Benzocyclobutenoacenaphthylene stilbenes. 1. Synthesis and thermal properties

Article abstract of DOI:10.1021/jo981016z

In this paper the synthesis and characterization of a new class of molecules based on 6b,10b-dihydrobenzo[j]cyclobut[a]acenaphthylene (DBCA) with potentially interesting optical and electronic properties are described. The mentioned compounds contain one

Full text of DOI:10.1021/jo981016z

9
698
J . Org. Chem. 1998, 63, 9698-9702
Ben zocyclobu ten oa cen a p h th ylen e Stilben es. 1. Syn th esis a n d
Th er m a l P r op er ties
Petra Buchacher, Roger Helgeson, and Fred Wudl*,†
Department of Chemistry and Biochemistry and Exotic Materials Institute, University of California,
Los Angeles, California 90095-1569
Received May 28, 1998
In this paper the synthesis and characterization of a new class of molecules based on 6b,10b-
dihydrobenzo[j]cyclobut[a]acenaphthylene (DBCA) with potentially interesting optical and electronic
properties are described. The mentioned compounds contain one or two DBCA units linked via a
double bond to an aromatic system. The synthesis of these compounds is mainly carried out by
Heck and/or Wittig reactions. The introduction of DBCA units in molecules is interesting in two
respects: (1) It will influence the electronic and optical properties of the compounds, and (2) it will
induce dimerization (polymerization) because DBCA can, upon thermolysis or photolysis, be
converted into a biradicaloid species (“pleiadene”) which dimerizes. Thus suitable compounds could
be used as monomers for photochemically or thermally induced polymerization.
In tr od u ction
Sch em e 1
The molecule 6b,10b-Dihydrobenzo[j]cyclobut[a]ace-
naphthylene (DBCA)1 is one of the precursors for the
generation of pleiadene, a π,π-biradicaloid hydrocarbon
that was studied theoretically and experimentally during
the seventies.3 Since it is a highly reactive molecule, it
,2
-5
6
immediately dimerizes upon formation (Scheme 1).
So far there are very few examples of the synthetic use
of the pleiadene unit generated from the DBCA ring
system. The pleiadene dimerization has been applied by
Stille’s group for a chain extension reaction in polymer
7
synthesis, and the reaction of pleiadene with fullerene
C
60 was reported by M u¨ llen’s group.8
The driving force to synthesize the compounds incor-
porating one or two DBCA unitssshown in Scheme 2s
was to study their influence on electronic and optical
properties compared to analogues with benzene rings. In
this respect the preparation of 8-styryl-DBCA (1) gave
us the opportunity to compare its properties with trans-
stilbene. The analogues with another DBCA unit (2) and
with one anthracene system (3) instead of a benzene ring
served for comparative studies as well. In addition, we
prepared monomers 5 and 6 containing two DBCA units
that could serve as polymer building blocks under ple-
iadene dimerization conditions. Especially for electronic
applications a “clean” thermally or photochemically
induced polymerization step is of great advantage in the
preparation of high-strength materials.
as well as the properties of derived polymers, are to be
discussed elsewhere. In this paper we concentrate on
their preparation and characterization.
Resu lts a n d Discu ssion
The starting materials, 8-halo-6b,10b-dihydrobenzo[j]-
cyclobut[a]acenaphthylene (8-X-DBCA, X ) Br, I), em-
ployed in the synthesis of the DBCA-based derivatives
were prepared according to the procedure of Upshaw and
7
Stille. The preparation of the compounds with one or
two DBCA units linked via double bonds to an aromatic
system was carried out by Heck and/or Wittig reactions.
In the case of compound 1 the Pd-catalyzed coupling
The detailed investigation of electronic and/or optical
properties of the DBCA-based molecules described below,
9
reaction of 8-I-DBCA and styrene by a Heck coupling
†
Phone: (310) 206-0941. Fax: (310) 825-0767. E-mail: wudl@
gave the target molecule in 75% yield (Scheme 3). We
could increase the original yield by using DMF instead
chem.ucla.edu.
(1) Kolc, J .; Michl, J . J . Am. Chem. Soc. 1970, 92, 4147-4148.
(2) Kolc, J .; Michl, J . J . Am. Chem. Soc. 1973, 95, 7391-7401.
(3) Binsch, G.; Tamir, I. J . Am. Chem. Soc. 1969, 91, 2450-2455.
(4) Kolc, J .; Michl, J . J . Am. Chem. Soc. 1970, 92, 4148-4150.
(5) Kolc, J .; Downing, J .; Manzana, W. A.; Michl, J . J . Am. Chem.
9
of acetonitrile since it is a better solvent for the iodo
derivative and a better stabilizer for the palladium
complex intermediate.
Soc. 1976, 98, 930-937.
The characterization data for 1 are given in the
Experimental Section. Differential scanning calorimetry
(
6) Cava, M. P.; Schlessinger, R. H. Tetrahedron 1965, 21, 3073-
3
081.
(
7) Upshaw, T. A.; Stille, J . K.; Droske, J . P. Macromolecules 1991,
2
4, 2143.
(9) (a) Dieck, H. A.; Heck, R. F. J . Am. Chem. Soc. 1974, 96, 1133.
(b) Heck, R. F. Adv. Catal. 1977, 26, 323. (c) Heck, R. F. Acc. Chem.
Res. 1979, 12, 146. (d) Heck, R. F. Org. React. 1981, 27, 345.
(8) Kraus, A.; Guegel, A.; Belik, P.; Walter, M.; M u¨ llen, K. Tetra-
hedron 1995, 51, 36, 9927-9940.
1
0.1021/jo981016z CCC: $15.00 © 1998 American Chemical Society
Published on Web 12/04/1998

Benzocyclobutenoacenaphthylene Stilbenes
J . Org. Chem., Vol. 63, No. 26, 1998 9699
Sch em e 2
Sch em e 3
Sch em e 4
Sch em e 5
(DSC) was carried out on a sample from 40 to 300 °C
under nitrogen, at a heating rate of 5 °C/min. The melting
endotherm appeared at 155 °C, and the maximum of the
ring-opening or dimerization exotherm occurred at 214
ring was observed at 223 °C, followed by a continuous
increase in the heat flow. Another exothermic peak was
observed at 374 °C which could be due to a reaction of
the anthracene with a pleiadene resulting from reversal
of a dimer.
°
C. In the case of 2, the homogeneously catalyzed Heck
reaction employed for compound 1 did not proceed as well
as before, so we used an alternative phase-transfer
catalytic system10 (Scheme 3). This approach provided
compound 2 with a satisfactory yield and complete
characterization.
According to the synthesis of compound 1 the prepara-
tion of the corresponding derivative containing two DBCA
units (5) could be carried out by a Heck reaction of 2 equiv
of 8-I-DBCA with p-divinylbenzene. Since the com-
mercially available p-divinylbenzene is only 80% pure,
it was prepared in-house. The olefin was used im-
mediately after the preparation, but under the common
Heck reaction conditions (palladium catalyst, about 100
°C) the p-divinylbenzene is not stable and leads to a
complex mixture of products. Alternatively, the reaction
could be carried out by coupling 8-vinyl-DBCA with 1,4-
diiodobenzene. The 8-vinyl derivative was prepared ac-
In the course of our research we were also interested
in compound 3, 8-(2′-(9′′-anthryl)ethenyl)-DBCA. As in
the prior case, the yield of the coupling reaction of 8-I-
DBCA and 9-vinylanthracene was improved by a change
from the homogeneous palladium(II) acetate/triethyl-
amine catalyst to the phase transfer catalytic system
palladium(II) acetate/tetrabutylammonium bromide/
potassium carbonate.11 A Wittig reaction was an even
better approach to synthesize the DBCA derivative 3. For
this route the originally obtained 8-halo derivative was
converted into the aldehyde 4 in 85-90% yield by a
straightforward reaction with n-butyllithium and N-
formylpiperidine. For the Wittig reagent, (9-chloro-
methyl)anthracene was converted to the triphenylphos-
phonium chloride and allowed to react with 8-DBCA-
carboxaldehyde to give the fluorescent compound 3 in
1
1
cording to the procedure described in the literature and
allowed to react with 1,4-diiodobenzene to give the
product (5) in 25% yield (Scheme 6).
A Wittig reaction of 8-DBCA carboxaldehyde (4) with
the corresponding commercially available p-xylenebis-
(triphenylphosphonium bromide) according to the proce-
dure for p-distyrylbenzene12 (Scheme 7) afforded 5 in 78%
yield and consisted of three isomers that differed in the
configuration of the double bonds. In contrast to the Heck
reaction, which leads only to the trans/trans-isomer, we
could separate the cis/cis-, cis/trans-, and trans/trans-
isomers by HPLC (Cosmosil column; solvent 10/90 toluene/
7
3% yield (Scheme 5).
Differential scanning calorimetry was carried out from
0 to 400 °C under nitrogen at a heating rate of 10 °C/
4
min. The ring-opening exotherm of the four-membered
(
(
10) Lansky, A.; Reiser, O.; de Meijere, A. Synlett 1990, 15, 405.
11) Sastre, A.; Wudl, F. Chem. Eur. J ., in press.
(12) Campbell, T. W.; McDonald, R. N. J . Org. Chem. 1959, 24, 1246.

9
700 J . Org. Chem., Vol. 63, No. 26, 1998
Buchacher et al.
Sch em e 6
8,8′-DBCA-MEH DVB), 6, was carried out as for 5, above.
The resulting product (6) was fully characterized, and
the DSC evaluation (40-400 °C, 10 °C/min) showed an
exothermic transition corresponding to the ring-opening
of the pleiadene unit, at 226 °C. As expected, the presence
of substituents in 6 increased the solubility and improved
the film-forming properties compared to 5. The 2,5-
substitution with alkoxy groups in 6 led to a shift of the
peak maximum in the UV/vis spectrum of about 30 nm
compared to 5 and enhanced the fluorescence dramati-
cally. Further studies and applications of this highly
luminescent material will be published in due course.
In conclusion, the preparation and characterization of
a new class of compounds based on DBCA are described.
The synthesis of these molecules containing one or two
DBCA units linked via a double bond to an aromatic
system was carried out by Heck and/or Wittig reactions.
The introduction of a DBCA unit in a molecule is
interesting in two respects: (1) The cyclobutane ring of
the DBCA can be thermally or photochemically opened
to give a biradicaloid species (“pleiadene”) that dimerizes
Sch em e 7
(or polymerizes), and (2) the influence of a DBCA unit
on the electronic and optical properties of the resulting
stilbenes, compared to analogues with benzene rings,
revealed an enhanced photoluminescence.
Exp er im en ta l Section
All catalysts were obtained from Strem Chemicals, Alfa
AESAR, or Aldrich. Solvents and reagents were from com-
mercial sources and were used as obtained, unless purified as
mentioned for a particular preparation.
8
-S t y r y l-6b ,10b -d i h y d r o b e n z o [j ]c y c lo b u t [a ]a c e -
n a p h th ylen e (1). A solution of 15 mg (0.067 mmol) of
hexane). Refluxing the isomer mixture for several hours
in toluene in the presence of a trace of iodine afforded
pure, fluorescent trans-trans-â,â′-bis-8,8′-DBCA-1,4-di-
vinylbenzene (5).
The expected exothermic peak at 240 °C, corresponding
to the ring-opening of the DBCA unit, was observed by
DSC. A total weight loss of about 4% until 500 °C (TGA)
indicated a high thermal stability of the polymer that is
formed by the dimerization of the generated pleiadene
units on both monomer termini.
palladium(II) acetate in 2 mL of dry dimethylformamide
(
DMF) was added to a mixture of 1 g (2.8 mmol) of 8-iodo-
DBCA, 0.6 mL (4.3 mmol) of dry triethylamine, and 0.4 mL
3.5 mmol) of freshly distilled styrene in 5 mL of dry DMF.
The mixture turned orange and became homogeneous at 30
C and was heated to reflux. The reaction mixture was refluxed
for 17 h.
After cooling of the mixture to room temperature, 50 mL of
(
°
water and 50 mL of diethyl ether were added and the aqueous
layer was extracted with ether. The organics were combined
and dried over Na
The residue was purified by flash column chromatography
SiO , 20:1 petroleum ether/CH Cl ): yield 75%; white solid;
mp 148-150 °C; H NMR (400 MHz, CDCl ) δ 5.32 (s, 2H),
.17 (d, J ) 7.6 Hz, 1H), 7.26-7.18 (m, 3H), 7.32 (t, 1H), 7.38
2 4
SO , and the solvent was removed in vacuo.
Since 5 is not very soluble, we expect that polymers
derived from it will be even less soluble. For a possible
application in electronics a polymer with a low solubility
and the corresponding monomer that tends to crystallize
might be a disadvantage. For this reason we introduced
substituents in the monomer in order to increase the
solubility and the film-forming properties. Hence, R,R′-
dichloro-p-[5-((2′-ethylhexyl)oxy)-2-methoxy]xylene, which
(
2
2
2
1
3
7
1
3
(s, 1H), 7.4-7.53 (m, 8H), 7.61 (d, J ) 7.6 Hz, 2H) ppm;
NMR (125 MHz, CDCl ) δ 53.8, 54.0, 119.9, 122.8, 123.91,
23.95, 126.6, 127.1, 127.6, 128.0, 128.1, 128.2, 128.8, 129.5,
32.7, 137.3, 137.6, 139.2, 143.0, 146.9, 147.7 ppm; FAB-MS
C
3
1
1
+
(
3
3-NOBA) m/z 330 [M , 100]; UV/vis (n-hexane) λ 228 (max),
10 nm; IR (KBr) ν 3041, 2942, 1603, 1493, 960, 785, 773, 690
1
3
was also used for the preparation of MEH-PPV, was
synthesized.14 This educt was converted to the corre-
sponding bis(triphenylphosphonium chloride) and al-
lowed to react with 8-DBCA-carboxaldehyde (4), following
the procedure used for the unsubstituted analogue
-1
cm ; DSC (40-300 °C, 5 °C/min) 155 °C (endotherm), 214 °C
exotherm). HRMS: calcd, 330.141; found, 330.140.
-(2′-(8-(6b ,10b -d i h y d r o b e n z o [j ]c y c lo b u t [a ]a c e -
(
8
n a p h t h yl)et h en yl)-6b ,10b -d ih yd r ob en zo[j]cyclob u t [a ]-
a cen a p h th ylen e (2). To a mixture of 372 mg (1.05 mmol) of
8
-iodo-DBCA, 5 mg (0.02 mmol) of palladium(II) acetate, 284
mg (0.88 mmol) of tetrabutylammonium bromide, and 290 mg
2.1 mmol) of dry potassium carbonate in 10 mL of dry DMF
(Scheme 7) to produce 6 in 70% yield. The four isomers,
a cis/cis-, two cis/trans- (depending on the location of the
cis double bond relative to the substituents), and one
trans/trans-isomer, could be separated and analyzed by
HPLC (Cosmosil column; 10/90 toluene/hexane). The
isomerization to the pure fluorescent trans-trans-â,â′-(bis-
(
1
1
was added 380 mg (1.5 mmol) of 8-vinyl-DBCA. The mixture
turned orange-brown and was heated to 100 °C for 63 h. After
cooling of the mixture to room temperature, 100 mL of
dichloromethane and 100 mL of water were added. The
organics were washed with water and dried over Na
the solvent was removed in vacuo. The residue was purified
by flash column chromatography (SiO , 3:1 petroleum ether/
CH Cl ): yield 47%; light yellow solid; H NMR (400 MHz,
2 4
SO , and
(
13) Srdanov, G.; Wudl, F. U.S. Patent No. 5,189,136, 1993.
(14) Barashkov, N. N.; Guerrero, D. J .; Olivos, H. J .; Ferraris, J . P.
2
1
Synth. Met. 1995, 75, 153.
2
2

Benzocyclobutenoacenaphthylene Stilbenes
CDCl
J . Org. Chem., Vol. 63, No. 26, 1998 9701
(125 MHz, CDCl ) δ 53.8, 54.5, 120.23, 120.25, 123.07, 123.12,
3
) δ 5.3 (s, 4H), 6.84 (s, 2H), 7.05-7.15 (m, 6H), 7.35-
3
1
3
7
.5 (m, 8H), 7.55 (d, J ) 8.0 Hz, 4H) ppm; C NMR (125 MHz,
124.26, 124.34, 128.16, 128.23, 131.5, 132.6, 136.5, 139.0,
CDCl
1
3
) δ 53.9, 54.0, 119.8, 119.9, 122.8, 123.91, 123.95, 127.0,
141.6, 142.0, 148.2, 154.6, 192.3 ppm; FAB-MS (3-NOBA) m/z
+
+
28.0, 128.9, 132.7, 137.4, 139.2, 143.0, 146.7, 147.7 ppm; FAB-
256 [M , 100], 226 [M + H - CHO, 16]; IR (KBr) ν 3051,
+
-1
MS (3-NOBA) m/z 480 [M , 100]; UV/vis (n-hexane) λ 226
2949, 2845, 1694, 1492, 1425, 1214, 1192, 828, 785, 771 cm ;
(max), 294, 306 (sh) nm.
DSC (40-400 °C, 10 °C/min) 145 °C (endotherm), 218 °C
(exotherm), 374 °C (exotherm). HRMS: calcd, 256.0888; found,
256.0887.
P r ep a r a tion of 8-(2′-(9′′-An th r yl)eth en yl)-6b,10b-d ih y-
d r oben zo[j]cyclobu t[a ]a cen a p h th ylen e (3). By Heck Re-
a ction . To a mixture of 0.5 g (1.4 mmol) of 8-iodo-DBCA, 6
mg (0.03 mmol) of palladium(II) acetate, 0.38 g (1.2 mmol) of
tetrabutylammonium bromide, and 0.39 g (2.8 mmol) of dry
potassium carbonate in 20 mL of dry DMF was added 0.41 g
â,â′-Bis[8,8′-(6b ,10b -d ih yd r ob en zo[j]cyclob u t [a ]a ce-
n a p h th ylen e)]-1,4-d ivin ylben zen e (5). By Heck Rea ction .
To a solution of 135 mg (0.41 mmol) of 1,4-diiodobenzene, 5
mg (0.022 mmol) of palladium(II) acetate, and 0.17 mL (1.2
mmol) of dry triethylamine in 7 mL of dry DMF was added
250 mg (0.98 mmol) of 8-vinyl-6b,10b-dihydrobenzo[j]cyclobut-
[a]acenaphthylene (prepared according to ref 11. The mixture
was heated to 110 °C and kept stirring at this temperature
for 17 h. After cooling of the mixture to room temperature,
100 mL of water and 100 mL of diethyl ether were added and
the aqueous layer was extracted with ether. The organic
extracts were washed with 2 N aqueous HCl, water, and
(2.0 mmol) of 9-vinylanthracene. The mixture turned brown
at once and was heated to 100 °C for 63 h. After cooling of the
mixture to room temperature, 150 mL dichloromethane was
added and the solids were filtered off. The organics were
washed with water and dried over Na
was removed in vacuo. The residue was purified by flash
column chromatography (SiO , 10:1 petroleum ether/CH Cl ):
2 4
SO , and the solvent
2
2
2
yield 56%; yellow, fluorescent (λ ) 366 nm) solid; for charac-
terization, see below.
aqueous saturated NaCl solution, followed by drying over Na
SO
isomer) was isolated by flash column chromatography (SiO
5:1 petroleum ether/CH Cl
(λ ) 366 nm) solid; for characterization, see below.
2
-
By Wittig Rea ction . A solution of 9-(chloromethyl)an-
thracene (1 g, 4.4 mmol) and 1.27 g (4.8 mmol) of triph-
enylphosphine in 8 mL of dry DMF was heated for 4 h at reflux
and cooled. The product was precipitated in diethyl ether and
centrifuged: yield 90%; yellow solid.
To a suspension of 0.46 g (1.8 mmol) of carboxaldehyde 4
and 0.8 g (1.6 mmol) of (9′-anthrylmethyl)triphenylphos-
phonium chloride in 30 mL of dry ethanol was added 3.3 mL
4
and solvent removal in vacuo. The product (trans/trans-
2
,
2
2
): yield 25%; yellow, fluorescent
By Wittig Rea ction . To a suspension of 0.5 g (1.95 mmol)
of the carboxaldehyde 4 and of 0.7 g (0.9 mmol) of p-xylenebis-
(triphenylphosphonium bromide) in 30 mL of USP ethanol was
added 3.5 mL (1 M in EtOH, 3.5 mmol) of lithium ethoxide.
The reaction mixture was heated for 17 h at reflux. After
cooling of the reaction to 25 °C, half of the ethanol was removed
in vacuo and 50 mL of water was added. The aqueous solution
was extracted with diethyl ether, and the organics were dried
(3.3 mmol) of lithium ethoxide (1 M in ethanol). The reaction
solution was heated for 20 h at reflux. After cooling of the
solution to 25 °C, half of the ethanol was removed in vacuo
and 50 mL of water was added. The aqueous solution was
extracted with dichloromethane and the organics were dried
over Na
trans-, and the trans/trans-isomers) was purified by flash
column chromatography (SiO , 10:1 petroleum ether/CH Cl ).
2 4
SO . The product (a mixture of the cis/cis-, the cis/
over Na
chromatography (SiO
2
SO
4
. The product was purified by flash column
, 5:1 petroleum ether/CH Cl ). Investiga-
2
2
2
2
2
2
tion by HPLC (UV detection) showed that the product was a
mixture of the cis- and trans-isomers. Even though the isomers
were separable by HPLC on a Cosmocil Buckyprep column (4:1
hexane/toluene), refluxing the mixture in toluene for several
hours in the presence of a trace of iodine gave the pure trans-
The mixture of isomers was dissolved in toluene and refluxed
for several hours in the presence of a trace of iodine to give
the pure trans-trans isomer: yield 78%; yellow solid; mp 225
1
°C, H NMR (400 MHz, CDCl
3
) δ 5.39 (s, 4H), 6.99 (dd, 4H),
7.17 (d, J ) 7.82 Hz, 2H), 7.21-7.28 (m, 2H), 7.41 (d, J ) 4.07
isomer: yield 73%; yellow, fluorescent (λ ) 366 nm) solid; mp
Hz, 6H), 7.43-7.55 (m, 8H), 7.63 (d, J ) 7.84 Hz, 4H) ppm;
1
13
2
1
7
20 °C; H NMR (400 MHz, CDCl
3
) δ 5.46 (s, 2H), 6.86 (d, J )
3
C NMR (125 MHz, CDCl ) δ 53.9, 54.1, 119.9, 120.0, 122.8,
6.2 Hz, 1H), 7.38-7.7 (m, 13H), 7.80 (d, J ) 17.3 Hz, 1H),
.99 (d, J ) 8.1 Hz, 2H), 8.28 (d, J ) 8.6 Hz, 2H), 8.38 (s, 1H)
ppm; C NMR (125 MHz, CDCl
23.0, 124.0, 124.1, 124.3, 125.4, 125.6, 126.2, 126.6, 127.2,
28.09, 128.13, 128.8, 129.9, 131.7, 132.8, 133.1, 137.3, 138.2,
123.9, 124.0, 126.9, 127.1, 127.8, 128.1, 129.4, 132.7, 136.8,
137.3, 139.2, 143.0, 146.9, 147.8 ppm; FAB-MS (3-NOBA) m/z
1
3
+
3
) δ 54.0, 54.2, 120.0, 120.1,
582 [M , 100]; UV/vis (n-hexane) trans/trans-isomer λ ) 320
1
1
1
(sh), 360 (max), cis/trans-isomer λ ) 293, 341 (max), cis/cis-
isomer λ ) 293 (max), 330 (sh); IR (KBr) ν 3026, 2929, 1603,
-
1
39.2, 142.9, 147.3, 148.0 ppm; FAB-MS (3-NOBA) m/z 430
1467, 1260, 957, 820, 739 cm ; DSC (40-400 °C, 10 °C/min)
240 °C (exotherm), starting from 260 °C (continuous endo-
therm); TGA (35-500 °C, 20 °C/min) weight loss of 2.18% until
250 °C, plateau until 333 °C, weight loss of another 1.5% until
500 °C. HRMS: calcd, 582.2347; found, 582.2345.
+
[
M , 100]; UV/vis (n-hexane) trans-isomer λ ) 294 (max), 385
nm, cis-isomer (HPLC, Cosmocil Buckyprep column, 4:1 hex-
ane/toluene) λ ) 294 (max), 387 nm; IR (KBr) ν 3044, 2929,
1
620, 1602, 1468, 1441, 1367, 969, 883, 843, 783, 772 cm-1
;
DSC (40-400 °C, 10 °C/min) 223 °C (exotherm), continuous
P r ep a r a tion of â,â′-[Bis(8′′,8′′′-(6b,10b-d ih yd r oben zo-
[j]cyclobu t[a ]acen aph th yl)]-5-((2′-eth ylh exyl)oxy)-2-m eth -
oxy-1,4-d ivin ylben zen e (6). A solution of 5 mL of 0.5 g (1.5
mmol) of R,R′-dichloro-p-[5-((2′-ethylhexyl)oxy)-2-methoxy]xy-
lene and 0.86 g (3.3 mmol) of triphenylphosphine in dry DMF
was heated for 4 h at reflux and cooled to 25 °C. The product
was precipitated in diethyl ether, centrifuged, and dried in
vacuo: yield 97%; light yellow solid; 1H NMR (400 MHz,
endothermic heat flow, 374 °C (exotherm). HRMS: calcd,
4
30.1722; found, 430.1721.
-(6b,10b-Dih ydr oben zo[j]cyclobu t[a ]acen aph th ylen e)-
ca r ba ld eh yd e (4). In a three-neck flask, 1.04 g (3.4 mmol) of
-bromo-DBCA was dissolved in 10 mL of dry THF and cooled
to -78 °C. Then 2.2 mL of n-butyllithium (1.7 M in pentane;
.7 mmol) was added slowly and the solution stirred for 1 h
8
8
3
at -78 °C. Following this, a solution of 0.8 mL (7.2 mmol) of
N-formylpiperidine in 5 mL of dry THF was added via syringe.
The color changed from brownish to pale-yellow, and the
solution was stirred for 10 min at -78 °C, another 2 h at 0
CDCl
(s, 1H), 6.84 (s, 1H), 7.7 (m, 30H) ppm; FAB-MS (3-NOBA)
m/z 523 [M - 2Cl - PPh , 100], 785 [M - 2Cl, 30].
To a suspension of 0.46 g (1.8 mmol) of carbaldehyde 4 and
0.7 g (0.82 mmol) of p-[5-((2′-ethylhexyl)oxy)-2-methoxyxylene]-
bis(triphenylphosphonium chloride) in 35 mL of dry ethanol
was added 3.3 mL (1 M in EtOH; 3.3 mmol) lithium ethoxide.
The reaction was heated for 4 h at reflux. After cooling of the
sample to 25 °C, half of the ethanol was removed in vacuo and
50 mL of water was added. The aqueous solution was extracted
3
) δ 0.6-1.3 (m, 15H), 2.89 (s+d, 5H), 5.40 (s, 4H), 6.69
3
°
C, and at room temperature overnight.
The reaction mixture was quenched with 3 N HCl (pH )
2
-3) and extracted with diethyl ether. The organics were
washed with saturated aqueous NaHCO
saturated aqueous NaCl solution and were dried over Na
The solvent was removed in vacuo, and the residue was
purified by flash column chromatography (SiO , 2:1 hexane/
3
solution, water, and
2
SO
4
.
2
1
with dichloromethane, and the organics were dried over Na
SO . The product was purified by flash column chromatogra-
phy (SiO , 5:1-3:1 petroleum ether/CH Cl ) and consisted of
a mixture of four isomers (cis/cis-, two cis/trans-, trans/trans-
2
-
Et
MHz, CDCl
.59 (m, 4H), 7.60-7.66 (m, 4H), 9.86 (s, 1H) ppm; 13C NMR
2
O): yield 88%; white solid; mp 144-146 °C; H NMR (400
4
3
) δ 5.43 (s, 2H), 7.35 (d, J ) 7.57 Hz, 1H), 7.44-
2
2
2
7

9
702 J . Org. Chem., Vol. 63, No. 26, 1998
Buchacher et al.
isomers; determined by HPLC). The isomers were dissolved
in toluene and refluxed for several hours in the presence of a
(KBr) 3042, 2953, 2869, 2859, 1602, 1495, 1464, 1414, 1365,
-
1
1237, 1204, 1037, 964, 784, 775 cm ; DSC (40-400 °C, 10 °C/
min) 226 °C (exotherm), starting from 250 °C (continuous
endotherm); TGA (35-500 °C, 20 °C/min) weight loss of 2.38%
until 400 °C, weight loss of another 41.42% until 600 °C.
HRMS: calcd, 740.3654; found, 740.3654.
trace of iodine to give the pure trans-trans-isomer: yield 70%;
1
yellow solid; mp 215 °C, H NMR (400 MHz, CDCl
(
3
) δ 0.8-1.0
m, 6H), 1.2-1.6 (m, 8H), 1.77 (m, 1H), 3.86 (s, 3H), 3.89 (d, J
)
7
5.57 Hz, 2H), 5.38 (s, 4H), 7.03 (dd, 4H), 7.16 (m, 2H), 7.21-
.4 (m, 6H), 7.41-7.55 (m, 8H), 7.63 (d, J ) 7.82 Hz, 4H) ppm;
1
3
C NMR (125 MHz, CDCl ) δ 11.6, 14.4, 23.3, 29.5, 31.1, 40.0,
3
5
1
1
3.9, 54.1, 56.6, 72.1, 119.9, 122.76, 122.8, 123.0, 123.9, 126.7,
27.0, 127.2, 128.0, 129.65, 129.67, 132.7, 137.86, 137.88,
Ack n ow led gm en t. We are grateful to the NSF for
support through Grant DMR-9704143. P.B. thanks the
Fonds zur F o¨ rderung der wissenschaftlichen Forschung
39.2, 143.0, 146.6, 147.7, 151.4, 151.5 ppm; FAB-MS (3-
+
NOBA) m/z 740 [M , 100]; UV/vis (n-hexane) trans-trans-
isomer λ ) 323, 392 (max), cis-trans-isomers λ ) 294, 377
(Vienna-Austria) for a postdoctoral fellowship.
(same intensity); cis-cis-isomer λ ) 292 (max), 361 nm; IR
J O981016Z