (CD3COCD3) δ 8.12 (s, 1H), 7.92 (d, 2H, J ) 8.0 Hz),
7.69 (d, 1H, J ) 7.9 Hz), 7.61 (d, 1H, J ) 7.9 Hz), 7.52 (d, 2H,
J ) 8.0 Hz), 3.85 (s, 3H), 2.50 (s, 3H), 2.46 (s, 3H), 2.41 (s,
3H); 13C NMR (CD3COCD3) δ 144.3, 139.2, 136.2, 134.3, 131.5,
130.6, 129.5, 127.9, 126.1, 122.9, 121.4 (q, J ) -319.9 Hz),
25.9, 19.6, 19.1, 16.9. Anal. Calcd for C17H19F3O3S3: C, 48.10;
H, 4.51. Found: C, 48.45; H, 4.38.
1.15 (t, 3H, J ) 7.0 Hz), 1.13 (t, 3H, J ) 7.0 Hz); 13C NMR
(CD2Cl2) δ 171.7, 61.7, 48.2, 46.2, 31.4, 14.2, 7.3. Anal. Calcd
for C7H14O3S: C, 47.17; H, 7.92. Found: C, 47.35; H, 7.99.
Dicyclop en tyl su lfoxid e (5c): yield 52%; oil; IR (Nujol)
1050 cm-1; 1H NMR (CDCl3) δ 3.01 (m, 2H), 2.13 (m, 2H), 1.87
(m, 4H), 1.75-1.57 (m, 10H); 13C NMR (CDCl3) δ 55.4, 25.9,
24.2, 23.7, 23.0. Anal. Calcd for C10H18OS: C, 64.47; H, 9.74.
Found: C, 64.13; H, 9.75.
;
Sulfonium salts 5g-i were prepared under this procedure,
but they were purified by crystallization (chloroform) instead
of column cromatography.
Diben zylm eth ylsu lfon iu m tr iflu or om eth a n esu lfon a te
(5i): yield 65%; mp 103-104 °C; IR (Nujol) 1300-1100, 1040,
990 cm-1 1H NMR (CDCl3) δ 7.53-7.21 (m, 10H), 4.82 (m,
;
Meth ylp h en yl[4-(m eth ylth io)p h en yl]su lfon iu m tr iflu -
or om eth a n esu lfon a te (5g): yield 67%; oil; IR (Nujol) 1300-
1100, 1040, 1000 cm-1; 1H NMR (CD3COCD3) δ 8.14 (d, 2H, J
) 7.4 Hz), 8.04 (d, 2H, J ) 7.4 Hz), 7.81-7.69 (m, 3H), 7.61
(d, 1H, J ) 7.9 Hz), 7.52 (d, 2H, J ) 8.6 Hz), 3.90 (s, 3H), 2.52
(s, 3H); 13C NMR (CD3COCD3) δ 148.9, 134.4, 131.5, 130.9,
130.1, 128.0, 127.4, 121.7, 121.6 (q, J ) -320.8 Hz), 27.5, 14.1.
Anal. Calcd for C15H15F3O3S3: C, 45.44; H, 3.81. Found: C,
45.56; H, 3.83.
4H), 2.70 (s, 3H); 13C NMR (CDCl3) δ 130.2, 129.8, 129.2, 126.7,
122.3 (q, J ) -320.0 Hz), 19.8. Anal. Calcd for C16H17
-
F3O3S2: C, 50.78; H, 4.53. Found: C, 50.53; H, 4.56.
Ack n ow led gm en t. The authors express their grati-
tude to Dr. I. D. Gridnev for the recording of high-
resolution NMR spectra.
Meth yl(4-m eth ylp h en yl)[2-[4-m eth yl(m eth ylth io)p h e-
n yl]su lfon iu m tr iflu or om eth an esu lfon ate (5h ): yield 73%;
J O9620270