Synthesis and chemistry of tricyclic cyclopropene-tricyclo[3.2.2.02,4]nona-2(4),6-diene

Article abstract of DOI:10.1016/S0040-4020(03)00046-2

The 1,2-bridged tricyclic cyclopropene, tricyclo[3.2.2.0^2,4]nona-2(4),6-diene (1), has been synthesized by the elimination of 2-bromo-4-chlorotricyclo[3.2.2.0^2,4]-non-6-ene (5). Cyclopropene 1 will undergo different isomerizations in ether solution and in neat conditions. Compound 1 rearranged to an anti-Bredt compound 4 via diradical mechanism in ether and tricyclic compound 6 via vinyl carbene mechanism in neat conditions. Compound 1 can be trapped with DPIBF at different temperatures yielding different results: the exo-endo adduct 2 (exo-addition from the view of the cyclopropene and endo-addition from the view of bicyclo[2.2.2]octene) is a sole product at 0°C by slowly addition of methyllithium, and the exo-endo adduct 2, endo-endo adduct 9, anti-Bredt adduct 3, and styrene 8 are isolated at ether refluxing temperature. Styrene 8 is proposed to be formed from endo-endo adduct 9 by diradical mechanism. The chemistry of exo-endo adduct 2 and endo-endo adduct 9 is as well studied. The exo-endo adduct 2 undergoes hydration in trifluoroacetic acid to generate 1,3-cis-diol 11 followed by eliminations of water and formaldehyde to give naphthalene 12. The endo-endo adduct 9 reacts with water in tetrahydrofuran-containing silica gel to yield 1,4-cis-diol 10. Both 9 and 10 react with trifluoroacetic acid to form trans-3-hydroxy trifluoroacetate 13. Compound 13 will undergo hydrolysis and isomerization to generate 1,3-cis-diol 11 in trifluoroacetic acid.

Full text of DOI:10.1016/S0040-4020(03)00046-2

Tetrahedron 59 (2003) 1539–1545
Synthesis and chemistry of tricyclic cyclopropene-
tricyclo[3.2.2.02,4]nona-2(4),6-diene
*
Gon-Ann Lee, Chih-Hwa Cherng, Ai Ni Huang and Yu-Hsien Lin
Department of Chemistry, Fu Jen Catholic University, 510 Chung Cheng Road, Hsinchuang, Taipei Hsien 24205, Taiwan, ROC
Received 30 November 2002; revised 3 January 2003; accepted 6 January 2003
Abstract—The 1,2-bridged tricyclic cyclopropene, tricyclo[3.2.2.02,4]nona-2(4),6-diene (1), has been synthesized by the elimination of
2-bromo-4-chlorotricyclo[3.2.2.02,4]-non-6-ene (5). Cyclopropene 1 will undergo different isomerizations in ether solution and in neat
conditions. Compound 1 rearranged to an anti-Bredt compound 4 via diradical mechanism in ether and tricyclic compound 6 via vinyl
carbene mechanism in neat conditions. Compound 1 can be trapped with DPIBF at different temperatures yielding different results: the exo–
endo adduct 2 (exo-addition from the view of the cyclopropene and endo-addition from the view of bicyclo[2.2.2]octene) is a sole product at
08C by slowly addition of methyllithium, and the exo–endo adduct 2, endo–endo adduct 9, anti-Bredt adduct 3, and styrene 8 are isolated at
ether refluxing temperature. Styrene 8 is proposed to be formed from endo–endo adduct 9 by diradical mechanism. The chemistry of exo–
endo adduct 2 and endo–endo adduct 9 is as well studied. The exo–endo adduct 2 undergoes hydration in trifluoroacetic acid to generate 1,3-
cis-diol 11 followed by eliminations of water and formaldehyde to give naphthalene 12. The endo–endo adduct 9 reacts with water in
tetrahydrofuran-containing silica gel to yield 1,4-cis-diol 10. Both 9 and 10 react with trifluoroacetic acid to form trans-3-hydroxy
trifluoroacetate 13. Compound 13 will undergo hydrolysis and isomerization to generate 1,3-cis-diol 11 in trifluoroacetic acid. q 2003
Elsevier Science Ltd. All rights reserved.
1. Introduction
to form three dimers, one 1,3,5-hexatriene and two
tricyclo[3.1.0.02,4]hexanes.9 On the other hand,
bicyclo[4.1.0]hept-1(6)-ene underwent two fashions of
dimerizations to form an ene dimer and a [2þ2] dimer.9a,10
Although the first authenticated synthesis of cyclopropene
was reported by Dem’yanoy and Doyarenko in 1922,1 the
chemistry of cyclopropene and its derivatives received little
attention until the mid-1950s when the cyclopropenes in
nature was recognized and plausible routes to cyclo-
propenes became a reality with the advent of carbene
chemistry.2 Cyclopropene contains 27.7 kcal/mol of olefinic
strain energy and 55.2 kcal/mol of total strain energy;3
therefore, it is of great interest and challenge to explore the
synthesis and chemistry of cyclopropenes.4 Cyclopropenes
undergo many unusual processes such as ene dimerization
to give 3-cyclopropylcyclopropenes,5 ring opening reaction
to form vinyl carbene,6 coupling dimerization to yield 1,3,5-
hexatrienes,7 and [2þ2] cycloaddition to generate
tricyclo[3.1.0.02,4]hexanes8 in order to release strain energy.
Cyclopropenes usually undergo the most-favored type of
isomerizations or dimerizations to release their high strain
energy. However, there are only very few cyclopropenes
which are reported to release their strain energy by
different types of isomerization and/or dimerization.
6-Bicyclo[4.1.0]hept-1-ylbicyclo[4.1.0]hept-1(7)-ene was
able to undergo coupling reaction in different conditions
The incorporation of the cyclopropene fused to carbocyclic
rings further increases the ring strain and often results in
more challenging syntheses and complicated chemistry.11
We have reported the synthesis of tricyclo[3.2.1.02,4]-octa-
2(4),6-diene and tricyclo[3.2.1.02,4]oct-2(4)-ene, the stereo-
chemistry of the Diels–Alder reactions of these cyclo-
propenes with DPIBF, and the chemistry of the adducts.12
We also reported the pioneering work of the higher
analogue, tricyclo[3.2.2.02,4]nona-2(4),6-diene (1), which
was generated and trapped by DPIBF at 08C and exo–endo
adduct 2 and 3 were isolated. Compound 3 was formed by
DPIBF with 8-methylenebicyclo[3.2.1]octa-1,6-diene (4)
which was produced via a diradical isomerization of 1.13
(Scheme 1). In this paper, we utilize the vacuum gas–solid
reaction (VGSR) technique14 to synthesize compound 1 in
order to study its chemistry in neat conditions. In addition,
compound 1 is trapped with DPIBF at room temperature in
solution, and additional chemical properties of these adducts
are also studied.
Keywords: tricyclo[3.2.2.02,4]nona-2(4),6-diene; 2-bromo-4-chloro-
tricyclo[3.2.2.02,4]-non-6-ene; exo–endo adduct.
2. Results and discussion
*
Corresponding author. Tel.: þ886-2290-311113563; fax: þ886-2290-
23209; e-mail: chem1010@mails.fju.edu.tw
The cyclopropene 1 can be generated by VGSR technique at
0040–4020/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4020(03)00046-2

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G.-A. Lee et al. / Tetrahedron 59 (2003) 1539–1545
Scheme 1.
room temperature by slowly passing 2-bromo-4-chloro-
tricyclo[3.2.2.02,4]non-6-ene (5)13 through a column packed
with methyllithium deposited on glass helices. Compound 1
is then kept neat under vacuum at room temperature for
30 min and 8-methylene-tricyclo[3.2.1.04,6]oct-2-ene (6) is
produced as a sole product isolated in 94% yield. Compound
1 will undergo ring opening reaction to form vinyl carbene 7
which was able to undergo two C–C bond and one C–H
bond insertions to generate anti-Bredt compounds 4, 4a, and
tricyclic compound 6, respectively (Scheme 2). However,
compound 6 was the only product formed in neat conditions.
This fact was further supported by the PM3 calculations that
the heats of formation of 4, 4a, and 6 are 96.8, 97.4, and
60.0 kcal/mol, respectively. Although the cyclopropene 1
underwent diradical mechanism to proceed an anti-Bredt
compound 4 in ether solution,13 isomerized via vinyl
carbene mechanism to yield tricyclic compound 6 in neat
conditions. Because the vinyl carbene formed from
cyclopropne can be stabilized by ether, the cyclopropene 1
undergoes biradical reaction better than the ring opening
reaction. In order to prove this transformation, compound 1
was generated by VGSR and trapped with DPIBF in ether
conditions. Four compounds, 2, 3, 8, and 9 were isolated
(Scheme 3).
Scheme 2.
Scheme 3.

G.-A. Lee et al. / Tetrahedron 59 (2003) 1539–1545
1541
To study the temperature effect, compound 1 was also
synthesized and trapped by DPIBF in ether solution at
gently refluxing temperature, and the reaction mixture was
purified by chromatography to give four compounds, 2, 3, 8,
and 9. The structure of 8 was further confirmed by single
crystal X-ray analysis (Fig. 1). Because the methylene group
and ethylene group of styrene are in the syn-configuration,
compound 8 should be generated from exo–endo adduct 2
or endo–endo adduct. In order to define the origin of
compound 8, adduct 2 was subjected to the reaction
conditions but underwent no change. Compound 2 does
not rearrange either in refluxing chloroform, in tetrahydro-
furan solution containing silica gel, or by irradiation. As a
result, we conclude that compound 8 is formed from the
endo–endo adduct. Based on the spectral data
(HRMS¼388.1827 and 13 peaks in 13C NMR), compound
9 was formed directly from 1 with DPIBF. According to the
Diels–Alder reaction of the lower analogue, of
tricyclo[3.2.1.02,4]octa-2(4),6-diene,12 we propose that
compound 9 is the endo–endo adduct of 1 with DPIBF.
There are two possible transformations for the isomerization
of 9 to 8. One is the same as the transformations of
tricyclo[3.2.12,4]oct-6-enes to tetracyclo[3.2.1.02,7.04,6]-
octanes in which the intermediates are diradicals.12,15
Another possibility may involve the acidic-catalyzed
isomerization during the purification. To prove the trans-
formation via diradical pathway and stereochemistry of 9,
compound 9 was irradiated, which resulted in formation of
styrene 8 with 94% isolated yield (Scheme 3).
Figure 1. X-Ray crystallographic analysis of compound 8.
In order to prove that the diradical transformation is the only
possible pathway, compound 9 was added to tetrahydro-
furan solution containing 1% silica gel and the 1,4-cis-diol
10 was isolated in 92% yield with no observation of 8. The
X-ray analysis of 10 was carried out as well (Fig. 2).
Because the methylene group in cyclopropane and the
ethylene group are in the syn-conformation, compound 10
should be formed from the endo–endo adduct and this result
also confirmed the stereochemistry of 9. When compound 9
was hydrated, 1,4-trans-diol was not obtained. This result
indicated that water was attracted by the protonated ether
and attack from the same side of the oxygen. The
mechanisms of isomerization and hydration of 9 are
Figure 2. X-Ray crystallographic analysis of compound 10.
Scheme 4.

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G.-A. Lee et al. / Tetrahedron 59 (2003) 1539–1545
Figure 3. X-Ray crystallographic analysis of compound 11.
Figure 5. X-Ray crystallographic analysis of compound 13.
shown by single-crystal X-ray analysis (Figs. 3 and 4). In
order to define the origin of naphthalene 12, compound 11
was subjected to the same reaction conditions and
compound 12 was isolated in 90% yield. The mechanism
of hydration of 2 and eliminations of water and formal-
dehyde of 11 are shown in Scheme 5.
The hydrations of exo–endo adduct 2 and endo–endo
adduct 9 are different. There are two effects that influence
the outcome. One is that both 2 and 9 contain an oxygen
atom that can direct the water to the syn-addition; another is
that the conformations of the cyclopropane ring and the
oxygen atom in these two compounds are different. When
exo–endo adduct 2 is protonated, water directed to oxygen
will add to the methylene of the cyclopropane to release the
strain energy and to generate 1,3-cis-diol 11. In the case of
the endo–endo adduct 9, however, water directed to oxygen
cannot add to the methylene of cyclopropane. When
compound 9 was subjected to the same conditions as the
hydration of 2, three compounds, 11, 12, and trans-3-
hydroxy trifluoroacetate 13, were isolated. The structure of
13 was shown by single-crystal X-ray analysis (Fig. 5). We
have learned that 9 can hydrate to form 1,4-cis-diol 10 under
mild acidic conditions. To study the transformation of this
reaction, 10 was treated with trifluoroacetic acid and trans-
3-hydroxy trifluoroacetate 13 was isolated in 95% yield.
When compound 13 was also treated with trifluoroacetic
acid, 1,3-cis-diol 11 and naphthalene 12 were isolated in 65
and 27%, respectively (Scheme 6). Because of the 1,3-cis-
diol 11 containing intramolecular hydrogen bonding, 13 will
undergo hydrolysis and isomerization to give 11 followed
by eliminations of water and formaldehyde to give 12.
Figure 4. X-Ray crystallographic analysis of compound 12.
shown in Scheme 4. These results are also confirmed by the
theoretical calculations of the heats of formation of 2 and 9
being 158.6 and 163.9 kcal/mol, respectively, which may
explain why compound 2 is the sole adduct when 1 is
trapped with DPIBF at 08C13 by slowly adding methyl-
lithium and stable in refluxing chloroform, in tetrahydro-
furan solution containing silica gel, and by UV irradiation.
To compare the hydration of 9 and to understand the
chemistry of 2, compound 2 was further treated with
trifluoroacetic acid in tetrahydrofuran and two compounds,
1,3-cis-diol 11 and naphthalene 12, were isolated
(yields¼82 and 5%). The structures of 11 and 12 were
3. Conclusion
The highly strained cyclopropene 1 favored the diradical
intermediate to generate an anti-Bredt compound 4 in ether
solution and the vinyl carbene intermediate to yield the
tricyclic compound 6 in neat conditions. The trapping
reaction of 1 with DPIBF is more complicated at room
Scheme 5.

G.-A. Lee et al. / Tetrahedron 59 (2003) 1539–1545
1543
Scheme 6.
temperature than that at 08C. The exo–endo adduct 2 is a
sole product at 08C by slowly addition of methyllithium and
the exo–endo adduct 2, endo–endo adduct 9, anti-Bredt
adduct 3, and styrene 8 are formed at ether refluxing
temperature. The endo–endo adduct 9 will isomerize to
styrene 8 via a diradical mechanism and convert to
naphthalene 12 via 1,4-cis-diol 10, trans-3-hydroxy tri-
fluoroacetate 13 and 1,3-cis-diol 11. The exo–endo adduct 2
also converts to naphthalene 12 but only via 1,3-cis-diol 11.
4.2.1. 2-Bromo-4-chlorotricyclo[3.2.2.02,4]non-6-ene (5).
A solution of tetrabutylammonium fluoride (n-Bu4NF,
45.72 g, 60.0 mmol) in CH2Cl2 (30 ml) was added slowly
in the mixture of 1-bromo-2,2-dichloro-1-trimethylsilyl-
cyclopropane (12.00 g, 45.8 mmol) and 1,3-cyclohexadiene
(30.50 g, 381.5 mmol) at room temperature under nitrogen
purge. After the addition of n-Bu4NF, the reaction mixture
was kept stirring for 12 h. The solution was washed with
water and concentrated under reduced pressure, and the
residue was purified by flash chromatography (hexanes) to
1
give 513 (6.59 g, 62%). Compound 5: H NMR (CDCl3): d
6.01–5.90 (m, 2H), 3.07 (d, 1H, J¼6.5 Hz), 2.98 (d, 1H,
J¼6.3 Hz), 2.11–2.06 (m, 2H), 1.58 (d, 1H, J¼7.7 Hz),
1.24–1.22 (m, 2H), 1.05 (d, 1H, J¼7.7 Hz); 13C NMR
(CDCl3): d 131.82 (CH), 131.51 (CH), 47.45 (C), 41.09
(CH), 40.59 (C), 39.48 (CH), 23.17 (CH2), 21.81 (CH2),
20.97 (CH2).
4. Experimental
4.1. General
Melting points were determined on a Fargo MP-1D and are
uncorrected. Proton and carbon-13 NMR spectra were
measured in CDCl3 with CHCl3 as the internal standard.
Chemical shifts (d) are expressed in ppm downfield from
tetramethylsilane. Coupling constants are expressed in
hertz. X-Ray data were recorded on a Seimens R3m/V
diffractometer for compounds 8, 10, and 13, and a Nonius
CAD 4 diffractometer for compounds 11 and 12. Infrared
spectra were recorded on a Beckman Acculab TM1
spectrophotometer. Calculation was performed using
HyperChem, Single Point, SemiEmpirical, molecule,
PM3. Silica gel (70–230 mesh) for column chromatography
and silica gel (230 mesh) for flash chromatography are from
E. Merck. Solvents are of reagent grade.
4.2.2. 8-Methylenetricyclo[3.2.1.04,6]oct-2-ene (6). 2-
Bromo-4-chlorotricyclo[3.2.1.02,4]non-6-ene (5) (0.25 g,
1.1 mmol) was passed through the column containing the
solid methyllithium at room temperature. After the product
had been collected onto the walls of a cold trap at 21968C,
the mixture was kept at room temperature for 30 min. The
reaction mixture was fractionated to give colorless liquid 6
(0.12 g, 94%). Compound 6: IR (neat, cm21): n 3052, 2944,
1
2858, 1665, 1613, 870, 714, 628; H NMR (CDCl3): d
6.00–5.86 (m, 2H), 4.83 (s, 1H), 4.70 (s, 1H), 2.82 (t, 1H,
J¼5.7 Hz), 2.02–1.94 (m, 1H), 1.90–1.86 (m, 1H), 1.83–
1.74 (m, 2H), 0.87 (d, 1H, J¼10.5 Hz); 13C NMR (CDCl3):
d 151.01 (C), 129.06 (CH), 122.52 (CH), 101.43 (CH2),
40.65 (CH), 28.83 (CH2), 21.51 (CH), 21.46 (CH), 18.69
(CH); MS m/z (%): 118 (Mþ, 75), 117 (Mþ21, 100), 91
(51), 77 (33), 51 (36), 39 (81), 27 (64); HRMS calcd for
C9H10 m/z 118.0783, found 118.0781. Anal. calcd for
C9H10: C, 91.47; H, 8.53. Found: C, 91.80; H, 8.21.
4.2. Vacuum gas–solid reaction apparatus
A modification of the apparatus previously reported was
used.14 The apparatus was prepared by charging a column
(30£3.5 cm with a 19/22 ground-glass joint at bottom) with
the adsorbed methyllithium. The glass helices were
supported on a glass–wool plug (1 cm) at the bottom of
the column. A series of two or three traps was used to collect
and/or fractionate the products from the top of the column.
The flask charged starting material was attached to the
bottom of the column and heated to 358C by using water
bath.
4.2.3. Trapping tricyclo[3.2.1.02,4]nona-2(4),6-diene (1)
with DPIBF by VGSR. 2-Bromo-4-chlorotricyclo-
[3.2.1.02,4]non-6-ene (5) (0.25 g, 1.1 mmol) was passed
through the column containing the solid methyllithium at
room temperature. After the product had been collected onto
the walls of a cold trap containing DPIBF (0.30 g,

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G.-A. Lee et al. / Tetrahedron 59 (2003) 1539–1545
1.1 mmol) at 21968C, ether (2.5 ml) was introduced to the
trap and the solution was kept stirring at room temperature
for 2 h. The reaction mixture was concentrated, and
chromatographed (hexanes/CH2Cl2 1:1) to give 213
(4.15 g, 50%), 313 (0.37 g, 5%), 8 (0.33 g, 4%) and 9
to give 2 (3.90 g, 47%), 3 (0.52 g, 7%), 8 (0.33 g, 4%) and 9
(2.91 g, 35%).
4.3. Isomerization of compound 9
1
(1.66 g, 20%). Compound 2: H NMR (CDCl3): d 7.75–
A solution of 9 (0.65 g, 1.7 mmol) in CHCl3 (10 ml) was
irradiated with a UVP BLAKRAY Longwave Ultraviolet
Lamp Model B 100 AP. After 24 h of irradiation, the
reaction mixture was concentrated and the residue was
purified by flash chromatography (hexanes/CH2Cl2 1:1) to
give 8 (0.62 g, 94%).
7.71 (m, 4H), 7.47–7.39 (m, 6H), 7.12–7.09 (m, 2H), 6.99–
6.96 (m, 2H), 5.12–5.09 (m, 2H), 2.96 (bs, 2H), 2.11 (d, 1H,
J¼6.1 Hz), 1.66 (d, 2H, J¼8.0 Hz), 1.53 (d, 1H, J¼6.1 Hz),
1.01 (d, 2H, J¼7.8 Hz); 13C NMR (CDCl3): d 149.84 (C),
136.74 (C), 128.73 (CH), 128.47 (CH), 128.41 (CH), 126.46
(CH), 121.10 (CH), 90.28 (C), 39.80 (C), 30.55 (CH), 25.55
(CH2), 22.45 (CH2). Compound 3: 1H NMR (CDCl3): d 7.79
(bs, 1H), 7.63–7.60 (m, 2H), 7.49–7.33 (m, 7H), 7.16–7.11
(m, 3H), 6.99–6.96 (m, 1H), 6.14 (dd, 1H, J¼3.1, 6.0 Hz),
5.90 (d, 1H, J¼6.0 Hz), 4.68 (s, 1H), 4.43 (s, 1H), 2.82–
2.78 (m, 1H), 2.23–2.17 (m, 1H), 1.67–1.53 (m, 2H), 1.32–
1.26 (m, 1H); 13C NMR (CDCl3): d 153.75 (C), 149.91 (C),
146.54 (C), 138.79 (C), 138.57 (CH), 138.42 (CH), 136.55
(C), 128.28 (CH), 127.25 (CH), 127.11 (CH), 126.96 (CH),
126.48 (CH), 126.08 (CH), 121.03 (CH), 117.08 (CH),
104.39 (CH2), 89.18 (C), 88.26 (C), 59.42 (C), 54.84 (CH),
44.22 (CH), 25.99 (CH2), 22.07 (CH2). Compound 8: mp
219–2218C; IR (neat, cm21): n 3041, 2929, 2867, 1681,
4.3.1. Hydration of compound 9. A solution of 9 (1.35 g,
3.5 mmol) in THF (20 ml) containing silica gel (0.20 g) was
stirred for 8 h at room temperature. The reaction mixture
was concentrated and the residue was purified by chroma-
tography (hexanes/CH2Cl2 1:1) to give 10 (1.31 g, 92%).
Compound 10: mp 280–2838C; IR (neat, cm21): n 3331,
3087, 3056, 3035, 2925, 2869, 1597, 1447, 1019, 764, 741,
1
696; H NMR (CDCl3): d 7.43–7.38 (m, 10H), 7.04 (dd,
2H, J¼3.4, 5.7 Hz), 6.66 (dd, 2H, J¼3.4, 5.7 Hz), 6.55 (dd,
2H, J¼2.8, 4.4 Hz), 3.21 (s, 2H), 2.63–2.62 (m, 2H), 1.55
(d, 1H, J¼6.9 Hz), 1.45 (d, 2H, J¼8.5 Hz), 1.18 (d, 1H,
J¼6.9 Hz), 0.99 (d, 2H, J¼8.5 Hz); 13C NMR (CDCl3): d
144.51 (C), 141.75 (C), 136.57 (CH), 128.55 (CH), 128.04
(CH), 127.98 (CH), 127.23 (CH), 79.11 (C), 39.74 (C),
31.82 (CH), 24.51 (CH2), 23.85 (CH2); MS m/z (%): 406
(Mþ, 100), 388 (19), 360 (13), 308 (15), 255 (17), 165 (7),
105 (20), 77 (12); HRMS calcd for C29H26O2 m/z 406.1933,
found 406.1934. Anal. calcd for C29H26O2: C, 85.68; H,
6.45. Found: C, 85.30; H, 6.62. X-Ray: CCDC 118757.
1
1099, 962, 760, 725, 692; H NMR (CDCl3): d 7.64–7.61
(m, 2H), 7.39–7.07 (m, 10H), 6.96 (dd, 1H, J¼1.3, 7.7 Hz),
6.82 (dd, 1H, J¼1.3, 7.7 Hz), 6.24 (t, 1H, J¼8.1 Hz), 6.05
(t, 1H, J¼8.1 Hz), 3.65 (d, 2H, J¼12.2 Hz), 3.34 (d, 1H,
J¼12.7 Hz), 3.21–3.17 (m, 1H), 2.27–2.19 (m, 1H), 1.87–
1.65 (m, 2H), 1.60–1.50 (m, 1H); 13C NMR (CDCl3): d
209.70 (C), 144.00 (C), 141.69 (C), 141.59 (C), 141.20 (C),
140.93 (C), 137.80 (CH), 134.34 (C), 133.60 (CH), 130.41
(CH), 130.35 (CH), 129.69 (CH), 128.43 (CH), 128.15
(CH), 127.89 (CH), 127.42 (CH), 127.19 (CH), 127.15
(CH), 127.00 (CH), 70.84 (C), 43.48 (CH), 37.72 (CH2),
36.08 (CH), 24.65 (CH2), 22.45 (CH2); MS m/z (%): 388
(Mþ, 100), 360 (19), 202 (27), 169 (69), 165 (32), 115 (13),
91 (31), 77 (15); HRMS calcd for C29H24O m/z 388.1827,
found 388.1820. Anal. calcd for C29H24O: C, 89.66; H, 6.23.
Found: C, 89.78; H, 6.11. X-Ray: CCDC 118756.
Compound 9: mp 189–1928C; IR (neat, cm21): n 3048,
2942, 2873, 1602, 1454, 1019, 746, 702; 1H NMR (CDCl3):
d 7.68 (dd, 4H, J¼1.3, 8.2 Hz), 7.56–7.51 (m, 4H), 7.44–
7.39 (m, 2H), 7.10 (dd, 2H, J¼3.0, 5.3 Hz), 6.98 (dd, 2H,
J¼3.0, 5.3 Hz), 6.05 (dd, 2H, J¼2.7, 4.4 Hz), 2.85 (bs, 2H),
1.72 (d, 1H, J¼7.4 Hz), 1.39 (d, 2H, J¼8.8 Hz), 0.94 (d, 2H,
J¼8.8 Hz), 0.59 (d, 1H, J¼7.4 Hz); 13C NMR (CDCl3): d
147.96 (C), 138.05 (C), 135.62 (CH), 128.33 (CH), 127.12
(CH), 126.50 (CH), 126.37 (CH), 118.11 (CH), 93.68 (C),
43.34 (C), 35.86 (CH2), 31.07 (CH), 23.90 (CH2); MS m/z
(%): 388 (Mþ, 100), 360 (71), 308 (67), 255 (56), 105 (42),
77 (44); HRMS calcd for C29H24O m/z 388.1827, found
388.1820. Anal. calcd for C29H24O: C, 89.66; H, 6.23.
Found: C, 90.08; H, 6.15.
4.3.2. Acidification of compound 2. A solution of 2 (1.69 g,
4.4 mmol) in THF (25 ml) containing trifluoroacetic acid
(2 ml) and water (0.5 ml) was stirred for 8 h at room
temperature. The reaction mixture was concentrated and the
residue was purified by chromatography (hexanes/CH2Cl2
1:1) to give 11 (1.45 g, 82%) and 12 (0.08 g, 5%).
Compound 11: mp 197–2008C; IR (neat, cm21): n 3500,
1
3333, 3056, 2944, 1411, 1072, 1011, 750, 733, 700; H
NMR (CDCl3): d 7.92 (d, 1H, J¼7.4 Hz), 7.46–7.35 (m,
5H), 7.28–7.05 (m, 6H), 6.77–6.74 (m, 2H), 5.23–5.12 (m,
2H), 4.61 (bs, 1H), 4.32 (d, 1H, J¼11.8 Hz), 3.83 (d, 1H,
J¼11.8 Hz), 3.22 (bs, 1H), 3.15–3.14 (m, 1H), 2.99–2.98
(m, 1H), 2.16–2.08 (m, 1H), 1.70–1.65 (m, 1H), 1.33–1.16
(m, 2H); 13C NMR (CDCl3): d 145.10 (C), 141.53 (C),
140.67 (C), 138.89 (C), 136.43 (C), 135.28 (CH), 131.05
(CH), 129.88 (CH), 129.63 (CH), 128.96 (CH), 128.55
(CH), 128.14 (CH), 127.85 (CH), 127.26 (CH), 127.14
(CH), 125.95 (CH), 125.50 (CH), 125.37 (CH), 83.43 (C),
67.48 (CH2), 53.03 (C), 35.70 (CH), 31.58 (CH), 23.42
(CH2), 23.12 (CH2); MS m/z (%): 388 (Mþ218, 41), 360
(34), 330 (100), 308 (38), 252 (46), 129 (27), 83 (60), 69
(88); HRMS calcd for C29H24O (M2H2O) m/z 388.1827,
found 388.1825. Anal. calcd for C29H26O2: C, 85.68; H,
6.45. Found: C, 85.58; H, 6.90. X-Ray: CCDC 118758.
Compound 12: mp 239–2408C; IR (neat, cm21): n 3044,
4.2.4. Trapping tricyclo[3.2.1.02,4]nona-2(4),6-diene (1)
with DPIBF in ether solution. To a solution of 2-bromo-4-
chlorotricyclo[3.2.1.02,4]non-6-ene (5) (5.00 g, 21.4 mmol)
and DPIBF (6.07 g, 22.5 mmol) in ether (50 ml) at room
temperature was added methyllithium (25 ml, 1.5 M in
ether) over 15 min. The mixture was stirred at mildly
refluxing temperature for another 2 h. The solution was
concentrated, and chromatographed (hexanes/CH2Cl2 1:1)
1
2922, 1489, 1428, 1361, 1261, 1067, 1022, 750, 706; H
NMR (CDCl3): d 7.58–7.49 (m, 8H), 7.47–7.40 (m, 4H),
7.32–7.26 (m, 2H), 6.50–6.47 (m, 2H), 3.94–3.93 (m, 2H),
1.52 (d, 2H, J¼8.7 Hz), 1.50 (d, 2H, J¼8.7 Hz); 13C NMR
(CDCl3): d 140.04 (C), 139.08 (C), 135.57 (CH), 132.37
(C), 130.87 (C), 130.56 (CH), 128.37 (CH), 127.16 (CH),

G.-A. Lee et al. / Tetrahedron 59 (2003) 1539–1545
1545
126.44 (CH), 124.80 (CH), 37.51 (CH), 25.60 (CH2); MS
m/z (%): 358 (Mþ, 18), 330 (100), 252 (16), 156 (15), 105
(3), 77 (2); HRMS calcd for C28H22 m/z 358.1721, found
358.1731. Anal. calcd for C28H22: C, 93.81; H, 6.19. Found:
C, 93.40; H, 6.78. X-Ray: CCDC 118759.
Cambridge Crystallographic Data Centre as supplementary
publication numbers CCDC 198756-198760.
Acknowledgements
4.3.3. Acidification of compound 11. A solution of 11
(0.20 g, 0.5 mmol) in THF (25 ml) containing trifluoro-
acetic acid (2 ml) and water (0.5 ml) was stirred for 8 h at
room temperature. The reaction mixture was concentrated
and the residue was purified by chromatography
(hexanes/CH2Cl2 1:1) to give 12 (0.16 g, 90%).
Financial support from the National Science Council of the
Republic of China (NSC 91-2113-M-030-006) is gratefully
acknowledged.
4.3.4. Acidification of compound 9. A solution of 9 (0.50 g,
1.3 mmol) in THF (25 ml) containing trifluoroacetic acid
(2 ml) and water (0.5 ml) was stirred for 8 h at room
temperature. The reaction mixture was concentrated and the
residue was purified by chromatography (hexanes/CH2Cl2
1:1) to give 11 (0.23 g, 44%), 12 (0.21 g, 45%) and 13
(0.03 g, 5%). Compound 13: mp 193–1948C; IR (neat,
cm21): n 3504, 3331, 3053, 2943, 1598, 1444, 1071, 1012,
773, 753, 728, 699; 1H NMR (CDCl3): d 8.08 (d, 1H,
J¼7.9 Hz), 7.56–7.49 (m, 2H), 7.42–7.35 (m, 4H), 7.30–
7.13 (m, 6H), 6.99 (d, 1H, J¼2.8 Hz), 6.90–6.80 (m, 2H),
5.92 (t, 1H, J¼7.1 Hz), 4.69 (d, 1H, J¼12.3 Hz), 4.30 (d,
1H, J¼12.3 Hz), 3.36–3.35 (m, 1H), 2.70–2.68 (m, 1H),
2.50 (s, 1H), 1.89–1.80 (m, 1H), 1.66–1.58 (m, 1H), 1.49–
1.40 (m, 1H), 1.27–1.17 (m, 1H); 13C NMR (CDCl3): d
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2
157.05 (q, JC–F¼42.4 Hz, C(vO)O), 139.37 (C), 138.62
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127.98 (CH), 127.95 (C), 127.79 (CH), 127.45 (CH), 127.40
1
(CH), 126.62 (CH), 126.25 (CH), 114.1 (q, JC–F
¼
286.1 Hz, CF3), 80.09 (C), 69.39 (CH2), 50.69 (C), 36.57
(CH), 33.27 (CH), 22.53 (CH2), 21.95 (CH2); MS m/z (%):
502 (Mþ, 3), 388 (100), 360 (77), 330 (47), 308 (80), 255
(43), 105 (33), 77 (16); HRMS calcd for C31H25F3O3 m/z
502.1756, found 502.1751. Anal. calcd for C31H25F3O3: C,
74.09; H, 5.01. Found: C, 74.38; H, 5.37. X-Ray: CCDC
118760.
7. (a) Padwa, A.; Kennedy, G. D.; Newkome, G. R.; Fronczek,
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4.3.5. Acidification of compound 10. A solution of 10
(0.30 g, 0.7 mmol) in ether (10 ml) containing trifluoro-
acetic acid (1 ml) and water (0.2 ml) was stirred for 8 h at
room temperature. The reaction mixture was concentrated
and the residue was purified by chromatography
(hexanes/CH2Cl2 1:1) to give 13 (0.29 g, 95%).
4.3.6. Acidification of compound 13. A solution of 13
(0.30 g, 0.7 mmol) in ether (10 ml) containing trifluoro-
acetic acid (1 ml) and water (0.2 ml) was stirred for 8 h at
room temperature. The reaction mixture was concentrated
and the residue was purified by chromatography
(hexanes/CH2Cl2 1:1) to give 11 (0.20 g, 65%) and 12
(0.07 g, 27%).
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4.4. Supporting material available
Crystallographic data (excluding structure factors) for the
structures in this paper have been deposited with the
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