Formation and reactivity of 2-styryl-1,4-benzoquinones

Article abstract of DOI:10.1002/1099-0690(200109)2001:17<3307::AID-EJOC3307>3.0.CO;2-T

The 2-styryl-1,4-benzoquinones 7a,b, generated by the oxidation of the corresponding hydroquinones 6a,b, dimerize at room temperature in a Diels-Alder reaction. The strictly chemo-, regio- and stereoselective process can be rationalized by means of frontier orbital interactions. The polycyclic adducts 8a,b undergo a further intramolecular cycloaddition (8a,b → 10a,b) after oxidation on silica gel.

Full text of DOI:10.1002/1099-0690(200109)2001:17<3307::AID-EJOC3307>3.0.CO;2-T

FULL PAPER
Formation and Reactivity of 2-Styryl-1,4-benzoquinones
Isabella Brehm[a] and Herbert Meier*[a]
Keywords: Cycloaddition / Oxidation / Polycycles / Quinones / Stilbenes
The 2-styryl-1,4-benzoquinones 7a,b, generated by the ox- ized by means of frontier orbital interactions. The polycyclic
idation of the corresponding hydroquinones 6a,b, dimerize
at room temperature in a Diels−Alder reaction. The strictly
chemo-, regio- and stereoselective process can be rational-
adducts 8a,b undergo a further intramolecular cycloaddition
(8a,b Ǟ 10a,b) after oxidation on silica gel.
Introduction
bromo substituent in 5b confers different electronic proper-
ties.
Oligo- and poly(1,4-phenylenevinylene)s (OPV, PPV) rep-
resent a class of compounds, which are of high current in-
terest in materials science, since many different applications
such as semiconductors, photoconductors, electrolumines-
cent systems, materials for nonlinear optics, and negative
photoresists have been found.[1Ϫ6] One problem of these
materials is an often-observed aging in the presence of oxy-
gen or other oxidants.[7] This sensitivity towards oxygen in-
creases with the increasing energy of the HOMO; thus, elec-
tron-rich compounds like, for example, alkoxy-substituted
OPVs or PPVs are particularly prone to oxidation reactions.
The cleavage of the olefinic double bonds leading to ter-
minal formyl or carboxy groups (via 1,2-dioxetanes) is a
plausible process. In addition to this degradation, we ob-
served a crosslinking of the chains. Therefore we present
here a study of the parent system, discussing two differently
substituted (E)-stilbenes in both of which one hydroquinone
ring is oxidized to 1,4-benzoquinone.
Oxidation of the hydroquinone 6a with silver(I) oxide led
to the desired quinone 7a,[8] which spontaneously dimerized
in solution (Scheme 2) to give the tricyclic tetraketone rac-
8a. Obviously the 2-styryl-1,4-benzoquinone 7a had reacted
in a neutral DielsϪAlder reaction with the olefinic double
bond and the conjugated double bond in the quinone ring
serving as the 4π component and the latter double bond in
another molecule as the 2π component. The oxidation of
6b under the same conditions delivered the expected qui-
none 7b, which could be isolated. Its dimerization to rac-8b
in a DielsϪAlder reaction took place in solution in chloro-
form after two days. Obviously, small electronic effects
cause different reaction rates for the dimerization.
The four protons on the central ring of the two phen-
anthrene derivatives 8a,b give simple ABCX spin patterns
in the 1H NMR spectra. The olefinic proton 10-H gives rise
to a triplet (δ ϭ 7.07 for 8a and δ ϭ 7.00 for 8b); the coup-
3
4
ling constants J(10-H, 9-H) and J(10-H, 4a-H) are both
5
3.3 Hz. The homoallylic coupling J(9-H, 4a-H) has virtu-
ally the same size, and 9-H also gives a triplet signal (δ ϭ
Results and Discussion
The 2-styrylhydroquinones 6 seemed to be appropriate
precursors for the generation of the corresponding qui-
nones. We started the preparation of 6a (Scheme 1) with
1,4-dihexylbenzene (1a), whose bromomethylation gave the
derivative 2a, which was subsequently transformed in an
almost quantitative Arbusov reaction to the phosphonate
3a. An analogous process yielded the phosphonate 3b from
2b, which is commercially available. The WittigϪHorner re-
action with 2,5-dimethoxybenzaldehyde (4) furnished the
trans-stilbenes 5a,b in high yields. The cleavage of the two
methyl ether functions (5a,b Ǟ 6a,b) was achieved by reac-
tion with boron tribromide. The WittigϪHorner reactions
of 3a,b with unprotected 2,5-dihydroxybenzaldehyde proved
not to be useful on a preparative scale. The two hexyl
groups in 5a guarantee an improved solubility, whereas the
[a]
Institute of Organic Chemistry, University of Mainz,
Duesbergweg 10Ϫ14, 55099 Mainz, Germany
Fax: (internat.) ϩ49-6131/392-5396
E-mail: hmeier@mail.uni-mainz.de
Scheme 1. Preparation of the 2-styrylhydroquinones 6a,b
Eur. J. Org. Chem. 2001, 3307Ϫ3311
WILEY-VCH Verlag GmbH, 69451 Weinheim, 2001
1434Ϫ193X/01/0917Ϫ3307 $ 17.50ϩ.50/0
3307

I. Brehm, H. Meier
FULL PAPER
Figure 1. Frontier orbitals of 2-styryl-1,4-benzoquinone calculated
by AM1
Scheme 2. Oxidation of 6a,b to the 2-styryl-1,4-benzoquinones 7a,b
and subsequent DielsϪAlder dimerization to the phenanthrene de-
rivatives 8a,b
4.55 for 8a and δ ϭ 4.19 for 8b). The protons 4a-H (δ ϭ
3.46 for 8a and δ ϭ 3.40 for 8b) and 4b-H (δ ϭ 4.06 for 8a
3
and δ ϭ 4.12 for 8b) show a typical cis coupling with J ϭ
4.2 Hz and 4.3 Hz, respectively. The transannular couplings
5
4J(4b-H, 9-H) and J(4b-H, 10-H) are below 1.0 Hz, and
therefore 4b-H appears as a doublet. The assignment of the
signals is based on 1H,1H and 1H,13C shift correlation
measurements as well as on decoupling and NOE experi-
ments. The resulting structures 8a,b are similar to the
dimers of other 2-styryl-1,4-benzoquinones obtained in
electrochemical oxidation processes.[9,10]
The quantitative dimerization 7a,b Ǟ 8a,b is a chemo-,
regio- and endo-stereoselective process. Semiempirical
quantum mechanics provide an explanation. Figure 1 shows
the frontier orbitals calculated by AM1.[11] In contrast to
the 4π component, there are, in principal, three possibilities
for the 2π component, namely both of the CϭC double
bonds in the quinone ring and the olefinic double bond of
the styryl group in 7a,b. The size of the coefficients cij evid-
ently favors the substituted side in the quinone ring. The
four remaining chemo- and regioselective variants can be
judged by the HOMOϪLUMO interactions in this neutral
DielsϪAlder reaction:
Scheme 3. Dehydrogenation of 8a,b and intramolecular
DielsϪAlder cycloaddition to 10a,b
reactions were observed on silica gel at room temperature.
From 8a,b we obtained the dehydrogenated products 10a,b
(Scheme 3).[12] We assume that an oxidation 8a,b Ǟ 9a,b
and another, now intramolecular, [2π ϩ 4π] cycloaddition
takes place.
S1 ϭ (c11·c21 ϩ c14·c22) ϩ (c21·c11 ϩ c24·c12) Ͼ
S2 ϭ (c11·|c22| ϩ |c14|·c21) ϩ (c21·c12 ϩ c24·c11) Ͼ
S3 ϭ (c11·|c23| ϩ |c14|·c24) ϩ (c21·|c13| ϩ |c24|·c14) Ͼ
S4 ϭ (c11·c24 ϩ c14·c23) ϩ (c21·|c14| ϩ |c24|·c13)
The resulting polycyclic system rac-10a,b contains a
1
three-membered ring with a characteristic coupling J(13C,
The chemoselectivity refers to S1, S2 Ͼ S3, S4 and the 1H) of 180 Hz. This HC-16 group belongs to a sequence of
regioselectivity to S1 Ͼ S2; this means that the sterically four adjacent methine groups in the central tricy-
more hindered CϭC double bond of the quinone ring acts clo[3.2.1.08,13]octene moiety. The assignment of the H and
1
as the 2π component, and it adds so that the aryl and styryl 13C NMR signals given in Figure 2 is based on one- and
groups in 8a,b are fixed on neighboring carbon atoms.
When the compounds 8a,b were stored in the refrigerator,
two-dimensional NMR techniques.
Steric reasons do not permit an opposite orientation of
they could be kept for several months; however, consecutive the 2π component in the cycloaddition, therefore the stereo-
3308
Eur. J. Org. Chem. 2001, 3307Ϫ3311

Formation and Reactivity of 2-Styryl-1,4-benzoquinones
FULL PAPER
Diethyl 2,5-Dihexylbenzylphosphonate (3a): Compound 2a (3.0 g,
8.9 mmol) and triethylphosphite (2.91 g, 17.5 mmol) were heated
for 4 h at 170 °C. The excess triethylphosphite was then removed
under vacuum (102 Pa). The product was purified by column chro-
matography on silica gel (70Ϫ230 mesh, 4 ϫ 40 cm) using petro-
leum ether (b.p. 40Ϫ70 °C)/ethyl acetate (5:4) as eluent; 3.22 g
(92%) of 3a was obtained as an almost colorless liquid. Ϫ 1H NMR
(200 MHz, CDCl3): δ ϭ 0.86 (m, 6 H, CH3), 1.27 (m, 18 H, CH2
and CH3 of OC2H5), 1.54 (m, 4 H, CH2), 2.52 (t, 2 H, CH2), 2.62
(t, 2 H, CH2), 3.14 (d, |2J(PH)| ϭ 22.0 Hz, 2 H, CH2P), 3.96 (m, 4
H, OCH2), 6.96 (dd, 1 H, 4-H), 7.06 (m, 2 H, 3-H, 6-H). Ϫ 13C
NMR (50 MHz, CDCl3): δ ϭ 14.1, 14.1 (CH3), 16.3 (CH3 of
OC2H5), 22.6, 29.4, 30.8, 31.5, 32.6, 35.4 (CH2, partly superim-
posed), 30.4 (d, |1J(CP)| ϭ 138 Hz, CH2P), 62.1 (OCH2), 127.1,
128.9, 129.2 (C-3, C-4, C-6), 130.8, 138.7, 140.2 (C-1, C-2, C-5). Ϫ
MS (EI, 70 eV): m/z (%) ϭ 396 (100) [Mϩ·], 339 (43). Ϫ C23H41O3P
(396.6): calcd. C 69.66, H 10.42; found C 69.82, H 10.25.
Figure 2. 1H and 13C NMR spectroscopic data [chemical shifts and
1J(C,H) coupling constants] of the central tricyclo[3.2.1.08,13]octene
scaffold of 10a
chemistry of rac-10a,b is a consequence of the stereochem-
istry of rac-8a,b. Both compounds contain four carbonyl
groups. The corresponding δC values are between 181 and
199 as one would expect for 1,4-benzoquinone and cyclo-
hex-2-ene-1,4-dione substructures.
Diethyl 4-Bromobenzylphosphonate (3b): This compound was pre-
pared according to a procedure described in the literature.[13]
(E)-1-(2,5-Dihexylphenyl)-2-(2,5-dimethoxyphenyl)ethene (5a):
A
solution of 3a (4.0 g, 10.1 mmol) and 2,5-dimethoxybenzaldehyde
(4) (1.68 g, 10.1 mmol) in dry DMF (100 mL) was added dropwise
to a solution of potassium tert-butoxide (4.0 g, 50.5 mmol) in dry
DMF (80 mL) under argon at 0 °C. The mixture was stirred at
room temperature overnight and then poured into ice/water
(200 mL) and 2  HCl (10 mL). After extraction with dichlorome-
thane (100 mL) the organic phase was washed with water (50 mL)
and a saturated solution of NaHCO3 (50 mL) and dried with
Na2SO4. The solvent was evaporated under vacuum (1 kPa) and
the product purified by column chromatography on silica gel
(70Ϫ230 mesh, 4 ϫ 40 cm) with chloroform as eluent; yield: 3.55 g
(86%) of 5a as an almost colorless oil. Ϫ 1H NMR (400 MHz,
CDCl3): δ ϭ 0.88 (m, 6 H, CH3), 1.33 (m, 12 H, CH2), 1.60 (m, 4
H, CH2), 2.61 (t, 2 H, CH2), 2.70 (t, 2 H, CH2), 3.82 (s, 3 H,
OCH3), 3.85 (s, 3 H, OCH3), 6.79 (dd, 1 H, aromat. H), 6.84 (d, 1
H, aromat. H), 7.02 (dd, 1 H, aromat. H), 7.08 (d, 1 H, aromat.
Conclusion
The substituted 2-styrylhydroquinones 6a,b yield the cor-
responding 2-styrylquinones 7a,b in quantitative oxidation
reactions. Compound 7a dimerizes spontaneously in solu-
tion, and 7b upon standing dissolved in chloroform within
two days. The dimerization represents a chemo-, regio- and
stereoselective DielsϪAlder reaction, a process which can
be understood in terms of frontier orbital theory. The ob-
tained cycloadducts 8a,b undergo oxidation on silica gel
and subsequent intramolecular cycloadditions to form
10a,b.
Experimental Section
3
H), 7.15 (d, 1 H, aromat. H), 7.31/7.38 (AB, Jtrans ϭ 16.4 Hz, 2
H, olefin. H), 7.46 (d, 1 H, aromat. H). Ϫ 13C NMR (50 MHz,
CDCl3): δ ϭ 14.1, 14.1 (CH3), 22.6, 29.1, 29.3, 31.3, 31.6, 31.7,
33.2, 35.7 (CH2, partly superimposed), 55.7, 56.3 (OCH3), 112.2,
113.1, 114.2, 124.1, 125.7, 127.5, 127.6, 129.5 (aromat. and olefin.
CH), 127.9, 135.9, 138.0, 140.6, 151.5, 153.6 (aromat. Cq). Ϫ FD-
MS: m/z (%) ϭ 408 (100) [Mϩ·]. Ϫ C28H40O2 (408.6): calcd. C
82.30, H 9.87; found C 82.15, H 10.03.
General Remarks: Melting points (uncorrected): Büchi apparatus.
Ϫ NMR: Bruker AM 400 and WT 200, CDCl3 as solvent if not
otherwise stated, TMS as internal standard. Ϫ MS: Varian MAT
CH7A and Finnigan MAT 95.
2-Bromomethyl-1,4-dihexylbenzene (2a): A 33% solution of HBr in
glacial acetic acid (7.1 mL, 0.04 mol) was added dropwise at room
temperature to 1,4-dihexylbenzene (1a) (9.0 g, 0.04 mol) and par-
aformaldehyde (1.2 g, 0.04 mol), dissolved in glacial acetic acid
(E)-1-(4-Bromophenyl)-2-(2,5-dimethoxyphenyl)ethene (5b): A solu-
(25 mL). The mixture was heated to 95 °C and kept at this temper- tion of 3b (2.89 g, 9.41 mmol) and 2,5-dimethoxybenzaldehyde (4)
ature for 3 days. After cooling to room temp., the mixture was (1.56 g, 9.41 mmol) in dry DMF (80 mL) was added dropwise to a
diluted with water (100 mL) and extracted with diethyl ether solution of potassium tert-butoxide (5.27 g, 47.1 mmol) in dry
(150 mL). The organic phase was neutralized with a saturated solu-
tion of NaHCO3, dried with Na2SO4 and the solvents evaporated.
DMF (90 mL) under argon at 0 °C. The mixture was stirred at
room temperature overnight and then poured into ice/water
Column chromatography of the residue on silica gel (70Ϫ230 mesh, (200 mL) and 2  HCl (10 mL). After extraction with dichlorome-
8 ϫ 30 cm) using petroleum ether (b.p. 40Ϫ70 °C) as eluent yielded
4.33 g (35%) of 2a as a colorless liquid. Ϫ 1H NMR (200 MHz,
CDCl3): δ ϭ 0.88 (m, 6 H, CH3), 1.33 (m, 12 H, CH2), 1.58 (m, 4
thane (200 mL) the organic phase was washed with water (50 mL)
and a saturated solution of NaHCO3 (50 mL) and dried with
Na2SO4. The solvent was evaporated under vacuum (1 kPa) and
H, CH2), 2.54 (t, 2 H, CH2), 2.67 (t, 2 H, CH2), 4.52 (s, 2 H, the product purified by column chromatography on silica gel
CH2Br), 7.07 (m, 3 H, aromat. H). Ϫ 13C NMR (50 MHz, CDCl3): (70Ϫ230 mesh, 4 ϫ 50 cm) using a mixture of petroleum ether (b.p.
δ ϭ 14.1, 14.1 (CH3), 22.6, 22.6, 29.0, 29.4, 31.0, 31.3, 31.7, 31.8, 40Ϫ70 °C) and diethyl ether (5:1) as eluent; yield: 2.73 g (91%) of
32.0, 32.1, 35.4 (CH2), 129.0, 129.6, 130.5 (C-3, C-5, C-6), 135.0 5b as colorless crystals, m.p. 75 °C. Ϫ 1H NMR (400 MHz,
(C-2), 139.0, 140.9 (C-1, C-4). Ϫ MS (EI, 70 eV): m/z (%) ϭ 340/
CDCl3): δ ϭ 3.80 (s, 3 H, OCH3), 3.83 (s, 3 H, OCH3), 6.79 (dd,
338 (5) [Mϩ·] Br isotope pattern, 189 (100). Ϫ C19H31Br (339.4): 1 H, aromat. H), 6.82 (d, 1 H, aromat. H), 7.00/7.42 (AB, 3Jtrans ϭ
calcd. C 67.25, H 9.21; found C 67.13, H 9.36.
16.4 Hz, 2 H, olefin. H), 7.11 (d, 1 H, aromat. H), 7.37/7.45
3309
Eur. J. Org. Chem. 2001, 3307Ϫ3311

I. Brehm, H. Meier
FULL PAPER
3
(AAЈBBЈ, 4 H, aromat. H). Ϫ 13C NMR (50 MHz, CDCl3): δ ϭ 1 H, benzoquinone ring), 7.06/ 7.37 (AB, Jtrans ϭ 16.4 Hz, 2 H,
55.8, 56.2 (OCH3), 111.7, 112.3, 114.0, 124.1, 128.0, 128.1, 131.7 olefin. H), 7.39/ 7.49 (AAЈBBЈ, 4 H, aromat. H). Ϫ 13C NMR
(aromat. and olefin. CH), 121.1, 126.9, 136.8, 151.5, 153.8 (aromat.
(100 MHz, CDCl3): δ ϭ 120.1, 135.0, 141.7 (aromat. and benzoqui-
Cq). Ϫ MS (EI, 70 eV): m/z (%) ϭ 320/318 (100) [Mϩ·] Br isotope none ring Cq), 123.8, 128.3, 129.0, 132.1 (aromat. and olefin. CH),
pattern, 305 (10), 224 (17). Ϫ C16H15BrO2 (319.2): calcd. C 60.21, 136.6, 136.7, 136.8 (CH, benzoquinone ring), 186.8, 187.5 (CO). Ϫ
H 4.74; found C 60.26, H 4.81.
MS (EI, 70 eV): m/z (%) ϭ 290/288 (100) [Mϩ·] Br isotope pattern,
164 (31). Ϫ C14H9BrO2 (289.1): calcd. C 58.16, H 3.14; found C
58.03, H 3.42.
(E)-2-[2-(2,5-Dihexylphenyl)ethenyl]hydroquinone (6a): A 1.0  so-
lution of boron tribromide (42.65 mL, 42.65 mmol) in n-hexane
was added with a syringe to a cold solution of 5a (3.59 g, 8.8 mmol)
rel-(4aS,4bR,8aS,9R)-9-(2,5-Dihexylphenyl)-8a-[(E)-2-(2,5-dihexyl-
in dichloromethane (350 mL) at 0 °C. The reaction was followed phenyl)ethenyl]-4a,4b,8a,9-tetrahydrophenanthrene-1,4,5,8-tetrone
by TLC (SiO2, CH2Cl2). After 4 h of stirring at room temperature, (rac-8a): MgSO4 (250 mg, 2.08 mmol) and freshly prepared Ag2O
the reaction mixture was poured into ice/water (300 mL) and the (244 mg, 1.06 mmol) were added to a solution of 6a (200 mg,
water layer was extracted with the same volume of ethyl acetate. 0.53 mmol) in dry diethyl ether (10 mL). After stirring for 1 h at
The combined organic phases were washed with brine, dried with
room temperature the solid parts were removed and the solvent
Na2SO4 and the solvents evaporated. The residue was purified by evaporated under vacuum (102 Pa). Compound 8a (199 mg) was
column chromatography on silica gel (70Ϫ230 mesh, 4 ϫ 40 cm)
using a mixture of petroleum ether (b.p. 40Ϫ70 °C) and ethyl acet-
ate (3:2) as eluent; yield: 1.57 g (47%) 6a as a liquid, which solidi-
obtained as a red oil in a quantitative yield. Ϫ 1H NMR (400 MHz,
CDCl3): δ ϭ 0.77Ϫ0.86 (m, 12 H, CH3), 1.26Ϫ1.60 (m, 32 H, CH2),
2.23Ϫ2.58 (m, 8 H, CH2), 3.46 (m, 1 H, 4a-H), 4.06 (d, 3J ϭ 4.2 Hz,
fied at 5 °C in the refrigerator. Ϫ 1H NMR (400 MHz, CDCl3): 1 H, 4b-H), 4.55 (t, J ϭ J ϭ 3.3 Hz, 1 H, 9-H), 5.97/6.20 (AB,
3
5
δ ϭ 0.85 (m, 6 H, CH3), 1.28 (m, 12 H, CH2), 1.58 (m, 4 H, CH2), 3J ϭ 10.3 Hz, 2 H) and 6.95/7.03 (AB, J ϭ 10.3 Hz, 2 H) [2-H/3-
3
2.58 (t, 2 H, CH2), 2.67 (t, 2 H, CH2), 6.63 (dd, 1 H, hydroquinone H and 6-H/7-H], 6.39 (d, 1 H), 6.92 (dd, 1 H) 6.99 (d, 1 H) 7.04
3
ring), 6.70 (d, 1 H, hydroquinone ring), 6.98 (d, 1 H, hydroquinone
(m, 2 H) 7.32 (‘‘s’’, 1 H) [aromat. H], 6.42/6.78 (AB, J ϭ 16.1 Hz,
ring), 7.01 (dd, 1 H, aromat. H), 7.06 (d, 1 H, aromat. H), 7.15/ 2 H, olefin. H), 7.07 (t, 3J ϭ 4J ϭ 3.3 Hz, 1 H, 10-H). Ϫ 13C NMR
3
7.31 (AB, Jtrans ϭ 16.1 Hz, 2 H, olefin. H), 7.41 (d, 1 H, aromat. (100 MHz, CDCl3): δ ϭ 13.8, 13.9 (CH3), 22.4, 22.5, 28.9, 29.0,
H). Ϫ 13C NMR (100 MHz, CDCl3): δ ϭ 14.0, 14.0 (CH3), 22.6, 29.1, 29.2, 31.2, 31.3, 31.4, 31.5, 31.6, 31.6, 31.7, 32.6, 33.1, 35.2,
22.6, 29.1, 29.2, 31.2, 31.5, 31.7, 31.7, 33.1, 35.7 (CH2), 113.3,
35.5 (CH2, partly superimposed), 42.5 (C-9), 43.1 (C-4a), 53.4 (C-
115.4, 117.0 (CH, hydroquinone ring), 123.4, 125.7, 127.9, 128.8, 4b), 59.2 (C-8a), 126.1, 128.3, 128.4, 129.5, 130.5, 131.1 (aromat.
129.5 (aromat. and olefin. CH), 126.2, 135.6, 138.0, 140.7, 147.2, CH), 129.4, 132.0 (olefin. CH), 132.0, 134.1, 135.2, 137.6, 138.2,
149.6 (aromat. Cq). Ϫ MS (EI, 70 eV): m/z (%) ϭ 380 (100) [Mϩ·],
141.0, 141.1 (C-10a and aromat. Cq), 137.8 (C-10), 138.7, 139.8,
309 (15). Ϫ C26H36O2 (380.6): calcd. C 82.06, H 9.53; found C 140.5, 142.1 (C-2, C-3, C-6, C-7), 183.8 (C-1), 194.0, 194.9, 198.2
81.79, H 9.66.
(C-4, C-5, C-8). Ϫ FD-MS: m/z (%) ϭ 757 (100) [Mϩ·]. Ϫ
C52H68O4 (757.1): calcd. C 82.49, H 9.05; found C 82.11, H 8.81.
(E)-2-[2-(4-Bromophenyl)ethenyl]hydroquinone (6b): A 1.0  solu-
tion of boron tribromide (31.3 mL, 31.3 mmol) in n-hexane was rel-(4aS,4bR,8aS,9R)-9-(4-Bromophenyl)-8a-[(E)-2-(4-bromo-
added with a syringe to a cold solution of 5b (2.0 g, 6.3 mmol) in
dichloromethane (240 mL) at 0 °C. After stirring for 16 h at room
temperature, the reaction mixture was poured into ice/water
phenyl)ethenyl]-4a,4b,8a,9-tetrahydrophenanthrene-1,4,5,8-tetrone
(rac-8b): Compound 7b (200 mg, 0.7 mmol) was dissolved in
CHCl3 (10 mL) and the mixture allowed to stand for two days. The
(350 mL) and the water layer was extracted with 200 mL of ethyl solution was then concentrated under vacuum (102 Pa) and pure
acetate. The combined organic phases were washed with brine, 8b precipitated after adding a mixture of petroleum ether (b.p.
dried with Na2SO4 and the solvents evaporated. The residue was
purified by column chromatography on silica gel (70Ϫ230 mesh, 4 (93%) yellow solid, m.p. 169 °C. Ϫ H NMR (400 MHz, CDCl3):
40Ϫ70 °C) and ethyl acetate (5:3) to the residue; yield: 185 mg
1
ϫ 50 cm) using a mixture of petroleum ether (b.p. 40Ϫ70 °C) and
δ ϭ 3.40 (m, 1 H, 4a-H), 4.12 (d, 3J ϭ 4.3 Hz, 1 H, 4b-H), 4.19 (t,
ethyl acetate (5:3) as eluent; yield: 693 mg (38%) of a colorless solid 1 H, 3J ϭ 5J ϭ 3.3 Hz, 9-H), 6.07/6.25 (AB, 3J ϭ 10.3 Hz, 2 H)
1
with m.p. 195 °C. Ϫ H NMR (200 MHz, [D6]DMSO): δ ϭ 6.54
and 6.95/7.02 (AB, 3J ϭ 10.6 Hz, 2 H) [2-H/3-H and 6-H/7-H], 6.44
(dd, 1 H, hydroquinone ring), 6.67 (d, 1 H, hydroquinone ring), (‘‘s’’, 2 H, olefin. H), 6.64 (br. s, 2 H), 7.26 (d, 2 H), 7.31 (d, 2 H),
6.93 (d, 1 H, hydroquinone ring), 7.05/ 7.36 (AB, 3Jtrans ϭ 16.6 Hz, 7.45 (d, 2 H) [aromat. H], 7.00 (t, J ϭ J ϭ 3.3 Hz, 1 H, 10-H).
3
4
2 H, olefin. H), 7.48/7.54 (AAЈBBЈ, 4 H, aromat. H), 8.80 (s, 1 H,
OH), 9.13 (s, 1 H, OH). Ϫ 13C NMR (50 MHz, [D6]DMSO): δ ϭ
111.9, 116.1, 116.6 (CH, hydroquinone ring), 119.1, 123.7, 136.9,
Ϫ
13C NMR (100 MHz, CDCl3): δ ϭ 43.2 (C-4a), 46.4 (C-9), 52.4
(C-4b), 58.6 (C-8a), 122.6, 122.6, 132.7, 134.4, 136.0 (C-10a and
aromat. Cq), 128.2, 131.9, 132.0, 132.1 (aromat. CH), 130.8, 131.3
147.9, 149.9 (aromat. Cq), 124.7, 126.1, 128.1, 131.5 (aromat. and (olefin. CH), 135.0 (C-10), 139.4, 139.6, 140.7, 142.1 (C-2, C-3, C-
olefin. CH). Ϫ MS (EI, 70 eV): m/z (%) ϭ 292/290 (100) [Mϩ·] Br
6, C-7), 184.0 (C-1), 193.6, 194.7, 198.9 (C-4, C-5, C-8). Ϫ FD-
isotope pattern, 165 (24). Ϫ C14H11BrO2 (291.2): calcd. C 57.76, H MS: m/z (%) ϭ 580/578/576 (47) [Mϩ·] Br2 isotope pattern, 290
3.81; found C 57.41, H 3.98.
(94), 288 (100). Ϫ C28H18Br2O4 (578.3): calcd. C 58.16, H 3.14;
found C 58.14, H 3.07.
(E)-2-[2-(4-Bromophenyl)ethenyl]benzoquinone
(7b):
MgSO4
(800 mg, 6.64 mmol) and freshly prepared Ag2O (727 mg,
3.14 mmol) were added to a solution of 6b (500 mg, 1.72 mmol) in
dry diethyl ether (40 mL). After stirring for 2 h at room temper-
ature the solid parts were removed and the solvent evaporated un-
Transformation of rac-8a,b into rac-10a,b: Column chromatography
of 8a,b on silica gel (70Ϫ230 mesh, 3 ϫ 70 cm) with petroleum
ether (b.p. 40Ϫ70 °C)/diethyl ether (5:2) yielded as a first fraction
viscous oils: 19% of rac-10a and 17% of rac-10b, respectively. In-
der vacuum (102 Pa). Compound 7b (498 mg) was obtained in creasing of the solvent mixture polarity by using petroleum ether
quantitative yield as a dark red solid, m.p. 190 °C. Ϫ 1H NMR
(400 MHz, CDCl3): δ ϭ 6.77 (m, 2 H, benzoquinone ring), 6.85 (d,
(b.p. 40Ϫ70 °C)/ethyl acetate (5:3) furnished 16% of a second com-
ponent.[12]
3310
Eur. J. Org. Chem. 2001, 3307Ϫ3311

Formation and Reactivity of 2-Styryl-1,4-benzoquinones
FULL PAPER
rel-(1S,8S,13R,14R,15R,16R)-14,15-Bis(2,5-dihexylphenyl)penta-
cyclo[6.6.2.02,7.08,13.013,16]hexadeca-2(7),4,10-triene-3,6,9,12-
tetrone (rac-10a): 1H NMR (400 MHz, CDCl3): δ ϭ 0.82Ϫ0.92 (m,
12 H, CH3), 1.06Ϫ1.71 (m, 32 H, CH2), 2.23 (t, 2 H, CH2), 2.45
(m, 2 H, CH2), 2.62Ϫ2.76 (m, 4 H, CH2), 2.87 (m, 1 H, 16-H),
Acknowledgments
We are grateful to the Deutsche Forschungsgemeinschaft, the
Fonds der Chemischen Industrie and the Materialwissen-
schaftliches Forschungszentrum der Universität Mainz for finan-
cial support.
3
3
3
4.02 (dd, J ϭ 4.3, J ϭ 2.4 Hz, 1 H, 15-H), 4.17 (t, J ϭ 4.3 Hz,
3
3
1 H, 1-H), 4.48 (d, J ϭ 4.3 Hz, 1 H, 14-H), 6.15/6.51 (AB, J ϭ
10.3 Hz, 2 H), 6.73/6.92 (AB, 3J ϭ 10.3 Hz, 2 H), [4-H, 5-H, 10-
H, 11-H], 6.17 (d, 1 H), 6.70 (d, 1 H), 6.79 (dd, 1 H), 6.90 (dd, 1
H), 6.95 (d, 1 H), 6.99 (d, 1 H) [aromat. H]. Ϫ 13C NMR
(100 MHz, CDCl3): δ ϭ 14.1 (CH3), 22.5, 22.5, 22.7, 22.7, 28.6,
28.7, 29.8, 31.0, 31.1, 31.2, 31.2, 31.6, 31.8, 31.8, 32.0, 32.0, 35.3,
35.3 (CH2, partly superimposed), 38.7, 46.1 (C-8, C-13), 39.0 (C-
1), 40.2 (C-15), 43.2 (C-16), 43.7 (C-14), 126.1, 127.3, 127.6, 127.6,
129.0, 129.2 (aromat. CH), 131.2, 132.6, 137.6, 137.9, 138.1, 138.8,
139.9, 140.3 (C-2, C-7 and aromat. Cq), 134.7, 136.9, 138.7, 138.9
(C-4, C-5, C-10, C-11), 181.7, 182.5, 189.0, 190.4 (C-3, C-6, C-9,
C-12). Ϫ FD-MS: m/z (%) ϭ 755 (100) [Mϩ·]. Ϫ C52H66O4 (755.1):
calcd. C 82.71, H 8.81; found C 82.33, H 9.19.
[1]
R. E. Martin, F. Diederich, Angew. Chem. 1999, 111,
1440Ϫ1469; Angew. Chem. Int. Ed. 1999, 38, 1350Ϫ1377.
[2]
U. Scherf, Topics Curr. Chem. 1999, 201, 162Ϫ222.
K. Müllen, G. Wegner, Electronic Materials: The Oligomer Ap-
[3]
proach, Wiley-VCH, Weinheim 1998.
[4]
˚
W. R. Salaneck, I. Lundström, B. Ranby, Conjugated Polymers
and Related Materials, Oxford University Press, Oxford 1993.
H. Meier, Angew. Chem. 1992, 104, 1425Ϫ1446; Angew. Chem.
Int. Ed. Engl. 1992, 31, 1399Ϫ1420.
H.-H. Hörhold, M. Helbig, D. Raabe, J. Opfermann, U.
Schurf, R. Stockmann, D. Weiß, Z. Chem. 1987, 27, 126Ϫ137.
See, for example: M. Lehmann, B. Schartel, M. Hennecke, H.
Meier, Tetrahedron 1999, 55, 13377Ϫ13394 and references
therein.
[5]
[6]
[7]
rel-(1S,8S,13R,14R,15R,16R)-14,15-Bis(4-bromophenyl)pentacyclo-
[8]
The often applied direct oxidation of a 1,4-dialkoxybenzene
with [Ce(NH4)(NO3)4]to the corresponding 1,4-benzoquinones
was not successful here.
[6.6.2.02,7.08,13.013,16]-hexadeca-2(7),4,10-triene-3,6,9,12-tetrone
1
(rac-10b): H NMR (400 MHz, CDCl3): δ ϭ 3.00 (br. s, 1 H, 16-
H), 3.89 (dd, 3J ϭ 4.7, 3J ϭ 2.3 Hz, 1 H, 15-H), 4.14 (t, 3J ϭ
4.7 Hz, 1 H, 1-H), 4.34 (d, 3J ϭ 4.7 Hz, 1 H, 14-H), 6.23/6.54 (AB,
[9]
H. Irngartinger, B. Stadler, Eur. J. Org. Chem. 1998, 605Ϫ626.
[10]
1
The assignment of the H NMR signals given in ref.[9] has to
3
3J ϭ 10.3 Hz, 2 H), 6.77/6.90 (AB, J ϭ 10.6 Hz, 2 H) [4-H, 5-H,
be changed.
AM1: Win MOPAC, version 2.0.1.
Compound 8a also gave an isomer C52H68O4 in a yield of 16%.
It turned out that the structure of the isomer is a complicated
polycyclic system, in which all four carbonyl groups of 8a dis-
appeared; the final proof for the structure will be given by an
X-ray investigation.
[11]
[12]
10-H, 11-H], 6.69 (d, 2 H), 6.94 (d, 2 H), 7.22 (d, 2 H), 7.34 (d, 2
H) [aromat. H]. Ϫ 13C NMR (50 MHz, CDCl3): δ ϭ 38.2, 45.9 (C-
8, C-13), 41.0, 41.9, 42.2, 45.5 (C-1, C-14, C-15, C-16), 121.3, 121.6,
131.0, 133.5, 134.5, 137.8 (C-2, C-7 and aromat. Cq), 128.6, 128.9,
131.7, 131.9 (aromat. CH), 134.7, 137.3, 138.9, 138.9 (C-4, C-5, C-
10, C-11), 181.8, 182.3, 188.4, 190.0 (C-3, C-6, C-9, C-12). Ϫ FD-
MS: m/z (%) ϭ 578/576/574 (100) [Mϩ·] Br2 isotope pattern. Ϫ
C28H16Br2O4 (576.3): calcd. C 58.36, H 2.80; found C 58.01, H
3.17.
[13]
H. Meier, R. Petermann, U. Dullweber, J. Prakt. Chem. 1998,
340, 744Ϫ754.
Received March 16, 2001
[O01126]
Eur. J. Org. Chem. 2001, 3307Ϫ3311
3311