Synthesis and reactivity of trans-tricyclo[4.2.0.0]oct-4-ene

Article abstract of DOI:10.1021/jo000215r

The first synthesis of trans-tricyclo[4.2.0.0]oct-4-ene (1), an ethenyl bridged spirohexane, was accomplished in four steps starting from Carpino et al. gem-dichloro ketone 6. An X-ray crystal structure of 1 with one substituent was obtained to provide geometry data on this novel ring system and to confirm the stereochemical assignment of the penultimate synthetic intermediate. Tricyclo[4.2.0.0]oct-4-ene is surprisingly stable. It reacts with glacial acetic acid but only slowly at 145 °C; the products were isolated and identified. A unimolecular rearrangement takes place at elevated temperatures (165 °C and higher), presumably, via a biradical intermediate to afford tricyclo[4.2.0.0]oct-3-ene (23). The structure of this 1,5-bridged bicyclo[2.1.0]pentane derivative was established by NMR and an X-ray crystal structure of its Diels-Alder adduct with isobenzofuran. Tricyclo[4.2.0.0]oct- 4-ene equilibrates with 23, so equilibrium constants and reaction rates were measured over a 20 °C temperature range from 180 °C to 200 °C. The difference in the heats of formation (ΔΔH°(f) (23 - 1)) is -2.1 kcal/mol, which is in good agreement with ab initio (HF and MP2) calculations using the 6-31G(d) basis set (-1.9 (HF) and -1.4 (MP2) kcal/mol). Computations on trans-tricyclo[4.2.0.0]octane and spirohexane also were carried out, and the structures and energies were compared.

Full text of DOI:10.1021/jo000215r

3530
J . Org. Chem. 2000, 65, 3530-3537
Syn th esis a n d Rea ctivity of tr a n s-Tr icyclo[4.2.0.01,3]oct-4-en e
Elena S. Koltun and Steven R. Kass*
Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455
Received February 15, 2000
The first synthesis of trans-tricyclo[4.2.0.01,3]oct-4-ene (1), an ethenyl bridged spirohexane, was
accomplished in four steps starting from Carpino et al. gem-dichloro ketone 6. An X-ray crystal
structure of 1 with one substituent was obtained to provide geometry data on this novel ring system
and to confirm the stereochemical assignment of the penultimate synthetic intermediate. Tricyclo-
[4.2.0.01,3]oct-4-ene is surprisingly stable. It reacts with glacial acetic acid but only slowly at 145
°C; the products were isolated and identified. A unimolecular rearrangement takes place at elevated
temperatures (165 °C and higher), presumably, via a biradical intermediate to afford tricyclo-
[4.2.0.01,5]oct-3-ene (23). The structure of this 1,5-bridged bicyclo[2.1.0]pentane derivative was
established by NMR and an X-ray crystal structure of its Diels-Alder adduct with isobenzofuran.
Tricyclo[4.2.0.01,3]oct-4-ene equilibrates with 23, so equilibrium constants and reaction rates were
measured over a 20 °C temperature range from 180 °C to 200 °C. The difference in the heats of
formation (∆∆H°f (23 - 1)) is -2.1 kcal/mol, which is in good agreement with ab initio (HF and
MP2) calculations using the 6-31G(d) basis set (-1.9 (HF) and -1.4 (MP2) kcal/mol). Computations
on trans-tricyclo[4.2.0.01,3]octane and spirohexane also were carried out, and the structures and
energies were compared.
In tr od u ction
interaction between the spiro moiety and the double bond
may promote rearrangements leading to formation of
less-strained and thermodynamically more stable com-
pounds. This interaction should be reflected in the
thermal behavior of these tricyclic olefins. Consistent
with this notion, 4,5-benzotricyclo[4.1.0.01,3]hept-4-ene (3)
dimerizes and rearranges to 2-methylnaphthalene at 30
°C.2c It has been suggested that spiro tricycloheptene 2
has eluded isolation because of a facile [σ2s + π2s + σ2s]
pericyclic rearrangement initially leading to 5-methylene-
1,3-cyclohexadiene, which subsequently undergoes a
hydrogen shift to afford toluene.2b,c,4 Tricyclo[4.2.0.01,3]-
oct-4-ene (1) contains only an extra methylene group in
comparison to tricyclo[4.1.0.04,6]hept-2-ene (2). Thus, in
principle, tricyclo[4.2.0.01,3]oct-4-ene (1) could undergo an
analogous pericyclic rearrangement which would ther-
mally destabilize the system and, potentially, lead to the
formation of spirobicyclo[5.2]octa-2,4-diene.
Structures and properties of small-ring bridged spiro
hydrocarbons such as spiropentane and spirohexane have
been a topic of interest for many years.1 These compounds
are challenging synthetic targets since they possess a
high degree of both torsional and angular strain which
often results in unusual rearrangements and new syn-
thetic transformations.2 trans-Tricyclo[4.2.0.01,3]oct-4-ene
(1)3 represents a novel structure that contains fused
three-, four-, and five-membered rings and a carbon-
carbon double bond. Even though a variety of saturated
bridged spiropentanes and spirohexanes containing 0-3
methylene groups has been reported (4),1 there is only
one known compound, 4,5-benzotricyclo[4.1.0.01,3]hept-
4-ene (3), with a two-carbon unsaturated bridge.2c
Synthesis of bridged spiro hydrocarbons is typically
accomplished via intramolecular addition of small ring
carbenes (i.e., divalent carbon in three- or four-membered
rings) to double bonds.1,2 Nevertheless, an attempt to
synthesize tricyclo[4.2.0.01,3]octane (5), the saturated
analogue of compound 1, by such an approach was not
successful primarily due to a competing ring contraction
reaction and 1,2-hydrogen migration to give methyl-
enecyclopropane and cyclobutene derivatives, respectively
(eq 1).1a Therefore, in the synthesis of tricyclo[4.2.0.01,3]-
oct-4-ene (1) an intramolecular cyclization sequence
originally described by Carpino, Gund, Springer, and
Gund5 in 1981 was used to prepare gem-dichloro ketone
6, which contains the complete tricyclic skeleton. A
subsequent reduction scheme led to the preparation of
It is thought that introduction of an olefin into the five-
membered ring destabilizes the tricyclic system.1a,g,4 An
* To whom correspondence should be addressed.
(1) (a) Brinker, U. H.; Schrievers, T.; Xu, L. J . Am. Chem. Soc. 1990,
112, 8609-8611. (b) Miebach, T.; Brinker, U. H. J . Org. Chem. 1993,
58, 6524-6525. (c) Wiberg, K. B.; McMurdie, N.; McClusky, J . V.;
Hadad, C. M. J . Am. Chem. Soc. 1993, 115, 10653-10657. (d) Wiberg,
K. B.; Snoonian, J . R. Tetrahedron Lett. 1995, 37, 1171-1174. (e)
Wiberg, K. B.; Snoonian, J . R.; Lahti, P. M. Tetrahedron Lett. 1996,
37, 8285-8288. (f) Wiberg, K. B.; Snoonian, J . R. J . Org. Chem. 1998,
63, 1390-1401. (g) Boese, R.; Blaser, D.; Gomann, K.; Brinker, U. H.
J . Am. Chem. Soc. 1989, 111, 1501-1503.
(2) (a) Skattebol, L. J . Org. Chem. 1966, 31, 2789-2794. (b) Brinker,
U. H.; Fleischhauer, I. Angew. Chem., Int. Ed. Engl. 1979, 18, 396-
397. (c) Brinker, U. H.; Streu, J . Angew. Chem., Int. Ed. Engl. 1980,
19, 631-632. (d) Brinker, U. H.; Gomann, K.; Zorn, R. Angew. Chem.,
Int. Ed. Engl. 1983, 22, 869-870. (e) Brinker, U. H.; Wilk, G.; Gomann,
K. Angew. Chem., Int. Ed. Engl. 1983, 22, 868-869. (f) Skattebol, L.
Chem. Ind. (London) 1962, 2146.
(4) (a) Dombrowski, G. Ph.D. Thesis, University of Minnesota,
Minneapolis, MN, 1995. (b) Sauer, J .; Sustman, R. Angew. Chem., Int.
Ed. Engl. 1980, 19, 779-807.
(5) Carpino, L.; Gund, P.; Springer, J ., P.; Gund, T. Tetrahedron Lett.
1981, 22, 371-374.
(3) The trans in trans-tricyclo[4.2.0.01, 3]oct-4-ene (1) will be omitted
for simplicity sake.
10.1021/jo000215r CCC: $19.00 © 2000 American Chemical Society
Published on Web 05/11/2000

trans-Tricyclo[4.2.0.01,3]oct-4-ene
J . Org. Chem., Vol. 65, No. 11, 2000 3531
Sch em e 1a
Sch em e 2a
a
Reagents and conditions: (a) CCl4, PPh3, Et2O; (b) LiAlH4,
Et2O, 17% overall.
convert tosylate 11 to the corresponding (inverted) bro-
mide or iodide were unsuccessful. When tosylate 11 was
treated with magnesium and iodine in diethyl ether and
the resulting product was reduced in situ with lithium
aluminum hydride, 1-vinylcyclohexa-1,3-diene (12), eth-
ylbenzene (13), and styrene (14) were isolated in a 4:1.2:1
ratio, respectively (eq 2). Formation of hydrocarbons 12-
14 suggests that the iodo derivative of alcohol 10 is
generated under these reaction conditions, but that it is
unstable and rapidly rearranges.
a
Reagents and conditions: (a) Cl3CCOCl, Zn(Cu), DME, 71%;
(b) CCl4, NBS, 83%; (c) DBN, Et2O, 31%; (d) Zn, TMEDA, AcOH,
EtOH, 94%; (e) LiAlH4, 95%; (f) TsCl, Py, 74%; (g) LiBEt3H, Et2O,
∼2%.
tricyclo[4.2.0.01,3]oct-4-ene (1) and enabled us to explore
its reactivity and thermal stability.
The desired olefin 1 was successfully prepared by
reduction of tosylate 11 with lithium triethylborohydride
(LiBHEt3, Super Hydride) in diethyl ether. Super Hy-
dride is commercially available as a 1 M solution in
tetrahydrofuran; however, it was necessary to switch to
a more volatile solvent like diethyl ether for better
separation of the volatile hydrocarbon product from the
solvent. Purification of the tricyclic olefin was accom-
plished by preparative gas chromatography. To our
disappointment the estimated yield of the final step was
only 2%, and it was difficult to generate sufficient
amounts of material in this way. Thus, another reduction
sequence for the preparation of hydrocarbon 1 was
developed. Alcohol 10 was transformed into chloride 15
(with inversion of configuration) using CCl4 and PPh3 in
Et2O at 45 °C7 and reduced in situ with LiAlH4 to give 1
in a 17% overall yield (Scheme 2). Chloride 15 was found
to be air and thermally sensitive and could not be isolated
from the solvent (Et2O or CCl4). Any traces of THF in
the reaction mixture led to decomposition of the product.
Thus, it was found that inverted chloride 15 is more
stable than the corresponding bromide or iodide, but less
stable than the tosylate derivative 11, which has the
same configuration as the original alcohol 10.
Ster eoch em istr y of Alcoh ol 10. Reduction of ketone
9 with LiAlH4 in the synthesis of tricyclo[4.2.0.01,3]oct-
4-ene (1) yields only one diastereomer of alcohol 10, thus
indicating that one side of the tricyclic skeleton is much
more hindered than the other. To determine which
epimer is formed and which face is more open to nucleo-
philic attack, the relative stereochemistry of the hydroxyl
group (or hydrogen H1) and the cyclopropyl ring must
be determined (Table 1). Upon the basis of molecular
models and the X-ray crystal structure of dichloro ketone
6,5 the two bridgehead hydrogen atoms H4 and H7 are
Resu lts a n d Discu ssion
Syn th esis of Tr icyclo[4.2.0.01,3]oct-4-en e (1). Tri-
cyclo[4.2.0.01,3]oct-4-ene (1) was formed via a reduction
sequence starting from the known dichloro ketone 6
(Scheme 1). The literature procedure for the preparation
of compound 7,5 however, was modified. Dichloroketene
addition to 1,3-cyclohexadiene followed by radical bro-
mination and subsequent distillation gave a single allylic
bromide (8, the relative stereochemistry of the bromine
was not deduced since it was removed in the next step)
in 59% overall yield. Deprotonation of ketone 8 with 1,5-
diazabicyclo[4.3.0]non-5-ene (DBN) in diethyl ether fol-
lowed by an intramolecular cyclization, as originally
described by Carpino et al.,5 enabled 6 to be obtained in
a 48% yield.
Dechlorination of 6 with zinc, tetramethylethylenedi-
amine (TMEDA), and acetic acid afforded ketone 9 in a
67% yield. This compound was found to be relatively
unstable and was rapidly carried on. Direct deoxygen-
ation of ketone 9 via its tosylhydrazone was unsuccessful
due to the thermal instability of the starting material.
Thus, tricyclic ketone 9 was converted into its corre-
sponding alcohol 10 with lithium aluminun hydride
(LiAlH4) in a 95% yield. It turned out that only one
diastereomer of alcohol 10 formed under these reaction
conditions. Attempts to reduce alcohol 10 by either a
Barton deoxygenation6 or by converting it to an iodide
or bromide (the latter two derivatives would have an
inverted configuration relative to alcohol 10) with sub-
sequent reduction failed, presumably, because of rapid
decomposition of the strained bridged spirohexane sys-
tem. The tosylate derivative 11 of alcohol 10 was suc-
cessfully prepared with p-toluenesulfonyl chloride and
pyridine at 0 °C and was found to be stable at room
temperature for several hours. However, all efforts to
(7) Temperature control is critical. Only decomposition products are
observed when the reaction is carried out above 45 °C, and the reaction
does not take place below 40 °C.
(6) Barton, D. H. R.; McCombie, S. W. J . J . Chem. Soc., Perkin
Trans. I 1975, 16, 1574-1585.

3532 J . Org. Chem., Vol. 65, No. 11, 2000
Koltun and Kass
Ta ble 1. Exp er im en ta l a n d Ca lcu la ted Cou p lin g
Con sta n ts in Her tza
structure at 173(2) K was obtained. Suitable single
crystals of p-nitrobenzoate 18 were formed by recrystal-
lization from a 1:1 ethanol/pentane mixture. The result-
ing crystals are orthorhombic, their space group is Pbca,
and the unit cell is comprised of eight molecules with the
following dimensions: a ) 7.215 (1) Å, b ) 12.496 (2) Å,
c ) 28.951 (4) Å, and R ) â ) γ ) 90°. Direct methods
were employed to solve the molecular structure and
further refinement by full-matrix least-squares methods
were carried out to a conventional R-factor of 0.0476 (full
details can be found in the Supporting Information). The
X-ray data indicate that the stereochemistry of alcohol
10 was deduced correctly via the coupling constants
analysis. In the initially formed alcohol 10, the hydroxyl
group is anti to the cyclopropane ring. Therefore, the
cyclopropyl side of the four-membered ring is more open
to attack by LiAlH4 than the bottom or cyclopentenyl side.
It follows that the inverted alcohol 17 has the syn
configuration and that the hydroxyl substituent is on the
same side as the three-membered ring.
cmpd
J 1,2
J 1,3
J 2,4
J 3,4
10
16
17
7.5 (7.6)
1.0 (0.2)
3.0 (0.2)
7.5 (7.0)
5.5 (6.7)
3.0 (6.7)
7.0 (7.1)
8.0 (7.1)
8.0 (7.1)
7.0 (6.5)
7.0 (6.5)
8.0 (6.5)
a
Parenthetical values were obtained using the Karplus equation
and the MP2/6-31G(d) geometry for 1.
Sch em e 3a
The X-ray crystal structure of ester 18 provides the
first geometrical data on this type of strained tricyclic
skeleton (preliminary X-ray results were reported for
dichloro ketone 6 but no geometry information was
provided5). Selected bond lengths, bond angles, and
dihedral angles are given in the Supporting Information
along with the corresponding MP2/6-31G(d) structural
parameters for 1; there is good agreement between the
experimental and computed values except for the carbon-
carbon (C5-C6) double bond length which is computed
to be 1.35 Å and found to be 1.31 Å. As expected, the
C2-C1-C8 bond angle is the most distorted one in the
molecule and is 138.8° (expt, 139.5° (MP2)), which is
about 30° more than an average C-C-C bond angle at
an sp3-hybridized center. The double bond is bent by only
0.2° (expt, 0.3° (MP2)) as indicated by the C4-C5-C6-
C7 dihedral angle, and is slightly shorter than an average
C-C double bond length of 1.34 Å.10
Several inverted (syn) derivatives of alcohol 10 were
found to be unstable. For example, anti tosylate 11 was
readily isolated whereas several attempts to prepare the
analogous syn derivative of the inverted alcohol 17 were
unsuccessful presumably because of the rapid decomposi-
tion of the product. Chloride 15, also is quite labile as
discussed above, and attempts to invert alcohol 17 by the
Mitsunobu method were unsuccessful. These results
suggest that inverted syn species are more reactive and
less stable due to rapid ring opening of the tricyclic
skeleton. This behavior is analogous to that of 2-substi-
tuted bicyclo[2.1.0]pentane derivatives11 in that a disro-
tatory ring opening of the C1-C7 bond toward the
backside of a syn leaving group should be facile whereas
the same process for an anti leaving group is structurally
retarded.
a
Reagents and conditions: (a) LiAlH4; (b) DEAD, PhCO2H,
PPh3; (c) LiAlH4; (d) DEAD, NO2PhCO2H, PPh3.
trans to one another in the tricyclic skeleton of 1. The
problem, therefore, comes down to determining the
relative configuration of hydrogens H1 and H4. This can
be done by establishing their positions relative to hydro-
gens H2 and H3 via 1H NMR coupling constants. It is
well-known that the relative configuration of two vicinal
hydrogen atoms can usually be assigned based upon their
coupling constants.8 The most reliable results are ob-
tained if both isomers are available; consequently, alcohol
10 was inverted by the Mitsunobu method9 to afford the
corresponding benzoate (16, Scheme 3). Subsequent
reduction of 16 with LiAlH4 afforded the inverted alcohol
17. Vicinal coupling constants for both diastereomers (10
and 17) and the benzoate 16 were obtained.
The Karplus equation (eq 3) relates the magnitude of
the coupling constant (3J ) to the dihedral angle (θ)
between the vicinal hydrogens. The constants J 0 and J 180
vary with the system but commonly are taken to be 8.5
and 9.5 Hz, respectively.8
3J ab ) J 0 cos2 θ - 0.28 (0° e θ e 90°)
(3a)
3J ab ) J 180 cos2 θ - 0.28 (90° e θ e 180°) (3b)
All of the vicinal dihedral angles between H1, H2, H3,
and H4 for both diastereomers were obtained from the
MP2/6-31G(d) geometry of the tricyclic hydrocarbon 1,
and the coupling constants were estimated using eq 3.
Our assignments were based on the agreement of the
calculated and experimental values, which is excellent
in the case of 10 and quite reasonable for 16 and 17.
To confirm our structural assignment, the inverted
p-nitrobenzoate 18 was synthesized from 10 via the
Mitsunobu reaction (Scheme 3), and an X-ray crystal
Rea r r a n gem en ts Stu d ies
Acetolysis. Tricyclo[4.2.0.01,3]oct-4-ene (1) is an un-
usual molecule due to the interaction between the spiro-
hexyl moiety and the ethenyl bridge. The thermal rear-
rangement of this hydrocarbon and its reactivity toward
electrophiles are of particular interest. Somewhat sur-
(8) Williams, D. H.; Fleming, I. Spectroscopic Methods in Organic
Chemistry, 4th ed.; McGraw-Hill: London, 1987; pp 91-101.
(9) Overman, L. E.; Bell, K., L.; Ito, F. J . Am. Chem. Soc. 1984, 106,
4192-4201.
(10) Bent, H. A. Chem. Rev. 1961, 61, 275-311.
(11) Wiberg, K. B.; Williams, V. Z., J r.; Friedrich, L. E. J . Am. Chem.
Soc. 1970, 92, 564-567.

trans-Tricyclo[4.2.0.01,3]oct-4-ene
J . Org. Chem., Vol. 65, No. 11, 2000 3533
Ta ble 2. Kin etic a n d Equ ilibr iu m Da ta for th e
Con ver sion of 1 to 23
Sch em e 4
T (°C)
k1 (h-1
)
k-1 (h-1
)
K
t1/2 (h)a
180
190
200
0.053
0.1
0.23
0.0035
0.0070
0.015
15.2 ( 0.3
14.6 ( 0.4
15.0 ( 0.1
12
6
3
a
The half-life time for achieving equilibrium in the 1 to 23
direction.
C2/c, and the unit cell is comprised of 16 molecules
with the following dimensions: a ) 37.761(9) Å, b )
6.284(2) Å, c ) 26.651(7) Å, and R ) γ ) 90°, â )
130.392(3)°. The asymmetric unit contains two mole-
cules (the same stereoisomers), and one of them is
involved in an intermolecular hydrogen bond (i.e., the
C22-H26‚‚‚O2′ distance is 2.56 Å; see the Supporting
Information for full details). Direct methods were em-
ployed to solve the molecular structure, and further
refinement by full-matrix least-squares methods were
carried out to a conventional R-factor of 0.0656. The X-ray
data indicates that the product is the endo isomer as
expected and provides the first geometrical data for this
type of strained tricyclic skeleton (a bridged 1,5-bicyclo-
[2.1.0]pentane). Selected experimental and calculated
bond lengths, bond angles, and dihedral angles are given
in the Supporting Information. As expected, the C2-C1-
C8 bond angle is the most distorted one in the molecule
and is 132.3° in one structure and 132.6° in the other
(expt, 133.9° MP2/6-31G(d)). Both angles are about 23°
more than a typical value at an sp3-hybridized center.
This angle, however, is less distorted than the C2-C1-
C8 bond angle in 1.
prisingly, 1 is relatively stable under acidic conditions.
Glacial acetic acid does not react with it at room tem-
perature and only slowly gives products at 145 °C. Gas
chromatography was used to monitor the reaction, and
after 8 h (≈1.1 half-lifes) two major products, ethylben-
zene (13) and acetate 19, were formed in 5:1 ratio,
respectively (Scheme 4). To identify the structure of the
isolated acetate, it was reduced with LiAlH4 to afford
alcohol 20. This compound was purified by column chro-
matography and its 1H NMR spectrum was found to
match the literature spectrum for 1-(2-hydroxyethyl)-
cyclohexa-1,4-diene.12 Formation of both products, 13 and
19, can be explained by protonation of the double bond
to afford a tricyclic cyclopropylcarbinyl cation (21) which
rearranges to bicyclic, homoallylic, tertiary cation 22.13
Nucleophilic attack by AcOH with concomitant cleavage
of the four-membered ring leads to the observed acetate.
Ethylbenzene may arise via the loss of a proton from 22
to afford 1-vinyl-1,4-cyclohexadiene followed by its isomer-
ization/aromatization, but it also maybe a secondary
product derived from 19.
The thermolysis of tricyclo[4.2.0.01,3]oct-4-ene (1) orig-
inally was carried out in toluene and then in xylene-d10
,
and to our surprise it is stable up to 165 °C. No deuterium
incorporation was detected, and since the same product
and approximate reactivity also was observed in decalin,
we chose to use this solvent for making quantitative
measurements. Spirohexane 1 and bicyclo[2.1.0]pentane
derivative 23 interconvert at elevated temperatures
so equilibrium data and rate constants were measured
over a 20 °C range from 180 °C to 200 °C (Table 2). The
resulting equilibrium constants are the same within
experimental error indicating that ∆S for the reaction
must be small (i.e., around zero). In accord with this, we
estimate that ∆S190 ) 0.9 cal/mol K by using standard
statistical mechanics expressions14 and MP2/6-31G(d)
structures and scaled vibrational frequencies (0.9427)15
for 1 and 23. The free energy difference for this reaction
(∆G190) is -2.5 kcal/mol, which leads to a difference in
the heats of formation (∆∆Hf(23 - 1) of -2.1 kcal/mol.
This is in a good accord with the HF/6-31G(d) and MP2/
6-31G(d) energy differences of -1.9 and -1.4 kcal/mol,
respectively. Rate constants for the forward reaction also
were measured, and the Arrhenius plot is linear and
leads to a rearrangement barrier (Ea) of 31 kcal/mol.16
Most likely the isomerization of 1 to 23 proceeds via
cleavage of the C1-C7 cyclopropane bond to afford
Th er m olysis. Investigation of the thermal rearrange-
ment of tricyclo[4.2.0.01,3]oct-4-ene (1) led to the isolation
of a bridged bicyclo[2.1.0]pentane derivative (23, eq 4).
The structural assignment for this hydrocarbon was
1
initially based upon H NMR data. We subsequently were
able to prepare the Diels-Alder adduct with isobenzo-
furan at 115 °C (25, eq 5), but not with the sterically more
encumbered 1,3-diphenylisobenzofuran; under these forc-
ing conditions the diene undergoes competitive dimer-
ization. Suitable, but less than optimal, single crystals
of 25 were obtained for X-ray crystallography by recrys-
tallization from a 1:1 acetonitrile/pentane mixture. The
resulting crystals are monoclinic, their space group is
(14) Herzberg, G. H. Molecular Spectra and Molecular Structure:
Infrared and Raman Spectra of Poliatomic Molecules; D. Van Nos-
trand: Princeton, NJ , 1945; Vol. 2, p 510.
(15) Pople, J . A.; Scott, A. P.; Wong, M. W.; Radom, L. Isr. J . Chem.
1993, 33, 345-350.
(16) Espenson, J . H. Chemical Kinetics and Reaction Mechanisms;
McGraw-Hill: New York, 1981. The A factor is 1013.8 s-1, but given
the limited temperature range and the fact that the rate constants
were measured only once, this value should not be over interrupted.
(12) Engel, P. S.; Allgren, R. L.; Chae, W.-K.; Leckonby, R. A.;
Marron, N. A. J . Org. Chem. 1979, 44, 4233-4239.
(13) Cation 22 has previously been invoked. For additional details,
see: Wiberg, K. B.; Olli, L. K.; Golembeski, N.; Adams, R. D. J . Am.
Chem. Soc. 1980, 102, 7467-7475.

3534 J . Org. Chem., Vol. 65, No. 11, 2000
Ta ble 3. Ca lcu la ted Hea ts of F or m a tion a n d Str a in En er giesa
Koltun and Kass
a
Computed energies are in hartrees, all other values in kcal/mol.
biradical intermediate 24, which can re-close at the other
end of the allylic system to give the observed bicyclo-
[2.1.0]pentane derivative. Ample literature precedents
exist for this pathway.17 For example, Frey and Roth18
proposed that the interconversion of cis- and trans-2-
methylvinylcyclopropanes occurs by way of a biradical
intermediate. The reported activation energy (Ea ) 48.6
kcal/mol) is 17 kcal/mol larger than in our case, but this
difference can readily be explained by the difference in
stability of the two biradicals; 24 has a tertiary radical
center compared to a primary one in Frey and Roth’s
compound, and in our case the C-C bond cleavage
relieves more strain.
According to the MP2 calculations, introduction of an
ethanyl bridge into spirohexane increases the strain
energy by only 5 kcal/mol. Tricyclo[4.2.0.01,3]oct-4-ene (1)
has about the same strain energy as its saturated
analogue, indicating that the double bond does not
increase the SE of the tricyclic system. In fact, it lowers
the strain energy at the HF and MP2 levels by 2.9 and
3.2 kcal/mol, respectively. This negative olefin strain
energy21 presumably is due to relief of hydrogen-
hydrogen eclipsing interactions in 5. Given these modest
energetic changes, it is not surprising that the bend (180°
-
a1b; see Figure 1 for the labeling scheme) and twist
(90° and -90° - 8ab2 and 7ab4) angles in 1 (20.8° and
6.8-7.0°, respectively) and 5 (19.7° and 6.6-11.0°, re-
spectively) are similar and relatively small.22
Ca lcu la tion s
Full geometry optimizations and vibrational frequen-
cies for tricyclo[4.2.0.01,3]oct-4-ene (1), its saturated
analogue trans-tricyclo[4.2.0.01,3]octane (5), bicyclo[2.1.0]-
pentane derivative 23, and spirohexane (26) were com-
puted at the HF and MP2 levels using the 6-31G(d) basis
set (Table 3). Calculated heats of formation (∆Hf) were
obtained using Wiberg’s group equivalent approach.1f,19
Strain energies (SE) for these compounds also were
computed using the calculated heats of formation and
Franklin group equivalents for the energies of corre-
sponding unstrained models.20 The MP2/6-31G(d) struc-
tures of tricyclo[4.2.0.01,3]oct-4-ene (1) and bicyclo[2.1.0]-
pentane derivative 23 are shown in Figure 1, and in both
cases there is good agreement with the related X-ray
crystal data.
Con clu sion s
Synthesis of the novel bridged spiro hydrocarbon 1 was
accomplished in four steps starting from the previously
reported tricyclic dichloro ketone 6. trans-Tricyclo[4.2.0.01,3]-
oct-4-ene (1) was found to be relatively stable toward
electrophiles only reacting with glacial acetic acid at 145
°C. 1-(2-Acetoxyethyl)cyclohexa-1,4-diene (19) and eth-
ylbenzene 13 were obtained in a 1:5 ratio, respectively.
Thermolysis of 1, contrary to our expectations, requires
temperatures of 165 °C or higher and leads to the
formation of tricyclo[4.2.0.01,5]oct-3-ene (23). Equilibrium
and rate constants were measured at various tempera-
tures and Ea ) 31 kcal/mol and ∆∆Hf(23 - 1) ) -2.1
kcal/mol. The latter quantity was computed at the HF
and MP2 levels with the 6-31G(d) basis set (-1.9 (HF)
and -1.4 (MP2) kcal/mol), and both values are in good
(17) (a) Willcott, M. R., III; Cargle, V. H. J . Am. Chem. Soc. 1969,
91, 4310-4311. (b) Doering, W. v. E.; Lambert, J . B. Tetrahedron 1963,
19, 1989-1994. (c) Doering, W. v. E.; Schmidt, E. K. G. Tetrahedron
1971, 27, 2005-2030.
(18) (a) Ellis, R. J .; Frey, H. M. J . Chem. Soc. 1964, 5578-5583. (b)
Roth, W. R.; Konig, W. R. J ustus Liebigs Ann. Chem. 1965, 688, 28-
29.
(21) (a) Maier, W. F.; Schleyer, P. v. R. J . Am. Chem. Soc. 1981,
103, 1891-1900. (b) Ibrahim, M. R.; Schleyer, P. v. R. J . Comput.
Chem. 1985, 6, 157-167.
(22) The corresponding bend and twist angles in spirohexane (26)
are 6.0° and 0°, respectively.
(19) Wiberg, K. B. J . Org. Chem. 1985, 50, 5285-5291.
(20) Franklin, J . L. J . Chem. Phys. 1953, 21, 2029-2033.

trans-Tricyclo[4.2.0.01,3]oct-4-ene
J . Org. Chem., Vol. 65, No. 11, 2000 3535
F igu r e 1. MP2/6-31G(d) calculated structures of tricyclo[4.2.0.01,3]oct-4-ene (1) and tricyclo[4.2.0.01,5]oct-3-ene (23). Points a
and b are at the C7-C8 and C2-C4 midpoints and lie in the C1-C7-C8 and C1-C2-C4 planes.
3.9, and 10.2 Hz, 1H), 5.98 (dd, J ) 3.9 and 10.2 Hz, 1H), 4.6
(m, 1H), 4.15 (dt, J ) 6.9 and 9.9 Hz, 1H), 3.58 (ddt, J ) 1.2,
3.0, and 9.6 Hz, 1H), 2.55 (m, 1H), 2.27 (q, J ) 7.2 Hz, 1H);
13C NMR (75 MHz, CDCl3) δ 194.5, 134.0, 124.8, 86.5, 51.9,
43.3, 39.9, 29.9.
agreement with experiment. Strain energies (SE) for
tricyclo[4.2.0.01,3]oct-4-ene (1) and its saturated analogue
also were calculated and are very similar.
X-ray crystal structures of the Diels-Alder adduct
between 23 and isobenzofuran and the p-nitrobenzoate
of 10 were obtained. These structures provide the first
geometrical data on these tricyclic systems and confirm
our spectroscopic assignments.
3,3-Dich lor otr icyclo[5.1.0.01,4]oct-5-en -2-on e (6).5,24
A
solution of DBN (3.47 mL, 0.028 mol) in 50 mL of Et2O was
added over a 1 h period to 7.5 g (0.028 mol) of bromide 7 in
70 mL of Et2O at -65 °C (dry ice/ethanol). The resulting brown
reaction mixture was stirred for an additional 30 min and
poured into 300 mL of an ice cold 1:1 H2O/Et2O mixture. The
cold aqueous layer was extracted with Et2O, and the combined
organic material was washed with ice cold H2O, 1 N HCl (until
the pH was < 7), sat. NaHCO3 and sat. NaCl. The resulting
solution was dried over anhydrous MgSO4 and concentrated
under reduced pressure. Distillation at 0.25 mm (bp 65-75
°C) afforded 1.6 g (31%) of white crystalline product. Alterna-
tively, 6 can be purified by column chromatography (Rf value
Exp er im en ta l Section
Gen er a l Meth od s. All reactions were carried out using
anhydrous solvents under an inert atomosphere of N2 in flame-
dried flasks. Ether and THF were distilled from sodium/
benzophenone ketyl prior to use. Dichloromethane was dis-
tilled from calcium hydride. All reagents were of commercial
grade and were either distilled or recrystallized prior to use.
Merck silica gel (230-400) mesh was used for flash chroma-
tography.
8,8-Dich lor obicyclo[4.2.0]oct-2-en -7-on e (7). To a mix-
ture of 9.8 g (0.15 mol) of Zn(Cu)23 couple and 4.4 g (0.05 mol)
of 1,3-cyclohexadiene in 90 mL of Et2O was added 20 g (0.11
mol) of trichloroacetyl chloride in 35 mL of DME over a 1 h
period. After 20 h at room temperature the resulting brown
mixture was filtered and the solid was washed with hexanes.
The filtrate was washed with ice cold 0.5 N HCl and 5% NaOH.
The organic layer was washed further with saturated NaCl
and then filtered through charcoal and a plug of silica gel. The
resulting solution was dried over anhydrous MgSO4 and
concentrated under reduced pressure. Distillation at 0.9 mm
(bp 55-67 °C) afforded 6.8 g (70.8%) of a colorless oil. The
proton NMR was as previously described.24 1H NMR (300 MHz,
CDCl3) δ 6.06 (m, 1H), 5.85 (m, 1H), 4.10 (m, 1H), 3.43 (m,
1H), 2.03 (m, 3H), 1.71 (m, 1H).
1
) 0.34 in 7% EtOAc/ hexanes). H NMR (300 MHz, CDCl3)24
δ 6.24 (d, J ) 4.8 Hz, 1H), 5.83 (d, J ) 4.8, 1H), 3.8 (m, 1H),
3.02 (td, J ) 2.8 and 6.0 Hz, 1H), 2.16 (dd, J ) 5.8 and 6.0 Hz,
1H), 1.31 (t, J ) 5.8 Hz, 1H); 13C NMR (75 MHz, CDCl3) δ
193.8, 137.5, 132.3, 98.2, 61.3, 47.3, 45.3, 23.0.
Tr icyclo[5.1.0.01,4]oct-5-en -2-on e (9). To a mixture of 2 g
of Zn dust and 4.5 mL of TMEDA (0.029 mol) in 10 mL of
absolute EtOH at 0 °C was added 1.9 mL (0.033 mol) of AcOH
over a 10 min period. The reaction mixture was maintained
at 0 °C while a solution of 1 g (5.3 mmol) of compound 6 in 2
mL of EtOH was added over a 10 min period. After an addi-
tional 15 min at 0 °C the reaction mixture was allowed to
warm to room temperature and stir for 2 h. The resulting gray
mixture was filtered, and the solid was washed with a 1:1
pentane/Et2O solution. The filtrate was extracted with ice cold
1 N HCl, H2O, sat. NaHCO3, and sat. NaCl. The resulting
material was dried over MgSO4 and concentrated under re-
duced pressure to afford 0.6 g (94%) of ketone 9 which was of
sufficient purity for subsequent transformations. 1H NMR (300
MHz, CDCl3) δ 5.99 (ddd, J ) 1.2, 2.1, and 5.4 Hz, 1H), 5.86
(dt, J ) 1.5 and 5.4 Hz, 1H), 3.12 (m, 1H), 3.09 (ddt, J ) 0.6,
7.8, and 15.0 Hz, 1H), 2.71 (dd, J ) 4.2 and 15.0 Hz, 1H), 2.68
(m, 1H), 1.96 (dddd, J ) 0.6, 1.5, 5.7, and 8.1 Hz, 1H), 1.1 (t,
J ) 5.7, 1H); 13C NMR (75 MHz, CDCl3) δ 136.6, 133.3, 53.2,
50.0, 42.7, 39.0, 21.6 (carbonyl resonance missing); IR (neat)
1758 (CO) cm-1; HRMS-EI M+ calcd for C8H8O 120.0575, found
120.0571.
4-Br om o-8,8-d ich lor obicyclo[4.2.0]oct-2-en -7-on e (8).5,24
A solution of 3.5 g (0.019 mol) of NBS, 3.45 g (0.018 mol) of
8,8-dichlorobicyclo[4.2.0]oct-2-en-7-one (7), and a catalytic
amount of AIBN in 60 mL of dry CCl4 was refluxed and
irradiated with a 60 W table lamp until a white precipitate
formed (1 h). The reaction mixture was left in a refrigerator
overnight so that all of the succinimide would crystallize out
of the solution. The cold carbon tetrachloride solution was
filtered, and the precipitate was washed with additional cold
CCl4. The filtrate was concentrated under reduced pressure
to yield 4.8 g (100%) of a yellow oil. Distillation at 1.1 mm (bp
115 °C) afforded 3.3 g (83%) of the product 8 as a single
stereoisomer. 1H NMR (300 MHz, CDCl3) δ 6.32 (ddd, J ) 1.8,
a n ti-Tr icyclo[5.1.0.01,4]oct-5-en -2-ol (10). To a 0 °C solu-
tion of 0.6 g (5.0 mmol) of ketone 9 in 10 mL of THF was added
3 mL of a 1 M solution of LiAlH4 in THF. The reaction mixture
was allowed to warm to room temperature and stir for an
additional 2 h. Ice cold Et2O (10 mL) was slowly added to the
reaction mixture followed by 5 mL of sat. NH4Cl. The organic
layer was washed with sat. NaCl and dried over MgSO4.
Concentration under reduced pressure afforded 0.58 g (95%)
(23) Danheiser, R. L.; Savariar, S.; Cha, D. D. Organic Syntheses;
Wiley: New York, 1993; Coll. Vol. VIII, pp 82-86.
(24) Gund, P. H. Ph.D. Thesis, University of Massachusetts, Am-
herest, MA, 1967.

3536 J . Org. Chem., Vol. 65, No. 11, 2000
Koltun and Kass
of alcohol 10 which was of sufficient purity for subsequent
reactions. H NMR (300 MHz, CDCl3) δ 5.94 (dt, J ) 1.5, and
29.6, 29.4, 16.7; HRMS-CI (self) M+ calcd for C8H11 107.0861,
found 107.0861.
1
5.0 Hz, 1H), 5.64 (dt, J ) 2.0, and 5.0 Hz, 1H), 4.80 (dd, J )
1.0 and 7.5 Hz, 1H), 2.72 (dt, J ) 7.5 and 11.0 Hz, 1H), 2.55
(dd, J ) 1.0 and 7.5 Hz, 1H), 1.96 (m, 1H), 1.70 (dt, J ) 7.5
and 11.0 Hz, 2H), 1.03 (ddtt, J ) 0.5, 1.0, 5.0, and 8.0 Hz, 1H)
0.43 (t, J ) 4.5 Hz, 1H); 13C NMR (75 MHz, CDCl3) δ 136.4,
136.1, 70.1, 43.0, 40.3, 38.5, 24.7, 16.0; IR (neat) 3587, 3411,
1430, 1419, 1397, 1074, 1019 cm-1. HRMS-EI M+ calcd for
C8H10O 122.0731, found 122.0741.
Meth od 2. A solution of 0.85 g (6.9 mmol) of alcohol 10, 1.0
mL (10 mmol) of CCl4, and 2.21 g (8 mmol) of PPh3 in 6 mL of
CH2Cl2 was stirred under reflux (40-45 °C bath) for a period
of 6 h. The resulting yellow solution was cooled to room
temperature, and 0.62 g of decalin in 8 mL of Et2O was added.
The resulting slurry was refrigerated overnight, and the liquid
was pipetted away from the precipitated triphenylphosphine
oxide (filtration leads to decomposition of the product). The
residue was washed with Et2O, and the combined organic
solutions were concentrated under vacuum (100 mm) without
an external heat source. The resulting decalin solution con-
tained the desired chloride (15) and some residual PPh3O and
Tr icyclo[5.1.0.01,4]oct-5-en -2-ol Tosyla te (11). Alcohol 10
(0.24 g, 2 mmol) was dissolved in 2 mL of dry pyridine at 0
°C. A catalytic amount of DMAP and p-TsCl (0.45 g, 2.4 mmol)
were added sequentially, and the reaction mixture was stirred
for 96 h at 0 °C. Saturated NH4Cl and water were added to
obtain a homogeneous solution that was extracted with ether.
The combined ether layers were washed with 1 N HCl (until
the pH was <7), H2O, sat. NaHCO3, and sat. NaCl and then
dried over MgSO4 at 0 °C. Concentration under reduced
pressure afforded 0.4 g (74%) of tosylate 11 that was of
sufficient purity for subsequent reactions. 1H NMR (300 MHz,
CDCl3) δ 7.75 (d, J ) 8.4 Hz, 2H), 7.33 (d, J ) 8.4 Hz, 2H),
5.93(dt, J ) 4.8 and 2.4 Hz, 1H), 5.56 (dt, J ) 4.8 and 1.5 Hz,
1H), 5.32 (t, J ) 7.2 Hz, 1H), 2.57 (m, 2H), 2.44 (s, 3H), 2.1
(m, 1H), 2.0 (m, 1H), 0.83 (ddd, J ) 1.0, 4.7, and 7.8 Hz, 1H),
0.34 (t, J ) 4.7 Hz, 1H); 13C NMR (75 MHz, CDCl3) δ 144.7,
136.9, 135.1, 133.8, 129.8, 127.8, 77.3, 41.1, 39.2, 35.4, 27.4,
1
was promptly carried on to the next step. H NMR (300 MHz,
CDCl3) δ 5.91 (dt, J ) 1.2 and 5.1 Hz, 1H), 5.65 (dt, J ) 1.8,
and 5.1 Hz, 1H), 4.63 (ddd, J ) 0.9, 2.7, and 3.9 Hz, 1H), 3.52
(m, 1H), 2.57 (dd, J ) 1.2 and 7.5 Hz, 1H), 2.56 (d, J ) 7.5 Hz,
1H), 2.02 (dddd, J ) 1.8, 3.0, 4.2, and 8.4 Hz, 1H), 1.19 (dddd,
J ) 0.6, 1.5, 5.4, and 8.4 Hz, 1H), 0.5 (dd, J ) 4.2 and 5.4 Hz,
1H).
The decalin solution containing 15 was cooled to 0 °C, and
4 mL of 1 M LiAlH4 in diethyl ether was added. The resulting
mixture was refluxed for 10 h (35-40 °C bath) until the
formation of a white precipitate was observed. The reaction
mixture was then cooled to 0 °C, and the liquid was pipetted
away from the precipitate. Ice cold H2O was slowly added to
the ether solution, and the aqueous layer was extracted with
Et2O. The combined organic extracts were dried overnight over
Na2SO4 at 0 °C. The liquid was pipetted away from the drying
agent and concentrated at atmospheric pressure to afford a
5:1 mixture of decalin and tricyclo[4.2.0.01,3]oct-4-ene (1) as
determined by GC, in a 17% overall yield. The final product
was purified by preparative gas chromatography (12 ft × 0.25
in. 20% Squalane on Chrom W column at 90 °C).
21.7, 15.7; HRMS-CI (isobutane) (M + H)+ calcd for C15H16
SO3 227.0898, found 227.0893.
-
Rea ction of Tr icyclo[5.1.0.01,4]oct-5-en -2-ol Tosyla te
(11) w ith Mg, I2, a n d LiAlH4. A solution of I2 (45 mg, 0.17
mmol) in 0.5 mL of Et2O was added over a period of 10 min to
a mixture of tosylate 11 (0.05 g, 0.19 mmol) and activated Mg
(15 mg, 0.63 mmol) in 1 mL of Et2O at 0 °C. The reaction
mixture was allowed to warm to room temperature and stir
for an additional 30 m. The resulting solution was cannulated
to a different reaction vessel and cooled to 0 °C. A 1 M solution
of LiAlH4 (0.3 mL, 0.3 mmol) in THF was slowly added, and
the reaction mixture was allowed to warm to room tempera-
ture and stir overnight. An ice-cold saturated solution of NH4-
Cl (0.5 mL) was added to the reaction mixture, and the organic
layer was washed with H2O and then dried over MgSO4. The
resulting solution was analyzed by GC-MS, and the products
were purified via preparative gas chromatography (12 ft × 0.2
in. 20% Squalane on Chrom W column at 90 °C). 1-Vinylcy-
clohexa-1,3-diene (12), ethylbenzene (13), and styrene (14)
were isolated in 4:1.2:1 ratio, respectively. 1-Vinylcyclohexa-
1,3-diene (12):25 1H NMR (300 MHz, CDCl3) δ 6.41 (dd, J )
11.0 and 17.4 Hz, 1H), 5.95 (m, 1H), 5.85 (m, 2H), 5.21 (d, J )
17.4 Hz, 1H), 5.03 (d, J ) 11.0 Hz, 1H), 2.34 (m, 2H), 2.25 (m,
2H); ethylbenzene (13): 1H NMR (300 MHz, CDCl3) δ 7.25 (m,
5H), 3.48 (q, 2H), 1.2 (t, 3H); styrene (13): 1H NMR (300 MHz,
CDCl3) δ 7.25-7.45 (m, 5H), 6.7 (dd, J ) 10.8 and 17.5 Hz,
1H), 5.75 (d, J ) 17.5 Hz, 1H), 5.25 (d, J ) 10.8 Hz, 1H).
Tr icyclo[4.2.0.01,3]oct-4-en e (1). Meth od 1. A 1 M solution
of LiEt3BH (3.2 mL, 3.2 mmol) in THF was concentrated with
a mechanical vacuum pump for 2 h and of 0.18 g of tosylate
11 (0.65 mmol) in 2 mL of Et2O was added at 0 °C. The reaction
mixture was stirred for 6 h at room temperature and 10 mL
of an ice-cold 10% NaOH solution was slowly added. The
resulting slurry was stirred for an additional 10 min at 0 °C
and extracted with Et2O. The organic phase was dried over
MgSO4, and the solvent was slowly distilled at atmospheric
pressure. The residue was bulb to bulb transferred and the
distillate was purified via preparative gas chromatography to
afford small amounts of compound 1. 1H NMR (300 MHz,
CDCl3) δ 5.95 (d, J ) 4.8 Hz, 1H), 5.57 (dt, J ) 1.8, and 4.8
Hz, 1H), 3.07 (t, J ) 7.2 Hz, 1H), 2.72 (m, 1H), 2.28 (dddd, J
) 4.2, 8.1, 8.4, and 12.3 Hz, 1H), 2.03 (m, 2H), 1.59 (m, 1H),
0.84 (ddt, J ) 0.6, 5.0, and 7.8 Hz, 1H), 0.18 (t, J ) 5.0 Hz,
1H); 13C NMR (75 MHz, CDCl3) δ 137.5, 135.6, 49.9, 31.4, 30.1,
Th er m olysis of Tr icyclo[4.2.0.01,3]oct-4-en e (1). Ther-
molyses were done at various temperatures using a Brinkman
K6 Lauda constant-temperature bath with temperature control
of (0.05 °C. Dilute solutions (ca. 0.4 mM) of 1 in decalin were
sealed under vacuum in 0.1 mL portions in 0.5 mL thick-walled
ampules. The tubes were heated for fixed times, and the
1
rearrangement was monitored by H NMR spectroscopy and
gas chromatography. Tricyclo[4.2.0.01,5]oct-3-ene (23) was puri-
fied via preparative gas chromatography (12 ft × 25 in. 20%
1
Squalane on Chrom W column at 90 °C). H NMR (300 MHz,
CDCl3) δ 5.80 (dddt, J ) 1.2, 1.2, 2.1, and 5.7 Hz, 1H), 5.43
(dt, J ) 2.1 and 5.7 Hz, 1H), 2.40 (br s, 2H), 2.25 (td, J ) 3.9
and 10.8 Hz, 1H), 2.11 (tt, J ) 3.6 and 10.8 Hz, 1H), 1.82 (m,
1H), 1.7 (dddd, J ) 3.6, 4.2, 5.4, and 10.8 Hz, 1H), 1.37 (dddq,
J ) 0.9, 3.6, 5.4, and 10.8 Hz, 1H), 1.11 (ddt, J ) 0.9, 2.1, and
4.2 Hz, 1H); 13C NMR (75 MHz, CDCl3) δ 132.4, 129.2, 38.0,
35.0, 31.4, 27.3, 23.3, 23.0. HRMS-CI (M + H)+ calcd for C8H11
107.0861, found 107.0862.
Rea ction of Tr icyclo[4.2.0.01,3]oct-4-en e (1) w ith AcOH.
A thick-walled glass tube containing 1 mL of a 0.02 M solution
of tricyclo[4.2.0.01,3]oct-4-ene (1) in AcOH was sealed under
vacuum and heated to 145 °C in a constant-temperature bath
for 8 h. The ampule was allowed to cool to room temperature
before being cracked open, and 2 mL of diethyl ether was
added. The resulting solution was extracted twice with H2O
and once with saturated NaCl. GC-MS analysis showed the
presence of starting material and two products, a hydrocarbon
and acetate derivative, in a 5:5:1 ratio, respectively. One-half
of the solution was purified via preparative gas chromatogra-
phy (12 ft × 25 in. 20% Squalane on Chrom W column at 100
°C), and one of the two products was collected directly in to a
trap containing CDCl3. This compound was identified by its
1H NMR spectrum as ethylbenzene (13). Its mass spectrum is
consistent with this assignment, and an authentic sample was
found to have the same GC retention time. The second half of
the ether solution was treated at 0 °C with 0.3 mL of 1 M
LiAlH4 (0.3 mmol) in Et2O, and the reaction mixture was
refluxed for 2 h. It was subsequently cooled to 0 °C and
quenched by slowly adding ice-cold H2O. The aqueous layer
was extracted with Et2O, and the combined ethereal solution
(25) Meier, H.; Hanold, N.; Molz, T.; Bissinger, H. J .; Kolshorn, H.;
Zountsas, J . Tetrahedron 1986, 42, 1711-1719.

trans-Tricyclo[4.2.0.01,3]oct-4-ene
J . Org. Chem., Vol. 65, No. 11, 2000 3537
was concentrated under reduced pressure. Purification of the
residue by column chromatography (30% EtOAc/hexanes)
afforded 1 mg of alcohol 20. The structural assignment was
made based upon the 1H NMR spectrum, which is the same
as previously reported for 1-(2-hydroxyethyl)cyclohexa-1,4-
diene (20).12 1H NMR (300 MHz, CDCl3) δ 5.71 (br s, 2H), 5.56
(br s, 1H), 3.7 (t, J ) 6.3 Hz, 2H), 2.7 (m, 4H), 2.25 (t, J ) 6.3
Hz, 2H), 1.6 (br s, 1H).
J ) 1.2, 7.4, and 12.9 Hz, 1H), 2.45 (ddd, J ) 5.4, 7.2, and
12.9 Hz, 1H), 2.08 (dddd, J ) 1.8, 2.1, 4.5, and 9.0 Hz, 1H),
1.29 (dddd, J ) 1.0, 1.6, 4.8, and 9.0 Hz, 1H), 0.43 (t, J ) 4.8
Hz, 1H); 13C NMR (75 MHz, CDCl3) δ 165.1, 150.7, 135.9,
136.2, 135.8, 131.0, 123.7, 81.7, 47.3, 39.0, 34.0, 30.8, 16.9;
HRMS-CI (M + H)+ calcd for C15H14NO4 272.0923, found
272.0919.
Diels-Ald er Rea ction of Tr icyclo[4.2.0.01,5]oct-3-en e
(23) w ith Isoben zofu r a n . A mixture of tricyclo[4.2.0.01,5]oct-
3-ene (23) (3 mg, 0.028 mmol) in 0.5 mL of decalin and freshly
prepared isobenzofuran26 (0.77 g, 0.66 mmol) in 4.5 mL of
benzene was sealed under argon in a thick-walled glass tube.
The reaction vessel was immersed in a 115 °C constant
temperature oil bath and was heated for 20 h. The ampule
was allowed to cool to room temperature before being opened,
and the contents were analyzed by GC-MS. Concentration
under reduced pressure and purification by column chroma-
tography (5% EtOAc/hexanes) afforded 0.05 g (79%) of com-
pound 25. Recrystallization from a 1:1 mixture of CH3CN and
pentane afforded useable crystals for X-ray crystallography.
1H NMR (300 MHz, CDCl3) δ 7.35 (m, 1H), 7.29-7.14 (m, 3H),
5.30 (d, J ) 5.1 Hz, 1H), 5.18 (d, J ) 5.4 Hz, 1H), 2.77 (tdd, J
) 4.2, 5.4, and 9.0 Hz, 1H), 2.66 (dd, J ) 5.1 and 9.0 Hz, 1H),
2.32 (m, 1H), 1.84 (tt, J ) 4.2 and 10.8 Hz, 1H), 1.72 (dd, J )
9.0 and 13.4 Hz, 1H), 1.65 (dd, J ) 4.2 and 10.8 Hz, 1H), 1.27
(d, J ) 4.2 Hz, 1H), 1.06 (quintet, J ) 5.4 Hz, 1H), 0.91 (dd, J
) 4.2 and 13.4 Hz, 1H), 0.84 (m, 1H); 13C NMR (75 MHz,
CDCl3) δ 144.2, 143.2, 126.5, 126.3, 121.5, 120.9, 83.2, 82.4,
47.8, 46.9, 34.1, 28.6, 28.0, 23.9, 21.7 [one quaternary carbon
P r ep a r a tion of syn -Tr icyclo[5.1.0.01,4]oct-5-en -2-ol Ben -
zoa te (16). To a room temperature mixture of alcohol 10 (0.04
g, 0.32 mmol), PPh3 (0.1 g, 0.39 mmol), and benzoic acid (0.047
g, 0.39 mmol) in 1.5 mL of THF was added DEAD (0.062 mL,
0.39 mmol) over a 5 min period. Stirring was continued
overnight, and then the reaction mixture was concentrated
under reduced pressure. The residue was purified by column
chromatography (5% EtOAc/hexanes) to afford 0.058 g (80%)
of compound 16. 1H NMR (300 MHz, CDCl3) δ 8.1-8.16 (m,
2H), 7.56 (m, 1H), 7.49 (m, 2H), 5.98 (dt, J ) 1.5 and 5.1 Hz,
1H), 5.69 (dt, J ) 1.5, and 5.1 Hz, 1H), 5.42 (dt, J ) 1.0, and
5.4 Hz, 1H), 3.41 (ddd, J ) 1.5, 7.0, and 8.0 Hz, 1H), 2.50 (ddd,
J ) 1.0, 8.0, and 12.5 Hz, 1H), 2.43 (ddd, J ) 6.0, 7.0, and
12.0 Hz, 1H), 2.06 (m, 1H ), 1.29 (ddd, J ) 1.5, 4.5, and 8.4
Hz, 1H), 0.41 (t, J ) 4.5 Hz, 1H); 13C NMR (75 MHz, CDCl3)
δ 167.0, 135.9, 135.8, 133.0, 130.9, 129.8, 128.5, 80.4, 47.3, 39.0,
34.1, 30.6, 16.9; HRMS-EI M+ calcd for C15H14O2 226.0994,
found 226.0993.
P r ep a r a tion of syn -Tr icyclo[5.1.0.01,4]oct-5-en -2-ol (17).
To a 0 °C solution of 0.056 g (0.24 mmol) of compound 16 in 2
mL of Et2O was added 0.25 mL of a 1 M solution of LiAlH4 in
THF. The reaction mixture was stirred overnight at room
temperature, and then Et2O and sat. NH4Cl solution were
added. The resulting slurry was extracted with Et2O, and the
organic phase was dried over MgSO4. Concentration under
reduced pressure followed by column chromatography (30%
EtOAc/hexanes) afforded 0.021 g (72%) of the inverted alcohol
17. 1H NMR (300 MHz, CDCl3) δ 5.91 (dt, J ) 1.5 and 5.0 Hz,
1H), 5.66 (dt, J ) 1.5 and 5.0 Hz, 1H), 4.50 (t, J ) 3.0 Hz,
1H), 3.40 (ddd J ) 1.5, 3.5, and 8.0 Hz, 1H), 2.24 (dd, J ) 3.0
and 8.0 Hz, 2H), 2.20 (br s, 1H), 1.83 (dddd, J ) 2.0, 3.0, 4.5,
and 8.5 Hz, 1H), 1.12 (ddd, J ) 1.0, 4.5, and 8.5 Hz, 1H), 0.32
(t, J ) 4.5 Hz, 1H); 13C NMR (75 MHz, CDCl3) δ 136.0, 135.4,
assignment is absent]; HRMS-FAB M+ calcd for C16H16
O
224.1201, found 224.1194; (M + Na)+ calcd for C16H16NaO
247.1098, found 247.1104.
Ack n ow led gm en t. We thank Dr. Gary Dombrowski
for bringing this molecule (1) to our attention, Drs.
Maren Pink and Victor G. Young, J r. of the X-ray
Crystallographic Laboratory at the University of Min-
nesota for solving the structures of 18 and 25, and Mr.
Dana Reed for assistance in obtaining mass spectrom-
etry data. Support from the National Science Founda-
tion, the donors of the Petroleum Research Foundation,
as administered by the American Chemical Society, the
Minnesota Supercomputer Institute, and the University
of Minnesota-IBM Shared Research Project also are
gratefully acknowledged.
77.0, 47.2, 42.0, 35.6, 30.2, 15.4; HRMS-EI M+ calcd for C8H10
122.0732, found 122.0732.
O
P r ep a r a tion of syn -Tr icyclo[5.1.0.01,4]oct-5-en -2-ol p-
Nitr oben zoa te (18). To a room temperature mixture of
alcohol 10 (0.04 g, 0.49 mmol), PPh3 (0.15 g, 0.58 mmol), and
p-nitrobenzoic acid (0.1 g, 0.59 mmol) in 3 mL of THF was
added DEAD (0.09 mL, 0.59 mmol) over a 5 min period. The
reaction mixture was stirred overnight, and then it was
concentrated under reduced pressure. Column chromatogra-
phy of the residue afforded 0.12 g (82%) of p-nitrobenzoate 18
(mp 82-84 °C). Recrystallization from a 1:1 mixture of EtOH
and pentane afforded crystals suitable for X-ray crystal-
lography. 1H NMR (300 MHz, CDCl3) δ 8.30 (m, 4H), 5.98 (dt,
J ) 1.0 and 5.1 Hz, 1H), 5.69 (dt, J ) 2.1 and 5.1 Hz, 1H),
5.44 (d, J ) 5.4 Hz, 1H), 3.43 (t, J ) 7.2 Hz, 1H), 2.56 (ddd,
Su p p or tin g In for m a tion Ava ila ble: X-ray data for 18
and 25, calculated MP2 structures (xyz coordinates) and
energies for all of the computed species in this work, and 1H
NMR data. This material is available free of charge via the
Internet at http://pubs.acs.org.
J O000215R
(26) Man, Y.-M.; Mak, T. C. W.; Wong, H. N. C. J . Org. Chem. 1990,
55, 3214-3221.