Synthesis and structure of 2,3-bis(5-tert-butyl-2-methoxyphenyl)buta-1,3- diene by bromine elimination of-1,4-dibromo-2,3-bis(5-tert-butyl-2- methoxyphenyl)-2-butene

Article abstract of DOI:10.1080/00397911.2011.577289

2,3-Bis(5-tert-butyl-2-methoxyphenyl)buta-1,3-diene was prepared by bromination of (Z)-and (E)-2,3-bis(5-tert-butyl-2-methoxyphenyl)-2-butene followed by treatment with zinc powder in a mixture of CH2^Cl2 and acetic acid, which was converted to the corresponding o-terphenyl skeleton by the condensation with dimethyl acetylenedicarboxylate followed by oxidation with 2,3-dichloro-5,6-dicyanobenzoquinone.

Full text of DOI:10.1080/00397911.2011.577289

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Synthesis and Structure of 2,3-Bis(5-
tert-butyl-2-methoxyphenyl)buta-1,3-
diene by Bromine Elimination of
(Z)-1,4-Dibromo-2,3-bis(5-tert-butyl-2-
methoxyphenyl)-2-butene
Kazuya Tazoe a , Yuki Uchikawa a , Xing Feng a & Takehiko Yamato a
a Department of Applied Chemistry, Faculty of Science and
Engineering , Saga University , Saga , Japan
Accepted author version posted online: 10 Jan 2012.Published
online: 17 Aug 2012.
To cite this article: Kazuya Tazoe , Yuki Uchikawa , Xing Feng & Takehiko Yamato (2012) Synthesis
and Structure of 2,3-Bis(5-tert-butyl-2-methoxyphenyl)buta-1,3-diene by Bromine Elimination of
(Z)-1,4-Dibromo-2,3-bis(5-tert-butyl-2-methoxyphenyl)-2-butene, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 42:21, 3128-3139,
DOI: 10.1080/00397911.2011.577289
To link to this article: http://dx.doi.org/10.1080/00397911.2011.577289
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Synthetic Communications1, 42: 3128–3139, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2011.577289
SYNTHESIS AND STRUCTURE OF 2,3-BIS(5-TERT-
BUTYL-2-METHOXYPHENYL)BUTA-1,3-DIENE BY
BROMINE ELIMINATION OF
(Z)-1,4-DIBROMO-2,3-BIS(5-TERT-
BUTYL-2-METHOXYPHENYL)-2-BUTENE
Kazuya Tazoe, Yuki Uchikawa, Xing Feng, and
Takehiko Yamato
Department of Applied Chemistry, Faculty of Science and Engineering,
Saga University, Saga, Japan
GRAPHICAL ABSTRACT
Abstract 2,3-Bis(5-tert-butyl-2-methoxyphenyl)buta-1,3-diene was prepared by
bromination of (Z)- and (E)-2,3-bis(5-tert-butyl-2-methoxyphenyl)-2-butene followed
by treatment with zinc powder in a mixture of CH2Cl2 and acetic acid, which was converted
to the corresponding o-terphenyl skeleton by the condensation with dimethyl acetylenedi-
carboxylate followed by oxidation with 2,3-dichloro-5,6-dicyanobenzoquinone.
Keywords Bromination; bromine elimination; conformations; diaryl-1,3-butadiene;
Diels–Alder reaction
INTRODUCTION
2,3-Diphenylbuta-1,3-diene is a compound of considerable interest to both
industrially and academically oriented organic chemists.[1–5] Unfortunately, most
of the numerous published syntheses of 2,3-diphenylbuta-1,3-diene are time- and
money-consuming multistep reactions that give poor yields or use expensive chemi-
cals. One of the first and simplest procedures for the synthesis of 2,3-diphenylbuta-
1,3-diene in good yields was reported by Alder and Haydn using a potassium
bisulfate–mediated dehydration of 2,3-diphenylbutane-2,3-diol.[6] Dodson et al.[7]
Received March 2, 2011.
Address correspondence to Takehiko Yamato, Department of Applied Chemistry, Faculty of
Science and Engineering, Saga University, Hanjo-machi 1, Saga 840-8502, Japan. E-mail: yamatot@
cc.saga-u.ac.jp
3128

SYNTHESIS OF 2,3-DIARYLBUTA-1,3-DIENE
3129
and Baldwin and Lusch,[8] however, were unable to reproduce these results. Wagner
and Brinker reported a novel and facile synthesis of 2,3-diphenylbuta-1,3-dienes
dehydration of 2,3-diphenylbutane-2,3-diol with hexamethylphosphoramide at
240 ꢀC along with rearrangement products. The separation of the desired 2,3-
diphenylbuta-1,3-dienes is quite tedious and not convenient.[9]
On the other hand, Ko¨nig and de Meijere reported the synthesis of 1,2-
dimethylene[2.2]paracyclophane using a copper-mediated coupling of 1,2-dibromo-
[2.2]-paracyclophan-1-ene with methylmagnesium bromide, followed by
bromine addition and bromine elimination with activated zinc promoted by ultra-
sound.[10]
Recently, we reported the preparation of 1,2-dimethyl[2.n]metacyclophan-
1-enes[11–14] by using the reductive coupling of carbonyl compounds by low-valent
titanium, the McMurry reaction,[15–21] as a key step. These compounds afforded
convenient starting materials for the attempted preparation of 1,2-dimethyle-
ne[2.n]-metacyclophan-1-enes. Thus, there is substantial interest in investigating
the convenient preparation of 2,3-diarylbuta-1,3-diene and application to the
dienes for Diels–Alder reactions. We report here on a convenient synthesis of
2,3-diarylbuta-1,3-diene by treatment with bromine of 2,3-diaryl-2-butene to afford
1,4-dibromo-2,3-diaryl-2-butenefollowed by bromine elimination with zinc powder.
The structural properties of 1,4-dibromo-2,3-diaryl-2-butene are also discussed in
solution and solid state.
RESULTS AND DISCUSSION
2,3-Bis(5-tert-butyl-2-methoxylphenyl)-2-butene 3 has been prepared accord-
ing our previous papers.[22] The TiCl4-catalyzed acetylation of 4-tert-butylanisole 1
with acetic anhydride at 20 ꢀC gave the desired 2-acetyl-4-tert-butylanisole 2 in good
yield. 2-Acetyl-4-tert-butylanisole 2 was subjected to reductive coupling by the
McMurry reaction following the improved Grutzmacher procedure[17] (Scheme 1).
¨
Thus, the reductive coupling reaction of 2 carried out using TiCl4-Zn in the presence
Scheme 1. Synthesis of 1,2-dimethylene[2.2]paracyclophane.

3130
K. TAZOE ET AL.
of pyridine in refluxing tetrahydrofuran (THF) afforded the desired compound
2,3-bis(5-tert-butyl-2-methoxyl-phenyl)-2-butene 3 in good yield (Scheme 2).
1
The H NMR spectrum of 3 shows two kinds of methoxy protons, each as a
singlet. By careful column chromatography (silica gel, Wako C-300), two isomers,
(E)-3 and (Z)-3, are separated in 32% and 10% yields, respectively.
The structures of products (E)-3 and (Z)-3 were also determined on the basis
1
of their elemental analyses and spectral data. H NMR signals of the olefinic pro-
tons for E- and Z-olefins should be observed at d > 7.4 (E) and <6.9 (Z).[23] 1
H
NMR spectrum of (E)-3 in CDCl3 shows d 6.86 (d, J ¼ 8.4 Hz), 7.22 (dd, J ¼ 2.4,
8.4 Hz), and 7.25 (d, J ¼ 2.4 Hz) ppm for the three protons of the aromatic rings.
1
In contrast, H NMR spectrum of (Z)-3 in CDCl3 shows at higher field, d 6.62
(d, J ¼ 8.3 Hz), 6.65 (d, J ¼ 2.4 Hz), and 6.94 (dd, J ¼ 2.4, 8.3 Hz) ppm, for the three
protons of the aromatic rings because of the face-to-face arrangement of the phenyl
groups. Also the tert-butyl proton of (Z)-3 was observed at higher field, d 1.00 ppm,
because of the strong shielding effect of the benzene ring. The structure of the
(Z)-isomer is also readily assigned from the chemical shift of the methoxy protons
at d 3.83 ppm for (E)-3 and d 3.77 ppm for (Z)-3. These data strongly support that
the structure of (E)-3 is the (E)-configuration and the structure of (Z)-3 is the
(Z)-configuration.
Bromination of (E)-2,3-bis(5-tert-butyl-2-methoxylphenyl)-2-butene (E)-3 with
excess of bromine in dichloromethane solution at room temperature for 24 h afforded
a mixture of the corresponding meso-(Z)- and dl-(Z)-1,4-dibromo-2,3-bis(5-tert-
butyl-2-methoxyphenyl)-2-butene meso-(Z)-4 and dl-(Z)-4 in 30% and 60% yields
along with the recovery of the starting compound (Scheme 3). Similar results were
Scheme 2. Synthesis of (Z)- and (E)-2,3-bis(5-tert-butyl-2-methoxylphenyl)-2-butene, (Z)-3 and (E)-3.

SYNTHESIS OF 2,3-DIARYLBUTA-1,3-DIENE
3131
Table 1. Crystal and refinement data for compound dl-(Z)-4
Parameter
dl-(Z)-4
Empirical formula
Formula weight
Crystal system
Space group
C
26H34Br4O2
538.33
Triclinic
P–1
˚
a (A)
10.154(2)
14.185(2)
9.815(2)
99.27(1)
106.63(1)
93.32(1)
3446.06 (11)
2
˚
b (A)
˚
c (A)
a (deg)
b (deg)
c (deg)
3
˚
V (A )
Z
Dcalcd (g cmꢁ3
T (K)
m(Mo Ka) (mmꢁ1
Total no. of reflections
Unique reflections
Rint
)
1.345
296
)
3.068
6100
2313
0.0687
2313
306
Observed reflections
Parameters refined
R [I > 2r(I)] and all data
wR [I > 2r(I)] and all data
0.087
0.1010
obtained in the case of (Z)-2,3-bis(5-tert-butyl-2-methoxyphenyl)-2-butene (Z)-3 to
afford meso-(Z)-4 and dl-(Z)-4 in the same ratio as in (E)-isomer (E)-3.
The former transformation probably occurred by addition of bromine to the
double bond followed by the twofold debromination to diene 5 (discussed later).
Interestingly, the compounds (E)- and (Z)-3 were treated with 4.5 equiv. of
benzyltrimethylammonium tribromide (BTMA Br3) at room temperature for 24 h
Scheme 3. Bromination of (E)- and (Z)-2,3-bis(5-tert-butyl-2-methoxylphenyl)-2-butene, (E)-3 and (Z)-3
with BTMA Br3.

3132
K. TAZOE ET AL.
afforded 1,4-dibromo-2,3-bis(5-tert-butyl-2-methoxyphenyl)-2-butene meso-(Z)-4
and dl-(Z)-4 in 32% and 61% yields, respectively. It was also found that the bromin-
ation of 2,3-bis(5-tert-butyl-2-methoxyphenyl)buta-1,3-diene 5 with an equimolar of
BTMA Br3 at room temperature for 5 min afforded 1,4-dibromo-2,3-bis(5-tert-
butyl-2-methoxyphenyl)-2-butene meso-(Z)-4 and dl-(Z)-4 in the same ratio in quan-
titative yield. This result strongly suggests that the 2,3-bis(5-tert-butyl-2-
methoxyphenyl)buta-1,3-diene 5 could be an intermediate during the formation of
1,4-dibromo-2,3-bis(5-tert-butyl-2-methoxyphenyl)-2-butene 4 in the bromination
of 2,3-bis(5-tert-butyl-2-methoxylphenyl)-2-butene.
The 300-MHz 1H NMR spectrum of meso-(Z)-4 showed a singlet of the meth-
oxy protons at d 3.79 ppm in addition to the resonances at higher field, d 6.64 (d,
J ¼ 8.7 Hz), 6.68 (d, J ¼ 2.4 Hz), and 7.03 (dd, J ¼ 2.4, 8.7 Hz) ppm, for the three pro-
tons of the aromatic rings because of the face-to-face arrangement of the phenyl
groups like those of (Z)-3. The methylene protons of the bromomethyl group were
observed as a singlet at d 4.59 ppm, which indicates the methylene protons in the
same environment. In contrast, the 300-MHz 1H NMR spectrum of dl-(Z)-4 showed
a singlet of the methoxy protons at d 3.79 ppm in addition to the resonances at lower
field, d 6.86 (d, J ¼ 8.7 Hz), 7.35 (dd, J ¼ 2.4, 8.7 Hz), and 7.60 (d, J ¼ 2.4 Hz) ppm,
for the three protons of the aromatic rings. Interestingly, the methylene protons of
the bromomethyl group were observed as a set of doublets at d 3.97 and 4.19 ppm
(J ¼ 9.6 Hz), which coalesced to a singlet at d 4.12 ppm above 75 ꢀC in CDBr3. Thus,
the introduction of bromo group to methyl group at the double bond in the present
2,3-bis(2-methoxyphenyl)-2-butene skeleton might inhibit the rotation around the
single bond of CꢁCH2Br, which makes the methylene protons a diasterotopic
environment.
The conformation of dl-(Z)-4 has also been confirmed by x-ray crystallo-
graphic analysis. Single colorless crystals of the dl-(Z)-1,4-dibromo-2,3-bis(5-tert-
butyl-2-methoxyphenyl)-2-butene dl-(Z)-4 suitable for x-ray crystallography were
obtained by recrystallization from methanol–chloroform (1:1). The perspective crys-
tal structure of dl-(Z)-4 is illustrated in Fig. 1.
Compound dl-(Z)-4 crystallized in triclinic space group, P–1, and is located
about a two-fold axis, because this molecule has crystallographic C2 symmetry.
Therefore, the asymmetric unit contains one half of a molecule (Z ¼ 2). Both meth-
oxy groups on the benzene ring of dl-(Z)-4 point toward the outer side against each
bromine atom in the bromomethyl group. This might help avoid the steric crowding
with the methoxy group and bromine atom of the bromomethyl group on the each
carbon in the double bond.
Several attempts using activated zinc powder in dioxane with irradiation by
ultrasound, following the reported procedure, to accomplish bromine elimination
of meso-(Z)-4 and afford 2,3-bis(5-tert-butyl-2-methoxyphenyl)buta-1,3-diene 5
failed. Only the recovery of the starting compound or the formation of an intractable
mixture of products resulted. Fortunately, we have found that when the present bro-
mine elimination of meso-(Z)-4 is carried out in CH2Cl2 at room temperature for
24 h in the presence of the commercially available zinc powder and a small amount
of the acetic acid, the desired 2,3-bis(5-tert-butyl-2-methoxyphenyl)buta-1,3-diene 5
is formed in quantitative yield. Similar treatment of dl-(Z)-4 with zinc powder
affords the corresponding diene 5 in quantitative yield. Compound 5 is too labile

SYNTHESIS OF 2,3-DIARYLBUTA-1,3-DIENE
3133
Figure 1. Crystal structure of dl-(Z)-4. Hydrogen atoms are omitted for clarity. (Figure is provided in
color online.)
Scheme 4. Synthesis and Diels–Alder reaction of of 2,3-bis(5-tert-butyl-2-methoxyphenyl)-buta-1,3-
diene 5.

3134
K. TAZOE ET AL.
of a solid to purify. Although in solution or exposed to air compound 5 slowly
decomposes, the compound is easily trapped by the reaction with dimethyl acetyle-
nedicarboxylate in toluene at reflux for 12 h to afford 6 in good yield (Scheme 4).
Diels–Alder adduct 6 was converted to o-terphenyl derivative 7 by aromatization
with dichlorodicyano-p-benzoquinone (DDQ) in 70% yield.
The structures of products 5 and 7 were determined on the basis of their elemen-
1
tal analyses and spectral data. For example, the H NMR spectrum of 5 shows two
singlets of the tert-butyl protons and methoxy protons at d 1.23 and 3.76 ppm in
addition to the resonances at d 6.72, 7.17, and 7.22 ppm for the three protons of
the aromatic rings. The exo-methylene protons were observed as singlets at d 5.12
and 5.14 ppm. These findings suggest that the conformationally flexible structure of
5 adopts an s-trans geometry, the same as that of 2,3-diphenylbuta-1,3-diene.[25] On
the other hand, the mass spectral data for 7 (Mþ ¼ 518) strongly supports the
1
Diels–Alder reaction followed by aromatization product. The H-NMR spectrum
of 7 shows the tert-butyl protons and the methoxy protons at d 1.11 and 3.52 ppm,
which are upfield shifts due to the ring current of the opposite benzene ring.[26,27]
The aromatic protons of 7 are observed at d 6.67, 6.95, and 7.15 ppm in addition
to the resonances at d 7.80 ppm for the newly constructed 3 and 6 aromatic protons.
CONCLUSIONS
In conclusion, we have succeeded for the first time in preparing 2,3-bis(5-tert-
butyl-2-methoxyphenyl)buta-1,3-diene by bromination of (Z)- and (E)-2,3-bis(5-tert-
butyl-2-methoxyphenyl)-2-butene followed by treatment with zinc powder, which
was converted to the corresponding o-terphenyl skeleton by the condensation with
dimethyl acetylenedicarboxylate followed by oxidation with DDQ. The present
method provides excellent yields, easy isolation of product 2,3-diarylbuta-1,3-diene,
and overcomes the previously reported problems. Further studies on the reaction of
the novel 2,3-bis(5-tert-butyl-2-methoxyphenyl)buta-1,3-diene 5 and dimethyl 4,5-
bis(5-tert-butyl-2-methoxyphenyl)benzene-1,2-dicarboxylate 7 are now in progress.
EXPERIMENTAL
All melting points are uncorrected. 1H NMR spectra were recorded at
300 MHz on a Nippon Denshi Jeol FT-300 NMR spectrometer in deuteriochloro-
form with Me4Si as an internal reference. Ultraviolet–visible (UV-VIS) spectra were
recorded on a Perkin-Elmer Lambda 19 UV=VIS=NIR spectrometer. Mass spectra
were obtained on a Nippon Denshi JMS-HX110A ultrahigh-performance mass spec-
trometer at 75 eV using a direct-inlet system. Elemental analyses were performed on
a Yanaco MT-5 instrument.
Preparation of 4-tert-butylanisole 1 was previously described.[28]
Preparation of 2-Acetyl-4-tert-butylanisole (2)
A solution of TiCl4 (57.8 mL, 527 mmol) in CH2Cl2 (25 mL) was added to a sol-
ution of 4-tert-butylanisole 1 (15.0 g, 91.0 mmol) and acetic anhydride (13.2 mL,
140 mmol) in CH2Cl2 (200 mL) at 0 ꢀC. After the reaction mixture was stirred at

SYNTHESIS OF 2,3-DIARYLBUTA-1,3-DIENE
3135
room temperature for 3 h, it was poured into a large amount of ice water (400 mL) and
extracted with CH2Cl2 (200mLꢂ 2). The combined extracts were washed with water,
dried with Na2SO4, and concentrated. The residue was distilled under reduced pressure
to give 2-acetyl-4-tertbutylanisole 2 (17.0g, 93%) as a colorless liquid. Bp 150–158ꢀC
(10torr). nmax(NaCl)=cmꢁ1: 1676 (C O). dH (CDCl3) 1.31 (s, 9H, tBu), 2.61 (s, 3H,
=
COMe), 3.89 (s, 3H, OMe), 6.91 (d, J¼ 8.4 Hz, 1H, ArH), 7.49 (dd, J¼ 2.6, 8.6 Hz,
1H, ArH), 7.76 (d, J ¼ 2.6 Hz, 1H, ArH). MS: m=z [Mþ] 206. Elemental analysis calcu-
lated for C13H18O2(206.284): C, 75.69; H, 8.8. Found: C, 75.52; H, 8.72.
McMurry Coupling Reaction of 2
The McMurry reagent was prepared from TiCl4 (13.8 mL, 125 mmol) and Zn
powder (18.0 g, 275 mmol) in 300 mL of dry THF, under nitrogen. A solution of
2-acetyl-4-tert-butylanisole 2 (5.4 g, 26.0 mmol) and pyridine (22.8 mL, 200 mmol)
in dry THF (100 mL) was added within 1 h to the black mixture of the McMurry
reagent using a high-dilution technique with continuous refluxing and stirring. The
reaction mixture was refluxed for an additional 12 h, cooled to room temperature,
and hydrized with aqueous 10% K2CO3 (500 mL) at 0 ꢀC. The reaction mixture was
extracted with CH2Cl2 (300 mL ꢂ 3). The combined extracts were washed with water,
dried with Na2SO4, and concentrated. The residue was chromatographed over silica
gel (Wako C-300, 500 g) with hexane, hexane–benzene, 3:1, and benzene–EtOAc, 4:1,
as eluents to give (Z)-3 (507 mg, 10%) and (E)-3 (1.6 g, 32%), respectively.
(Z)-2,3-Bis(5-tert-butyl-2-methoxylphenyl)-2-butene
(Z)-3. Colorless
prisms (MeOH). Mp 95–96 ꢀC. nmax(KBr)=cmꢁ1: 2958, 1603, 1502, 1464, 1301,
1247, 1058, 1033, 801. dH (CDCl3) 1.00 (s, 18H, tBu), 2.14 (s, 6H, Me), 3.77 (s,
6H, OMe), 6.62 (d, J ¼ 8.3 Hz, 2H, ArH), 6.65 (d, J ¼ 2.4 Hz, 2H, ArH), 6.94
(dd, J ¼ 8.3, 2.4 Hz, 2H, ArH). dC (CDCl3) 21.15, 31.16, 34.12, 55.67, 110.45,
125.59, 125.81, 129.15, 137.17, 143.03, 154.35. MS: m=z [Mþ] 380. Elemental analysis
calculated for C26H36O2(380.56): C, 82.06; H, 9.53. Found: C, 81.98; H, 9.45.
(E)-2,3-Bis(5-tert-butyl-2-methoxylphenyl)-2-butene
(E)-3. Colorless
prisms (MeOH); mp 88–89 ꢀC. nmax(KBr)=cmꢁ1: 2957, 1601, 1502, 1461, 1299,
1247, 1056, 1030, 807. dH (CDCl3) 1.31 (s, 18H, tBu), 1.76 (s, 6H, Me), 3.83 (s,
6H, OMe), 6.86 (d, J ¼ 8.4 Hz, 2H, ArH), 7.22 (dd, J ¼ 8.4, 2.4 Hz, 2H, ArH),
7.25 (d, J ¼ 2.4 Hz, 2H, ArH). dC (CDCl3) 21.24, 31.61, 34.12, 55.69, 110.55,
123.95, 127.60, 131.13, 132.71, 143.13, 154.55. MS: m=z [Mþ] 380. Elemental analysis
calculated for C26H36O2(380.56): C, 82.06; H, 9.53. Found: C, 81.95; H, 9.56.
Bromination of (E)-3 with Br2
A solution of bromine Br2 (0.2 mL, 2.6 mmol) in CH2Cl2 (1 mL) was added to a
solution of (E)-3 (100 mg, 0.26 mmol) in CH2Cl2 (10 mL) at room temperature. After
the reaction mixture was stirred at room temperature for 12 h, it was poured into a
large amount of icewater (10 mL) and extracted with CH2Cl2 (10 mL ꢂ 2). The
combined extracts were washed with water, dried with Na2SO4, and concentrated.
The residue was chromatographed over silica gel (Wako C-300, 200 g) with hexane

3136
K. TAZOE ET AL.
and hexane–benzene, 1:1, as an eluent to give meso-(Z)-4 (42 mg, 30%) and dl-(Z)-4
(84 mg, 60%), respectively.
meso-(Z)-1,4-Dibromo-2,3-bis(5-tert-butyl-2-methoxyphenyl)-2-butene,
meso-(Z)-4. Colorless prisms (hexane). Mp 115–116 ꢀC. nmax(KBr)=cmꢁ1: 2959,
1601, 1502, 1247, 1056, 1030, 809. dH (CDCl3) 1.08 (18H, s, tBu), 3.80 (6H, s,
OMe), 4.59 (4H, s, CH2), 6.64 (2H, d, J ¼ 8.7 Hz, ArH), 6.68 (2H, d, J ¼ 2.4 Hz,
ArH), 7.03 (dd, J ¼ 8.7, 2.4 Hz, 2H, ArH). dC (CDCl3) 31.51, 34.12, 35.28, 55.68,
110.44, 125.48, 125.79, 129.31, 137.96, 143.02, 154.29. MS: m=z [Mþ] 536, 538,
540. Elemental analysis calculated for C26H34Br2O2(538.37): C, 58.01; H, 6.37.
Found: C, 57.93; H, 6.28.
dl-(Z)-1,4-Dibromo-2,3-bis(5-tert-butyl-2-methoxyphenyl)-2-butene,
dl-(Z)-4. Colorless prisms (hexane). Mp 146–147 ꢀC. nmax(KBr)=cmꢁ1: 2952, 1605,
1502, 1244, 1100, 1026, 805. dH (CDCl3) 1.39 (s, 18H, tBu), 3.79 (s, 6H, OMe),
3.97 (d, J ¼ 9.6 Hz, 2H, CH2), 4.19 (2H, d, J ¼ 9.6 Hz, CH2), 6.86 (2H, d, J ¼ 8.7 Hz,
Hz, ArH), 7.35 (2H, dd, J ¼ 8.7, 2.4 Hz, ArH), 7.60 (2H, d, J ¼ 2.4 Hz ArH). dC
(CDCl3) 31.48, 34.15, 35.33, 55.71, 110.48, 125.51, 125.82, 129.36, 137.92, 143.96,
154.25. MS: m=z [Mþ] 536, 538, 540. Elemental analysis calculated for
C26H34Br2O2(538.37): C, 58.01; H, 6.37. Found: C, 57.97; H, 6.37.
Bromination of (Z)-3 with Br2
A solution of bromine Br2 (0.2 mL, 2.6 mmol) in CH2Cl2 (1 mL) was added to a
solution of (Z)-3 (100 mg, 0.26 mmol) in CH2Cl2 (10 mL) at room temperature. After
the reaction mixture was stirred at room temperature for 12 h, it was poured into a
large amount of ice water (10 mL) and extracted with CH2Cl2 (10 mL ꢂ 2). The com-
bined extracts were washed with water, dried with Na2SO4, and concentrated. The
residue was chromatographed over silica gel (Wako C-300, 200 g) with hexane and
hexane–benzene (1:1) as an eluent to give meso-(Z)-4 (42 mg, 30%) and dl-(Z)-4
(84 mg, 60%), respectively.
Bromination of (E)-3 with BTMA Br3
BTMA Br3 (440 mg, 1.2 mmol) was added to a solution of (E)-3 (100 mg,
0.26 mmol) in CH2Cl2 (10 mL) at room temperature. After the reaction mixture was
stirred at room temperature for 24 h, it was poured into a large amount of ice water
(100 mL) and extracted with CH2Cl2 (50 mL ꢂ 2). The combined extracts were washed
with water, dried with Na2SO4, and concentrated. The residue was treated as described
previously to give meso-(Z)-4 (45 mg, 32%) and dl-(Z)-4 (85 mg, 61%), respectively.
Bromination of (Z)-3 with BTMA Br3
BTMA Br3 (440 mg, 1.2 mmol) was added to a solution of (E)-3 (100 mg,
0.26 mmol) in CH2Cl2 (10 mL) at room temperature. After the reaction mixture
was stirred at room temperature for 24 h, it was poured into a large amount of ice
water (100 mL) and extracted with CH2Cl2 (50 mL ꢂ 2). The combined extracts were
washed with water, dried with Na2SO4, and concentrated. The residue was treated as

SYNTHESIS OF 2,3-DIARYLBUTA-1,3-DIENE
3137
described previously to give meso-(Z)-4 (44 mg, 31%) and dl-(Z)-4 (87 mg, 62%),
respectively.
Bromination of 5 with BTMA Br3
BTMA Br3 (98 mg, 0.26 mmol) was added to a solution of 5 (98 mg, 0.26 mmol)
in CH2Cl2 (10 mL) at room temperature. After the reaction mixture was stirred at
room temperature for 12 h, it was poured into a large amount of icewater (10 mL)
and extracted with CH2Cl2 (10 mL ꢂ 2). The combined extracts were washed with
water, dried with Na2SO4, and concentrated. The residue was chromatographed over
silica gel (Wako C-300, 200 g) with hexane and hexane–benzene (1:1) as an eluent to
give meso-(Z)-4 (45 mg, 32%) and dl-(Z)-4 (87 mg, 62%), respectively.
Debromination of 4 with Zinc Powder
Acetic acid (0.28 mL, 4.8 mmol) was gradually added to a suspension of meso-
(Z)-4 (130 mg, 0.24 mmol) and Zn powder (317 mg, 4.9 mmol) in CH2Cl2 (6 mL) and
stirred at room temperature for 24 h. The reaction mixture was filtered and washed
with CH2Cl2 (5 mL ꢂ 3). The filtrate was condensed under the reduced pressure to
leave the crude 2,3-bis(5-tert-butyl-2-methoxyphenyl)buta-1,3-diene 5 (91 mg,
100%) as a colorless solid. Mp 115–116 ꢀC. nmax(KBr)=cmꢁ1: 2966, 1505, 1459,
1247, 1034, 805. dH (CDCl3) 1.23 (s, 18H, tBu), 3.76 (s, 6H, OMe), 5.12 (s, 2H,
CH2), 5.14 (s, 2H, CH2), 6.72 (d, J ¼ 8.4 Hz, 2H, ArH), 7.17 (dd, J ¼ 8.4, 2.4 Hz,
2H, ArH), 7.22 (d, J ¼ 2.4 Hz, 2H, ArH). dC (CDCl3) 31.55, 34.02, 55.90, 110.53,
116.00, 124.88, 128.37, 130.29, 142.84, 147.74, 154.74. MS: m=z [Mþ] 378. Elemental
analysis calculated for C26H34O2(378.56): C, 82.49; H, 9.05. Found: C, 82.63; H, 9.18.
Similar treatment of dl-(Z)-4 with zinc powder afforded the corresponding
diene 5 in quantitative yield.
Diels–Alder Reaction of 5 with Dimethyl Acetylenedicarboxylate
A solution of crude 5 (285 mg, 0.75 mmol) and dimethyl acetylenedicarboxylate
(128 mg, 0.90 mmol) in toluene (5 mL) was heated at 100 ꢀC for 24 h. After the reac-
tion mixture was cooled to room temperature, the solvent was condensed under
reduced pressure to leave the residue. The residue was column chromatographed
over silica gel with benzene as eluent to give compound 6 (285 mg, 73%) as a pale
yellow oil. dH (CDCl3) 1.01 (s, 18H, tBu), 3.76 (s, 6H, OMe), 3.80 (s, 10H, CH2,
COOMe), 6.63 (d, J ¼ 8.6 Hz, 2H, ArH), 6.72 (d, J ¼ 2.3 Hz, 2H, ArH), 6.99 (dd,
J ¼ 8.6, 2.3 Hz, 2H, ArH). MS: m=z [Mþ] 520. Elemental analysis calculated for
C32H40O6(520.66): C, 73.82; H, 7.74. Found: C, 73.93; H, 7.68.
Oxidation of 6 with DDQ
A solution 6 (100 mg, 0.19 mmol) and DDQ (44 mg, 0.25 mmol) in benzene
(5 mL) was heated at 50 ꢀC for 12 h. After the reaction mixture was cooled to rt,
the solvent was condensed under the reduced pressure to leave the residue. The resi-
due was column chromatographed over silica gel with ethyl acetate as eluent to give

3138
K. TAZOE ET AL.
a colorless solid. Recrystallization from methanol afforded dimethyl 4,5-bis(5-tert-
butyl-2-methoxyphenyl)benzene-1,2-dicarboxylate 7 (68 mg, 70%) as colorless prisms
(MeOH). Mp 123–124 ꢀC. nmax(KBr)=cmꢁ1: 2959, 1730 (C O), 1502, 1432, 1288,
=
1255, 1126, 1070, 812. dH (CDCl3) 1.11 (18H, s, tBu), 3.52 (6H, s, OMe), 3.92
(6H, s, COOMe), 6.67 (2H, d, J ¼ 8.6 Hz, Ar-H), 6.95 (2H, d, J ¼ 2.4 Hz, ArH),
7.15 (2H, dd, J ¼ 8.6, 2.4 Hz ArH), 7.80 (2H, s, ArH). dC (CDCl3) 31.38, 33.85,
52.52, 55.20, 109.98, 125.33, 128.20, 128.50, 130.02, 131.59, 141.92, 142.66, 153.92,
168.26. MS: m=z [Mþ] 518. Elemental analysis calculated for C32H38O6(518.64): C,
74.11; H, 7.39. Found: C, 74.27; H, 7.36.
Crystallographic Data for dl-(Z)-4
Crystal data for dl-(Z)-4: C26H34Br4O2, M ¼ 538.33, triclinic, P–1, a ¼ 10.154(2),
3
˚
˚
b ¼ 14.185(2), c ¼ 9.815(2) A, V ¼ 1328.8(4) A , a ¼ 99.27(1), b ¼ 106.63(1), c ¼
93.32(1), Z ¼ 2, Dc ¼ 1.345 g cmꢁ3, m(Mo-Ka) ¼ 3.068 mmꢁ1, T ¼ 296 K, colorless
prisms; 6100 reflections measured on a Rigaku AFC5S CCD diffractometer, of which
2313 were independent, data corrected for absorption on the basis of symmetry equiva-
lent and repeated data (min and max transmission factors: 0.9987, 0.9987) and Lp
effects, Rint ¼ 0.06870, structure solved by direct methods (version 3.5.1. Rigaku=
MSC), F2 refinement, R1 ¼ 0.0870 for 2313 data with F2 > 2s(F2), wR2 ¼ 0.1010 for
all data, 306 parameters. Crystallographic data (excluding structure factors) for the
structures in this article have been deposited with the Cambridge Crystallographic
Data Centre as supplementary publication number CCDC 702663. Copies of the
data can be obtained, free of charge, on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: 144-1223-336033 or e-mail: deposit@ccdc.cam.ac.uk).
ACKNOWLEDGMENT
This research was supported by a Grant-in-Aid for Scientific Research (C), No.
22550040, from the Japan Society for the Promotion of Science.
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