The crossed [2+2] cycloaddition of 1-phenylcyclopropene and 1-bromo-2-phenylcyclopropene

Article abstract of DOI:10.1021/jo901636k

(Chemical Equation Presented) 1-Bromo-2-phenylcyclopropene (2) underwent [2+2] dimerization to generate 1,2-dibromo-4,5-diphenyltricyclo[ 3.1.0.0 ^2,4]hexane (5), which was heated to form 1,2-dibromo-4,5- diphenylcyclohexa-1,4-diene (6) followed

Full text of DOI:10.1021/jo901636k

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unusual processes, such as ene dimerizations,2 coupling
The Crossed [2þ2] Cycloaddition of
1-Phenylcyclopropene and 1-Bromo-2-
phenylcyclopropene
reactions,3 rearrangement,4 and [2þ2] cyclizations to release
strain energy.5 Cyclopropenes usually will isomerize, dimer-
ize, and/or react with other reagents to simultaneously form
products due to their highly strained energy.
Gon-Ann Lee,* Wen-Chieh Wang, Shih-Fen Jiang,
Chih-Yi Chang, and Ru-Ting Tsai
The control of the crossed reactions between two different
cyclopropenes is an important issue to expand their applica-
tions. In the literature, there are only a few crossed reactions
between two different cyclopropenes reported. Three types
of cyclopropenes, bicyclo[5.1.0]oct-1,8-ene,6 1-phenylcyclo-
propene,7 and 1-trimethylsilyl-3-phenylcyclopropene,8 un-
derwent ene trimerization, which was a type of crossed ene
reaction of a monomer and an ene dimer. We also found that
1-trimethylsilyl-2-phenylcyclopropene was tetramerized via
ene dimerizations to generate two different ene dimers, exo-
form and endo-form, followed by crossed coupling to give a
triene tetramer.9 There is only one designed crossed reaction
between two different cyclopropenes reported by Baird and
co-workers. They claimed that 3,3-dimethylcyclopropene-
carboxylic acid and 2-tert-butylcyclopropenecarboxylic acid
underwent a crossed ene reaction. This crossed ene reaction
Department of Chemistry, Fu Jen Catholic University,
Hsinchuang, Taipei 24205, Taiwan, Republic of China
016850@mail.fju.edu.tw
Received July 27, 2009
(2) (a) Baird, M. S.; Hussein, H. H.; Clegg, W. J. Chem. Res., Miniprint
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K. B.; Artis, D. R. J. Org. Chem. 1996, 61, 764–770.
1-Bromo-2-phenylcyclopropene (2) underwent [2þ2] di-
merization to generate 1,2-dibromo-4,5-diphenyltri-
cyclo[3.1.0.02,4]hexane (5), which was heated to form
1,2-dibromo-4,5-diphenylcyclohexa-1,4-diene (6) fol-
lowed by oxidation to yield 40,50-dibromo-o-terphenyl
(7). o-Terphenyl 7 could be synthesized in one-pot reac-
tions from 1,1,2-tribromocyclopropane (3). When cyclo-
propane 3 was treated with 1.5 equiv of methyllithium
followed by slowly adding the proton source, crossed
[2þ2] adduct 8 was isolated in 40% yield. Compound 8
was heated and oxidated to produce 40-bromo-o-terphe-
nyl (11).
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Cyclopropene has attracted the attention of both theore-
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Published on Web 09/17/2009
DOI: 10.1021/jo901636k
r
2009 American Chemical Society

Lee et al.
JOCNote
resulted from two different cyclopropenes but only one of
them contained 3-hydrogen.10
SCHEME 1. Synthesis and Trapping of Cyclopropene 2
When cyclopropenes undergo [2 þ 2] cyclizations, a step-
wise diradical mechanism is consistent with the regiospecific
formation of adducts based on the stabilization of the
diradicals and on the reaction conditions.11 Due to the highly
strained energy, cyclopropenes usually undergo self- or
intramolecular [2 þ 2] cycloadditions to release the strain
energy. To the best of our knowledge, no crossed [2þ2]
cycloaddition between two different cyclopropenes has been
reported. Only the crossed [2 þ 2] cycloaddition reaction of
cyclopropenes with olefins has been reported. Padwa found
that 1-phenyl-2-carbomethoxy-3,3-dimethylcyclopropene
underwent photochemical [2 þ 2] cycloaddition with alkenes
and alkyne to give bicyclo[2.1.0]pentanes and bicyclo-
[2.1.0]pent-2-ene. That reaction was carried out by using a
slight excess of alkenes and alkyne in the presence of a triplet
sensitizer. Dolgii and co-workers reported that both 3,3-
dimethylcyclopropene and 3-cyclopropyl-3-methylcyclo-
propene underwent crossed [2 þ 2] cycloaddition with nor-
bornenes by using Ph3P and CuCl as catalysts. Franck-
Neumann reported that electrophilic gem-dimethylcyclo-
propenes underwent [2 þ 2] cycloaddition with enamines
and ynamines to give 2-aminobicyclo[2.1.0]pentanes and
2-aminobicyclo[2.1.0]pent-2-enes.12
Phenylcyclopropenes undergo [2 þ 2] dimerizations to
form diphenyltricyclo[3.1.0.02,4]hexanes that can isomerize
to diphenylcyclohexa-1,4-dienes. Obata and Moritani have
reported that both 3-acetyl- and 3-benzoyl-1,2-diphenyl-
cyclopropenes undergo dimerizations to tricyclo[3.1.0.02,4]-
hexanes upon irradiation.13 Deboer also reported that sensi-
tized irradiation of 1,2-diphenylcyclopropenes gives tricyclo-
[3.1.0.02,4]hexanes.11 The tricyclohexanes are thermally
rearranged to 1,4-cyclohexadienes, which can be converted
to benzenes. Weyerstahl reported that 1-chloro-2-phenylcy-
clopropene in benzene at rt for 2 days gave a 4% [2 þ 2]
dimer, which isomerized to 1,2-dichloro-4,5-diphenylcyclo-
hexa-1,4-diene followed by oxidation to form 40,50-dichloro-
o-terphenyl.14 We have reported that 1-phenylcyclopropene
SCHEME 2. Synthesis of Compounds 5, 6, and 7
(1) underwent [2 þ 2] dimerization to generate 1,2-diphenyl-
tricyclo[3.1.0.02,4]hexane that was heated to form 1,2-diphenyl-
cyclohexa-1,4-diene followed by oxidation to yield o-ter-
phenyl.7 We now report that 1-bromo-2-phenylcyclopro-
pene (2) undergoes [2 þ 2] dimerization in 35% isolated
yield. We also provided a method to synthesize the crossed
[2 þ 2] cycloadduct between cyclopropenes 1 and 2.
1,1,2-Tribromocyclopropanes are very useful precursors
for the synthesis of a series of 1-substituted cyclopropenes.1e
Cyclopropenes 1 and 2 were prepared and trapped in solu-
tion by the method shown in Scheme 1. 1,1,2-Tribromo-2-
phenylcycloproane (3)7,9,15 was treated with 1.0 equiv of
methyllithium followed by treatment with cyclopentadiene
at rt, then two compounds, 4 and 5, were isolated (94% and
trace). The major product 4 was formed from cyclopropene 2
with cyclopentadiene (Scheme 1). The structure of the minor
product 5 was shown by X-ray crystallography to be a dimer
formed from anti head-to-head [2 þ 2] cycloaddition of 2.
Cyclopropene 2 under neat conditions at rt for 1 h gave
5% of dimer 5 along with a polymeric aromatic material.
To improve the yield of 5, cyclopropane 3 was treated with
1.0 equiv of methyllithium, and the reaction mixture was
concentrated and kept at -20 °C until cyclopropene 2
completely disappeared, as monitored by 1H NMR, and
three compounds, 5, 6, and 7, were isolated in yields of 35%,
3%, and 2%, respectively. The structures of 6 and 7,16 1,2-
dibromo-4,5-diphenylcyclohexa-1,4-diene and 40-50-dibromo-
o-terphenyl, were shown by X-ray crystallography. When
the adduct 5 was heated at toluene refluxing temperature for
24 h, compounds 6 and 7 were obtained in yields of 65% and
33%, respectively. Cyclohexadiene 6 was treated with DDQ
to generate o-terphenyl 7 in 97% yield. In the one-pot
synthesis of o-terphenyl 7, when treated with methyllithium,
heated at toluene refluxing temperature, and treated with
DDQ, 7 was obtained in 49% isolated yield (Scheme 2).
In our previous report, cyclopropene 1 underwent ene
trimerization to give ene trimer 10 and [2 þ 2] dimerization to
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Lee et al.
JOCNote
form 1,2-diphenyltricyclo[3.1.0.02,4]hexane (9) in the isolated
yields of 88% and 8%, respectively.7 Although both cyclopro-
penes 1 and 2 would undergo [2 þ 2] cycloadditions, cyclopro-
pene 2was treated with 1at rt to give a very low yield (>1%) of
1-bromo-4,5-diphenyltricyclo[3.1.0.02,4]hexane (8). We at-
tempted to design a method that would enhance the yield of
the crossed [2 þ 2] cycloaddition between 1and 2 to expand the
application of these phenylcyclopropenes.
SCHEME 3. Enhanced Yield of Adduct 8 and Synthesized 11
Since the [2 þ 2] cycloadditions of cyclopropenes are via
stepwise diradical mechanisms, to find the difference in the
energy gaps of HOMO-LUMO for these two cyclopropenes
would be very important in the design of a method to control
the crossed reaction. According to the theoretical calcula-
tions at the HF/6-31þþG** level of ab initio theory, the
energy difference (217.8 kcal/mol) between HOMO and
LUMO of 1 is smaller than that for bromocyclopropene 2
(218.3 kcal/mol). We also simultaneously studied the stabi-
lity of 1 and 2, taking the 1H NMR spectra for both at rt after
they were synthesized at low temperature. Cyclopropene 1
was completely decomposed before the 1H NMR spectrum
was taken. The 1H NMR spectrum of 2 could be taken with
no decomposition, and the single CH2 peak disappeared
after 1 day. On the basis of the theoretical and experimental
results, cyclopropene 1 is more easily excited to its diradical
intermediate. When the less stable cyclopropene 1 in ether
was slowly added to the more stable cyclopropene 2 at
-78 °C in an ether solution, the yield of the crossed [2 þ 2]
adduct 8 increased to 10%.
According to the results, we designed the reaction condi-
tions to enhance the yield of the crossed [2 þ 2] cycloaddi-
tion. Cyclopropene 1 was slowly generated in a solution
containing cyclopropene 2 at 0 °C. Tribromocyclopropane 3,
the immediate precursor of both 1 and 2, was treated with 1.5
equiv of methyllithium followed by slowly adding proton
source, and the yield of the crossed [2þ2] adduct 8 rose to a
40% isolated yield. Compound 8 was treated with DDQ at
toluene refluxing temperature to generate 40-bromo-o-ter-
phenyl (11)17 in a 97% isolated yield (Scheme 3).
for 12 h. The mixture was poured into a 250-mL beaker with
100 g of crushed ice. The organic layer was separated and
washed with water and brine, and then dried over anhydrous
magnesium sulfate. After filtration, the solvent was removed on
a rotary evaporator and the residue was purified by column
chromatography (hexanes) to give colorless oil 4 (3.46 g, 94%)
and white solid 5 (trace). Compound 4: IR (neat, cm-1) 3058,
2987, 2967, 2868, 1599, 1576, 1496, 1443, 1319, 1256, 1100, 1077,
1011, 854, 765, 737, 699; 1H NMR (300 MHz, CDCl3) δ
7.42-7.33 (m, 4H), 7.30-7.25 (m, 1H), 6.22-6.18 (ddd, 1H,
J = 1, 3.2, 5.4 Hz), 6.10 (dd, 1H, J = 3.2, 4.8 Hz), 3.27-3.24 (m,
1H), 3.09-3.06 (m, 1H), 2.64 (dt, 1H, J = 1.8, 7.4 Hz), 1.93 (dd,
1H, J = 1.1, 7.4 Hz), 1.81 (d, 1H, J = 6.3 Hz), 1.78 (d, 1H, J =
6.3 Hz); 13C NMR (75 MHz, CDCl3) δ 140.4 (C), 135.8 (CH),
134.7 (CH), 128.5 (CH), 128.2 (CH), 126.5 (CH), 61.1 (CH2),
54.9 (CH), 52.3 (CH), 47.0 (C), 33.3 (C), 32.8 (CH2); MS m/z (%)
262 (Mþ þ 2, 3.0), 260 (Mþ, 3.1). HRMS calcd for C14H13Br m/z
260.0201, found 260.0191. Anal. Calcd for C14H13Br: C 64.39, H
5.02. Found: C 64.56, H 4.78. Compound 5: mp 93.5-94 °C; IR
(neat, cm-1) 3054, 3026, 2923, 2852, 1598, 1498, 1444, 1262,
1225, 1184, 1008, 965, 805, 775, 747, 695; 1H NMR (300 MHz,
CDCl3) δ 7.41-7.25 (m, 10H), 2.42 (d, 2H, J = 5.8 Hz), 2.22 (d,
2H, J = 5.8 Hz); 13C NMR (75 MHz, CDCl3) δ 133.5 (C), 128.6
(CH), 127.0 (CH), 126.4 (CH), 45.2 (C), 40.7 (C), 39.9 (CH2);
MS m/z (%) 392 (Mþ þ 4, 5), 390 (Mþ þ 2, 10), 388 (Mþ, 6).
HRMS calcd for C18H14Br2 m/z 387.9462, found 387.9458.
Anal. Calcd for C18H14Br2: C 55.42, H 3.62. Found: C 55.34,
H 3.53.
In summary, cyclopropene 2 underwent [2þ2] dimeriza-
tion to generate 5 in 35% isolated yield, which was heated to
form compound 6 followed by oxidation to yield o-terphenyl
7. o-Terphenyl 7 was synthesized in 49% isolated yield in a
one-pot reaction from tribromocyclopropane 3. We applied
theoretical and experimental results to provide a method to
synthesize a crossed [2þ2] cycloadduct. When tribromocy-
clopropane 3 was treated with 1.5 equiv of methyllithium
followed by slowly adding proton source, the yield of the
crossed [2þ2] adduct 8 rose to a 40% isolated yield. Com-
pound 8 was heated and oxidated to produce 11.
[2 þ 2] Cycloaddition of 1-Bromo-2-phenylcyclopropene (2). To
a stirred solution of compound 3 (5.0 g, 14.1 mmol) in 30 mL
of dry ether at -78 °C was added methyllithium (1.5 M in ether,
9.4 mL, 14.1 mmol) dropwise from a syringe. The mixture was
allowed to warm to rt and stirred for 0.5 h. Ether was removed
under reduced pressure and the residue was kept at -20 °C until
cyclopropene 2 had completely disappeared as monitored by 1H
NMR. About 30 mL of ether was added, then the mixture was
poured into a 250-mL beaker with 100 g of crushed ice. The ether
layer was separated, the aqueous layer was extracted with 30 mL
of ether, and the combined ether solution was washed with about
100 mL of water and brine. The ether solution was dried with
anhydrous magnesium sulfate. After filtration, the solvent was
removed on a rotary evaporator and the residue was purified by
column chromatography (hexanes) to give white solid 5 (0.96 g,
35%), 6 (82.5 mg, 3%), and 7 (54.7 mg, 2%). Compound 6: mp
97.5-98.5 °C; IR (neat, cm-1) 3059, 3028, 2866, 2809, 1667,
1599, 1490, 1441, 1419, 976, 758, 697; 1H NMR (300 MHz,
CDCl3) δ 7.18-7.10 (m, 6H), 7.01-6.98 (m, 4H), 3.65 (s, 4H);
13C NMR (75 MHz, CDCl3) δ 140.2 (C), 131.5 (C), 128.6 (CH),
128.0 (CH), 126.8 (CH), 119.7 (C), 44.3 (CH2); MS m/z (%) 392
(Mþ þ 4, 23), 390 (Mþ þ 2, 52), 388 (Mþ, 26), 230 (100), 229 (72),
228 (39). HRMS calcd for C18H14Br2 m/z 387.9462, found
387.9464. Anal. Calcd for C18H14Br2: C 55.42, H 3.62. Found:
Experimental Section
Trapping 1-Bromo-2-phenylcyclopropene (2) with Cp. Methyl-
lithium (1.5 M in ether, 9.4 mL, 14.1 mmol) was added dropwise
from a syringe to a stirred solution of compound 3 (5.0 g, 14.1
mmol) in 30.0 mL of dry ether at -78 °C. The mixture was
allowed to warm to rt and stirred for 0.5 h. The mixture was
cooled to -40 °C, and then cyclopentadiene (11.5 mL, 0.14 mol)
was added. The mixture was allowed to warm to rt and stirred
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766–772. (b) Takashi, A.; Toshihiro, I.; Hidetsugu, I.; Hiroaki, N.; Ryusuke, W.;
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C 55.66, H 3.75. Compound 7: mp 110-111 °C; IR (neat, cm-1
)
7996 J. Org. Chem. Vol. 74, No. 20, 2009

Lee et al.
JOCNote
3062, 3022, 2903, 1652, 1456, 1346, 1012, 775, 699; 1H NMR (300
MHz, CDCl3) δ 7.68 (s, 2H), 7.23-7.21 (m, 6H), 7.10-7.07 (m,
4H); 13C NMR (75 MHz, CDCl3) δ 141.2 (C), 139.1 (C), 135.2
(CH), 129.5 (CH), 128.1 (CH), 127.2 (CH), 123.6 (C); MS m/z
(%) 390 (Mþ þ 4, 50), 388 (Mþ þ 2, 100), 386 (Mþ, 52), 228 (59).
HRMS calcd for C18H12Br2 m/z 385.9306, found 385.9310. Anal.
Calcd for C18H12Br2: C 55.71, H 3.12. Found: C 55.95, H 3.34.
1,2-Dibromo-3,4-diphenylcyclohexa-1,4-diene (6) and 40-50-
Dibromo-o-terphenyl (7). A solution of compound 5 (0.11 g,
0.28 mmol) in toluene (10 mL) was stirred and refluxed for 24 h.
Toluene was removed under reduced pressure and the residue
was purified by chromatography (hexanes) to give white solid 6
(72 mg, 65%) and 7 (36 mg, 33%).
J = 5.2 Hz), 2.12 (dd, 1H, J = 1.4, 5.2 Hz), 2.01-1.98 (m, 2H);
13C NMR (75 MHz, CDCl3) δ 137.9 (C), 135.5 (C), 128.45 (CH),
128.40 (CH), 126.5 (CH), 126.3 (CH), 126.0 (CH), 125.5 (CH),
42.0 (C), 38.8 (CH2), 38.5 (C), 34.9 (CH), 34.8 (C), 32.6 (CH2);
MS m/z (%) 312 (Mþ þ 2, 13), 310 (Mþ, 15), 231 (100), 216 (57),
215 (84), 153 (46). HRMS calcd for C18H15Br m/z 310.0357,
found 310.0359. Anal. Calcd for C18H15Br: C 69.47, H 4.86.
1
Found: C, 69.14, H 5.14. Compound 9: H NMR (300 MHz,
CDCl3) δ 7.32-7.14 (m, 10H), 2.02 (dd, 2H, J = 2.5, 3.7 Hz),
1.85-1.82 (m, 4H); 13C NMR (75 MHz, CDCl3) δ 140.4 (C),
128.3 (CH), 125.5(CH), 125.1 (CH), 32.4 (C), 31.3 (CH2), 29.3
(CH). Compound 10: 1H NMR (300 MHz, CDCl3) δ 7.54-7.07
(m, 15H), 2.43-2.30 (m, 2H), 2.03 (d, 1H, J = 3.9 Hz),
1.80-1.74 (m, 1H), 1.67-1.53 (m, 2H), 1.31-1.21 (m, 1H),
1.02-0.92 (m, 2H); 13C NMR (75 MHz, CDCl3) δ 143.8 (C),
143.3 (C), 130.1 (C), 128.7 (CH), 128.6 (CH), 128.5 (CH), 128.3
(CH), 127.5 (CH), 126.1 (CH), 126.0 (CH), 125.9 (CH), 125.2
(CH), 120.7 (C), 111.4 (C), 27.6 (CH), 26.3 (CH), 22.5 (CH), 21.8
(CH), 20.5 (CH), 16.3 (CH2), 15.7 (CH2).
Enhanced Yield of Crossed [2 þ 2] Cycloaddition of Cyclopro-
pene 1 and 2. Methyllithium (1.5 M in ether, 14.1 mL, 21.2 mmol)
was added dropwise from a syringe to a stirred solution of
compound 3 (5.0 g, 14.1 mmol) in 30.0 mL of dry ether at
-78 °C. The mixture was allowed to warm to rt and stirred for
0.5 h. A solution of Et3NHCl (0.92 g, 16.8 mmol) in dry THF
(25 mL) was added slowly (over 1 h) to the vigorously stirred ether
solution at 0 °C, which was then stirred for 24 h. The mixture was
poured into a 250-mL beaker with 100 g of crushed ice. The organic
layer was separated and washed with water and brine, and then
dried over anhydrous magnesium sulfate. After filtration, the
solvent was removed on a rotary evaporator and the residue was
purified by column chromatography (hexanes) to give white solid 8
(0.88 g, 40%), 9 (82 mg, 10%), and 10 (0.11 g, 13%)
Oxidation of Compound 6. A solution of 6 (30 mg, 0.077
mmol) in toluene (10 mL) containing DDQ (20.9 mg, 0.092
mmol) was refluxed for 3 h. Toluene was removed under reduced
pressure and the residue was purified by column chromatogra-
phy (hexanes) to give white solid 7 (29 mg, 97%).
One-Pot Synthesis of 40-50-Dibromo-o-terphenyl (7). To a
stirred solution of cyclopropane 3 (5.0 g, 14.1 mmol) in 30 mL
of dry ether at -78 °C was added methyllithium (1.5 M in ether,
9.4 mL, 14.1 mmol) dropwise from a syringe. The mixture was
allowed to warm to rt and stirred for 0.5 h. The mixture was
poured into a 250-mL beaker with 100 g of crushed ice. The ether
layer was separated and the aqueous layer extracted with 30 mL
of ether. The combined ether extracts were washed with about
100 mL of water and brine. The ether solution was dried with
anhydrous magnesium sulfate. After fitration, ether was re-
moved under reduced pressure and the residue was kept at
-20 °C for 12 h. Toluene (50 mL) was added, and the mixture
was refluxed for 24 h. The reaction mixture was cooled to rt and
DDQ (1.59 g, 7 mmol) was added. The reaction mixture was
refluxed for 3 h. Toluene was removed under reduced pressure
and the residue was purified by column chromatography
(hexanes) to give white solid 7 (1.34 g, 49%).
Crossed [2þ2] Cycloaddition of Cyclopropenes 1 and 2: Pre-
paration of Cyclopropene 1: Methyllithium (1.5 M in ether,
23.5 mL, 35.3 mmol) was added dropwise from a syringe to a
stirred solution of compound 3 (5.0 g, 14.1 mmol) in 30.0 mL of
dry ether at -78 °C. The mixture was allowed to warm to rt and
stirred for 0.5 h. Ammonium chloride (5.6 g, 0.105 mol) was
added at -78 °C. Preparation of cyclopropene 2: Methyllithium
(1.5 M in ether, 9.4 mL, 14.1 mmol) was added dropwise from a
syringe to a stirred solution of compound 3 (5.0 g, 14.1 mmol) in
30.0 mL of dry ether at -78 °C. The mixture was allowed to
warm to rt and stirred for 0.5 h. A solution of cyclopropene 1
was transferred to the solution of cyclopropene 2 at -78 °C.
After the solution was added, the mixture was allowed to warm
to rt and stirred for 12 h. The mixture was poured into a 250-mL
beaker with 100 g of crushed ice. The organic layer was
separated and washed with water and brine, and then dried
over anhydrous magnesium sulfate. After filtration, the solvent
was removed on a rotary evaporator and the residue was
purified by column chromatography (hexanes) to give white
solid 5 (0.14 g, 5%), 8 (0.44 g, 10%), 9 (0.16 g, 10%), and 10
(0.49 g, 30%). Compound 8: decomposition temperature 44 °C;
IR (neat, cm-1) 3060, 3033, 2984, 2920, 1603, 1498, 1448, 1285,
1224, 1137, 1022, 756, 695; 1H NMR (300 MHz, CDCl3) δ
7.38-7.12 (m, 10H), 2.55 (dd, 1H, J = 2.7, 3.9 Hz), 2.31 (d, 1H,
Synthesis of 40-Bromo-o-terphenyl (11). A solution of 8 (0.1 g,
0.32 mmol) in toluene (10 mL) was refluxed for 24 h. The
reaction was cooled to rt and DDQ (87 mg, 0.35 mmol) was
added. The reaction mixture was refluxed for 3 h. Toluene was
removed under reduced pressure and the residue was purified by
column chromatography (hexanes) to give white solid 11 (96 mg,
1
97%). Compound 11: H NMR (300 MHz, CDCl3) δ 7.58 (d,
1H, J = 2.1 Hz), 7.54 (dd, 1H, J = 2.1, 8.2 Hz), 7.29 (d, 1H, J =
8.2 Hz), 7.23-7.19 (m, 6H), 7.14-7.08 (m, 4H); 13C NMR
(75 MHz, CDCl3) δ 142.5 (C), 140.4 (C), 140.2 (C), 139.5 (C),
133.3 (CH), 132.1 (CH), 130.4 (CH) 129.7 (CH), 129.69 (CH),
128.0 (CH), 127.99 (CH), 126.98 (CH), 126.8 (CH), 121.4 (C).
Acknowledgment. Financial support from the National
Science Council of the Republic of China (NSC 96-2113-
M-030-003-MY2) and the National Center for Highperfor-
mance Computing for computer time and facilities is grate-
fully acknowledged. We thank Professor M. Shieh and Mr.
T.-S. Kuo at NTNU for the X-ray structure determination.
Supporting Information Available: X-ray structure determi-
1
nations for 5, 6, 7, 8, and 11 in CIF format and H, 13C, and
DEPT NMR spectra for compounds 4, 5, 6, 7, 8, and 11. This
material is available free of charge via the Internet at http://
pubs.acs.org.
J. Org. Chem. Vol. 74, No. 20, 2009 7997