Tetracyanoethylene oxide not only oxidizes sulfides to sulfoxides but also reduces sulfoxides to sulfides

Article abstract of DOI:10.1016/j.tetlet.2005.01.057

It was found that tetracyanoethylene oxide not only oxidizes sulfides to sulfoxides but also reduces sulfoxides to sulfides with generation of two molecules of carbonyl cyanide. The reaction thus also functions as a new method for generation of carbonyl cyanide.

Full text of DOI:10.1016/j.tetlet.2005.01.057

Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 1395–1397
Tetracyanoethylene oxide not only oxidizes sulfides to
sulfoxides but also reduces sulfoxides to sulfides
Juzo Nakayama,* Ayako Tai, Sachiko Iwasa, Tomohiro Furuya and Yoshiaki Sugihara
Department of Chemistry, Faculty of Science, Saitama University, Saitama, Saitama 338-8570, Japan
Received 21 December 2004; revised 7 January 2005; accepted 13 January 2005
Available online 25 January 2005
Abstract—It was found that tetracyanoethylene oxide not only oxidizes sulfides to sulfoxides but also reduces sulfoxides to sulfides
with generation of two molecules of carbonyl cyanide. The reaction thus also functions as a new method for generation of carbonyl
cyanide.
Ó 2005 Elsevier Ltd. All rights reserved.
Here we report that tetracyanoethylene oxide (TCNEO)
reduces sulfoxides to sulfides with liberation of two mole-
cules of carbonyl cyanide (COCN) (Scheme 1). Previ-
ously, the following have been reported on the reactions
of TCNEO with sulfides.1,2 TCNEO reacts with sulfides,
with liberation of COCN, to furnish the corresponding
sulfur ylides in 36–80% yields.2b In addition, the reac-
tion gives rise to the corresponding sulfoxides as by-
product in less than 40% yield with liberation of tetracy-
anoethylene (TCNE),2b that is, TCNEO also acts as an
oxidizing agent toward sulfides (Scheme 2). Therefore
the present findings meet with an interesting paradox
that TCNEO not only oxidizes sulfides to sulfoxides
but also reduces sulfoxides to sulfides.
with 4, but instead gave 3,5 the Diels–Alder adduct of
1 with COCN, in 52% yield.4 Thiophene 2, reduction
product of 1, was also formed in 27% yield. These results
can be explained by assuming that TCNEO reduced 1 to
give 2 and COCN, and then the resulting COCN under-
went the Diels–Alder reaction with 1 to furnish 3
(Scheme 3). We therefore investigated the reaction of
TCNEO with sulfoxides in more detail.
The reaction of TCNEO with the simplest sulfoxide
DMSO was investigated initially. Reportedly, TCNEO
reacts with dimethyl sulfide in ether to give ylide 5 in
better than 80% yield.2a Re-examination of the reaction
in CDCl3 at room temperature revealed that the reaction
is completed within 5 h to give DMSO in 3% yield as a
by-product together with 5 in 84% yield.6 On the other
hand, the reaction of TCNEO with DMSO was sluggish.
The reaction in CDCl3 at room temperature for 8 h gave
5 in 8% yield and a trace amount of dimethyl sulfide,
and for 6 days gave 5 in 47% yield and a trace amount
of dimethyl sulfide.6 Therefore TCNEO reduces DMSO,
though slowly, to dimethyl sulfide, which is quickly
It is known that TCNEO thermally equilibrates with the
carbonyl ylide 4 that functions as a typical 1,3-dipole.3
For our interest in 3,4-di-tert-butylthiophene 1-oxide
(1) as a 1,3-dipolarophile,4 we have examined the reac-
tion of 1 with TCNEO in refluxing toluene. The reaction
failed to give the expected 1,3-dipolar cycloadduct of 1
Scheme 1.
Keywords: Oxidation and reduction; Sulfur ylide; Carbonyl cyanide;
Sulfide; Sulfoxide.
*
Corresponding author. Tel.: +81 48 858 3390; fax: +81 48 858
3390; e-mail: nakaj@post.saitama-u.ac.jp
Scheme 2.
0040-4039/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.01.057

1396
J. Nakayama et al. / Tetrahedron Letters 46 (2005) 1395–1397
the presence of the diene, the adduct 6 was obtained in
good yield.7
For diaryl sulfides, oxidation (sulfoxide formation) pre-
dominates over ylide formation. Thus heating an equi-
molar mixture of di-p-tolyl sulfide and TCNEO in
refluxing benzene for 0.5 h produced di-p-tolyl sulfoxide
and ylide 8 in 54% and 18% yield, respectively, with 28%
recovered starting sulfide, while an equimolar mixture of
di-p-tolyl sulfoxide and TCNEO under the same condi-
tions gave di-p-tolyl sulfide and 8 in 44% and 8% yields,
respectively, with 48% recovered sulfoxide (Scheme 6).
These tell us that the use of excess TCNEO for the reac-
tion with the sulfide would increase the yield of 8 since
the resulting sulfoxide is re-converted to the sulfide
and then converted to 8 by TCNEO. The same will be
true for the reaction of TCNEO with the sulfoxide.
Thus, heating di-p-tolyl sulfide with 5 M amounts of
TCNEO gave 8 and di-p-tolyl sulfoxide in 59% and
25% yields, respectively, with 16% recovered sulfide,
and heating di-p-tolyl sulfoxide with 5 M amounts of
TCNEO gave 8 and di-p-tolyl sulfide in 55% and 18%
yields with 26% recovered sulfoxide (Scheme 6). Accord-
ingly, similar-ratio mixtures of di-p-tolyl sulfide, di-p-tol-
yl sulfoxide, and 8 become obtainable, when TCNEO
was used in excess, whether the starting material is the
sulfide or the sulfoxide. Similar results were also ob-
tained for the reaction of TCNEO with diphenyl sulfide
or diphenyl sulfoxide; also for this case, the adduct 6
was obtained in good yield in the presence of the diene.
Heating a 2:1 mixture of TCNEO and dibenzothiophene
S-oxide gave dibenzothiophene in 74% yield with
recovery of a small amount of the S-oxide,10 thereby
giving 6 in good yield in the presence of the diene.
Scheme 3.
converted to 5 by TCNEO. Thus the whole results
would be depicted as shown in Scheme 4. The COCN,
produced by the two reactions shown in Scheme 4,
was trapped by [2+4] cycloaddition with a diene. Thus
when TCNEO (0.28 mmol) and DMSO (0.12 mmol)
was heated in the presence of excess 2,3-diphenyl-1,3-
butadiene,7 the adduct 65 was obtained in good isolated
yield (0.19 mmol)8 (Scheme 5). The reaction thus pro-
vides a new method for generation of COCN.9
The reaction of TCNEO with thioanisole in CDCl3 at
room temperature for 6.5 h produced methyl phenyl
sulfoxide and ylide 7 in 6% and 73% yields, respectively,
with 21% recovered starting sulfide (Scheme 5). Mean-
while the reaction of TCNEO with methyl phenyl sulf-
oxide under the same conditions for 6 days gave 7 in
38% yield and a trace amount of methyl phenyl sulfide
with 61% recovered starting sulfoxide. When the reac-
tion of TCNEO with the sulfoxide was carried out in
Scheme 4.
Scheme 5.
Scheme 6.

J. Nakayama et al. / Tetrahedron Letters 46 (2005) 1395–1397
1397
Scheme 7.
Chem. Soc. 1965, 87, 3665; (d) Brown, P.; Cookson, R. C.
Proc. Chem. Soc. 1964, 185.
4. For cycloaddition chemistry of 1, see: Nakayama, J. J.
Synth. Org. Chem. Jpn. 2003, 61, 1106, and references
cited therein.
For the reduction, we propose a mechanism that in-
volves a zwitterion intermediate A, which produces sul-
fide and two molecules of COCN by a simultaneous
cleavage of the C–C and O–S bonds (Scheme 7).11 On
the other hand, a mechanism that involves a zwitterion
B as a common intermediate is proposed for the forma-
tion of ylide and sulfoxide, where we assume that B is in
equilibrium with sulfurane C. Thus, ylide and COCN
are produced by C–C bond cleavage of B, while sulfox-
ide and TCNE are given by a simultaneous C–O and C–
S bond cleavage of C (path a) or through C–C bond
cleavage of zwitterion D (path b). The zwitterions A
and B would be formed by electrophilic attack of
TCNEO on the sulfoxide oxygen and the sulfide sulfur,
respectively, and not by electrophilic attack of the ther-
mally-formed ylide 4, because both sulfides and sulfox-
ides react with TCNEO even at room temperature,
though slowly for sulfoxides, and seemingly TCNEO
equilibrates with 4 only when heated.3
5. Compound 3: mp 184 °C (dec); 1H NMR (200 MHz,
CDCl3): d 1.33 (s, 9H), 1.37 (s, 9H), 5.03 (d, J = 1.9 Hz,
1H), 5.93 (d, J = 1.9 Hz, 1H); 13C NMR (50 MHz,
CDCl3): d 31.4, 32.1, 34.5, 35.1, 64.5, 75.1, 102.0, 109.8,
112.8, 144.5, 147.2; IR (KBr) 2248, 1110, 1089 cmÀ1. Anal.
Calcd for C15H20N2O2S: C, 61.61; H, 6.89; N, 9.58.
Found: C, 61.48; H, 6.93; N, 9.53. Compound 6: mp 99–
101 °C; 1H NMR (400 MHz, CDCl3): d 3.24 (t, J = 2.3 Hz,
2H), 4.71 (t, J = 2.3 Hz, 2H), 6.99–7.04 (m, 4H), 7.12–7.20
(m, 6H); 13C NMR (100.6 MHz, CDCl3): d 39.1, 63.3,
67.3, 112.7, 127.0, 127.7, 128.0, 128.3, 128.4, 128.5, 128.8,
133.2, 135.6, 138.1; IR (KBr) 2248 (C„N) cmÀ1. HRMS
(EI, 70 eV) calcd for C19H14N2O: 286.1106. Found:
286.1106.
6. Progress of the reactions was monitored by 1H NMR and
1
the yields were determined by H NMR analysis.
7. The reaction was carried out in refluxing acetonitrile,
where the reduction of DMSO to dimethyl sulfide took
place in a practical rate.
References and notes
8. Note that COCN is produced by both reduction of DMSO
to dimethyl sulfide and ylide formation from the resulting
sulfide; theoretically, three molecules of COCN are
produced from two molecules of TCNEO.
9. Carbonyl cyanide is most conveniently prepared by
reaction of TCNEO with dibutyl sulfide; Martin, E. L.
Org. Synth. Coll. Vol. 1988, 6, 268, see also Ref. 2a.
10. The corresponding ylide might be seemingly formed, but
could not be isolated.
1. For a review on TCNEO, see: Ciganek, E.; Linn, W. J.;
Webster, O. W. In The Chemistry of Cyano Group;
Rappoport, Z., Ed.; Interscience: London, 1970; Chapter
9.
2. (a) Linn, W. J.; Webster, O. W.; Benson, R. E. J. Am.
Chem. Soc. 1965, 87, 3651; (b) Friedrich, K.; Rieser, J.
Liebigs Ann. Chem. 1976, 641.
3. (a) Linn, W. J.; Webster, O. W.; Benson, R. E. J. Am.
Chem. Soc. 1963, 85, 2032; (b) Linn, W. J.; Benson, R. E.
J. Am. Chem. Soc. 1965, 87, 3657; (c) Linn, W. J. J. Am.
11. Proposed intermediates such as A–D would be short-lived;
any intermediates could not be detected by H NMR.
1