Remote Pummerer Reaction via Intermolecular Through-Space Interaction between Sulfonium and Sulfenyl Sulfur Atoms

Article abstract of DOI:10.1021/jo982377h

The remote Pummerer reaction of the mono-sulfoxide of p-bis(methylthio)-aromatic 1 is described. The reaction of 1 with (CF₃CO)₂O in CH₂Cl₂ gave a mixture of the corresponding mono-Pummerer product 2, the bis-Pummerer product 3, and the bis-sulfide 4 in an n:1:1 ratio (n ≥ 2). The 1:1 formation of 3 and 4 indicates an intermolecular interaction between sulfur atoms. The reaction with the deuterium-labeled 1-d₃ showed that the formation of 2 occurs at the sulfenyl as well as sulfinyl groups in 1a-d₃-1d-d₃, in which the product ratio of 2-d₃:2-d₂ is in the range of 3.5-10. On the other hand, the Pummerer reaction of 1e-d₃ occurred preferably at the sulfinyl group in a usual manner. The reaction of a 1:1 mixture of the bis-sulfide 4 and the bis-sulfoxide 5 with (CF₃-CO)₂O also gave 2, 3, and 4 in a ratio similar to that for the reaction of 1. The mechanism in the present remote Pummerer reactions is discussed in light of an intermolecular through-space interaction between the sulfonium and sulfenyl sulfur atoms, and a dithia dication dimer B and/or a bis(dithia dication) cyclic dimer C are proposed as intermediates.

Full text of DOI:10.1021/jo982377h

3190
J . Org. Chem. 1999, 64, 3190-3195
Rem ote P u m m er er Rea ction via In ter m olecu la r Th r ou gh -Sp a ce
In ter a ction betw een Su lfon iu m a n d Su lfen yl Su lfu r Atom s
Kenji Kobayashi,* Emiko Koyama, Kazuhiko Namatame, Toyokazu Kitaura, Chihiro Kono,
Mariko Goto, Takanobu Obinata, and Naomichi Furukawa*
Department of Chemistry and Tsukuba Advanced Research Alliance Center, University of Tsukuba,
Tsukuba, Ibaraki 305-8571, J apan
Received December 3, 1998
The remote Pummerer reaction of the mono-sulfoxide of p-bis(methylthio)-aromatic 1 is described.
The reaction of 1 with (CF3CO)2O in CH2Cl2 gave a mixture of the corresponding mono-Pummerer
product 2, the bis-Pummerer product 3, and the bis-sulfide 4 in an n:1:1 ratio (n g 2). The 1:1
formation of 3 and 4 indicates an intermolecular interaction between sulfur atoms. The reaction
with the deuterium-labeled 1-d 3 showed that the formation of 2 occurs at the sulfenyl as well as
sulfinyl groups in 1a -d 3-1d -d 3, in which the product ratio of 2-d 3:2-d 2 is in the range of 3.5-10.
On the other hand, the Pummerer reaction of 1e-d 3 occurred preferably at the sulfinyl group in a
usual manner. The reaction of a 1:1 mixture of the bis-sulfide 4 and the bis-sulfoxide 5 with (CF3-
CO)2O also gave 2, 3, and 4 in a ratio similar to that for the reaction of 1. The mechanism in the
present remote Pummerer reactions is discussed in light of an intermolecular through-space
interaction between the sulfonium and sulfenyl sulfur atoms, and a dithia dication dimer B and/or
a bis(dithia dication) cyclic dimer C are proposed as intermediates.
Sch em e 1
In tr od u ction
Although the study of a σ-bonded dithia dication
formed by an intramolecular through-space interaction
between bifunctional sulfur atoms in close proximity has
attracted considerable attention in heteroatom chemis-
try,1 such a bond formation via an intermolecular inter-
action has not been explored extensively.2 Recently,
Nenajdenko and co-workers reported the preparation and
reactivity of a dithia dication which is generated from
the combination of dimethyl sulfoxide, triflic anhydride,
and dimethyl sulfide.3 Such a formation of dithia dication
by an intermolecular interaction would be worth pursu-
ing from the viewpoint of molecular assembly, as well as
organosulfur conducting materials.4
especially useful for the construction of cyclic aromatic
compounds and quinones.6 Kaji and co-workers reported
the reaction of aryl methyl sulfoxide with dimethyl
sulfide in the presence of (CF3CO)2O to form aryl methyl
sulfide and (trifluoroacetoxy)methyl methyl sulfide, in
which a dithia dication is proposed as an intermediate.7
Our attention has been focused on whether an inter-
molecular interaction of the sulfur atom of an acyl-
oxysulfonium salt with a sulfur functional group es-
sentially occurs in the course of Pummerer reaction7-9
and on whether an intermolecular or through-bond
interaction is more favorable. To this end, we have chosen
the monooxide of p-bis(methylthio)-aromatic 1 as a
model.10 The two sulfur atoms in 1, which are separated
For the past decades, Pummerer rearrangement reac-
tions have been widely studied in light of mechanistic
interests and synthetic applications (Scheme 1).5 Pum-
merer-type reactions via through-bond interactions are
(1) (a) Musker, W. K. Acc. Chem. Res. 1980, 13, 200-206. (b)
Furukawa, N. Bull. Chem. Soc. J pn. 1997, 70, 2571-2591 and
references therein.
(2) For dithio dications by dimerization of sulfide radical cations,
see: (a) Musker, W. K.; Wolford, T. L.; Roush, P. B. J . Am. Chem. Soc.,
1978, 100, 6416-6421. (b) Tamaoki, M.; Serita, M.; Shiratori, Y.; Itoh,
K. J . Phys. Chem., 1989, 93, 6052-6058.
(3) Nenajdenko, V. G.; Shevchenko, N. E.; Balenkova, E. S. Tetra-
hedron 1998, 54, 5353-5362.
(4) (a) Nakasuji, K.; Sasaki, M.; Kotani, T.; Murata, I.; Enoki, T.;
Imaeda, K.; Inokuchi, H.; Kawamoto, A.; Tanaka, J . J . Am. Chem. Soc.
1987, 109, 6970-6975. (b) Urayama, H.; Yamochi, H.; Saito, G.;
Nozawa, K.; Sugano, T.; Kinoshita, M.; Sato, S.; Oshima, K.; Kawa-
moto, A.; Tanaka, J . Chem. Lett. 1988, 55-58. (c) Heywang, G.; Roth,
S. Angew. Chem., Int. Ed. Engl. 1991, 30, 176-177. (d) Adam, D.;
Schuhmacher, P.; Simmerer, J .; Ha¨ussling, L.; Siemensmeyer, K.;
Etzbach, K. H.; Ringsdorf, H.; Haarer, D. Nature, 1994, 371, 141-
143.
(5) (a) Oae, S.; Numata, T.; Yoshimura, T. In The Chemistry of the
Sulphonium Group; Stirling, C. J . M., Ed.; J ohn Wiley: New York,
1981; pp 571-672. (b) Lucchi, O. D.; Miotti, U.; Modena, G. In Organic
Reactions; Paquette, L. A., Ed.; J ohn Wiley: New York, 1991; Chapter
3, pp 157-184. (c) Grierson, D. S.; Husson, H. P. In Comprehensive
Organic Synthesis; Trost, B. M., Ed.; Pergamon: Oxford, 1991; Vol. 6,
pp 909-947.
(6) (a) J ung, M. E.; Kim, C.; von dem Bussche, L. J . Org. Chem.
1994, 59, 3248-3249. (b) Kuethe, J . T.; Cochran, J . E.; Padwa, A. J .
Org. Chem. 1995, 60, 7082-7083. (c) Kita, Y.; Takeda, Y.; Matsugi,
M.; Iio, K.; Gotanda, K.; Murata, K.; Akai, S. Angew. Chem., Int. Ed.
Engl. 1997, 36, 1529-1531. (d) Akai, S.; Takeda, Y.; Iio, K.; Takahashi,
K.; Fukuda, N.; Kita, Y. J . Org. Chem. 1997, 62, 5526-5536.
(7) (a) Tanikaga, R.; Nakayama, K.; Tanaka, K.; Kaji, A. Chem. Lett.
1977, 395-396. (b) Drabowicz, J .; Oae, S. Chem. Lett. 1977, 767-768.
(8) For the reactions of sulfonium sulfur atoms with heteroatoms,
see: (a) Tidwell, T. T. Synthesis 1990, 857-870. (b) Reference 5a.
(9) For the reactions of sulfonium sulfur atoms with aromatic rings,
see: Yamamoto, K.; Shouji, E.; Nishide, H.; Tsuchida, E. J . Am. Chem.
Soc. 1993, 115, 5819-5820.
(10) For an intermolecular interaction between sulfur atoms in the
oxygen atom migration reaction of 1a mediated by CF3CO2H, see:
Kobayashi, K.; Obinata, T.; Furukawa, N. Chem. Lett. 1997, 1175-
1176.
10.1021/jo982377h CCC: $18.00 © 1999 American Chemical Society
Published on Web 04/10/1999

Remote Pummerer Reaction
Ch a r t 1
J . Org. Chem., Vol. 64, No. 9, 1999 3191
Ta ble 1. Rea ction of Mon ooxid e of
p-Bis(m eth ylth io)-Ar om a tic 1 w ith TF AAa
product ratio
run
substrate concn, mM
2:3:4
total yields, %
1
2
3
4
5
6
7
8
1a
1b
1b
1c
1c
1d
1d
1e
70
70
1
70
1
70
1
70
12.8:1.0:0.9
3.1:1.0:1.0
2.9:1.0:1.0
3.3:1.0:1.0
3.2:1.0:1.4
2.1:1.0:1.0
2.4:1.0:0.7
7.8:1.0:0.9
94
97
97
95
97
91
97
97
a
Carried out in a ratio of 1:TFAA ) 1:5 in CH2Cl2 at -20 °C to
room temperature for 10 h.
Sch em e 3
Sch em e 2
Ta ble 2. Rea ction of Deu ter iu m -La beled 1 w ith TF AAa
intramolecularly by aromatic spacers so as not to contact
each other, may allow an intermolecular through-space
or intramolecular through-bond interaction. We report
here the remote Pummerer reaction, where an intermo-
lecular interaction between the sulfur atom of acyl-
oxysulfonium salt of 1 and the sulfenyl sulfur atom of a
second molecule predominantly occurs to form a dithia
dication prior to the Pummerer reaction and consequently
leads to the Pummerer product at the sulfenyl moiety of
1.
product ratio
run
substrate
2-d 3:2-d 2:3-d 2:4-d 3
1
2
3
4
5
1a -d 3
1b-d 3
1c-d 3
1d -d 3
1e-d 3
3.5:1.0:-b:-b
5.0:0.5:1.0:0.8
3.6:0.7:1.0:1.0
2.3:0.5:1.0:0.8
2.0:4.3:1.0:1.0
a
Carried out in a ratio of 1-d 3:TFAA ) 1:5 in CH2Cl2 at -20
b
°C to room temperature for 10 h. Not available.
3 and 4. The formation of 3 and 4 could be attributed to
an intermolecular reaction. The ratio of 3 to 2 relatively
increases with increasing the spacer length. The product
ratio resulting from 1d with the methylene bridge is
similar to those obtained for 1b and 1c having π-conju-
gate spacers. In all cases, the ratio of 2, 3, and 4 is almost
independent of the concentration of 1 at least in the range
of 1-70 mM.
Deu ter iu m -La beled Exp er im en t. The Pummerer
reaction of trideuteriomethylsulfinyl-methylthio-aromatic
1-d 3 with TFAA was conducted (Scheme 3). The totally
isolated yields of the (trifluoroacetoxy)methylthio-trideu-
teriomethylthio-aromatic 2-d 3, the (trifluoroacetoxy)-
dideuteriomethylthio-methylthio-aromatic 2-d 2, the (tri-
fluoroacetoxy)dideuteriomethylthio-(trifluoroacetoxy)-
methylthio-aromatic 3-d 2, and the trideuteriomethylthio-
methylthio-aromatic 4-d 3 were almost the same as those
for unlabeled ones (ca. 90% yield). The product ratio of
2-d 3:2-d 2:3-d 2:4-d 3 is shown in Table 2.
Resu lts a n d Discu ssion
Rem ote P u m m er er Rea ction of Mon ooxid e of
p-Bis(m eth ylth io)-Ar om a tic 1. The monooxides of p-
bis(methylthio)-aromatics 1 (mono-sulfoxides) studied
here are 1-(methylsulfinyl)-4-(methylthio)benzene (1a ),
4-(methylsulfinyl)-4′-(methylthio)biphenyl (1b), [4-(meth-
ylsulfinyl)phenyl]-[4′-(methylthio)phenyl] sulfide (1c),
[4-(m et h ylsu lfin yl)ph en yl]-[4′-(m et h ylt h io)ph en yl]-
methane (1d ), and 1-(methylsulfinyl)-4-(methylthio)-
2,3,5,6-tetramethylbenzene (1e) (Chart 1).
When the mono-sulfoxide 1 was treated with 5 equiv
of (CF3CO)2O (TFAA) in CH2Cl2 at -20 °C to room
temperature for 10 h under an Ar atmosphere, a mixture
of the (trifluoroacetoxy)methylthio-methylthio-aromatic
2 (mono-Pummerer product), the bis[(trifluoroacetoxy)-
methylthio]-aromatic 3 (bis-Pummerer product), and the
bis-sulfide 4 was obtained exclusively as shown in
Scheme 2. The totally isolated yields were more than
90%. The product ratio of the reaction under the standard
conditions is summarized in Table 1.
It is noted that the ratio of the mono-Pummerer
products, 2-d 3:2-d 2, from 1a -d 3-1d -d 3 is significantly
large and in the range of 3.5-10. In general, the
Pummerer reaction should proceed at the methylsulfinyl
group, but not at the methylsulfenyl group. In the present
In all cases, the ratio of the bis-Pummerer product 3
to the bis-sulfide 4 is constantly 1:1, although the yield
of the mono-Pummerer product 2 is higher than those of

3192 J . Org. Chem., Vol. 64, No. 9, 1999
Kobayashi et al.
Sch em e 4
Sch em e 5
Ta ble 4. Rea ction of a 1:1 Mixtu r e of Bis-Su lfid e 4 a n d
Bis-Su lfoxid e 5 w ith TF AAa
product ratio
Ta ble 3. Qu ick Qu en ch of th e Rea ction Mixtu r e of
Deu ter iu m -La beled 1 a n d TF AA w ith Aqu eou s Na HCO3
a
run
substrates
2:3:4
total yields, %
1
2
3
4
4a + 5a
4b + 5b
4c + 5c
4d + 5d
13.2:1.0:0.9
2.5:1.0:1.0
3.2:1.0:1.1
2.3:1.0:1.1
97
95
91
88
product ratio
run
substrate
temp, °C
time, s
1-d 3:1′-d 3:4-d 3:5-d 3
1
2
3
4
1a -d 3
1b-d 3
1c-d 3
1d -d 3
-15
-25
-15
-15
5
900
5
1.0:1.0:0.2:0.2
1.0:1.1:0.8:0.2
1.0:1.0:0.5:0.3
1.0:0.9:0.7:0.3
a
Carried out in a ratio of 4:5:TFAA ) 1:1:10 in CH2Cl2 at -20
°C to room temperature for 10 h.
10
a
Carried out in a ratio of 1-d 3:TFAA ) 1:5 in CH2Cl2.
Sch em e 6
reaction, this is not the case. The above results unam-
biguously indicate that the formation of 2 occurs at both
groups in 1 which are located at the remote position by
the intervention of spacers. In marked contrast, the
product ratio of 2e-d 3:2e-d 2 from 1e-d 3 as a sterically
hindered analogue of 1a was 0.47. This result indicates
that a normal Pummerer reaction at the sulfinyl group
dominates in 1e.
Qu en ch a t th e In itia l Sta ge of th e Rea ction . We
turned our attention to the initial stage of the present
Pummerer reaction. When the reaction of the deuterium-
labeled mono-sulfoxide 1-d 3 with TFAA in CH2Cl2 at
-15 °C was quickly quenched with aqueous NaHCO3 in
5-900 s, a mixture of 1-d 3, the methylsulfinyl-trideute-
riomethylthio-aromatic 1′-d 3, 4-d 3, and the trideuteri-
omethylsulfinyl-methylsulfinyl-aromatic 5-d 3 was ob-
tained exclusively instead of Pummerer products as
shown in Scheme 4. The product ratio of 1-d 3:1′-d 3:4-d 3:
5-d 3 is listed in Table 3.
It is noteworthy that the product ratios for the reac-
tions of 4a -d with 5a -d are 2a -d :3a -d :4a -d ) n:1:1
(n g 2) and are similar to those for the reactions of the
mono-sulfoxides 1a -d , respectively. The product ratios
were also approximately independent of the concentra-
tion of the substrates. These results strongly suggest that
the reactions shown in both Schemes 2 and 5 proceed
via the same intermediate.
Rea ction of Dia r yl Su lfoxid e w ith Bis-Su lfid e. The
reactions of 4a with 1 and 2 equiv of bis(p-tolyl) sulfoxide
6 in the presence of 5 equiv of TFAA quantitatively gave
the mono-Pummerer product 2a and the bis-Pummerer
product 3a , respectively, together with the bis(p-tolyl)
sulfide 7 (Scheme 6). This result shows an intermolecular
interaction of the sulfonium intermediate formed by 6
and TFAA with the methylsulfenyl group of 4a , leading
to the Pummerer product.7a Furthermore, this indicates
that when 1 equiv of 6 was used, the mono-Pummerer
product 2a formed at the initial stage does not react with
the sulfonium intermediate during the course of the
reaction.
In tr a m olecu la r Th r ou gh -Bon d vs In ter m olecu la r
Th r ou gh -Sp a ce In ter a ction s betw een Su lfon iu m
a n d Su lfen yl Su lfu r Atom s. The reaction of the mono-
sulfoxide 1 with TFAA affords the bis-Pummerer product
3 and the bis-sulfide 4 in a 1:1 ratio, as well as the mono-
Pummerer product 2 (Scheme 2), and the reaction of a
1:1 mixture of 4 and the bis-sulfoxide 5 with TFAA
produces 2 in addition to 3 and 4 (Scheme 5). These
results clearly indicate the mechanism including an
In all cases, the ratio of 1-d 3:1′-d 3 is approximately
1:1.10 The total yields of 1-d 3 and 1′-d 3 are higher than
those of 4-d 3 and 5-d 3. The facts of a 1:1 formation of
1-d 3 and 1′-d 3, as well as no formation of the Pummerer
products, show that at the initial stage of the reaction
an intermolecular or intramolecular interaction of the
sulfonium with the sulfenyl sulfur atoms is much more
favorable than the abstraction of an R-proton of the
sulfonium group leading to the Pummerer products.
Rem ote P u m m er er Rea ction of Bis-Su lfid e 4 w ith
Bis-Su lfoxid e 5. In the presence of TFAA (5 equiv), the
bis-sulfide 4 itself completely remained unchanged,
whereas the bis-sulfoxide 5 afforded only the bis-Pum-
merer product 3 quantitatively. On the other hand, as
shown in Scheme 5, the reaction of a 1:1 mixture of 4
and 5 with 5 equiv of TFAA exclusively gave a mixture
of the mono-Pummerer products 2, 3, and 4 (total yields
are more than 88%). The product ratio obtained here is
summarized in Table 4.

Remote Pummerer Reaction
J . Org. Chem., Vol. 64, No. 9, 1999 3193
Sch em e 7
intermolecular through-space interaction between the
sulfonium and the sulfenyl sulfur atoms. The favorable
formation of 2-d 3 more than 2-d 2 in the reaction of the
deuterium-labeled 1-d 3 also indicates an intramolecular
through-bond and/or intermolecular interactions between
sulfur atoms (Scheme 3). Furthermore, the quenching
experiment at the initial stage of the reaction shows that
intramolecular and/or intermolecular interactions of the
sulfonium with the sulfenyl sulfur atoms are much more
favorable than the abstraction of an R-proton of the
sulfonium group leading to the Pummerer products
(Scheme 4).
On the basis of these observations, the following three
types of intermediates are envisaged in the present
reactions as shown in Scheme 7: a dithiaquinodimethane-
like dication (A), a dithia dication dimer (or oligomer)
(B),3,7a and a bis(dithia dication) cyclic dimer (C).10 At
this stage, these intermediates have not been detected
even at -40 °C. The mono-sulfoxide 1 and the bis-
sulfoxide 5 react with TFAA to form the trifluoroacetoxy-
sulfonium salt D and bis-sulfonium salt E, respectively.11
An intramolecular through-bond interaction between the
sulfonium and the sulfenyl sulfur atoms in D would
afford intermediate A. The abstraction of an R-proton of
A by trifluoroacetate followed by the addition of trifluo-
roacetate to the resulting methylenesulfonium salt would
give only the mono-Pummerer product 2. On the other
hand, the nucleophilic attack by the sulfenyl sulfur atom
of one D on the sulfonium sulfur atom of the other D
and by those of 4 on those of E via an intermolecular
through-space interaction would produce intermediates
B and/or C, respectively. The abstraction of an R-proton
of B and/or C by trifluoroacetate from side a would give
two molecules of 2, whereas the proton abstraction from
side b would afford the bis-Pummerer product 3 and the
bis-sulfide 4 in the 1:1 ratio.
Coexistence of two reaction pathways, where the mono-
Pummerer product 2 results from the intermediate A and
the bis-Pummerer product 3 and the bis-sulfide 4 arise
from the intermediates B and/or C, is not plausible,
because the ratio of 2 to 3 in the present Pummerer
reaction is independent of the concentration of 1 as shown
in Table 1. Otherwise this ratio would increase with a
decrease in the concentration of 1 when the intermediate
A is dominant in the reaction. It is also decisive that the
product ratio of 2, 3, and 4 for the reaction of 1 with
TFAA is similar to that for the reaction of a 1:1 mixture
of 4 and 5 and that the 1:1 formation of 3 and 4 is
invariable in all cases presented here (Tables 1 and 4).
The most plausible mechanism which could fit all the
results described above should involve the intermediates
B and/or C, but not A.12
Further evidence for the proposed mechanism comes
from the following two types of experiments. First, the
reaction of 1d -d 3, in which an intramolecular through-
bond interaction is not available due to the insulation of
π-conjugation by the methylene bridge, gave the ratio of
2d -d 3:2d -d 2 ) 4.6 in the mono-Pummerer products,
which is in the range of those from 1a -d 3-1c-d 3 having
π-conjugate spacer (runs 4 vs 1, 2, and 3 in Table 2).
Second, the reaction of 1e-d 3 as a sterically hindered
analogue of 1a gave the ratio of 2e-d 3:2e-d 2 ) 0.47, which
is in marked contrast to that obtained from 1a -d 3 (runs
5 vs 1 in Table 2). This result shows that a normal
Pummerer reaction at the sulfinyl group dominates in
1e probably due to disadvantage of an intermolecular
through-space interaction between sulfur atoms by a
steric hindrance of the methyl groups at the 2,6-positions
of the aromatic ring. This result also indicates that an
intramolecular through-bond interaction between sulfur
atoms is essentially unfavorable.
Con clu sion
(11) The trifluoroacetoxysulfonium salt D and the bis-sulfonium salt
E were detected at -40 °C by the 1H NMR spectra of the reaction
mixture of 1 or 4 and 5 with TFAA in CDCl3. The signals of the mono-
sulfoxide 1 and the bis-sulfoxide 5 in the 1H NMR instantaneously
We have demonstrated that the remote Pummerer-
type reaction proceeds via an intermolecular through-
disappeared when added TFAA to them, and those of D and
E
(12) An another intermediate from a reaction of the sulfonium salt
D with 1 might be formed. However, this is not the case, because at
the initial stage of the present reaction 1 was completely consumed
by TFAA and D was instantaneously produced.11
appeared, respectively. The chemical shifts of methylsulfonium groups
of D and E are shifted downfield by ca. 0.3 ppm relative to those of
methylsulfinyl groups of 1 and 5, respectively.

3194 J . Org. Chem., Vol. 64, No. 9, 1999
Kobayashi et al.
for 12 h. The reaction mixture was washed with saturated
aqueous NaHCO3 and brine and dried over MgSO4. After
evaporation of solvent, the residue was subjected to column
chromatography on silica gel to give 1 and 5.
1-(Meth ylsu lfin yl)-4-(m eth ylth io)ben zen e (1a ): yield
79%; mp 101-102 °C; 1H NMR (CDCl3) δ 2.52 (s, 3H), 2.71 (s,
3H), 7.36, 7.56 (ABq, J ) 8.6 Hz, 4H); 13C NMR (CDCl3) δ 15.2,
44.0, 124.0, 126.3, 141.6, 143.1; MS m/z 186 (M+).
1,4-Bis(m eth ylsu lfin yl)ben zen e (5a ): yield 10%; mp 129-
130 °C; 1H NMR (CDCl3) δ 2.78 (s, 6H), 7.82 (s, 4H); 13C NMR
(CDCl3) δ 44.0, 124.5, 149.2; MS m/z 202 (M+).
4-(Meth ylsu lfin yl)-4′-(m eth ylth io)bip h en yl (1b): yield
56%; mp 170-171 °C; 1H NMR (CDCl3) δ 2.54 (s, 3H), 2.77 (s,
3H), 7.35, 7.54 (ABq, J ) 8.4 Hz, 4H), 7.71 (s, 4H); 13C NMR
(CDCl3) δ 15.6, 44.0, 124.1, 126.8, 127.5, 127.7, 136.3, 138.9,
143.4, 144.3; MS m/z 262 (M+).
space interaction between the sulfonium and the sulfenyl
sulfur atoms which is much more favorable than an
intramolecular through-bond interaction and the abstrac-
tion of an R-proton of the sulfonium group leading to the
Pummerer product. The results presented here may
provide for the understanding of the electric conductivity
mechanisms of materials bearing sulfur functional-
ities.4,13,14
Exp er im en ta l Section
Gen er a l. 1H NMR spectra were recorded at 270 or 400
MHz, and 13C NMR spectra were taken at 67.5 or 100 MHz.
High-resolution mass spectra (HRMS) were recorded at 70 eV
by electron impact. Preparative HPLC was performed on a
J apan Analytical Industry Co., Ltd., model LC-908. Dichlo-
romethane and THF were distilled from CaH2 and sodium-
benzophenone ketyl, respectively, under N2. Trifluoroacetic
anhydride (TFAA) was purchased from Wako Pure Chemical
Industries, Ltd. and used without further purification.
P r ep a r a tion of Bis-Su lfid e 4. To a solution of the p-
dibromo- or p-diiodo-aromatic (10.0 mmol) in dry THF (50 mL)
at -78 °C under an Ar atmosphere was added a solution of
n-BuLi in hexane (1.6 M, 13.8 mL, 22.0 mmol). After stirring
for 10 min, dimethyl disulfide (2.0 mL, 22.0 mmol) was added
at -78 °C. The resulting mixture was allowed to warm to room
temperature overnight, pored into water, and extracted with
CH2Cl2. The organic layer was washed with brine and dried
over MgSO4. After evaporation of solvents, the residue was
subjected to column chromatography on silica gel to give 4.
1,4-Bis(m eth ylth io)ben zen e (4a ):15a yield 72%; mp 78-
4,4′-Bis(m eth ylsu lfin yl)bip h en yl (5b): yield 20%; mp
132-133 °C; 1H NMR (CDCl3) δ 2.79 (s, 6H), 7.76 (s, 8H); 13
C
NMR (CDCl3) δ 44.0, 124.2, 128.2, 142.6, 145.5; MS m/z 278
(M+).
[4-(Meth ylsu lfin yl)ph en yl]-[4′-(m eth ylth io)ph en yl] su l-
1
fid e (1c): yield 63%; mp 66-67 °C; H NMR (CDCl3) δ 2.51
(s, 3H), 2.71 (s, 3H), 7.25, 7.40 (ABq, J ) 8.4 Hz, 4H), 7.29,
7.51 (ABq, J ) 8.4 Hz, 4H); 13C NMR (CDCl3) δ 15.3, 43.8,
124.2, 126.9, 127.9, 128.4, 134.2, 140.2, 142.5, 142.8; MS m/z
294 (M+).
Bis[4-(m eth ylsu lfin yl)p h en yl] su lfid e (5c): yield 21%;
mp 92-93 °C; 1H NMR (CDCl3) δ 2.75 (s, 6H), 7.49, 7.61 (ABq,
J ) 8.4 Hz, 8H); 13C NMR (CDCl3) δ 43.9, 124.5, 131.6, 138.7,
145.0; MS m/z 310 (M+).
[4-(Met h ylsu lfin yl)p h en yl]-[4′-(m et h ylt h io)p h en yl]-
1
m eth a n e (1d ): yield 46%; mp 41-42 °C; H NMR (CDCl3) δ
2.47 (s, 3H), 2.71 (s, 3H), 3.99 (s, 2H), 7.10, 7.33 (ABq, J ) 8.2
Hz, 4H), 7.21, 7.56 (ABq, J ) 8.3 Hz, 4H); 13C NMR (CDCl3) δ
15.8, 41.0, 43.8, 123.7, 126.8, 129.3, 129.7, 136.2, 136.8, 143.1,
144.4; MS m/z 276 (M+).
1
79 °C; H NMR (CDCl3) δ 2.46 (s, 6H), 7.02 (s, 4H); 13C NMR
(CDCl3) δ 16.4, 127.6, 135.1; MS m/z 170 (M+).
4,4′-Bis(m eth ylth io)bip h en yl (4b):15a yield 91%; mp 185-
1
186 °C; H NMR (CDCl3) δ 2.52 (s, 6H), 7.31, 7.49 (ABq, J )
Bis[4-(m eth ylsu lfin yl)p h en yl]m eth a n e (5d ): yield 23%;
oil; 1H NMR (CDCl3) δ 2.72 (s, 6H), 4.10 (s, 2H), 7.35, 7.60
(ABq, J ) 8.2 Hz, 8H); 13C NMR (CDCl3) δ 41.4, 43.9, 123.9,
129.9, 143.4, 143.7; MS m/z 292 (M+).
1-(Meth ylsu lfin yl)-4-(m eth ylth io)-2,3,5,6-tetr a m eth yl-
ben zen e (1e): yield 72%; mp 181-182 °C; 1H NMR (CDCl3) δ
2.20 (s, 3H), 2.56 (s, 6H), 2.58 (s, 6H), 2.89 (s, 3H); 13C NMR
(CDCl3) δ 15.9, 18.7, 18.8, 38.5, 133.9, 134.3, 140.0, 140.4; MS
m/z 242 (M+).
8.4 Hz, 8H); 13C NMR (CDCl3) δ 15.9, 127.0, 127.1, 137.3,
137.5; MS m/z 246 (M+).
Bis[4-(m eth ylth io)p h en yl] su lfid e (4c):16 yield 42%; mp
1
86-87 °C; H NMR (CDCl3) δ 2.47 (s, 6H), 7.18, 7.24 (ABq, J
) 8.5 Hz, 8H); 13C NMR (CDCl3) δ 15.8, 127.1, 131.4, 132.1,
137.7; MS m/z 278 (M+).
Bis[4-(m et h ylt h io)p h en yl]m et h a n e (4d ):15b yield 82%;
1
mp 55-56 °C; H NMR (CDCl3) δ 2.46 (s, 6H), 3.89 (s, 2H),
7.09, 7.19 (ABq, J ) 8.1 Hz, 8H); 13C NMR (CDCl3) δ 16.1,
P r ep a r a tion of 1-d 3. To a solution of 1 (1.0 mmol) in dry
THF (10 mL) at room temperature under an Ar atmosphere
was added a solution of sodium (90 mg, 3.9 mmol) in metha-
nol-d (2.0 mL, 49 mmol). The resulting mixture was stirred
at room temperature for 24 h, quenched with 1 M HCl, and
extracted with CH2Cl2. The organic layer was washed with
brine and dried over MgSO4. After evaporation of solvents, the
residue was subjected to column chromatography on silica gel
to give 1-d 3. In all cases, the deuterium contents were more
than 95%.
Rea ction of Mon ooxid e of p-Bis(m eth ylth io)-Ar om a tic
1 w ith TF AA. Typ ica l P r oced u r e (Sch em e 2, Ta ble 1,
Ru n 2). To a solution of 1b (100 mg, 0.38 mmol) in dry CH2-
Cl2 (6 mL) at -20 °C under an Ar atmosphere was added TFAA
(270 µL, 1.91 mmol). The mixture was allowed to warm to room
temperature for 10 h, and saturated aqueous NaHCO3 was
added to quench the reaction. The aqueous layer was quickly
extracted with CH2Cl2. The organic layer was washed with
brine and dried over MgSO4. After evaporation of solvent, an
analytically pure mixture of 2b, 3b, and 4b was obtained (134
mg), and the ratio was determined to be 2b:3b:4b ) 3.1:1.0:
1.0 by the integration of the 1H NMR spectrum. The separation
of the mixture was performed with preparative HPLC eluted
with CHCl3.
40.8, 127.0, 129.4, 135.8, 138.0; MS m/z 260 (M+).
1,4-Bis(m et h ylt h io)-2,3,5,6-t et r a m et h ylb en zen e (4e):
1
yield 54%; mp 157-158 °C; H NMR (CDCl3) δ 2.12 (s, 6H),
2.52 (s, 12H); 13C NMR (CDCl3) δ 18.9, 19.8, 136.5, 138.8; MS
m/z 226 (M+).
P r ep a r a tion of Mon ooxid e of p-Bis(m eth ylth io)-Ar o-
m a tic 1 a n d Bis-Su lfoxid e 5. To a solution of 4 (4.0 mmol)
in CH2Cl2 (400 mL) at -20 °C was added dropwise a solution
of m-CPBA (707 mg, 4.1 mmol) in CH2Cl2 (400 mL) over a
period of 10 h. The resulting mixture was stirred at -20 °C
(13) The conductivity of oligothiophenes results from a π-dimer of
the radical cation, as well as a π-conjugation of polarons/bipolarons.
(a) Hill, M. G.; Penneau, J .-F.; Zinger, B.; Mann, K. R.; Miller, L. L.
Chem. Mater. 1992, 4, 1106-1113. (b) Zinger, B.; Mann, K. R.; Hill,
M. G.; Miller, L. L. Chem. Mater. 1992, 4, 1113-1118. (c) Miller, L.
L.; Mann, K. R. Acc. Chem. Res. 1996, 29, 417-423. (d) Graf, D. D.;
Duan, R. G.; Campbell, J . P.; Miller, L. L.; Mann, K. R. J . Am. Chem.
Soc. 1997, 119, 5888-5899.
(14) The 1,2,4,6-chalcogenatriazinyl radicals and the diradical benzo-
1,2:4,5-bis(1,3,2-dithiazolyl) form dimers having chalcogen-chalcogen
bonds, respectively. (a) Oakley, R. T.; Reed, R. W.; Cordes, A. W.; Craig,
S. L.; Graham, J . B. J . Am. Chem. Soc. 1987, 109, 7745-7749. (b)
Barclay, T. M.; Cordes, A. W.; de Laat, R. H.; Goddard, J . D.; Haddon,
R. C.; J eter, D. Y.; Mawhinney, R. C.; Oakley, R. T.; Palstra, T. T. M.;
Patenaude, G. W.; Reed, R. W.; Westwood, N. P. C. J . Am. Chem. Soc.
1997, 119, 2633-2641.
1-[(Tr iflu or oa cet oxy)m et h ylt h io]-4-(m et h ylt h io)b en -
1
zen e (2a ): oil; H NMR (CDCl3) δ 2.48 (s, 3H), 5.55 (s, 2H),
(15) (a) Engman, L.; Hellberg, J . S. E. J . Organomet. Chem. 1985,
296, 357-366. (b) Streitwieser, A., J r.; Vorpagel, E. R.; Chen, C.-C. J .
Am. Chem. Soc. 1985, 107, 6970-6975.
(16) Tsuchida, E.; Yamamoto, K.; Nishide, H.; Yoshida, S.; J ikei,
M. Macromolecules 1990, 23, 2101-2106.
7.20, 7.40 (ABq, J ) 7.8 Hz, 4H); 13C NMR (CDCl3) δ 15.3,
73.1, 114.2 (1J CF ) 283.9 Hz), 126.7, 128.3, 132.8, 140.3, 156.8
(2J CF ) 42.9 Hz); MS m/z 282 (M+); HRMS calcd for C10H9F3O2S2
281.9996, found 282.0025.

Remote Pummerer Reaction
J . Org. Chem., Vol. 64, No. 9, 1999 3195
1,4-Bis[(tr iflu or oa cetoxy)m eth ylth io]ben zen e (3a ): oil;
1H NMR (CDCl3) δ 5.62 (s, 4H), 7.46 (s, 4H); 13C NMR (CDCl3)
(2J CF ) 42.7 Hz); MS m/z 484 (M+); HRMS calcd for C19H14F6-
O4S2 484.0238, found 484.0247.
δ 72.0, 114.2 (1J CF ) 284.1 Hz), 132.1, 133.5, 156.8 (2J CF
)
1-[(Tr iflu or oacetoxy)m eth ylth io]-4-(m eth ylth io)-2,3,5,6-
42.7 Hz); MS m/z 394 (M+); HRMS calcd for C12H8F6O4S2
393.9768, found 393.9743.
1
tetr a m eth ylben zen e (2e): mp 57-58 °C; H NMR (CDCl3)
δ 2.20 (s, 3H), 2.54 (s, 6H), 2.60 (s, 6H), 5.42 (s, 2H); 13C NMR
(CDCl3) δ 18.9, 19.8, 20.2, 73.8, 114.3 (1J CF ) 283.8 Hz), 131.5,
138.6, 139.3, 139.4, 156.9 (2J CF ) 42.5 Hz); MS m/z 338 (M+);
HRMS calcd for C14H17F3O2S2 338.0622, found 338.0614.
4-[(Tr iflu or oacetoxy)m eth ylth io]-4′-(m eth ylth io)biph en -
yl (2b): mp 107-108 °C; 1H NMR (CDCl3) δ 2.53 (s, 3H), 5.64
(s, 2H), 7.32, 7.50 (ABq, J ) 8.4 Hz, 4H), 7.55 (d, J ) 2.6 Hz,
4H); 13C NMR (CDCl3) δ 15.6, 72.7, 114.3 (1J CF ) 283.9 Hz),
126.7, 127.2, 127.6, 131.4, 132.2, 136.5, 138.4, 140.9, 156.8
(2J CF ) 43.0 Hz); MS m/z 358 (M+); HRMS calcd for C16H13F3-
O2S2 358.0309, found 358.0319.
1,4-Bis[(tr iflu or oacetoxy)m eth ylth io]-2,3,5,6-tetr am eth -
1
ylben zen e (3e): mp 110-111 °C; H NMR (CDCl3) δ 2.56 (s,
12H), 5.43 (s, 4H); 13C NMR (CDCl3) δ 20.3, 73.5, 114.3 (1J CF
) 283.5 Hz), 133.4, 140.0, 156.9 (2J CF ) 41.9 Hz); MS m/z 450
(M+); HRMS calcd for C16H16F6O4S2 450.0394, found 450.0416.
4,4′-Bis[(tr iflu or oacetoxy)m eth ylth io]biph en yl (3b): oil;
1H NMR (CDCl3) δ 5.65 (s, 4H), 7.57 (s, 8H); 13C NMR (CDCl3)
δ 72.5, 114.3 (1J CF ) 283.9 Hz), 127.9, 132.2, 132.4, 140.2, 156.9
(2J CF ) 43.0 Hz); MS m/z 470 (M+); HRMS calcd for
Rea ction of a 1:1 Mixtu r e of Bis-Su lfid e 4 a n d Bis-
Su lfoxid e 5 w ith TF AA. Typ ica l P r oced u r e (Sch em e 5,
Ta ble 4, Ru n 4). To a solution of 4d (110 mg, 0.42 mmol)
and 5d (123 mg, 0.42 mmol) in dry CH2Cl2 (10 mL) at -20 °C
under an Ar atmosphere was added TFAA (600 µL, 4.23 mmol).
The mixture was allowed to warm to room temperature for
10 h, and saturated aqueous NaHCO3 was added to quench
the reaction. The aqueous layer was quickly extracted with
CH2Cl2. The organic layer was washed with brine and dried
over MgSO4. After evaporation of solvent, an analytically pure
mixture of 2d , 3d , and 4d was obtained (272 mg), and the ratio
was determined to be 2d :3d :4d ) 2.3:1.0:1.1 by the integration
C
18H12F6O4S2 470.0081, found 470.0106.
{4-[(Tr iflu or oa cet oxy)m et h ylt h io]p h en yl}-[4′-(m et h -
ylth io)p h en yl] su lfid e (2c): mp 84-85 °C; 1H NMR (CDCl3)
δ 2.50 (s, 3H), 5.57 (s, 2H), 7.17, 7.36 (ABq, J ) 8.2 Hz, 4H),
7.23, 7.36 (ABq, J ) 8.2 Hz, 4H); 13C NMR (CDCl3) δ 15.3,
72.7, 114.2 (1J CF ) 283.6 Hz), 126.9, 129.0, 129.3, 130.1, 132.5,
133.6, 138.9, 139.5, 156.7 (2J CF ) 42.9 Hz); MS m/z 390 (M+);
HRMS calcd for C16H13F3O2S3 390.0030, found 390.0035.
Bis{4-[(t r iflu or oa cet oxy)m et h ylt h io]p h en yl} su lfid e
(3c): oil; 1H NMR (CDCl3) δ 5.61 (s, 4H), 7.31, 7.42 (ABq, J )
7.9 Hz, 8H); 13C NMR (CDCl3) δ 72.3, 114.2 (1J CF ) 283.5 Hz),
131.7, 131.9, 132.0, 132.4, 156.8 (2J CF ) 43.0 Hz); MS m/z 502
(M+); HRMS calcd for C18H12F6O4S3 501.9802, found 501.9813.
{4-[(Tr iflu or oa cet oxy)m et h ylt h io]p h en yl}-[4′-(m et h -
ylth io)p h en yl]m eth a n e (2d ): oil; 1H NMR (CDCl3) δ 2.45
(s, 3H), 3.93 (s, 2H), 5.56 (s, 2H), 7.09, 7.19 (ABq, J ) 8.2 Hz,
4H), 7.16, 7.40 (ABq, J ) 8.1 Hz, 4H); 13C NMR (CDCl3) δ 16.0,
40.9, 73.0, 114.2 (1J CF ) 284.1 Hz), 127.0, 129.4, 129.9, 130.1,
132.3, 136.1, 137.2, 141.9, 156.9 (2J CF ) 42.9 Hz); MS m/z 372
(M+); HRMS calcd for C17H15F3O2S2 372.0466, found 372.0479.
B i s {4 -[(t r i fl u o r o a c e t o x y )m e t h y l t h i o ]p h e n y l }-
1
of the H NMR spectrum. The separation of the mixture was
performed with preparative HPLC eluted with CHCl3.
Ack n ow led gm en t. This work was supported in part
by grants-in-aid from the Ministry of Education, Sci-
ence, Sports and Culture, J apan (No. 09239103) and
University of Tsukuba (TARA project fund).
1
Su p p or tin g In for m a tion Ava ila ble: Copies of H NMR
spectra for compounds 1a -1e, 2a -2e, 3a -3e, 4a -4e, and
5a -5d . This material is available free of charge via the
Internet at http://pubs.acs.org.
1
m eth a n e (3d ): oil; H NMR (CDCl3) δ 3.98 (s, 2H), 5.58 (s,
4H), 7.17, 7.42 (ABq, J ) 8.2 Hz, 8H); 13C NMR (CDCl3) δ 41.0,
72.9, 114.3 (1J CF ) 283.7 Hz), 129.9, 130.4, 132.3, 141.2, 156.8
J O982377H