A novel method for the construction of a benzene ring: A facile ring-closing reaction of (1E,3E,5E)-1-chloro-3-(p-tolylsulfonyl)-1,3,5-alkatrienes

Article abstract of DOI:10.1016/S0040-4039(01)00022-3

(1E,3E,5E)-1-Chloro-3-(p-tolylsulfonyl)-1,3,5-alkatrienes (1) underwent facile ring-closure followed by spontaneous removal of hydrogen chloride to form a benzene ring. This reaction sequence occurred at relatively low temperature.

Full text of DOI:10.1016/S0040-4039(01)00022-3

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 1923–1925
A novel method for the construction of a benzene ring:
a facile ring-closing reaction of
(1E,3E,5E)-1-chloro-3-(p-tolylsulfonyl)-1,3,5-alkatrienes
Katsuyuki Ogura,a,* Mineko Takeda,b Jian R. Xie,a Motohiro Akazomea and Shoji Matsumotoa
aDepartment of Materials Technology, Faculty of Engineering, Chiba University, 1-33 Yayoicho, Inageku,
Chiba 263-8522, Japan
bGraduate School of Science and Technology, Chiba University, 1-33 Yayoicho, Inageku, Chiba 263-8522, Japan
Received 16 November 2000; revised 25 December 2000; accepted 28 December 2000
Abstract—(1E,3E,5E)-1-Chloro-3-(p-tolylsulfonyl)-1,3,5-alkatrienes (1) underwent facile ring-closure followed by spontaneous
removal of hydrogen chloride to form a benzene ring. This reaction sequence occurred at relatively low temperature. © 2001
Elsevier Science Ltd. All rights reserved.
Recently, new methods for constructing a benzene ring
have been receiving much attention especially in the field
of useful functional materials with a p-electron system.
Among many precedent methods, we focused on the
utilization of electrocyclic interconversion1 between hex-
atriene (I) and cyclohexadiene (II) that can be led to the
benzene ring (III) by the elimination of an appropriate
moiety. This route has been well investigated mainly in
terms of the photochemical transformation of stilbene
derivatives into the corresponding phenanthrene.2 In
contrast, there are few reports on utilization of this route
for preparing simple benzene rings, probably because it
works less efficiently. However, it is conceivable that, if
a good leaving group (Y) was introduced in the hexa-
triene, this route would work more efficiently to give the
expected III.3
In order to put this reaction sequence into practice, there
were three problems to be solved: (1) a stereoselective
synthesis of the starting hexatriene that has the central
bond bearing two substituents (b and c) in Z geometry;
(2) the development of a method whereby the 1,3,5-alka-
triene adopts conformations around the 2,3- and 4,5-
Scheme 1.
Keywords: benzenes; electrocyclic reactions; sulfones; trienes.
* Corresponding author. Fax +81-43-290-3402; e-mail: katsu@galaxy.tc.chiba-u.ac.jp
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)00022-3

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K. Ogura et al. / Tetrahedron Letters 42 (2001) 1923–1925
bonds that are favorable for the cyclization; (3) the
selection of an appropriate leaving group (Y) that does
not disturb the cyclization and can be easily removed
after the cyclization. In this letter, we wish to report the
facile transformation of a (1E,3E,5E)-1-chloro-3-(p-
tolyl or methylsulfonyl)-1,3,5-alkatriene (1) into a ben-
zene derivative (3) which is brought about by thermal
electrocyclization followed by spontaneous elimination
of the hydrogen chloride moiety. For synthesizing the
starting 1,3,5-alkatriene (1), the following reaction
sequence was devised: lithiation of (E)-1-chloro-(p-tolyl
or methylsulfonyl)propene (4)4 followed by the addition
of acetic anhydride gives an adduct (6). If this adduct
(6) is treated with a base, the expected 1 would be
obtained.
R2=Me) gave the corresponding 1a and 3a in 5 and
39% yields, respectively.10 Complete conversion of 1a
(R1=H, R2=Me) to 3a (R1=H, R2=Me) in CDCl3
took place at room temperature.
The reaction of 6a (R1=Ph, or p-MeOC6H4; R2=H)
with NaH at room temperature did not give 3, the
corresponding 1a in 57 or 90% yield, respectively. The
complete conversion of 1a (R1=Ph, or p-MeOC6H4;
R2=H) to the corresponding 3a was accomplished by
heating it in toluene at 80°C. This implied that the
presence of the R2 substituent facilitates the electrocy-
clization of 1. For the present 1,3,5-alkatriene, many
conformations such as 1A–D have to be taken into
consideration, though conformation (1A) is favorable
for the electrocyclization. The presence of the sub-
stituent (R2) and the p-tolylsulfonyl group can be con-
sidered to increase the population of conformation 1A.
This is due to the repulsive interactions of the R2 and
p-tolylsulfonyl groups with the terminal 2-chloro-
ethenyl group (Scheme 2).
According to Scheme 1, we prepared the adduct (6),
which consisted of two diastereomers except for 6a
(R1=Ph, R2=Me).6,7 In order to form the correspond-
ing 1, (R*,R*)-6a (R1=Ph, R2=Me)6 was subjected to
the reaction with NaH (1.3 equiv) in THF (room
temperature/38 h). To our surprise, we did not obtain
1a (R1=Ph, R2=Me), but the final product 3 (R1=Ph,
R2=Me) was given in 78% yield. On similar treatment
with NaH (room temperature/48 h), both (R*,R*)- and
(R*,S*)-diastereomers of 6b (R1=Ph, R2=Me)
afforded 3b (R1=Ph, R2=Me) in 80 and 54% yields,
respectively, along with the starting materials (20 and
40% yields, respectively). These facts implied that, irre-
spective of the diastereomeric structures of 6, the
present reaction with NaH effects the stereoselective
elimination9 of the acetic acid moiety to give only the
desired geometric isomer of 1 (R1=Ph, R2=Me) that is
smoothly derived into 3 (R1=Ph, R2=Me). When
(R*,R*)-6a (R1=Me, R2=Me) was treated with NaH
at room temperature for a short period of time (24 h),
the intermediary 1a (R1=Me, R2=Me) was afforded in
23% yield along with 3 (R1=Me, R2=Me) (41% yield)
and the starting material (24%). Transformation of 1
(R1=Me, R2=Me) into the corresponding 3 in CDCl3
could be pursued by 1H NMR (300 MHz). It was
completed within 65 h at room temperature in the dark
and no signal for 2a was observed, indicating that the
release of hydrogen chloride from 2 occurred sponta-
neously and smoothly. Similarly, (R*,R*)-6a (R1=H,
Molecular orbital calculation at the PM3 level11
revealed that, in the case of 1a (R1=Ph and R2=Me),
the most stable energy-minimized conformations corre-
sponding to 1A–D are comparable in energy (within
0.34 kcal mol−1). When R2 is H, the most stable energy-
minimized conformation that corresponds to 1B was
calculated to be more stable by 2.3 kcal mol−1 than 1A.
Thus, it was shown that (1E,3E,5E)-1-chloro-3-(p-tolyl
or methylsulfonyl)-1,3,5-alkatriene (1) provides an ideal
system for construction of a benzene ring via thermal
electrocyclization with subsequent elimination of
hydrogen chloride. The Woodward–Hoffmann rule pre-
dicts that conformation (1A) thermally closes a ring in
a disrotatory mode. It is noteworthy that the ring-
closure of 1 in this direction can avoid the repulsive
interaction between R1 and Cl to be smoothly led to 2.
In contrast, irradiation of 1 (R1=Ph, R2=H) with
ultraviolet light (>290 nm) did not form the benzene
derivative (3; R1=Ph, R2=H), and only the isomeriza-
tion around the C3ꢀC4 double bond was observed. This
indicated the ring-closure in a conrotatory mode is
disfavored probably because of the repulsive interaction
between R1 and Cl (Scheme 3).
Scheme 2.
Scheme 3.

K. Ogura et al. / Tetrahedron Letters 42 (2001) 1923–1925
1925
Scheme 4.
Finally, we would like to comment on the role of the
chlorine atom. If this chlorine atom is replaced by
hydrogen, the last elimination step to a benzene ring
will become slow. In fact, the treatment of 4-acetoxy-5-
methyl-3-(p-tolylsulfonyl)-1,5-heptadiene with NaH
resulted in the formation of stable 5-methyl-3-(p-tolyl-
sulfonyl)-1,3,5-heptatriene. We also prepared a geomet-
ric isomer (7) of 1. These compounds (7) were thermally
so stable as to remain unchanged at 80°C. However, the
electrocyclization of 7 (R1=Ph, R2=H) was achieved
by irradiation with UV light (>290 nm) to form the
corresponding 3 in 50% yield along with the starting
material (47% yield). These findings are in complete
accordance with the Woodward–Hoffmann rule:1 the
thermal ring-closure of 7 in a disrotatory mode under-
goes severe steric repulsion between R1 and Cl (Scheme
4), but the photochemical ring-closure in a conrotatory
mode proceeds without such repulsive interaction.
4. Pure
(Z)-1-chloro-3-(p-tolylsulfonyl)propene
was
reported, but its (E)-isomer (4) has been not isolated in a
pure form.5 We prepared a 58:42 mixture of (E)- and
(Z)-chloro-3-(p-tolylsulfonyl)propenes from 1,3-dichloro-
propene and sodium p-toluenesulfinate. Preparative
HPLC of the mixture gave 4 as colorless crystals: mp
81.2–81.9°C. Anal. calcd for C10H11ClO2S: C, 52.06; H,
4.81%. Found: C, 52.15; H, 4.72%. Its NMR data
accorded with those reported in Ref. 5.
5. (a) Hirata, T.; Sasada, Y.; Ohtani, T.; Asada, T.;
Kinoshita, H.; Senda, H.; Inomata, K. Bull. Chem. Soc.
Jpn. 1992, 65, 75; (b) Correa, C. M. M. da S.; Fleming,
M. D. C. M.; Oliveira, M. A. B. C. S.; Garrido, E. M. J.
J. Chem. Soc., Perkin Trans. 2 1994, 1993.
6. Typical procedure: n-Butyllithium (1.63 M in hexane, 2.1
mmol) was added to a solution of 4 (0.61 mmol) in THF
(3 mL) at −78°C. Then, a-methylcinnamaldehyde (0.63
mmol) was added and the resulting mixture was further
stirred at −78°C for 20 min. After the addition of acetic
anhydride (0.72 mmol), the stirring was continued at the
same temperature for 2 h. The usual workup and column
chromatography on silica gel gave 6 (R1=Ph, R2=Me)
(83% yield) as one diastereomer. Its stereochemistry was
determined by single-crystal X-ray analysis7 to be
(R*,R*). In a similar manner, 6 (R1=Me, R2=Me), 6
(R1=H, R2=Me), 6 (R1=Me, R2=H), 6 (R1=Ph, R2=
H), and 6 (R1=p-MeOC6H4, R2=H) were prepared. In
these reactions, two diastereomers were formed in the
ratios of 89:11, 69:31, 70:30. 75:25, and 69:31, respec-
tively. Their analogy in 1H NMR suggested that the
major isomers, which were isolated by preparative
HPLC, have (R*,R*)-stereochemistry.
In conclusion, (1E,3E,5E)-1-chloro-3-(p-tolylsulfonyl)-
1,3,5-alkatrienes (1) were shown to be good precursors
for the construction of a benzene ring, which was
achieved by thermal ring-closure followed by easy
removal of the hydrogen chloride moiety. Now we are
investigating the application of the present system to
other 3-functionalized 1-chloro-1,3,5-alkatrienes.
Acknowledgements
This work was supported by ‘Research for the Future’
Program (JSPS-RFTF96P00304) from the Japan Soci-
ety for the Promotion of Science.
,
7. The data were collected with Cu Ka (u=1.54178 A)
radiation on a Mac Science MXC18 diffractometer. The
structure was solved and refined by direct methods (SIR
928 on a computer program package: Crystan GM ver.
6.2.1 from MAC Science Co. Ltd.): Orthorhombic,
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