Reactions of benzeneselenyl and benzenesulfenyl chlorides with syn-and anti-9-9′-bibenzonorbornenylidenes

Article abstract of DOI:10.1002/hc.1094

Reaction of syn-9,9′-bibenzonorbornenylidene (1a) with benzeneselenyl chloride produced vic-dichloride (4) exclusively, which corresponds to the cis-addition product of 1a with molecular chlorine, with retention of the original alkene configuration. Moreo

Full text of DOI:10.1002/hc.1094

Heteroatom Chemistry
Volume 12, Number 7, 2001
R
eactions of Benzeneselenyl and
Benzenesulfenyl Chlorides with syn-
0
and anti-9,9 -Bibenzonorbornenylidenes
Koichi Noda, Yoshiaki Sugihara, and Juzo Nakayama
Department of Chemistry, Faculty of Science, Saitama University,
Saitama, Saitama 338-8570, Japan
Received 24 April 2001; revised 29 May 2001
reactions at the double bond but also a study of
the neighboring group participation by the benzene
rings. Thus, the sulfuration of 1a by elemental sulfur
0
ABSTRACT: Reaction of syn-9,9 -bibenzonorbor-
nenylidene (1a) with benzeneselenyl chloride produced
vic-dichloride (4) exclusively, which corresponds
to the cis-addition product of 1a with molecu-
lar chlorine, with retention of the original alkene
resulted in the exclusive formation of episulfides
0
2
a and 2a with retention of the original stereo-
chemistry of 1a [2] (Scheme 1). The sulfuration
of 1b also gave the episulfide 2b exclusively with
retention of the stereochemistry. Trithiolane and
pentathiepane derivatives, which often form in the
sulfuration of cyclic alkenes, were not formed. On
the other hand, molecular bromine underwent an
exclusive cis-addition to 1a to give vic-dibromide
0
configuration. Moreover, the reaction of anti-9,9 -
bibenzonorbornenylidene (1b) with benzeneselenyl
chloride gave the same vic-dichloride (4) exclusively
with inversion of the original alkene configuration. No
expected benzeneselenyl chloride adducts were formed
in both cases. On the other hand, reactions of 1a
and 1b with benzenesulfenyl chloride only resulted in
the syn–anti isomerization of the alkenes without any
adduct formation. Mechanisms of these reactions are
discussed in some detail. �C 2001 John Wiley & Sons, Inc.
(
3) with retention of the original stereochemistry,
while it underwent an exclusive trans-addition to
b to give the same bromide 3 with inversion of
1
the original stereochemisrty [3] (Scheme 1). These
results prompted us to investigate the reactions of
Heteroatom Chem 12:625–629, 2001
1a and 1b with benzeneselenyl chloride and ben-
zenesulfenyl chloride, which are known to undergo
generally stereospecific trans-additions to alkenes
INTRODUCTION
[4].
0
0
Quite recently, we have synthesized syn-9,9 -
bibenzonorbornenylidene (1a) and anti-9,9 -
bibenzonorbornenylidene (1b) [1]. The use of a
pair of these alkenes as the substrate enabled us to
carry out not only a stereochemical study of many
RESULTS AND DISCUSSION
Reactions of 1a and 1b with Benzeneselenyl
Chloride
The reaction of the syn-alkene 1a with an equimo-
Correspondence to: Juzo Nakayama; e-mail: nakaj@post.
saitama-u. ac.jp.
Contract Grant Sponsor: Ministry of Education, Science, Sports
and Culture, Japan.
�
lar amount of benzeneselenyl chloride at � 78 C
in CDCl
3
did not form the expected benzenese-
lenyl chloride adduct even in a trace amount, but
furnished a 50% yield of the vic-dichloride (4), which
Contract Grant Sponsor: Sumitomo Foundation to Y.S.
�
c 2001 John Wiley & Sons, Inc.
625

626 Noda, Sugihara, and Nakayama
SCHEME 1
corresponds to the cis-addition product of 1a with
molecular chlorine (Table 1, run 1) (Scheme 2). The
syn-alkene 1a was recovered in 50% yield, without
any isomerization to the anti-alkene 1b. In addition,
diphenyl diselenide was formed quantitatively. The
formation of 4 by addition of molecular chlorine
to 1a was previously reported and its structure was
determined unambiguously [3]. The reaction of the
anti-alkene 1b with benzeneselenyl chloride under
the same conditions also furnished the same chlorine
adduct 4 in 50% yield (Table 1, run 3) with quanti-
tative formation of diphenyl diselenide (Scheme 2).
The syn-alkene 1b was recovered in 50% yield with-
out any isomerization to 1a. The same products were
also obtained in similar yields by reactions carried
out at room temperature (Table 1, runs 2,4). The use
of two equimolar amounts of benzeneselenyl chlo-
ride furnished the adduct 4 quantitatively (Table 1,
runs 5,6). Thus, the net results of the reaction of
1a with benzeneselenyl chloride involve an exclu-
sive cis-addition of molecular chlorine to 1a with
retention of the configuration, the addition thereby
taking place at the more sterically crowded ethylene
chain side; the X-ray crystallographic analysis of 1a
revealed that the ethylene chain side is more crowded
than the benzene ring side [1]. On the other hand, the
reaction of 1b with benzeneselenyl chloride shows
that the chlorine addition now proceeded by inver-
sion of the configuration of 1b with exclusive trans-
addition.
The following are the probable mechanisms that
can best accommodate the experimental observa-
tions. Initially, benzeneselnyl chloride adds to 1a in
the usual manner from the ethylene chain side to
produce the episelenonium ion 5a. The episelenon-
ium ion 5a, thus formed, should come to equilibrium
with the ring-opened form, carbocation 6a. Both
5a and 6a would be stabilized by the anchimeric
TABLE 1 Reactions of Alkenes 1a and 1b with Benzeneslenyl Chloride in CDCl3
Conditions
Products; yield (%)b
Runs
Alkenes
PhSecla
Temperature
4
1a
1b
�
1
2
3
4
5
6
1a
1a
1b
1b
1a
1b
1
1
1
1
2
2
� 78 C
50
50
50
50
100
100
50
50
c
RT
�
� 78 C
50
50
RT
�
� 78 C
�
� 78 C
a
Equimolar amounts of PhSeCl used.
b
c
1
Yields were determined by H NMR spectrum analyses.
RT stands for room temperature.

0
Reactions of Benzeneselenyl and Benzenesulfenyl Chlorides with syn- and anti-9,9 -Bibenzonorbornenylidenes 627
5
b, which would also come to equilibrium with the
ring-opened form, carbocation 6b. The carbocation
b, which is stabilized by anchimeric assistance of
only the one benzene ring, would be less stable than
6
6
6
a, and thus undergoes a conformational change to
a by free rotation about the cabon–carbon bond to
give 4 as the final product. In this way, the same
product 4 would be formed, both from 1a and 1b.
The recovery of 1a and 1b without any isomeriza-
tion indicates that additions of benzeneselenyl chlo-
ride to both 1a and 1b are irreversible.
SCHEME 2
assistance of the two benzene rings. Moreover, the
episelenonium ion intermediate 5a , formed by the
Reactions of 1a and 1b with Benzenesulfenyl
Chloride
0
addition from the benzene ring side, cannot enjoy
such stabilization. This would explain the addition
of benzeneselenyl chloride from the ethylene chain
side. Next, the covalent bond formation of 6a with
the chloride ion takes place at the ethylene chain side
to give the cis-adduct 7 because the benzene ring
side is blocked by the anchimeric assistance of the
benzene rings. The reaction of 7 with benzeneselenyl
chloride then produces the selenonium ion 8. Elim-
ination of diphenyl diselenide from 8, followed by
the addition of the chloride ion from the same side,
would explain the final formation of the cis-addition
product 4 (Scheme 3). Reportedly, the reaction of
In contrast to the reactions of benzeneselenyl chlo-
ride with 1a and 1b, those of benzenesulfenyl chlo-
ride gave neither benzenesulfenyl chloride adducts
nor chlorine adducts; benzenesulfenyl chloride only
worked as the catalyst of the mutual isomerization of
1a and 1b. Thus, treatment of 1a with an equimolar
amount of benzenesulfenyl chloride at room temper-
ature for 38 h gave a mixture of 1a (57%) and 1b
(38%), while treatment of 1b with benzenesulfenyl
chloride gave 1a (33%) and 1b (61%) (Scheme 4). For
these reactions, prior to the product isolation proce-
dure, excess tetramethylethylene was added to the
reaction mixtures to scavenge the benzenesulfenyl
chloride, which remained unchanged. Otherwise ad-
dition of the molecular chlorine, produced by de-
composition of the benzenesulfenyl chloride, to 1a
and 1b takes place to give 4. Thus, 2,3-dimethyl-1-
phenylthio-2-butene (11) [6], which is a secondary
1
-phenylcyclohexene with two molar amounts of
benzeneselenyl chloride afforded a 77:23 cis–trans
mixture of 1,2-dichloro-1-phenylcyclohexane quan-
titatively [5].
On the other hand, the addition of benzenese-
lenyl chloride to 1b produces the episelenonium ion
SCHEME 3

628 Noda, Sugihara, and Nakayama
equilibrium with a selenurane intermediate 14, thus
placing the chloride ion closer to the carbocation
center to favor the covalent bond formation, whereas
in the sulfur case the ion pairs are solvent-separated
and disfavor the bond formation.
EXPERIMENTAL
Solvents were purified and dried in the usual man-
ner. All of the reactions were carried out under argon.
Silica-gel column chromatography was performed
1
13
on silica gel 7734 (Merck, 70-230 mesh). H and
C
NMR spectra were recorded on a Bruker ARX400
or a Bruker AM400 spectrometer using CDCl
solvent with TMS as the internal standard.
3
as the
SCHEME 4
product, produced from the initial adduct 9 during
workup by silica-gel column chromatography, was
isolated in about 40% yield in both cases (Scheme
Reaction of the Alkene 1a with Benzeneselenyl
Chloride
4
). A separate reaction of tetramethylethylene with
A solution of 68 mg (0.35 mmol) of benzeneselenyl
chloride in 2 ml. of dichloromethane was added to
a solution of 100 mg (0.35 mmol) of 1a in 80 ml.
benzenesulfenyl chloride gave 11 in a better yield
of 60%.
�
The isomerization, discussed earlier, might be
explained as follows. Benzenesulfenyl chloride re-
acts with 1a and 1b to reversibly form episulfo-
nium ions 12a and 12b. These sulfonium ions would
then come to equilibrium with the ring-opened car-
bocations 13a and 13b, respectively, which are in-
terconvertible through bond rotation (Scheme 5).
The whole process would result in the isomerization
between 1a and 1b. These considerations mean that
the chloride ion does not undergo covalent bond for-
mation with the carbocations 13a and 13b, unlike
the selenium case. One of plausible explanations is
that in the selenium case the episelenium ion is in an
of dichloromethane at � 78 C. The reaction mixture,
which turned from red to yellow after 10 min, was
�
warmed to � 18 C and evaporated under reduced
pressure. The residue was chromatographed on a
column of silica gel. Elution of the column with hex-
ane/chloroform (4:1) gave 57 mg (57%) of 1a and a
mixture of the dichloride 4 and diphenyl diselenide.
The mixture part was further purified by GPC (gel
permeation chromatography) to give 54 mg (43%)
of 4 and 49 mg (89%) of diphenyl diselenide. The
structure of 4 was determined by comparison with
an authentic sample that was obtained by addition
of molecular chlorine to 1a [3].
SCHEME 5

0
Reactions of Benzeneselenyl and Benzenesulfenyl Chlorides with syn- and anti-9,9 -Bibenzonorbornenylidenes 629
The data given in Table 1 were obtained by
carrying out the reactions in an NMR tube, with
CDCl as the solvent.
the yellow color of benzenesulfenyl chloride. The
mixture was evaporated and the residue was puri-
fied by silica-gel column chromatography and then
by GPC to give 47 mg (95%) of a mixture of 1a and 1b
in the ratio 65:35 and 13 mg (40%) of 2,3-dimethyl-
3
Reaction of the Alkene 1b with Benzeneselenyl
Chloride
1
-phenylthio-2-butene (11) [6].
A solution of 68 mg (0.35 mmol) of benzeneselenyl
chloride in 2 ml. of dichloromethane was added to
a solution of 100 mg (0.35 mmol) of 1b in 80 ml.
Reaction of the Alkene 1b with Benzenesulfenyl
Chloride
�
of dichloromethane at � 78 C. The reaction mixture,
The reaction was carried out under the same con-
ditions as that described earlier. The mixture was
also purified in the same way as described previously
to give 47 mg (95%) of a mixture of 1a and 1b in
the ratio 40:60 and 14 mg (40%) of 2,3-dimethyl-1-
phenylthio-2-butene (11).
which turned from red to yellow after 10 min, was
�
warmed to � 18 C and evaporated under reduced
pressure. The residue was purified as described pre-
viously to give 61 mg (61%) of 1b, 50 mg (39%) of 4,
and 47 mg (86%) of diphenyl diselenide.
The data given in Table 1 were obtained by
carrying out the reactions in an NMR tube, with
CDCl
3
as the solvent.
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[
[
[
[
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3] Sugihara, Y.; Noda, K.; Nakayama, J. Tetrahedron
Lett 2000, 41, 8907.
4] Schmid, G. H.; Garratt, D. G. In The Chemistry of
Double-bonded Functional Groups, Part 2 (Supple-
ment A); Patai, S. (Ed.); Wiley: London, 1977, Ch. 9.
Reaction of the Alkene 1a with Benzenesulfenyl
Chloride
Benzenesulfenyl chloride was prepared from thio-
phenol and sulfuryl chloride and used immediately
�
after purification by distillation (54 C;2 mm Hg).
A dichloromethane solution containing 26 mg
(
0.18 mmol) of benzenesulfenyl chloride was added
[5] Morella, A. M.; Ward, A. D. Tetrahedron Lett 1984, 25,
197. This paper also reported that the trans-adducts
1
to a solution of 50 mg (0.18 mmol) of 1a in 10 ml.
of dichloromethane at room temperature. After the
mixture had been stirred for 38 h at room tempera-
ture, ca. 100 mg (1.2 mmol) of tetramethylethylene
was added, which brought about disappearance of
of benzeneselenyl chloride adducts with alkenes are
converted to cis-dichlorides by reaction with chlorine
and tetrabutylammonium chloride.
[
6] Clenann, E. L.; Chen, X. J Am Chem Soc 1989, 111,
5787.