A versatile and efficient method for the synthesis of benz[a]azulenic enones starting from readily available o-(2-furyl)cycloheptatrienylbenzenes

Article abstract of DOI:10.1039/b005948j

A facile, one-pot synthesis of β-(benz[a]azulen-10-yl)-α,β-unsaturated ketones from the corresponding o-(2-furyl)cycloheptatrienylbenzenes is reported. A mechanism involving a novel ring-opening cyclisation reaction by the intramolecular attack of the tropylium ion to the 2-position of the furan ring is proposed. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/b005948j

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A versatile and efficient method for the synthesis of
benz[a]azulenic enones starting from readily available
o-(2-furyl)cycloheptatrienylbenzenes1
1
Misako Sasabe,a Yuuko Houda,a Hideki Takagi,a Takashi Sugane,b Xu Boa and
Kimiaki Yamamura*b
a Graduate School of Science and Technology, Kobe University, Nada, Kobe 657-8501, Japan
b Department of Chemistry, Faculty of Science, Kobe University, Nada, Kobe 657-8501, Japan
Received (in Cambridge, UK) 24th July 2000, Accepted 5th September 2000
First published as an Advance Article on the web 30th October 2000
A facile, one-pot synthesis of β-(benz[a]azulen-10-yl)-α,β-unsaturated ketones from the corresponding
o-(2-furyl)cycloheptatrienylbenzenes is reported. A mechanism involving a novel ring-opening cyclisation
reaction by the intramolecular attack of the tropylium ion to the 2-position of the furan ring is proposed.
Introduction
Azulene and its derivatives, which are typical non-benzenoid
aromatic hydrocarbons, have been investigated extensively from
the chemical, physical, pharmaceutical and physiological points
of view, since the first isolation of azulene derivatives from the
distillation of chamomile oil in about the middle of the 19th
century. Moreover, from the viewpoint of advanced materials
with special optical and electrical properties,2 increasing inter-
est has recently been focussed on azulenoid compounds.
Benz[a]azulene and its derivatives, annelated with a benzene
ring on the five-membered ring of the azulene ring, are also
interesting compounds. In spite of the fundamental significance
of benz[a]azulene, synthetic difficulties, particularly for substi-
tuted systems, have impeded progress in these areas.3 We report
in this paper on a novel, one-pot synthesis of β-(benz[a]azulen-
10-yl)-α,β-unsaturated ketones from the corresponding
o-(2-furyl)cycloheptatrienylbenzenes. This method should
provide efficient access to a variety of α,β-unsaturated carbonyl
derivatives of benz[a]azulene.
Results and discussion
Synthesis of the precursors, o-(2-furyl)cycloheptatrienyl-
benzenes 3
The synthetic sequence leading to the precursors for the title
benz[a]azulenic enones 4 is depicted in Schemes 1 and 2. The
common starting material for the synthesis of the title benz[a]-
azulenic enones, o-cycloheptatrienylbromobenzene 1, was
prepared4 as an isomeric mixture from commercially available
cyclohepta-1,3,5-triene and o-bromoiodobenzene utilising
Heck arylation.5 As shown in Scheme 1, the palladium()-
catalysed Stille reaction6 of 1 with 5-substituted 2-trimeth-
Scheme 1
ylstannylfurans 2a–f, prepared according to the known
procedure,7 gave the corresponding o-(2-furyl)cyclohepta-
yields. The structures of the obtained o-(2-furyl)cyclohepta-
trienylbenzenes 3a–i were determined by their H NMR, IR
1
trienylbenzenes 3a–f, in 60.0–81.8% yields. As shown in
Scheme 2, the other desired precursors for 4h and i were
synthesized from 3f utilising a Wittig reaction. Thus, 3f was
treated with pyridinium toluene-p-sulfonate (PPTS)8 in acetone
to afford o-(5-formyl-2-furyl)cycloheptatrienylbenzene 3g
in almost quantitative yield. Then, treatment of 3g with
an equimolar amount of the requisite Wittig reagent,
benzyltriphenylphosphonium bromide or cinnamyltriphenyl-
phosphonium chloride,9 in the presence of 18-crown-6 and
potassium hydroxide in benzene gave the corresponding o-(2-
furyl)cycloheptatrienylbenzenes 3h and 3i, respectively, in good
and mass spectra as well as elemental analysis. Since 3a–i were
1
isolated as isomeric mixtures, their H NMR spectra were not
completely assigned, but they did show the expected spectra
features.
Conversion of 3 to benz[a]azulenic enones 4
Conversion of 3 to the title benz[a]azulenic enones 4 was
successfully carried out as follows, and is illustrated in
Scheme 3. The results are shown in Table 1.
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J. Chem. Soc., Perkin Trans. 1, 2000, 3786–3790
This journal is © The Royal Society of Chemistry 2000
DOI: 10.1039/b005948j

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Table 1
Entry
o-(2-Furyl)cycloheptabenzene
Benz[a]azulenic enone
Yield (%)a
1
2
3
4
5
6
7
8
9
R = -CH3
3a
R = -CH3
4a
4b
4c
4d
4e
—
—
4h
4i
40.0
39.3
32.9
48.6
41.3b
—
—
32.4
41.3
R = -CH2CH3
R = -CH2(CH2)3CH3
R = -C6H5
3b
3c
3d
3e
3f
R = -CH2CH3
R = -CH2(CH2)3CH3
R = -C6H5
R = -C(C6H5)3
—
R = H
R = 1,3-Dioxolan-2-yl
R = -CHO
3g
3h
3i
—
R = -CH᎐CH-C6H5
R = -CH᎐CH-C6H5
᎐
᎐
R = -(CH᎐CH)2-C6H5
R = -(CH᎐CH)2-C6H5
᎐
᎐
a Yields are of isolated and purified products. b Double the molar quantity of trityl tetrafluoroborate was used.
Scheme 4
Scheme 2
Scheme 5
The formation of 4 from 3 can best be rationalised by the
mechanism given in Scheme 5.
It is well-known that the 2-position of the furan ring is much
more reactive towards the electrophiles than the 3-position, and
that the furans bearing electron-donating groups on their 2(5)-
positions are readily ring-opened to 1,4-diketones under acidic
conditions.12 The intramolecular electrophilic attack of the
initially formed trityl substituted cation 7 on the 2-position of
the furan ring gives a five-membered spiro-type intermediate 8,
which can be converted to the final product by a ring unraveling
reaction and aromatisation. In fact, when 3a was treated with
an equimolar amount of trityl tetrafluoroborate in dichloro-
methane for 5 minutes at 0 ЊC, followed by addition of dry
ether, a cationic reddish precipitate was obtained. Although its
1H NMR spectrum was not completely assigned because it
changed rapidly into a mixture including 4a, this reddish
precipitate could be assigned to be o-tropylio(5-ethyl-2-furyl)-
benzene 7 as inferred from its UV–Vis and IR spectra. When
a dichloromethane or acetonitrile solution of 7 was allowed
to stand for 10 h, 4b was obtained in 35.0% yield, together with
a small amount of 1-(benz[a]azulen-10-yl)butan-3-one.
Scheme 3
A mixture of 3 with an equimolar amount of triphenylmethyl
(trityl) tetrafluoroborate in dichloromethane solution (ca. 0.05
mol LϪ1) was allowed to stand overnight at ambient temper-
ature. After usual work-up, the corresponding benz[a]azulenic
enones could be isolated as deep-coloured crystals (entries 1–5, 8
and 9). The structures of the obtained benz[a]azulenic enones
4 were confirmed by their 1H NMR, IR, UV–Vis and MS
spectra as well as elemental analysis. The structures of 4e and
4i were also established by X-ray crystallography.10 When o-(2-
thienyl)cycloheptatrienylbenzene 5, which is an analogue of 3,
was treated with trityl tetrafluoroborate in dichloromethane for
70 h, tetracyclic cyclohepta[3,4]naphtho[1,2-b]thiophenylium
ion 6, which is an isoelectronic cation of triphenylene, was
obtained (Scheme 4).11 Thus, a markedly different result
was obtained between the furan derivative and the thiophene
derivative.
If this mechanism is correct, the carbonyl group and the
benz[a]azulene ring should be cis to each other. However the
coupling constants of ca. 16 Hz between the olefinic protons on
4 indicate a trans configuration between the carbonyl group and
benz[a]azulene ring. This can be explained by the assumption
that the initially formed cis isomer changes spontaneously into
J. Chem. Soc., Perkin Trans. 1, 2000, 3786–3790
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the more stable trans isomer by the acid generated in the course
of the reaction.
stirred under N2 at Ϫ78 ЊC for 1 h. The mixture was then stirred
for 3 h at 20 ЊC, and then cooled to Ϫ78 ЊC. Trimethylstannyl
chloride (23.7 g, 120 mmol) in 20 ml of dry ether was added
dropwise via a syringe and stirred for 2 h at Ϫ78 ЊC. The mix-
ture was stirred overnight at room temperature. The reaction
mixture was quenched with aqueous NH4Cl and extracted with
2 × 80 ml of ether. The combined ether layers were dried over
Na2SO4 and concentrated in vacuo. The residue was purified by
distillation to give the 2-trimethylstannylfuran 2.
With 3e, which has no substituent on the 5-position of its
furan ring, one may expect the formation of α,β-unsaturated
aldehyde 9. However, when 3e was treated with trityl tetra-
fluoroborate in a similar manner, the expected aldehyde 9
was not obtained,13 and 1,1,1-triphenyl-4-(benz[a]azulen-10-
yl)but-3-en-2-one 4e was obtained in 25% yield (Scheme 6).
2-Methyl-5-trimethylstannylfuran 2a. 2-Methyl-5-trimethyl-
stannylfuran was isolated as a colourless oil; yield: 82.1%;
bp 60 ЊC/8 mmHg; δH (60 MHz) 6.44 (1H, d, J = 3.0 Hz, furan),
5.95 (1H, d, J = 3.0 Hz, furan), 2.30 (3H, s, methyl), 0.27 (9H, s,
Me) ppm.
2-Ethyl-5-trimethylstannylfuran 2b. 2-Ethyl-5-trimethylstan-
nylfuran was isolated as a colourless oil; yield: 48.4%, bp 82 ЊC/
11 mmHg; δH (60 MHz) 6.67 (1H, d, J = 3.0 Hz, furan), 6.16
(1H, d, J = 3.0 Hz, furan), 2.88 (2H, q, J = 7.5 Hz, methylene),
1.44 (3H, t, J = 7.5 Hz, methyl), 0.30 (9H, s, Me) ppm.
2-n-Pentyl-5-trimethylstannylfuran 2c. 2-n-Pentyl-5-trimethyl-
stannylfuran was isolated as a pale yellow oil; yield: 42.5%; bp
73 ЊC/9 mmHg; δH (60 MHz) 6.47 (2H, d, J = 3.0 Hz, furan),
5.99 (1H, d, J = 3.0 Hz, furan), 2.65 (2H, t, J = 7.6 Hz, meth-
ylene), 1.70–0.80 (9H, m, methylene), 0.30 (9H, s, Me) ppm.
Scheme 6
Apparently, the trityl salt acts as both an electrophile and a
hydride abstraction reagent in the reaction. When 2.5 equiv-
alent of trityl salt was employed, the yield of 4e reached 41.3%
(entry 5). DDQ,14 phosphorus pentachloride,15 ammonium
nitrate–trifluoroacetic acid,16 1,3-benzodithiolylium salt17 and
tris(p-bromophenyl)amminium salt18 were tried as hydride
abstraction reagents in order to obtain the α,β-unsaturated
aldehyde 9, however satisfactory results were not obtained.
When the substituent on the furan ring is alkyl, phenyl or
alkenyl, the desired α,β-unsaturated ketones were thus
obtained. However, attempted conversion of formyl derivative
3g to the corresponding α,β-unsaturated ketone 4 was unsuc-
cessful (entry 7). The starting material 3g was recovered
unchanged even after prolonged reaction times at elevated
temperatures. Presumably, the non-reactivity of 3g is a reflec-
tion of the decrease of nucleophilicity of the 2-position in the
furan ring due to the electrophilicity of the formyl group.
With 3f, since the 1,3-dioxolane ring reacted with trityl salt,19
a complex mixture was obtained instead of the desired benz[a]-
azulenic enone (entry 6).
2-Phenyl-5-trimethylstannylfuran 2d. 2-Phenyl-5-trimethyl-
stannylfuran was isolated as a colourless oil; yield: 66.0%; bp
110–113 ЊC/2.5 mmHg; δH (60 MHz) 6.53–7.68 (5H, m, phenyl),
7.52 (1H, d, J = 3.0 Hz, furan), 7.13 (1H, d, J = 3.0 Hz, furan),
0.26 (9H, s, Me) ppm.
2-Trimethylstannylfuran 2e. 2-Trimethylstannylfuran was
isolated as a colourless oil; yield: 56.7%; bp 87–89 ЊC/55
mmHg; δH (60 MHz) 7.85 (1H, d, J = 2.0 Hz, furan), 7.76 (1H,
d, J = 3.0 Hz, furan), 6.57 (1H, dd, J = 2.0, 3.0 Hz, furan), 0.25
(9H, s,) ppm.
2-(1,3-Dioxolan-2-yl)-5-trimethylstannylfuran 2f. 2-(1,3-
Dioxolan-2-yl)-5-trimethylstannylfuran was isolated as a yellow
oil; yield: 52.0%; bp 107 ЊC/3 mmHg; δH (60 MHz) 6.52 (1H,
d, J = 3.0, furan), 6.44 (1H, d, J = 3.0, furan), 5.99 (1H, s,
methine), 4.16–3.97 (4H, m, methylene), 0.32 (9H, s, Me) ppm.
Although a few tropylium ion-mediated azulene syntheses
have been reported,20 to our knowledge, this is the first case of
a tropylium ion-mediated furan-ring-opening reaction to give
benz[a]azulene derivatives. Since 2-substituted furans are
readily available and the procedure is simple, and further, the
formation of benz[a]azulenic enones is difficult by other
synthetic methods, it is considered that this is a valuable
general synthetic methodology leading to various benz[a]-
azulenic enones.
General procedure for the synthesis of o-(2-furyl)cyclohepta-
trienylbenzenes 3
A mixture of o-cycloheptatrienylbromobenzene 1 (4.44 g,
18 mmol), the 2-trimethylstannylfuran 2 (23.4 mmol), bis-
(triphenylphosphine)palladium() chloride (1.0 g, 1.42 mmol)
and 70 ml of dry tetrahydrofuran was refluxed for 20 h under
an N2 atmosphere. The reaction mixture was concentrated
in vacuo. The residue was purified by column chromatography
over silica gel using hexane as eluent to give the o-(2-furyl)-
cycloheptatrienylbenzene 3.
Experimental
All melting points are uncorrected. 1H NMR spectra were
determined in CDCl3 on Hitachi R-1500 (60 MHz) and/or
Bruker DPX-250 (250 MHz) Fourier Transform spectrometers.
All chemical shifts are reported in ppm downfield from tetra-
methylsilane as the internal standard. UV–Vis spectra were
determined in dichloromethane on a Shimadzu UV2200
spectrometer. Mass spectra were determined on a Shimazdu
GCMS QP2000A instrument.
o-(5-Methyl-2-furyl)cycloheptatrienylbenzene
3a.
o-(5-
Methyl-2-furyl)cycloheptatrienylbenzene was obtained as a
pale yellow oil; yield: 62.8%; m/z: 248 (Mϩ); Found: C, 87.25;
H, 6.36. Calc. for C18H16O: C, 87.06; H, 6.49%.
o-(5-Ethyl-2-furyl)cycloheptatrienylbenzene 3b. o-(5-Ethyl-2-
furyl)cycloheptatrienylbenzene was obtained as a pale yellow
oil; yield: 61.0%; m/z: 262 (Mϩ); Found: C, 87.06; H, 6.82.
Calc. for C19H18O: C, 86.99; H, 6.92%.
General procedure for the synthesis of 2-trimethylstannylfurans 2
o-(5-n-Pentyl-2-furyl)cycloheptatrienylbenzene 3c. o-(5-n-
Pentyl-2-furyl)cycloheptatrienylbenzene was obtained as a
yellow oil; yield: 91.3%; m/z: 304 (Mϩ); Found: C, 86.92; H,
8.12. Calc. for C22H24O: C, 86.80; H, 7.95%.
Furan (112 mmol) was dissolved in 75 ml of dry ether and
cooled to Ϫ78 ЊC. After addition of a hexane solution of
n-butyllithium (75 ml, 1.6 mol, 120 mmol), the solution was
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o-(5-Phenyl-2-furyl)cycloheptatrienylbenzene 3d. o-(5-Phenyl-
2-furyl)cycloheptatrienylbenzene was obtained as a pale yellow
oil; yield: 60.0%; m/z: 310 (Mϩ); Found: C, 89.23; H, 5.98.
Calc. for C23H18O: C, 89.05; H, 5.85%.
membered ring), 7.19 (1H, dd, J = 9.0, 11.0 Hz, seven-
membered ring), 7.11 (1H, d, J = 16.0 Hz, olefin), 2.49 (3H, s,
methyl) ppm; m/z: 246 (Mϩ); Found: C, 87.66; H, 5.81. Calc. for
C18H14O: C, 87.78; H, 5.73%.
o-(2-Furyl)cycloheptatrienylbenzene 3e. o-(2-Furyl)cyclo-
heptatrienylbenzene was obtained as a pale yellow oil; yield:
60.0%; m/z: 234 (Mϩ); Found: C, 87.31; H, 6.22. Calc. for
C17H14O: C, 87.15; H, 6.02%.
(E)-1-(Benz[a]azulen-10-yl)pent-1-en-3-one 4b. (E)-1-(Benz-
[a]azulen-10-yl)pent-1-en-3-one was isolated as dark-green
needles; yield: 39.3%; mp 85–90 ЊC; δH (250 MHz) 8.46 (1H, d,
J = 8.4 Hz, seven-membered ring), 8.43 (1H, d, J = 16.0 Hz,
olefin), 8.43 (1H, d, J = 7.9 Hz, six-membered ring), 8.41 (1H,
d, J = 10.9 Hz, seven-membered ring), 8.29 (1H, d, J = 8.1 Hz,
six-membered ring), 7.81 (1H, t, J = 7.6, six-membered ring),
7.59 (1H, t, J = 7.4 Hz, six-membered ring), 7.41 (1H, dd,
J = 9.5, 10.0 Hz, seven-membered ring), 7.26 (1H, dd, J = 8.7,
10.0 Hz, seven-membered ring), 7.17 (1H, dd, J = 8.1, 11.0 Hz,
seven-membered ring), 7.13 (1H, d, J = 16.0 Hz, olefin), 2.79
(2H, q, J = 7.3 Hz, methylene), 1.26 (3H, t, J = 7.3 Hz, methyl)
ppm; m/z: 260 (Mϩ); Found: C, 87.78; H, 6.25. Calc. for
C19H16O: C, 87.66; H, 6.19%.
o-[5-(1,3-Dioxolan-2-yl)-2-furyl]cycloheptatrienylbenzene 3f.
o-[5-(1,3-Dioxolan-2-yl)-2-furyl]cycloheptatrienylbenzene was
obtained as a yellow oil; yield: 77.5%; m/z: 336 (Mϩ); Found: C,
89.47; H, 6.08. Calc. for C25H20O: C, 89.25; H, 5.99%.
Synthesis of o-(5-formyl-2-furyl)cycloheptatrienylbenzene 3g
A mixture of 3f (3.4 g, 11.11 mmol), PPTS (0.871 g, 3.47
mmol), 5 ml of H2O and 50 ml of acetone was refluxed for 1 h.
After evaporating the solvent, the residue was dissolved in
ether. The ether solution was washed with aqueous NaHCO3,
dried over Na2SO4, and concentrated in vacuo. The residue was
purified by column chromatography over silica gel using
benzene–hexane (1:1) as eluent to give 3g (2.06 g); yield:
77.5%, colourless precipite; m/z: 262 (Mϩ); Found: C, 89.47;
H, 6.08. Calc. for C18H14O2: C, 82.42; H, 5.38%.
(E)-1-(Benz[a]azulen-10-yl)oct-1-en-3-one 4c. (E)-1-(Benz-
[a]azulen-10-yl)oct-1-en-3-one was isolated as dark-green
needles; yield: 32.9%; mp 63–66 ЊC; δH (250 MHz) 8.47 (1H, d,
J = 8.2 Hz, seven-membered ring), 8.43 (1H, d, J = 8.4 Hz, six-
membered ring), 8.42 (1H, d, J = 14.8 Hz, olefin), 8.41 (1H, d,
J = 11.6 Hz, seven-membered ring), 8.29 (1H, d, J = 8.1 Hz, six-
membered ring), 7.82 (1H, t, J = 7.6 Hz, six-membered ring),
7.59 (1H, t, J = 7.6 Hz, six-membered ring), 7.41 (1H, dd,
J = 9.5, 9.7 Hz, seven-membered ring), 7.26 (1H, dd, J = 9.0,
10.1 Hz, seven-membered ring), 7.17 (1H, dd, J = 9.6, 10.1 Hz,
seven-membered ring), 7.13 (1H, d, J = 15.4 Hz, olefin), 2.75
(2H, t, J = 7.5 Hz, methylene), 1.80–1.74 (2H, m, methylene),
1.48–1.36 (2H, m, methylene), 0.94 (3H, t, J = 7.3 Hz, methyl)
ppm; m/z: 302 (Mϩ); Found: C, 87.50; H, 7.39. Calc. for
C22H22O: C, 87.38; H, 7.33%.
Synthesis of o-(5-styryl-2-furyl)cycloheptatrienylbenzene 3h
To an ice-cooled solution of benzyltriphenylphosphonium
bromide (847 mg, 1.95 mmol), 3g (501 mg, 1.91 mmol), 18-
crown-6 (47 mg, 0.195 mmol), 10 ml of dichloromethane and
powdered KOH (213 mg, 3.8 mmol) were added, and stirred
for 2 h at ambient temperature. After diluting with 20 ml of
dichloromethane, unsoluble materials were filtered off, and then
the dichloromethane layer was washed with water, and dried
over Na2SO4. The solvent was evaporated in vacuo. The residue
was purified by column chromatography over silica gel using
hexane–ethyl acetate (4:1) as eluent to give 3h (498 mg) as a
yellow oil; yield: 76.8%; m/z: 336 (Mϩ); Found: C, 89.47; H,
6.08. Calc. for C25H20O: C, 89.25; H, 5.99%.
(E)-3-(Benz[a]azulen-10-yl)-1-phenylprop-2-en-1-one 4d. (E)-
3-(Benz[a]azulen-10-yl)-1-phenylprop-2-en-1-one was isolated
as dark-green needles; yield: 48.6%; mp 174 ЊC; δH (250 MHz)
8.69 (1H, d, J = 15.4, olefin), 8.47 (1H, d, J = 11.0, seven-
membered ring), 8.45 (1H, d, J = 8.5 Hz, six-membered ring),
8.41 (1H, d, J = 8.1 Hz, seven-membered ring), 8.35 (1H, J = 8.0
Hz, six-membered ring), 8.12 (2H, dd, J = 1.5, 7.5 Hz, phenyl),
7.86 (1H, d, J = 15.5, olefin), 7.83 (1H, t, J = 7.6 Hz,
six-membered ring), 7.57 (1H, t, J = 7.5, six-membered ring),
7.50–7.61 (3H, m, phenyl), 7.41 (1H, dd, J = 9.2, 10.3, seven-
membered ring), 7.25 (1H, t, J = 8.9, seven-membered ring),
7.18 (1H, dd, J = 8.5, 10.9, seven-membered ring) ppm; m/z: 308
(Mϩ); Found: C, 89.45; H, 5.36. Calc. for C23H16O: C, 89.58;
H, 5.23%.
Synthesis of o-[5-(4-phenylbuta-1,3-dienyl)-2-furyl]cyclohepta-
trienylbenzene 3i
o-[5-(4-Phenylbuta-1,3-dienyl)-2-furyl]cycloheptatrienylbenz-
ene was prepared as described for 3h, using triphenylcinnam-
ylphosphonium chloride as Wittig reagent as a yellow oil; yield:
81.8%; m/z: 362 (Mϩ); Found: C, 89.25; H, 6.22. Calc. for
C27H22O: C, 89.47; H, 6.12%.
General procedure for the synthesis of benz[a]azulenic enones 4
o-(2-Furyl)cycloheptatrienylbenzene 3 (5.84 mmol) in 5 ml of
dry CH2Cl2 was added to a solution of trityl tetrafluorobotate
(1.93 g, 5.85 mmol) in 15 ml of dry CH2Cl2 at ambient temper-
ature. The mixture was stirred for 5 min, and then dry CH2Cl2
(200 ml) was added. The solution was stirred overnight at
ambient temperature. The solvent was removed in vacuo. The
product was purified by column chromatography (silica gel,
hexane–ethyl acetate (4:1)) and recrystallised from benzene–
hexane (1:1).
(E)-1,1,1-Triphenyl-4-(benz[a]azulen-10-yl)but-3-en-2-one 4e.
(E)-1,1,1-Triphenyl-4-(benz[a]azulen-10-yl)but-3-en-2-one was
isolated as black prisms; yield: 41.3%;21 mp 295 ЊC; δH (250
MHz) 8.45 (1H, d, J = 15.1, olefin), 8.45 (1H, d, J = 11.0 Hz,
seven-membered ring), 8.42 (1H, d, J = 10.8 Hz, seven-
membered ring), 8.39 (1H, d, J = 8.1 Hz, six-membered ring),
8.30 (1H, dd, J = 8.0, 8.3 Hz, six-membered ring), 7.80 (1H, dd,
J = 8.0, 7.8 Hz, six-membered ring), 7.58 (1H, dd, J = 7.8,
8.1 Hz, seven-membered ring), 7.43 (1H, dd, J = 8.8, 11.0 Hz,
seven-membered ring), 7.41 (15H, m, phenyl), 7.30 (1H, dd, 1H,
J = 9.0, 10.9 Hz, seven-membered ring), 7.00 (d, 1H, J = 15.2
Hz, olefin) ppm; m/z: 474 (Mϩ); Found: C, 90.12; H, 5.48. Calc.
for C36H26O: C, 89.97; H, 5.59%.
(E)-4-(Benz[a]azulen-10-yl)but-3-en-2-one 4a. (E)-4-(Benz[a]-
azulen-10-yl)but-3-en-2-one was isolated as dark-green needles;
yield: 40.0%; mp 112 ЊC; δH (250 MHz) 8.47 (1H, d, J = 7.5 Hz,
six-membered ring), 8.45 (1H, d, J = 11.0 Hz, seven-membered
ring), 8.41 (1H, d, J = 11.0 Hz, seven-membered ring), 8.38 (1H,
d, J = 16.0 Hz, olefin), 8.29 (1H, d, J = 8.0 Hz, six-membered
ring), 7.81 (1H, t, J = 7.5 Hz, six-membered ring), 7.60 (1H,
t, J = 7.5 Hz, six-membered ring), 7.42 (1H, t, J = 9.0 Hz,
seven-membered ring), 7.28 (1H, dd, J = 9.0, 11.0 Hz, seven-
(E,E)-1-(Benz[a]azulen-10-yl)-5-phenylpenta-1,4-dien-3-one
4h.
(E,E)-1-(Benz[a]azulen-10-yl)-5-phenylpenta-1,4-dien-3-
one was isolated as dark-green needles; yield: 44.6%; mp 146–
150 ЊC; δH (250 MHz) 8.63 (1H, d, J = 15.5 Hz, olefin), 8.51
(1H, d, J = 10.9 Hz, seven-membered ring), 8.49 (1H, d, J = 8.4
J. Chem. Soc., Perkin Trans. 1, 2000, 3786–3790
3789

View Article Online
37, 813; (b) C. Wentrup and J. Becker, J. Am. Chem. Soc., 1984, 106,
Hz, six-membered ring), 8.45 (1H, d, J = 8.0 Hz, six-membered
ring), 8.37 (1H, d, J = 7.5 Hz, six-membered ring), 7.84 (1H,
t, J = 7.5 Hz, six-membered ring), 7.81 (1H, d, J = 16.3 Hz,
olefin), 7.69–7.65 (2H, m, phenyl), 7.60 (1H, t, J = 7.5 Hz,
six-membered ring), 7.43 (1H, d, J = 15.2, olefin), 7.42 (1H, dd,
J = 9.0, 10.4 Hz, seven-membered ring), 7.46–7.40 (3H, m,
phenyl), 7.29 (1H, dd, J = 8.6, 9.1 Hz, seven-membered ring),
7.21 (1H, dd, J = 9.1, 10.5 Hz, seven-membered ring), 7.17 (1H,
d, J = 16.3 Hz, olefin) ppm; m/z: 334 (Mϩ); Found: C, 89.90;
H, 5.51. Calc. for C25H18O: C, 89.79; H, 5.43%.
3705; (c) K. Mizuno, K. Okada and M. Oda, Tetrahedron Lett.,
1984, 25, 2999; (d) Y. N. Gupta and K. N. Houk, Tetrahedron Lett.,
1985, 26, 607; (e) H. Duddeck, M. Kennedy, M. A. Mckervey and
F. M. Twohig, J. Chem. Soc., Chem. Commun., 1988, 1586; ( f )
M. Yasunami, T. Sato and M. Yoshifuji, Tetrahedron Lett., 1995, 36,
103 and references cited therein.
4 K. Yamamura, K. Nakatsu, K. Nakao. T. Nakazawa and I. Murata,
Tetrahedron Lett., 1979, 4999.
5 (a) H. A. Dieck and R. F. Heck, J. Am. Chem. Soc., 1974, 96, 1133;
(b) R. F. Heck, Acc. Chem. Res., 1979, 12, 146; (c) R. F. Heck, Org.
React., 1981, 27, 345.
6 (a) J. K. Stille, Angew. Chem., Int. Ed. Engl., 1986, 25, 508; (b)
T. R. Bailey, Tetrahedron Lett., 1986, 27, 4407; (c) A. Dondoni,
A. R. Mastellari, A. Medict, E. Negrini and P. Pedrini, Synthesis,
1986, 757; (d) V. N. Kalnin, Synthesis, 1992, 413; (e) T. N. Mitchell,
Synthesis, 1992, 803.
(E,E,E)-1-(Benz[a]azulen-10-yl)-7-phenylhepta-1,4,6-trien-3-
one 4i. (E,E,E)-1-(Benz[a]azulen-10-yl)-7-phenylhepta-1,4,6-
trien-3-one was isolated as dark-green prisms; yield: 32.4%; mp
101–106 ЊC; δH (250 MHz) 8.59 (1H, d, J = 15.7, olefin), 8.53
(1H, d, J = 13.2 Hz, seven-membered ring), 8.46 (1H, d,
J = 12.6 Hz, seven-membered ring), 8.45 (1H, d, J = 8.1 Hz,
six-membered ring), 8.36 (1H, d, J = 8.1 Hz, six-membered
ring), 7.84 (1H, d, J = 7.5 Hz, six-membered ring), 7.65–7.51
(6H, m, six-membered ring, olefin, phenyl), 7.38 (1H, d,
J = 15.2, olefin), 7.33 (1H, dd, J = 11.1, 8.6 Hz, seven-
membered ring), 7.21 (1H, dd, J = 11.0, 8.0 Hz, seven-
membered ring), 7.43–7.26 (4H, m, seven-membered ring,
phenyl), 6.78 (1H, d, J = 15.1, olefin) ppm; m/z: 360 (Mϩ);
Found: C, 89.88; H, 5.63. Calc. for C27H20O: C, 89.97; H,
5.59%.
7 (a) E. Kukevics, N. P. Erchak, J. Popelis and I. Dipaus, Zh. Obshch.
Khim., 1977, 47, 802; (b) D. E. Seitz, S. H. Lee, R. N. Hanson and
J. C. Bottaro, Synth. Commun., 1983, 13, 121; (c) L. S. Liebeskind
and J. Wang, J. Org. Chem., 1993, 58, 3550.
8 R. Sterzycki, Synthesis, 1979, 724.
9 R. N. McDonald and T. W. Campbell, Org. Synth., 1960, 40, 36.
10 K. Yamamura, M. Hashimoto, H. Takagi, M. Sasabe and Y. Houda,
unpublished work.
11 K. Yamamura, H. Miyake, S.-I. Nakatsuji and I. Murata, Chem.
Lett., 1992, 1213.
12 (a) H. Gilman, Organic Chemistry, John Wiley and Sons Inc., New
York, 1953, vol. IV, p. 740; (b) M. V. Sargent and T. M. Cresp,
Comprehensive Organic Chemistry, Pergamon, Oxford, 1979, vol. 4,
p. 693 and references cited therein.
13 Treatment of 3e with trityl tetrafluoroborate at 0 ЊC for 3 min,
followed by addition of dry ether gave a red precipitate. The
dichloromethane solution of this precipitate was allowed to stand
overnight. The α,β-unsaturated aldehyde 9 was obtained as greenish
needles in very low yield, 0.5%. mp 158 ЊC; δH (250 MHz) 9.79 (1H,
d, J = 7.8 Hz, CHO), 8.56 (1H, d, J = 8.2 Hz, seven-membered ring),
8.44 (1H, d, J = 7.7 Hz, six-membered ring), 8.43 (1H, d, J = 11.2
Hz, seven-membered ring), 8.26 (1H, d, J = 7.9 Hz, six-membered
ring), 8.24 (1H, d, J = 159 Hz, olefin), 8.43 (1H, t, J = 7.6 Hz, six-
membered ring), 7.50 (1H, m, seven-membered ring), 7.09 (1H, dd,
J = 7.7, 15.8 Hz, olefin) ppm; m/z: 232, 203, 202, 178, 101, 97, 85, 71,
57; Found: C, 89.78; H, 5.28. Calc. For C17H12O: C, 89.90;
H, 5.21%.
14 D. H. Reid, M. Fraser, B. B. Molly, H. A. S. Payne and R. G.
Sutherland, Tetrahedron Lett., 1961, 530.
15 D. N. Kursanov and M. E. Vol’pin, Dokl. Akad. Nauk SSSR, 1957,
113, 339; K. Conrow, Org. Synth., 1963, 43, 101.
16 J. V. Crivello, Synth. Commun., 1973, 3, 9.
17 J. Nakayama, K. Fujiwara and M. Hoshino, Chem. Lett., 1975,
1099.
18 P. Beresford and A. Ledwith, Chem. Commun., 1970, 15.
19 D. H. Barton, P. D. Magnus, G. Smith, G. Streckert and D. Zurr,
J. Chem. Soc., Perkin Trans. 1, 1972, 542.
Acknowledgements
The authors thank Miss Masuko Nishinaka, Faculty of
Science, Kobe University, for elemental analyses and are
grateful to Mr Taihei Yamane, Miss Yasuko Mizutani and
Reiko Yamamura for their kind collaboration.
References and notes
1 A part of this paper has appeared as a communication: K.
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3 Several successful studies have been achieved in recent years; cf. (a)
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21 Double the molar quantity of trityl tetrafluoroborate was used.
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J. Chem. Soc., Perkin Trans. 1, 2000, 3786–3790