Annulation of seven-membered rings to [2.2]paracyclophane

Article abstract of DOI:10.1002/ejoc.200800171

Tropylidenes 16 and 17 were prepared from [2.2]paracyclophane (10). On treatment with the corresponding trityl salts they were converted into tropyliophanes 26a (tetrafluoroborate) and 26b (perchlorate). With acetone, 26a furnished trapping product 27, wh

Full text of DOI:10.1002/ejoc.200800171

FULL PAPER
DOI: 10.1002/ejoc.200800171
Annulation of Seven-Membered Rings to [2.2]Paracyclophane[‡]
[
a]
[a]
[b]
[a]
Sonja Margaretha Ramm, Henning Hopf,* Peter G. Jones, Peter Bubenitschek,
[b]
[c]
Birte Ahrens, and Ludger Ernst
Keywords: Cyclophanes / Annulation / Cycloaddition / Tropylium cation / Homo-Diels–Alder addition
Tropylidenes 16 and 17 were prepared from [2.2]paracyclo-
phane (10). On treatment with the corresponding trityl salts
they were converted into tropyliophanes 26a (tetrafluoro-
borate) and 26b (perchlorate). With acetone, 26a furnished
trapping product 27, which underwent a homo-Diels–Alder
addition with tetracyanoethylene to afford adduct 29. All
new compounds were characterized by their spectroscopic
and analytical data and for most – including 17 and 26b – the
structures were also determined by X-ray diffraction.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
Introduction
straightforward. In many cases, the amount of material
available at the end of a synthetic sequence was just suf-
ficient to obtain the spectroscopic data – the question of
the chemical properties, however, had to be left open in the
hope that at “some later time” enough material would
accumulate to address reactivity questions.
In comparison to the huge effort that has been devoted
to the preparation and study of aromatic cyclophanes dur-
[2]
ing the last half century, little is known about the synthe-
sis of nonbenzenoid cyclophanes.[ Furthermore, although
3]
[4a,4b]
various cyclopropenyliophanes (1),
cyclopentadienido-
troponophanes (3),[6a–6f] tropyliophanes
(Scheme 1) and phanes containing a nonbenzen-
We decided to begin closing this gap by preparing annu-
lated tropyliophane 5 and hoped at the same time that the
knowledge gained during its synthesis could be applied to
the preparation of bis(tropylium salt) 6. We were encour-
aged in these efforts by our previous preparation of the an-
[
5]
phanes (2),
(
4),[
7a–7h]
[3]
oid 10 π-system have been described, little is known about
the chemical behavior of these compounds.
[
8]
ionic sister molecules of 5 and 6, viz. 7 and 8, the elec-
tronic properties of which were investigated by NMR spec-
troscopy and which also served as starting materials for
[
9]
novel metallocenophanes such as 9 (Scheme 2).
Scheme 1. A selection of nonbenzenoid cyclophanes.
The main reason for this lack of knowledge is that the
syntheses of these unusual compounds are often far from
1]
[
[
‡] Cyclophanes, LXI. Part LX: Ref.[
a] Institut für Organische Chemie, Technische Universität
Braunschweig,
Hagenring 30, 38106 Braunschweig, Germany
Fax: +49-531-391-5388
E-mail: H.Hopf@tu-bs.de
[
[
b] Institut für Anorganische und Analytische Chemie, Technische
Universität Braunschweig,
Postfach 3329, 38023 Braunschweig, Germany
Fax: +49-531-391-5387
E-mail: P.Jones@tu-bs.de
c] NMR-Laboratorium der Chemischen Institute der Technischen
Universität Braunschweig,
Hagenring 30, 38106 Braunschweig, Germany
Fax: +49-531-391-8192
E-mail: L.Ernst@tu-bs.de
Scheme 2. Charged [2.2]phanes with 10 π-electron decks.
2948
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 2948–2959

Annulation of Seven-Membered Rings to [2.2]Paracyclophane
An interesting hybrid of the two ion types would be a also confirmed by X-ray structural analysis (see below). The
cyclophane in which one deck is positively charged (benzo- alcohol obtained from 13 after lithium aluminum hydride
tropylium cation) and the other negatively (indenyl reduction in THF (mixture of diastereomers) was not iso-
[
10]
anion).
lated but directly subjected to acid-catalyzed dehydration.
Olefin 14 was obtained in a gratifying 85% yield and its
structure determined by spectroscopic measurements and
X-ray analysis (see below). The allylic bromination of 14 to
Results and Discussion
1
5 (mixture of isomers) turned out to be the bottleneck of
The Preparation of Benzotropylidenophanes 16 and 17
the synthesis, which resulted in a severe loss of intermediate
Starting from the commercial substrate [2.2]paracyclo- material. The mixture of bromides 15, obtained in only
phane (10) the two isomeric cycloheptatriene derivatives 16 34% yield, was not purified further. The attack of the halo-
and 17 were prepared as summarized in Scheme 3.
gen atom at both the allylic and the benzylic position of 14
Formylation of 10 under Rieche conditions (TiCl4/ was made obvious in the ensuing elimination step (potas-
Cl CHOCH ) first provided 4-formyl[2.2]-paracyclo- sium tert-butoxide in DMSO at room temperature) that fur-
2
3
[
11]
phane,
which was subsequently chain elongated by a nished a mixture of the two benzotropylidenes 17 and 16 in
Wittig–Horner reaction with triethyl 4-phosphonocrotonate 3:1 ratio (total yield 60%). Both hydrocarbons were charac-
to afford dienoate 11. The structure of the compound fol- terized by the usual spectroscopic methods (see Experimen-
lows from its spectroscopic data (see Experimental Section), tal Section) and 17 also by X-ray diffraction (see below).
in particular its all-trans configuration from the two coup-
A surprising observation was made when the solvent in
3
3
ling constants J17,18 = 15.4 Hz and J19,20 = 15.3 Hz, the above elimination reaction was replaced by toluene, and
respectively, for the two double bonds. Catalytic hydrogena- the reaction temperature increased to reflux (111 °C).
tion over Pd in ethyl acetate gave the saturated ester (98%), Rather than providing dienes 16 and 17, [2]paracyclo-
which was saponified to acid 12 with aqueous sodium hy- [2](1,4)-naphthalenophane (20) was now isolated in 22% as
droxide solution in 93% yield. This compound was pre- the sole product. For its formation we propose the pathway
pared previously by Nugent and Vigo by a different route presented in Scheme 4.
and in poorer overall yield.[ Surprisingly, in our hands
12]
Starting from allyl bromide 18, dehydrobromination
the subsequent Friedel–Crafts cyclization in the presence of could lead to norcaradiene intermediate 19, which provides
polyphosphoric acid did not provide the 75% reported in the isolated hydrocarbon by loss of bromocarbene. To the
[
12]
the literature. At best, we could obtain 15% under these best of our knowledge, such a base-induced process has not
conditions, and in the product mixture at least four compo- been described in the chemical literature, although thermal
nents were detected in which the ethano bridges of 13 had and photochemical carbene eliminations of cycloheptatri-
been ruptured by ipso substitution. In the end, a 10% solu- ene and benzocyclopheptatriene derivatives have been re-
[
13]
[14a–14c]
tion of phosphorus pentoxide in methanesulfonic acid
ported.
Photochemical carbene removal from benzo-
[15]
gave the best results and furnished ketone 13 in 56% yield. and dibenzonorcaradienes has also been observed.
The
Although the structure of this compound follows unambig- essential role of bromine in the above ring-contraction pro-
uously from the spectroscopic and analytical data, it was cess was demonstrated in a control experiment, in which
Scheme 3. Annulation of a seven-membered ring to [2.2]paracyclophane (10).
Eur. J. Org. Chem. 2008, 2948–2959
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S. M. Ramm, H. Hopf, P. G. Jones, P. Bubenitschek, B. Ahrens, L. Ernst
FULL PAPER
Scheme 4. Fragmentation of 18 to naphthalenophane 20.
Scheme 5. Some reactions of annulated [2.2]paracyclophanes.
dienes 16 and 17 were subjected to the same conditions as of 21 with lithium aluminum hydride in THF took a dif-
8: both hydrocarbons were isolated unchanged after the ferent course and led – after workup in the presence of 6 
intended elimination process. HCl in chloroform – to a product mixture consisting of
1
An alternative, higher yielding route to symmetrical unsaturated hydrocarbons 14 (main product) and 17 as well
benzocycloheptatriene 17 started directly from ketone 13 as bridged ether 25. We assume that initially produced endo
and is presented in Scheme 5.[ Heating ketone 13 in the alcohol 22 (outside hydride attack, see above) has at least
presence of NBS and AIBN in carbon tetrachloride resulted three different options to react. Like other unsaturated
16]
[
17]
in the direct formation of enone 21, which was isolated in alcohols,
the ate complex present before hydrolysis and/
74% yield after column chromatography. Reduction of 21 or acid treatment can undergo reduction of its sterically ne-
with sodium borohydride in isopropyl alcohol furnished a arby double bond to provide the corresponding saturated
mixture of alcohols 22 and 23 in 4:1 ratio (combined yield alcohol. This, upon acidic workup, furnishes olefin 14 as in
81%), which was separable by column chromatography on the reduction/elimination of 13 (see Scheme 3). Dehy-
silica gel. The structure assignment follows from the spec- dration of 22 leads to benzotropylidene 17. Finally, regiose-
troscopic data (Experimental Section) and in particular lective protonation of the double bond of 22 creates a ben-
from the X-ray structural analysis of major product 22. As zylic cation that can be trapped by the opposing hydroxy
shown below, the hydroxy functionality of this isomer functionality (see structure 24), which thus generates endo
points to the “interior” of the cyclophane moiety, which ether 25. The stereochemistry of the latter was again proved
indicates that the hydride transfer takes place preferentially by X-ray structural analysis (see below).
from the sterically less-shielded “outside” of the starting
ketone. Still, the reducing agent is able to pass the bridging
p-xylylene unit of 21, which thus leads to exo alcohol 23
also. Treatment of a solution of 22 in dichloromethane with
Preparation of Tropyliophane 26
hydrochloric acid at room temperature provided symmetri-
Having sufficient amounts of 16 and/or 17 in hand, the
cal tropylidenophane 17 in essentially quantitative yield. stage was set for the generation of tropylium ion 5. In fact,
This route makes the compound available in amounts of reaction of either 16 or 17 with trityl fluoroborate or per-
several hundred mg and, furthermore, provided single crys- chlorate, respectively, in dichloromethane at room tempera-
tals suitable for X-ray analysis (see below). The reduction ture gave salts 26a and 26b in acceptable yields (Scheme 6).
2950
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Eur. J. Org. Chem. 2008, 2948–2959

Annulation of Seven-Membered Rings to [2.2]Paracyclophane
Scheme 6. Preparation of tropyliophanes 26.
Both salts are beautifully deep-red, crystalline compounds, Table 1. Comparison of the NMR spectroscopic data[a] of 26 and
the structures of which follow from their spectroscopic data. 20.
The NMR spectra of 26a and 26b were identical apart
from small chemical shift differences ( H: 0.01–0.02 ppm,
C: 0.2–0.3 ppm). The values given in Table 1 are averages.
20[b,c]
2
6
∆δ
1
Proton chemical shifts [ppm]
1
3
1 [
a
d]
3.40
3.23
3.73
4.29
9.67
8.74
9.05
7.87
6.77
5.48
3.09
2.88
3.05
3.79
7.68
7.38
0.31
0.35
0.68
0.50
1.99
1.36
The protons of the benzotropylium part of 26 are strongly
deshielded (δ = 9.67–7.87 ppm; Table 1) due to the positive
charge residing in this part of the molecule. These are
downfield shifted between 1.1 and 2.0 ppm relative to naph-
thalenophane 20. Similarly, there are strong effects of the
1
2
2
4
5
6
1
1
s
a
s
1
3
positive charge upon the shifts of the C nuclei (∆δ = 14.3–
0
5
6.73
6.44
5.58
1.14
0.33
–0.10
2.01
2
6.9 ppm). The largest values of these charge effects are vir-
tually identical with the shift differences between the tropyl- 18
9
.28 (C
7
H
7
+)
6 6
7.27 (C H )
ium cation and benzene (∆δ = 2.01 ppm, ∆δ = 27.1 ppm;
H
C
see Table 1). At 400 MHz, the four-spin bridge proton spec-
trum of 26 is completely first-order because of the widely
spaced chemical shifts. The assignments were achieved by
Coupling constants [Hz]
J(1a,1s)
J(1a,2a)
–13.6
10.4
2.7
6.1
10.2
–14.6
–13.2
10.7
2.0
6.2
10.2
–13.6
common 2D techniques (HSQC, HMBC) and started with J(1a,2s)
J(1s,2a)
J(1s,2s)
J(2a,2s)
the observation of the NOE between 2-H and 4-H. The
syn
1
1
H, H coupling constants in 26 are rather similar to those
in 20, yet the geminal coupling in the methylene group adja-
cent to the charged aromatic system is algebraically smaller
by 1.0 Hz.
Carbon chemical shifts [ppm]
1
2
3
3
4
5
6
36.4
34.4
32.9
136.6
135.3
125.3
124.8
2.0
3.8
14.3
14.7
27.1
17.3
1
36.7[
It seemed interesting to compare the H chemical shifts
e]
150.9
of the endo protons 18-H and 19-H of the para-phenylene
rings in 26 and 20, which are under the influence of the
ring current of the opposing annulated aromatic ring: trop-
[e]
a
150.0
152.4
142.1
156.3
145.0
141.1
134.2
135.2
ylium in 26 versus benzene in 20. The magnetic field in-
duced aromatic ring current[18] is normally used to explain
10
130.6
137.9
132.2
127.8
14.4
3.2
2.0
7.4
26.9
1
1
4
5
the deshielding of aromatic relative to olefinic protons and
the shielding of protons residing above aromatic systems. 18
Some theoretical calculations indicate that the ring current
1
55.4 (C
7
H
7
+)
128.5 (C
6
H
6
)
is somewhat smaller in the tropylium ion than in benzene.
According to Jusélius and Sundholm,[ for example, the [a] Solvents: [D]TFA for 26, CDCl
19]
for 20; internal references:
TMS for 26 ( H and C) and 27 ( H), CDCl (δ = 77.01 ppm) for
7 ( C). [b] A. Akkermann-Kubillus, L. Ernst, H. Hopf, unpub-
3
1
13
1
3
difference is of the order of 20%. The simplistic assumption
that the shielding difference of the endo protons 18-H and
1
3
2
lished results, 1987. [c] To facilitate the comparison with 26, carbon
atoms in 20 are numbered 1–5 and 7–19. [d] a, s: anti, syn with
19-H in benzotropyliophane 26 relative to their analogues
in naphthalenophane 20 is solely due to the decrease in the respect to the annulated ring. [e] Interchangeable assignments.
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S. M. Ramm, H. Hopf, P. G. Jones, P. Bubenitschek, B. Ahrens, L. Ernst
FULL PAPER
ring current would lead one to expect a deshielding of these (29). In general, the cyclophane moieties display the usual
protons in 26 with respect to 20. However, the opposite is distortions: the bridge single bonds are elongated, the
found, albeit only by a small measure: the protons in ques- angles in the bridges are widened, the six-membered rings
tion are shielded by 0.10 ppm. We suggest that there is a display flattened boat conformations (whereby the bridge-
combination of (at least) three different, partly counter-
acting, effects: (a) The effect of reduced ring current may
be estimated by taking 20% of the difference between the
chemical shift of the endo protons in 20 (δ = 5.58 ppm) and
in [2.2]paracyclophane (δ = 6.48 ppm), that is, –0.18 ppm.
(b) Additionally, one would expect a charge-transfer effect
of the benzotropylium moiety onto the para-phenylene ring.
This effect could be taken equal to the difference between
the shift of the exo protons (15-H, 16-H) in 26 and in 20,
that is, +0.29 ppm. (c) Finally, there should be a geometric
effect. As the C–C–C bond angles in an equilateral hepta-
gon are larger (ideally 128.57°) than the 120° angles of a
hexagon, the endo protons in 26 are closer to the center of
the ring current of the tropylium moiety than they are with
respect to the center of the annulated benzene ring in 20,
that is, they undergo an effect of relative shielding. The geo-
metric effect would have to be of the order of –0.2 ppm for Figure 1. The molecule of compound 13 in the crystal. Ellipsoids
represent 30% probability levels.
the total effect to agree with the experimental shift differ-
ence between 26 and 20.
The structure of 26b was confirmed by X-ray crystal-
lography (see below). Reingold and coworkers have re-
ported that tropylium ions react with enolizable ketones
[
20]
such as acetone to yield α-cycloheptatrienyl ketones. An
analogous reaction took place when 26b was dissolved in
acetone: after 30 min at room temperature the sole product
isolated was methyl ketone 27. Repeating this experiment
with 26a in [D ]acetone in the presence of tetracyanoethy-
6
lene (TCNE) as a trapping agent resulted in the formation
of adduct 29 as the sole product. To learn more about its
mechanism of formation, both tropylidenes 16 and 17 were
treated with TCNE in dichloromethane at room tempera-
ture. Whereas 16 did not react, 17 provided homo-Diels–
Alder adduct 28, the structure of which was determined by
spectroscopic (see Experimental Section) and X-ray struc-
tural analysis (see below). The cycloaddition of suitable
Figure 2. The molecule of compound 17 in the crystal. Ellipsoids
dienophiles to cycloheptatrienes and benzocycloheptatri- represent 30% probability levels.
enes is a well-established phenomenon and has been pro-
[
21a–21d]
posed to take place via a norcaradiene intermediate.
In the present case, evidently only 17 can form this interme-
diate under the mild conditions used. The important role
of the reactivity of the dienophile in the cycloaddition was
demonstrated by attempting to add maleic anhydride to
either 16 or 17: both compounds survived the addition ex-
periment even if it was performed in 1,2-dichlorobenzene at
185 °C. In the case of 26a, a ketone of type 27 is obviously
produced first, which is subsequently intercepted by
TCNE.
X-ray Structural Analysis of Annulated Compounds 13, 17,
22, 25, 26b, 28, and 29
The seven structures studied here are depicted in Fig-
ures 1 (13), 2 (17), 3 (22), 4 (25), 5 (26b), 6 (28), and 7 represent 30% probability levels.
Figure 3. The molecule of compound 22 in the crystal. Ellipsoids
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Eur. J. Org. Chem. 2008, 2948–2959

Annulation of Seven-Membered Rings to [2.2]Paracyclophane
Figure 4. The molecule of compound 25 in the crystal. Ellipsoids
represent 30% probability levels.
Figure 7. The molecule of compound 29 in the crystal (excluding
the solvent molecule). Ellipsoids represent 30% probability levels.
29 (see below) the ring planes remain parallel (interplanar
angles Ͻ2°). Compound 26b shows exact mirror symmetry
in both cation and anion, whereas compounds 17, 25, and
28 display the same symmetry to a good approximation
(rms deviations 0.02, 0.09, and 0.09 Å).
In compounds 28 and 29, the paracyclophane rings are
no longer exactly parallel [interplanar angles between non-
bridgehead planes are 8.9(1) and 13.3(2)°, respectively].
This may be associated with the formation of very short
intramolecular contacts, which can be interpreted as C–
H···π interactions from a hydrogen at C6 to the midpoints
of the bond C18–C19. Normalizing the C–H bond lengths
to 1.08 Å, the H···π distances are 2.44 and 2.31 Å and the
C–H···π angles are 176 and 164°, respectively.
Figure 5. The formula unit of compound 26b in the crystal. Only
the asymmetric unit is numbered. Ellipsoids represent 30% prob-
ability levels.
The crystal packing of each compound (except that of
hydrocarbon 17) involves weak hydrogen bonds of the form
C–H···X (X = O or N). In 13, the contact H13B···O 2.47 Å
connects the molecules to form zigzag chains parallel to
Figure 6. The molecule of compound 28 in the crystal. Ellipsoids
represent 30% probability levels.
head atoms lie ca. 0.15–0.20 Å outside the plane of the
other four atoms), and the ring angles at the bridgehead
atoms are narrowed. Except for Diels–Alder adducts 28 and y axis. C–H···O interactions are indicated by thick dashed bonds.
Figure 8. Packing diagram for compound 26b viewed parallel to the
Eur. J. Org. Chem. 2008, 2948–2959
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2953

S. M. Ramm, H. Hopf, P. G. Jones, P. Bubenitschek, B. Ahrens, L. Ernst
the z axis. In 22, the contact H12B···O 2.54 Å connects the (Düren). Column chromatography was performed with Kieselgel
FULL PAPER
6
0 (70–230 mesh) purchased from Merck (Darmstadt). Melting
molecules to form chains parallel to [011]; surprisingly, the
OH hydrogen atom is not involved in secondary interac-
tions. In 25, the contacts H12A···O 2.52 Å and H13B···O
points were determined with a Büchi 530 melting-point apparatus
or by differential scanning calorimetry (DSA), Rheometric Scien-
tific (Piscataway, USA) and are uncorrected. NMR spectra were
2
.57 Å connect the molecules to form spirals parallel to the
z axis. In 26b, the contacts H4···O1 2.28 Å, H1B···O2
.54 Å, and H2A···O3 2.51 Å connect the ions in layers par-
allel to the xz plane (Figure 8). In 28, the contacts H7···N1
1
recorded with the following instruments: Bruker AC-200 [ H NMR
13
1
(
(
0
200.1 MHz), C NMR (50.3 MHz)], Bruker WM-400 [ H NMR
2
13
400.1 MHz), C NMR (100.6 MHz)]. Tetramethylsilane (δ
.00 ppm) and CDCl (δ = 77.05 ppm) were used as internal refer-
.52 Å and H8···N3 2.34 Å connect the molecules to form ences. IR spectra were recorded with a Nicolet 320 FTIR instru-
H
=
3
C
2
tapes that are two molecules (or one b translation) broad ment as KBr pellets. UV/Vis spectra were recorded with a Beckman
and parallel to the x axis (Figure 9). In 29, the contacts UV 5230 and HP 8452 A Diode Array. MS were recorded with a
Finnigan MAT 8430 (EI, 70 eV) instrument.
H4···O1 2.41 Å, H2A···N3 2.62 Å, H5···N3 2.55 Å, and
H20A···N3 2.46 Å link the molecules in the same manner Ethyl 5-(4-[2.2]Paracyclophanyl)penta-(2E,4E)-dienoate (11): To a
solution of triethyl 4-phosphonocrotonate[ (6.35 g, 26 mmol) in
anhydrous THF (200 mL) was added n-butyllithium (ca. 1.4  in
hexane, 19 mL, ca. 26.6 mmol) under an atmosphere of nitrogen at
23]
as that for 28 (Figure 10).
0
°C. The solution turned yellow-orange. After stirring for 20 min
at room temperature, 4-formyl-[2.2]paracyclophane[
11]
(6.00 g,
5.4 mmol) was added in portions, and the mixture was stirred for
h at room temperature. For workup, ice water was added
2
4
(
200 mL), and the product mixture was extracted carefully with
ether. The combined organic phase was washed with water and
dried with magnesium sulfate, and the solvent was removed by ro-
tary evaporation. After column chromatography of the remaining
1
oil, 6.33 g (75%) of 11 was isolated as a yellow oil. H NMR
(
(
7
(
400.1 MHz, CDCl
m, 7 H) and 3.45–3.50 (m, 1 H, ethano bridges), 4.25 (q, J =
.1 Hz, 2 H, OCH ), 6.00 (d, J = 15.3 Hz, 1 H, 20-H), 6.36–6.62
m, 7 H, 5-, 7-, 8-, 12-, 13-, 15-, 16-H), 6.67 (dd, J = 15.4, 11.2 Hz,
3 3
): δ = 1.33 (t, J = 7.1 Hz, 3 H, CH ), 2.80–3.18
Figure 9. Packing diagram for compound 28 viewed parallel to the
z axis. C–H···O interactions are indicated by thick dashed bonds.
H atoms not involved in short contacts are omitted for clarity.
2
1
1
H, 18-H), 6.97 (d, J = 15.4 Hz, 1 H, 17-H), 7.53 (dd, J = 15.3,
1
3
1.2 Hz, 1 H, 19-H) ppm. C NMR (100.6 MHz, CDCl
), 33.7, 34.8, 35.1, 35.3 (all CH , C-1, -2, -9, -10), 60.3
OCH ), 120.6 (CH, C-20), 126.3, 130.1, 130.4, 131.6, 132.9, 133.0,
33.2, 135.1, 138.4 (all CH, C-5, -7, -8, -12, -13, -15, -16, -17, -18),
36.1, 139.0, 139.3, 139.4, 140.1 (all C , C-3, -4, -6, -11, -14), 145.1
, COO) ppm. IR (KBr): ν˜ = 3011 (w), 2985
m), 2915 (s), 2892 (m), 2852 (m), 1703 (vs), 1616 (vs), 1366 (s),
3
): δ = 14.3
(CH
3
2
(
1
1
2
q
(
CH, C-19), 167.1 (C
q
(
1
7
2
335 (s), 1295 (m), 1244 (vs), 1177 (s), 1136 (vs), 1035 (s), 1006 (s),
97 (m), 714 (m) cm . UV (acetonitrile): λmax (log ε) = 192 (4.54),
–
1
24 (sh, 4.26), 256 (4.09), 330 (4.11) nm. MS (EI, 70 eV): m/z (%)
Figure 10. Packing diagram for compound 29 viewed parallel to the
z axis. C–H···O interactions are indicated by thick dashed bonds. H
atoms not involved in short contacts are omitted for clarity.
+
= 332 (32) [M] , 259 (9), 228 (22), 227 (100), 199 (66), 182 (34),
181 (54), 155 (28), 154 (21), 153 (20), 141 (14), 128 (13), 104 (822),
103 (5). HRMS: calcd. for C23
24 2
H O 332.1776; found 332.1776.
5-(4-[2.2]Paracyclophanyl)pentanoic Acid (12): Ester 11 (6.06 g,
Conclusions
18.0 mmol) dissolved in ethyl acetate (300 mL) was hydrogenated
over 10% Pd on charcoal (1.8 g) at room temperature under nor-
mal pressure. After the hydrogen uptake had ceased, the catalyst
was removed by filtration, and the solvent was removed in vacuo.
We prepared tropyliophane system 5, which is a novel
type of cyclophane in which a nonbenzenoid 10 π-electron
system forms one of the decks by a short synthetic se- The remaining oil was chromatographed on silica gel (dichloro-
quence, from the commercial product [2.2]paracyclophane methane) to furnish 5.94 (98%) of the saturated ester as a colorless
1
(
10). It remains to be seen whether dication 6 can be synthe- oil. H NMR (400.1 MHz, CDCl
3
): δ = 1.23 (t, J = 7.2 Hz, 3 H,
CH
-, 10-, 17-, 20-H), 4.10 (q, J = 7.2 Hz, 2 H, OCH
1.8 Hz, 1 H, 5-H), 6.35–6.51 (m, 5 H, 7-, 8-, 12-, 13-, 16-H), 6.65
3
), 1.42–1.65 (m, 4 H, 18-, 19-H), 2.22–3.35 (m, 12 H, 1-, 2-,
sized by a comparable approach. Because cycloheptatrienes
9
2
), 6.10 (d, J ≈
have been used as ligands for novel transition-metal sand-
[
22a–22c]
wich complexes
16 and 17 could in principle be em-
1
3
(
dd, J = 7.8, 1.9 Hz, 1 H, 15-H) ppm. C NMR (100.6 MHz,
CDCl ): δ = 14.2 (CH ), 24.9 (CH , C-19), 29.9 (CH , C-17), 33.4,
3.9, 34.18, 34.20 (all CH , C-1, -2, -18, -20), 35.0, 35.3 (both CH
C-9, -10), 60.1 (OCH ), 128.7 (CH, C-15), 130.2, 132.0, 133.1,
33.2, 134.5, 134.6 (all CH, C-5, -7, -8, -12, -13, -16), 137.3 (C , C-
), 139.31, 139.32, 139.6 (all C , C-6, -11, -14), 141.4 (C , C-4),
, COO) ppm. IR (KBr): ν˜ = 3028 (w), 2982 (m), 2929 (s),
1733 (vs), 1458 (m), 1442 (m), 1414 (m), 1372 (m), 1300 (m), 1094
ployed for the synthesis of novel multilayered metal com-
3
3
2
2
plexes.
3
2
2
,
2
1
3
q
Experimental Section
q
q
General Remarks: DSC was performed with commercial DC-plates
Polygram Sil G/UV254) purchased from Macherey, Nagel & Co.
173.6 (C
q
(
2954 www.eurjoc.org © 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 2948–2959

Annulation of Seven-Membered Rings to [2.2]Paracyclophane
–1
+
(
m), 1033 (m), 797 (m), 717 (m) cm . UV (acetonitrile): λmax (log
290 (100) [M] , 275 (13), 186 (49), 185 (74), 183 (25), 171 (63), 143
ε) = 194 (4.68), 208 (sh, 4.29), 226 (4.26) nm. MS (EI, 70 eV): m/z (16), 128 (22), 115 (21), 104 (30).
+
(
(
(
%) = 336 (100) [M] , 291 (40), 232 (29), 231 (60), 229 (26), 187
1,2-(4,5-[2.2]Paracyclophano)cyclohepta-1,3-diene (14): A solution
17), 159 (21), 158 (34), 143 (51), 142 (42), 141 (33), 129 (18), 118
19), 105 (20), 104 (40), 91 (13). C23H O (336.52): calcd. C 82.09,
28 2
of 13 (280 mg, 0.96 mmol) in anhydrous THF (10 mL) was added
dropwise to lithium aluminum hydride (148 mg, 3.9 mmol) in THF
H 8.39; found C 81.93, H 8.38.
(30 mL) at 0 °C under an atmosphere of nitrogen. After boiling the
reaction mixture to reflux (3 h), it was cooled to ice water tempera-
ture and hydrolyzed carefully with ice water. Hydrochloric acid
For saponification, this ester (7.0 g, 20.8 mmol) was heated at re-
flux in a mixture of ethanol (150 mL) and 15% aqueous sodium
hydroxide solution (200 mL) for 15 h. After cooling to room tem-
perature, the solution was neutralized with 2  hydrochloric acid,
and the precipitate thus formed was removed by filtration. The
crude acid was dissolved in saturated hydrogen carbonate solution,
and the resulting solution filtered. Compound 12 was reprecipi-
tated by the addition of 2  hydrochloric to pH 2. The precipitate
was filtered off and dried under high vacuum to yield 5.96 g (93%)
(
6 , 10 mL) and chloroform (10 mL) were added, and the reaction
mixture was stirred for 2.5 h at room temperature. The phases were
separated, and the aqueous phase was extracted with chloroform
(
2ϫ). The combined organic phase was dried with magnesium sul-
fate, and the solvent was removed in vacuo. After silica gel
chromatography (dichloromethane), 224 mg (85%) of 14 was ob-
tained as colorless cubes (ethanol/dichloromethane). M.p. 158 °C.
1
3
H NMR (400.1 MHz, CDCl ): δ = 1.69–1.86 (m, 2 H) and 1.99–
[12]
of 12 as colorless needles. M.p. 80–81 °C (ref. 78–80 °C). As the
2
5
1
3
.10 (m, 3 H, 4-, 5-, 6-H), 2.68–3.41 (m, 9 H, 1-, 2-, 4-, 12-, 13-H),
[12]
spectroscopic data are incomplete in ref.
they are listed here in
): δ = 1.47–1.53, 1.56–1.66 (both
m, 2 H each, 18-, 19-H), 2.24–2.64 (m, 4 H, 17-, 20-H), 2.73–2.81
m, 1 H) and 2.88–3.15 (m, 6 H) and 3.28–3.35 (m, 1 H, 1-, 2-,
.99–6.05 (m, 1 H, 7-H), 6.38–6.55 (m, 7 H, 8-, 10-, 11-, 15-, 16-,
1
full. H NMR (400.1 MHz, CDCl
3
1
3
8-, 19-H) ppm. C NMR (100.6 MHz, CDCl
3
): δ = 27.5, 29.3,
, C-1, -2,
1.9 (all CH , C-4, -5, -6), 32.6, 33.7, 33.9, 34.3 (CH
2
2
(
-
12, -13), 128.0, 128.4, 128.9, 131.0, 132.5, 132.8, 133.0 (all CH, C-
9
6
7
-, 10-H), 6.11 (d, J ≈ 1.8 Hz, 1 H, 5-H), 6.36–6.42 (m, 3 H) and
.45 (dd, J ≈ 7.8, 1.8 Hz, 1 H) and 6.51 (dd, J ≈ 7.8, 1.8 Hz, 1 H,
-, 8-, 12-, 13-, 16-H), 6.65 (dd, J = 7.8, 1.8 Hz, 1 H, 15-H) ppm.
8
1
, -10, -11, -15, -16, -18, -19), 131.2 (C-7), 137.1, 137.5, 137.6,
38.7, 138.9, 141.2 (all C , C-3, -3a, -8a, -9, -14, -17) ppm. IR
q
(
(
λ
KBr): ν˜ = 3423 (m), 2925 (vs), 2845 (vs), 1461 (m), 1435 (s), 1411
13
C NMR (100.6 MHz, CDCl
C-17), 33.5, 33.88, 33.92, 34.2 (all CH
both CH , C-9, -10), 128.8 (CH, C-15), 130.3, 132.1, 133.1, 133.3,
34.5, 134.7 (all CH, C-5, -7, -8, -12, -13, -16), 137.4 (C , C-3),
39.35, 139.39, 139.7 (all C , C-6, -11, -14), 141.3 (C , C-4), 179.8
, COOH) ppm. IR (KBr): ν˜ = 3052 (m), 3002 (m), 2927 (vs),
854 (s), 1707 (vs), 1699 (vs), 1434 (m), 1413 (m), 1288 (m), 1249
3
): δ = 24.5 (CH
2 2
, C-19), 29.8 (CH ,
–
1
m), 869 (m), 776 (s), 740 (m), 715 (m) cm . UV (acetonitrile):
max (log ε) = 192 (4.42), 212 (4.43), 240 (sh, 4.11) 282 (3.72) nm.
2
, C-1, -2, -18, -20), 35.0, 35.3
(
1
1
2
+
MS (EI, 70 eV): m/z (%) = 274 (39) [M] , 260 (18), 246 (12), 232
q
(
(
12), 231 (69), 224 (27), 192 (16), 155 (13), 125 (16), 124 (29), 107
73), 104 (100), 91 (67). C21 22 (274.4): calcd. C 91.91, H 8.09;
q
q
H
(C
q
found C 91.97, H 8.25.
NBS Bromination of 14: To a solution of 14 (158 mg, 0.58 mmol) in
4.67), 210 (4.17), 226 (4.23), 228 (4.23), 244 (3.55) nm. MS (EI, anhydrous carbon tetrachloride (30 mL) was added NBS (102 mg,
2
–1
(
(
m), 939 (m), 716 (m) cm . UV (acetonitrile): λmax (log ε) = 194
+
70 eV): m/z (%) = 308 (87) [M] , 204 (37), 203 (81), 145 (100), 144
0.58 mmol) and AIBN (20 mg), and the mixture was heated to re-
flux for 3 h. After cooling to room temperature, the succinimide
was removed by filtration and washed carefully with carbon tetra-
chloride. The solvent of the combined organic phase was removed
in vacuo and the remainder purified by thick-layer chromatography
on silica gel (dichloromethane) to yield 70 mg (34%) of 15 as a
(40), 129 (23), 118 (27), 114 (20), 105 (31), 104 (52), 91 (17).
2,3-(4,5-[2.2]Paracyclophano)cyclohept-2-en-1-one (13): To freshly
distilled methanesulfonic acid (30 mL) was added phosphorus
pentoxide (4.5 g) under an atmosphere of nitrogen. After stirring
the mixture for 2 h at room temperature, 12 (1.0 g, 3.2 mmol) was
added slowly in portions. The mixture quickly turned violet-black,
and after stirring for 5 h at room temperature, the cyclization was
terminated by the addition of ice water, followed by 15% aqueous
sodium hydroxide solution. The hydrolysate was carefully extracted
with dichloromethane, and the combined organic phase was dried
with magnesium sulfate. The solid obtained after solvent removal
by rotary evaporation was purified by silica gel column chromatog-
raphy (dichloromethane) to yield 0.52 g (56%) of 13 as colorless
8
1
+
colorless oil. MS (EI, 70 eV): m/z (%) = 354 (16) [M, Br] , 352
7
9
+
(16) [M, Br] , 274 (42), 250 (21), 248 (23), 170 (100), 169 (36),
155 (45), 154 (21), 153 (22), 142 (18), 141 (18), 128 (15), 115 (13),
104 (25).
1,2-(4,5-[2.2]Paracyclophano)cyclohepta-1,3,5-triene (16) and 3,4-
(
4,5-[2.2]Paracyclophano)cyclohepta-1,3,5-triene (17): To a solution
of 15 (433 mg, 1.2 mmol) in anhydrous DMSO (15 mL) was added
potassium tert-butoxide (202 mg, 1.8 mmol). The reaction mixture
quickly turned black, and it was stirred for 1 d at room tempera-
ture. For workup, water was added (15 mL), and the product mix-
ture was extracted thoroughly with ether. The residue obtained af-
ter solvent removal was purified by thick-layer chromatography on
[12]
cubes (ethanol/dichloromethane). M.p. 120 °C (ref. 122–124 °C).
As no spectroscopic data are given in ref.[ we report them here
12]
in full. The use of undistilled methanesulfonic acid results in yield
1
reduction of about 15%. H NMR (400.1 MHz, CDCl
3
): δ = 1.27–
silica gel (dichloromethane/petroleum ether, 40:60) to afford
1
7
.38 (m, 1 H) and 1.53–1.65 (m, 2 H) and 1.68–1.78 (m, 1 H, 6-,
-H), 2.32–3.38 (m, 12 H, 1-, 2-, 5-, 8-, 12-, 13-H), 6.43, 6.59 (both
1
2
00 mg (60%) of a mixture of 16 and 17 in a 1:3 ratio ( H NMR
spectroscopic analysis). This mixture can be used for the prepara-
tion of the tropylium cations (see below). The selective preparation
of 17 is described below, and pure 16 was obtained as follows:
d, J = 7.8 Hz, 1 H each, 10-, 11-H), 6.40, 6.49, 6.54, 6.70 (each m, 1
H each, 15-, 16-, 18-, 19-H) ppm. 13C NMR (100.6 MHz, CDCl
): δ
20.7 (CH , C-6), 24.9 (CH , C-7), 27.3 (CH , C-8), 32.8, 34.0,
4.2, 35.3 (all CH , C-1, -2, -12, -13), 42.1 (CH , C-5), 128.9, 130.1,
32.1, 132.6, 133.3 (all CH, C-11, -15, -16, -18, -19), 137.2 (CH, C-
0), 136.6, 137.3, 137.4, 139.0, 139.1, 139.8 (all C , C-3, -3a, -8a,
3
=
2
2
2
3
1
1
2
2
To a solution of 14 (768 mg, 2.80 mmol) in anhydrous carbon tetra-
chloride (80 mL) was added NBS (520 mg, 2.92 mmol) and AIBN
(15 mg). The mixture was heated under reflux for 6 h and worked
q
-9, -14, -17), 208.3 (C
q
, C-4) ppm. IR (KBr): ν˜ = 2967 (w), 2929 up as described above for the bromination of 14. Aside from
(
9
2
vs), 2859 (s), 1668 (vs), 1556 (m), 1440 (m), 1268 (m), 1257 (m), 157 mg (20%) of recovered starting material 14, 293 mg (38%) of
–1
1
55 (w), 719 (m) cm . UV (acetonitrile): λmax (log ε) = 192 (4.52), 16 was isolated as colorless needles. M.p. 130 °C. H NMR
14 (4.33), 280 (3.48), 326 nm (3.30). MS (EI, 70 eV): m/z (%) = (400.1 MHz, CDCl ): δ = 2.28–2.33 (m, 1 H, 4-H), 2.80–3.19 (m,
3
Eur. J. Org. Chem. 2008, 2948–2959
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2955

S. M. Ramm, H. Hopf, P. G. Jones, P. Bubenitschek, B. Ahrens, L. Ernst
-H) and 3.34–3.55 (m, 2 H, 1-, 2-, 4-, 12-, 13-H), 5.63–5.69 and and dried (magnesium sulfate), and the solvent was removed in
FULL PAPER
7
6
1
.02–5.97 (both m, 1 H each, 5-, 6-H), 6.32–6.60 (m, 7 H, 7-, 10-,
vacuo. The oily raw product was purified by silica gel plate
chromatography (dichloromethane/pentane, 7:3) to provide 285 mg
1
3
1-, 15-, 16-, 18-, 19-H), 7.06 (d, J = 11.6 Hz, 1 H, 8-H) ppm.
): δ = 30.7 (CH , C-4), 33.1, 33.4, 34.2,
, C-1, -2, -12-, -13), 125.7, 126.9, 128.0, 128.7, 130.1,
30.9, 131.2, 132.5, 132.8, 134.8 (all CH, C-5, -6, -7, -8, -10, -11,
C
NMR (100.6 MHz, CDCl
3
2
(65%) of 22 and 70 mg (16%) of 23 as colorless solids. Data for
1
3
1
4.6 (all CH
2
22: M.p. 125 °C. H NMR (400.1 MHz, CDCl
3
): δ = 1.74–1.83 (m,
1 H), 2.16–2.27 (m, 2 H) and 2.36 (m, 1 H, 5-, 6-H), 2.72 (d, J =
6.9 Hz, 1 H, OH), 2.70–2.78, 2.88–3.03, 3.08–3.21, 3.25–3.44 (all
-
q
15, -16, -18, -19), 135.5, 136.4, 136.9, 138.4, 138.8 (2 C) (all C ,
C-3, -3a, -8a, -9, -14, -17) ppm. IR (KBr): ν˜ = 3028 (m), 2968 (m), m, 1 H each, 1-, 2-, 12-, 13-H), 4.98–5.03 (m, 1 H, 4-H), 5.94–6.00
941 (s), 2921 (s), 1585 (w), 1498 (m), 1461 (m), 1437 (m), 1410 (m, 1 H, 7-H), 6.29–6.62 (m, 6 H) and 6.70–6.73 (m, 1 H, 8-, 10-,
2
–
1
13
(
(
2
[
m), 934 (m), 871 (m), 798 (vs), 786 (vs), 771 (s), 718 (vs) cm . UV 11-, 15-, 16-, 18-, 19-H) ppm. C NMR (100.6 MHz, CDCl
acetonitrile): λmax (log ε) = 194 (4.58), 202 (sh, 4.52), 224 (sh, 4.19), 25.1 (CH , C-6), 32.5, 32.8, 34.3, 35.3, 35.7 (all CH , C-1, -2, -5,
54 (3.83), 298 nm (3.76). MS (EI, 70 eV): m/z (%) = 272 (34) -12, -13), 68.1 (d, C-4), 126.9, 129.8, 131.7, 132.1, 132.8, 132.9,
M] , 170 (32), 168 (100), 167 (44), 165 (19), 155 (19), 153 (48), 152 133.0, 134.1 (all CH, C-7, -8, -10, -11, -15, -16, -18, -19), 133.5 (C
30). C21 20 (272.4): calcd. C 92.59, H 7.41; found C 92.62, C-3), 138.3, 138.8, 138.9, 139.1, 140.1 (all C , C-3a, -8a, -9, -14,
H 7.40. -17) ppm. IR (KBr): ν˜ = 3557 (s), 3020 (w), 2939 (s), 2925 (vs),
896 (s), 2850 (m), 1439 (m), 1414 (m), 1390 (m), 1176 (m), 1046
3
): δ =
2
2
+
q
,
(
H
q
2
(
[
2]Paracyclo[2](1,4)naphthalinophane (20): A solution of 15 (see also
structure 18, 127 mg, 0.36 mmol) and potassium tert-butoxide
561 mg, 5 mmol) in anhydrous toluene (10 mL) was heated to
0 °C for 5 h. After cooling to room temperature, water (20 mL)
–1
vs), 831 (m), 794 (m), 715 (m) cm . UV (acetonitrile): λmax (log
ε) = 192 (4.37), 214 (4.43), 238 (sh, 4.15), 284 (3.80), 290 (sh, 3.72),
10 (sh, 3.13), 324 (sh, 2.86) nm. MS (EI, 70 eV): m/z (%) = 290
16) [M] , 185 (12), 168 (34), 167 (24), 155 (14), 153 (16), 129 (12),
8 (12), 86 (64), 84 (95), 51 (34), 49 (100). C21 22O (290.4): calcd.
C 86.85, H 7.64; found C 86.92, H 7.75. Data for 23: M.p. 93 °C.
3
): δ = 2.04–2.50 (m, 4 H, 5-, 6-H),
.77–3.16 (m, 7 H) and 3.43–3.55 (m, 2 H, 1-, 2-, 12-, 13-H and
OH), 5.01 (br. d, 1 H, 4-H), 6.02 (m, 1 H, 7-H), 6.33–6.56 (m, 7
H, 8-, 10-, 11-, 15-, 16-, 18-, 19-H) ppm. C NMR (100.6 MHz,
): δ = 24.3 (CH , C-6), 30.1, 33.6, 34.4, 34.85, 34.93 (all CH ,
3 2 2
C-1, -2, -5, -12, -13), 69.3 (d, C-4), 125.6, 129.7, 129.9, 132.7, 132.8,
33.2, 133.4, 134.9 (all CH, C-7, -8, -10, -11, -15, -16, -18, -19),
34.9 (C , C-3), 138.7, 138.8, 139.2, 140.1, 141.1 (all C , C-3a,
8a, -9, -14, -17) ppm. IR (KBr): ν˜ = 3386 (s, br.), 3032 (w), 2926
vs), 2875 (m), 2855 (s), 1718 (m), 1701 (m), 1457 (m), 1411 (m),
248 (m), 1048 (s), 1028 (m), 794 (m) cm . UV (acetonitrile): λmax
log ε) = 194 (4.49), 214 (sh, 4.31), 226 (sh, 4.22), 248 (sh, 3.82),
86 (3.57), 314 (sh, 2.87) nm. MS (EI, 70 eV): m/z (%) = 290 (20)
M] , 185 (12), 169 (32), 167 (20), 155 (13), 153 (16), 88 (12), 86
(
8
3
(
8
+
was added, and the reaction mixture was carefully extracted with
diethyl ether. The combined organic phase was washed with water
and dried (magnesium sulfate), and the solvent was removed by
rotary evaporation. Purification by thick-layer chromatography (sil-
ica gel, trichloromethane) furnished 20 mg (22%) of 20, which was
identical in all analytic and spectroscopic data with those in the
H
1
H NMR (400.1 MHz, CDCl
2
13
[
24]
literature. When the experiment was repeated with a mixture of
6 and 17, hydrocarbon 20 could be detected, in traces at best, by
NMR spectroscopic analysis.
CDCl
1
1
1
-
(
1
(
2
[
(
2
,3-(4,5-[2.2]Paracyclophano)cyclohepta-2,4-dien-1-one (21): To a
solution of 13 (2.00 g, 6.9 mmol) in anhydrous carbon tetrachloride
150 mL) was added NBS (1.35 g, 7.6 mmol) and AIBN (20 mg)
q
q
(
–
1
under an atmosphere of nitrogen. The yellow solution was heated
to reflux for 4 h, and after cooling to room temperature, the pre-
cipitated succinimide was removed by filtration and washed with
carbon tetrachloride. The solvent of the combined organic phase
was removed by rotary evaporation, and the remaining solid resi-
due was purified by silica gel chromatography (dichloromethane/
+
64), 84 (94), 51 (34), 49 (100).
Dehydration of 22 to 17: To a solution of 22 (250 mg, 0.86 mmol)
in dichloromethane (20 mL) was added hydrochloric acid (6 ,
0 mL), and the mixture was stirred for 30 h at room temperature.
The two phases of the green solution were separated. The aqueous
phase was extracted with dichloromethane, and the combined or-
ganic phase was dried (magnesium sulfate). After solvent removal
by rotary evaporation, the remaining solid was purified by silica
gel column chromatography (dichloromethane) to afford 215 mg
92%) of 17 as colorless needles (ethanol/dichloromethane). M.p.
81–183 °C. H NMR (400.1 MHz, CDCl
.6, 1.9 Hz, 1 H, 6-H), 2.59 (dt, J = 13.4, 7.9 Hz, 1 H, 6-H), 2.82–
2.90, 2.99–3.09, 3.14–3.21, 3.50–3.57 (all m, 2 H each, 1-, 2-, 12-,
3-H), 5.90 (ddd, J = 10.0, 8.0, 5.6 Hz, 2 H, 5-, 7-H), 6.32–6.33
(m, 2 H, 18-, 19-H), 6.47 (s, 2 H, 10-, 11-H), 6.53–6.56 (m, 4 H,
-, 8-, 15-, 16-H) ppm. C NMR (100.6 MHz, CDCl
CH , 1 C, C-6), 33.0, 33.8 (both CH , C-1, -2, -12, -13), 126.7
CH, C-4, -8), 127.8 (CH, C-5, -7), 129.4 (CH, C-18, -19), 131.3
CH, C-10, -11), 132.9, (CH, C-15, -16), 136.9, 138.2, 138.6 (all C
pentane, 1:4) to afford 1.47 g (74%) of 21 as colorless needles. M.p.
1
1
65 °C. H NMR (400.1 MHz, CDCl
3
): δ = 2.19–2.46 (m, 2 H, 6-
1
H), 2.65–3.45 (m, 10 H, 1-, 2-, 5-, 12-, 13-H), 6.06 (dt, J = 11.4,
.8 Hz, 1 H, 7-H), 6.41–6.72 (m, 7 H, 8-, 10-, 11-, 15-, 16-, 18-, 19-
5
13
H) ppm. C NMR (100.6 MHz, CDCl
3
1
3
): δ = 24.9 (CH
, C-1, -2, -12, -13), 46.5 (CH
27.5, 130.0, 130.5, 130.8, 131.9, 133.0, 133.8, 136.6 (all CH, C-7,
2
, C-6),
2.8, 33.9, 34.2, 35.4 (all CH
2
2
, C-5),
-8, -10, -11, -15, -16, -18, -19), 133.4, 137.4, 138.2, 138.8, 139.1,
(
1
5
1
39.8 (all C , C-3, -3a, -8a, -9, -14, -17), 204.8 (s, C-4) ppm. IR
q
1
3
): δ = 1.55 (dtt, J = 13.4,
(KBr): ν˜ = 3033 (w), 2955 (m), 2935 (s), 2924 (s), 2899 (m), 2855
(m), 1762 (w), 1674 (vs), 1457 (m), 1267 (s), 1255 (s), 1103 (m),
–1
1
012 (m), 941 (m), 891 (m), 778 (m) cm . UV (acetonitrile): λmax
1
(log ε) = 192 (4.49), 208 (4.47), 246 (4.03), 262 (sh, 3.93), 294 (sh,
+
3
(
(
.35) nm. MS (EI, 70 eV): m/z (%) = 288 (36) [M] , 185 (26), 184
56), 183 (100), 171 (18), 169 (34), 155 (25), 141 (28), 128 (20), 115
20), 104 (22), 69 (16). HRMS: calcd. for C21 20O 288.15142;
1
3
4
3
): δ = 25.8
(
(
(
2
2
H
found 288.151.
q
,
2
,3-(4,5-[2.2]Paracyclophano-endo-1-hydroxycyclohepta-2,4-diene C-3, -3a, -8a, -9, -14, -17) ppm. IR (KBr): ν˜ = 3032 (vs), 3006 (s),
(
22) and 2,3-(4,5-[2.2]Paracyclophano-exo-1-hydroxycyclohepta-2,4- 2925 (vs), 2900 (vs), 2853 (s), 1499 (m), 1441 (s), 1413 (m), 932 (m),
–
1
diene (23): To a solution of 21 (431 mg, 1.5 mmol) in 2-propanol
868 (m), 796 (vs), 778 (vs), 719 (m) cm . UV (acetonitrile): λmax
(log ε) = 192 (4.47), 208 (sh, 4.42), 216 (4.45), 238 (4.23), 266 (4.05),
286 (sh, 3.64), 320 (sh, 2.95) nm. MS (EI, 70 eV): m/z (%) = 272
(80 mL) was added sodium borohydride (756 mg, 20.0 mmol), and
the mixture was heated under reflux for 6 h. After cooling to 0 °C,
water (130 mL) and hydrochloric acid (6 , 1 mL) were added to
decompose excess borohydride. The solution was extracted with
ether (3ϫ), the combined organic phase was washed with water
+
(56) [M] , 169 (16), 168 (100), 167 (80), 165 (24), 153 (55), 152 (38),
115 (10). C21
7.46.
H20 (272.4): calcd. C 92.59, H 7.41; found C 92.67, H
2956
www.eurjoc.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 2948–2959

Annulation of Seven-Membered Rings to [2.2]Paracyclophane
–
1
Reduction of 21 Followed by Dehydration to 14, 17, and 25: To a
suspension of lithium aluminum hydride (584 mg, 15.0 mmol) in
THF (50 mL) was added a solution of 21 (1.11 g, 3.85 mmol) in
anhydrous THF (80 mL) under an atmosphere of nitrogen at room
temperature. After heating to reflux for 5.5 h, the reaction mixture
was cooled to 0 °C and hydrolyzed with water (20 mL), followed
by 6  hydrochloric acid until acidic. The mixture was extracted
carefully with ether, and the combined organic phase was washed
with water and dried (magnesium sulfate). After solvent removal,
the raw reaction mixture was separated by thick-layer plate
chromatography (silica gel; dichloromethane/pentane, 1:4) to pro-
vide three fractions: 14 (560 mg, 53%), 17 (150 mg, 14%), and ether
(s), 1122 (vs), 1085 (vs), 973 (m), 838 (m), 765 (m) cm . UV (aceto-
nitrile): λmax (log ε) = 192 (4.53), 212 (sh, 4.38), 230 (4.31), 284
(4.20), 352 (3.90), 396 (sh, 3.55), 464 (sh, 3.06) nm. UV (dichloro-
methane): λmax (log ε) = 232 (4.32), 288 (4.24), 358 (3.92), 444 (sh,
3.32), 488 (sh, 3.09) nm. MS (FAB+, NBA): m/z (%) = 987 (1)
[(5)
(FAB–, NBA): m/z (%) = 1160 (1) [(5)
(BF ], 445 (22) [5(BF ], 87 (100) [BF ].
3
(BF
4
)
2
], 629 (5) [(5)
2
BF
4
], 271 (100) [5], 167 (30) [5 – 104]. MS
3
(BF ], 802 (3) [(5)
4
)
4
2
4
)
3
4
)
2
4
(
4,5-[2.2]Paracyclophano)tropylium Perchlorate (26b): Tritylium
perchlorate was prepared from triphenylmethanol (104 mg,
.4 mmol) and perchloric acid (16% aqueous solution, 68 mg,
0.4 mmol). After the addition of dichloromethane (8 mL, orange
solution) either 16 or 17 or a mixture of these two components
0
5 (190 mg, 17%) as colorless needles. M.p. 154 °C. 1H NMR
400.1 MHz, CDCl ): δ = 0.97–1.10 (m, 1 H, 6-H), 1.96–2.05 (m,
2
(
3
(
109 mg, 0.4 mmol) in dichloromethane (8 mL) was added, and the
2
1
1
H, 5-, 7-H), 2.21–2.38 (m, 3 H, 5-, 6-, 7-H), 2.85–3.10 (m, 8 H,
-, 2-, 12-, 13-H), 4.90 (d, J = 3.0 Hz, 2 H, 4-, 8-H), 6.35 (s, 2 H,
0-, 11-H), 6.52–6.53 and 6.59–6.60 (m, 2 H each, 15-, 16-, 18-, 19-
color of the reaction mixture turned to deep red. Out of the solu-
tion, salt 26b (114 mg, 77%) crystallized as dark-red prisms. M.p.
185 °C (decomp.). Whether the pure benzotropylidenes or their
mixture is employed has no influence on the yield of the process.
H and C NMR: see main part. IR (KBr): ν˜ = 3028 (w), 2930
w), 1588 (w), 1567 (w), 1374 (m), 1143 (vs), 1088 (vs), 752 (w),
13
H) ppm. C NMR (100.6 MHz, CDCl
3
): δ = 16.5 (CH
, C-2, -12), 34.6 (CH , C-1, -13),
8.2 (CH, C-4, -8), 131.2, 132.7, 133.8 (all CH, C-10, -11, -15,
, C-3, -3a, -8a, -9, -14, -17)
ppm. IR (KBr): ν˜ = 3010 (w), 2941 (vs), 2913 (m), 2894 (m), 1433
w), 1060 (m), 1022 (s), 934 (m), 863 (s), 796 (m), 777 (m), 716 (m)
2
, 1 C, C-
6), 29.0 (CH
2
, C-5, -7), 32.1 (CH
2
2
1
13
7
(
6
2
-16, -18, -19), 130.7, 139.0, 143.6 (all C
q
–
1
36 (s), 627 (s) cm . UV (acetonitrile): λmax (log ε) = 192 (4.21),
06 (sh, 4.11), 232 (4.03), 284 (3.95), 352 (3.65), 390 (sh, 3.35), 448
(
–1
(sh, 2.82) nm. UV (dichloromethane): λmax (log ε) = 234 (4.14), 288
4.07), 358 (3.76), 464 (sh, 2.98), 480 (sh, 2.88), 490 (2.84) nm. MS
(FAB+, NBA): m/z (%) = 641 (1) [(5) ClO ], 271 (100) [5], 167 (40)
5 – 104]. MS (FAB–, NBA): m/z (%) = 837 (1) [(5) (ClO ], 471
4) [5(ClO ], 469 (7) [5(ClO ], 101 (34) [ClO ], 99 (100) [ClO ].
cm . UV (acetonitrile): λmax (log ε) = 196 (4.62), 212 (sh, 4.23),228
4.26), 254 (sh, 3.38) nm. MS (EI, 70 eV): m/z (%) = 290 (70)
(
(
+
2
4
[
(
8
M] , 187 (20), 186 (100), 171 (16), 158 (26), 143 (24), 128 (16), 115
16), 104 (45). C21 20O (290.4): calcd. C 86.85, H 7.64; found C
6.77, H 7.67.
[
2
4 3
)
H
(
4
)
2
4
)
2
4
4
6
Addition of [D ]Acetone and TCNE to 26a: In an NMR tube, 26a
Diels–Alder Addition of TCNE to 17 and 16: To a solution of 17
40 mg, 0.15 mmol) in CDCl (0.7 mL) in an NMR tube at room
(
60 mg, 0.17 mmol) and TCNE (22 mg, 0.17 mmol) were dissolved
(
3
in [D ]acetone (1 mL), and the reaction mixture was left until the
6
temperature was added TCNE (19 mg, 0.15 mmol). The progress
1
solvent had evaporated. The remaining solid (29, 82 mg, 100%),
of the cycloaddition was monitored by H NMR spectroscopy, and
was washed with dichloromethane to afford colorless needles. M.p.
after 1 week at room temperature the cycloaddition to 28 was com-
plete. The solid isolated after solvent removal (59 mg, 100%) was
1
1
85 °C (decomp.). H NMR (400.1 MHz, [D
6
]acetone): δ = 1.73–
1.75 (m, 2 H, 5-, 7-H), 1.79–1.83 (m, 1 H, 6-H), 3.08–3.33 (m, 8
recrystallized from acetone to afford colorless needles. M.p. 165 °C
1
H, 1-, 2-, 12-, 13-H), 4.87 (m, 2 H, 4-, 8-H), 6.57 (s, 2 H, 10-, 11-
(
decomp.). H NMR (400.1 MHz, [D
6
]acetone): δ = 1.08 (dt, J =
1
3
H), 6.59, 6.96 (both m, 2 H each, 15-, 16-, 18-, 19-H) ppm.
NMR (100.6 MHz, [D ]acetone): δ = 15.0 (CH, C-5, -7), 15.5 (CH,
C, C-6), 31.3 (CH , C-2, -12), 35.7 (CH , C-1, -13), 43.6 (CH, C-
4, -8), 45.5 (C , C-23, -24), 111.9, 113.2 (both C , CϵN), 128.7
, C-3a, -8a), 132.7, 133.8, 136.6 (all CH, C-10, -11, -15, -16,
18, -19), 137.4, 140.2 (both C , C-3, -9, -14, -17), 206.1 (C , C-
1) ppm; signals of deuterated carbon atoms C-20 and C-22 not
observed. IR (KBr): ν˜ = 3111 (w), 3030 (w), 2957 (m), 2932 (m),
C
7
7
4
2
.8, 5.6 Hz, 1 H, 6-H), 1.22 (m, 1 H, 6-H), 1.86–1.91 (m, 2 H, 5-,
-H), 3.07–3.20, 3.25–3.32 (both m, 4 H each, 1-, 2-, 12-, 13-H),
6
1
2
2
.84 (m, 2 H, 4-, 8-H), 6.56 (s, 2 H, 10-, 11-H), 6.38, 6.96 (both m,
H each, 15-, 16-, 18-, 19-H) ppm. 13C NMR (100.6 MHz,
q
q
(
C
q
[
D
6
]acetone): δ = 7.2 (CH
CH , C-1, -2, -12, -13), 44.0 (CH, C-4, -8), 45.7 (C
12.0, 113.3 (both C , CϵN), 128.2 (both C , C-3a, -8a), 132.1,
34.1, 136.8 (all CH, C-10, -11, -15, -16, -18, -19), 137.5, 140.3
, C-3, -9, -14, -17) ppm. IR (KBr): ν˜ = 3036 (w), 2994 (m),
956 (vs), 2931 (vs), 2890 (m), 2854 (m), 2249 (w), 1586 (m), 1503
2
, C-6), 8.7 (CH, C-5, -7), 31.2, 35.6 (both
-
q
q
2
q
, C-20, -21),
2
1
1
(
2
(
(
q
q
–
1
2
249 (w), 1707 (vs), 1262 (m), 1256 (m), 798 (w), 740 (w) cm . UV
both C
q
(
acetonitrile): λmax (log ε) = 196 (4.59), 214 (sh, 4.25), 228 (4.17),
+
–
1
250 (sh, 3.81) nm. MS (EI, 70 eV): m/z (%) = 461 (9) [M] , 333
m), 1054 (m), 896 (s), 879 (m), 821 (s), 798 (s), 755 (m) cm . UV
acetonitrile): λmax (log ε) = 196 (4.63), 218 (sh, 4.23), 228 (4.21),
(
(
21), 270 (11), 229 (53), 183 (30), 167 (53), 166 (23), 165 (32), 152
19 5 4
16), 128 (16), 104 (100), 76 (14). HRMS: calcd. for C30H D N O
2
44 (sh, 3.93), 270 (3.18) nm. MS (EI, 70 eV): m/z (%) = 400 (15)
+
461.22640; found 461.226.
[
M] , 273 (18), 272 (68), 168 (100), 167 (70), 165 (36), 128 (30), 153
60), 15 (48), 128 (30), 104 (55), 84 (25), 76 (22). HRMS: calcd. for
400.1688; found 400.168.
(
X-ray Structure Determinations: Crystal data and refinement details
are presented in Tables 2 and 3. Crystals were mounted in inert
oil on glass fibers and transferred to the cold gas stream of the
diffractometer (13, 26b: Siemens R3; 17, 22, 28: Siemens P4; 25,
27 20 4
C H N
Under nearly the same conditions (dichloromethane, 40 °C) 16 did
not react with TCNE.
29, Stoe STADI-4, with appropriate low-temperature attachments).
(
4,5-[2.2]Paracyclophano)tropylium Tetrafluoroborate (26a): To a
solution of either pure 16 or 17 or a mixture of both hydrocarbons
50 mg, 0.18 mmol) in anhydrous dichloromethane (5 mL) was
Measurements were performed with monochromated Mo-K radia-
α
2
tion. The structures were refined anisotropically against F (pro-
gram SHELXL-97, G. M. Sheldrick, University of Göttingen). Hy-
drogen atoms were included with rigid methyl groups or a riding
model. For 22, the OH hydrogen was poorly resolved; the group
was refined as a rigid group allowed to rotate. In the absence of
significant anomalous dispersion, Friedel opposite reflections were
merged and the Flack parameter is thus indeterminate. To improve
(
added tritylium tetrafluoroborate (61 mg, 0.18 mmol) in dichloro-
methane (5 mL). The reaction mixture turned deep red immedi-
ately. Out of the solution, 39 mg (60%) of 26a crystallized in the
form of deep-red needles. M.p. 201 °C. H and C NMR: see main
part. IR (KBr): ν˜ = 3010 (w), 2930 (w), 1590 (w), 1374 (s), 1174
1
13
Eur. J. Org. Chem. 2008, 2948–2959
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2957

S. M. Ramm, H. Hopf, P. G. Jones, P. Bubenitschek, B. Ahrens, L. Ernst
FULL PAPER
Table 2. Details of X-ray structure analyses.
Compound
Formula
13
17
22
25
26b
C
21
H
22
O
C
21
H
20
C
21
H
22
O
C
21
H
22
O
21 4
C H19ClO
370.81
M
r
290.39
272.37
290.39
290.39
Habit
colorless block
0.8ϫ0.7ϫ0.4
monoclinic
colorless block
0.8ϫ0.7ϫ0.6
monoclinic
colorless prism
0.8ϫ0.6ϫ0.4
orthorhombic
pale-yellow prism
0.8ϫ0.4ϫ0.3
rhombohedral
red prism
0.45ϫ0.25ϫ0.2
orthorhombic
Cmc2
1
Crystal size [mm]
Crystal system
Space group
Cell constants:
a [Å]
b [Å]
c [Å]
¯
P2
1
/c
P2
1
/c
Pna2
1
R3
12.102(4)
9.570(3)
13.270(4)
90
13.3494(14)
8.1539(10)
13.1895(14)
90
13.876(2)
13.654(2)
7.9586(10)
90
28.468(4)
28.468(4)
9.889(2)
90
9.221(2)
12.243(3)
14.872(3)
90
α [°]
β [°]
91.98(3)
90
1536.0
4
1.256
0.08
624
94.057(8)
90
1432.1
4
1.263
0.07
584
90
90
1507.8
4
1.279
0.08
624
–100
55
90
120
6940
18
1.251
0.08
2808
–120
55
90
90
1678.9
4
1.467
0.25
776
–95
55
γ [°] 3
V [Å ]
Z
D
–3
x
[mgm ]
–1
µ [mm ]
F(000)
T [°C]
–95
50
–100
50
2θ
max
No. of reflections
Measured
Independent
3234
2716
0.017
199
0.127
0.042
1.01
4850
2511
0.016
191
0.105
0.039
1.05
2827
1856
0.018
201
0.106
0.041
1.01
3904
3539
0.031
199
0.143
0.059
1.07
1966
1405
0.035
124
0.145
0.046
1.00
R
int
Parameters
2
wR (F , all refl.)
R [F, Ͼ4σ(F)]
S
–3
max. ∆ρ [eÅ ]
0.31
0.24
0.25
0.24
0.20
Table 3. Details of X-ray structure analyses.
ioacetone solvate, one acetone methyl group (at C91) was poorly
resolved. Hydrogen atoms at C20 and C22 were assumed to have
been replaced by deuterium. CCDC-663211 (for 13), -663248 (for
Compound
Formula
28
3 6
29·C D O
C
27
H
20
N
4
33 19 11 4 2
C H D N O
17), -663246 (for 22), -663247 (for 25), -663208 (for 26b), -663212
M
r
400.47
530.61
(for 28), and -663209 (for 29) contain the supplementary crystallo-
Habit
colorless tablet
0.8ϫ0.35ϫ0.2
monoclinic
colorless tablet
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Crystal size [mm]
Crystal system
Space group
Cell constants:
a [Å]
0.55ϫ0.25ϫ0.15
monoclinic
P2 /c
1
P2
1
/c
7.8407(8)
13.972(2)
17.963(2)
90
93.228(8)
90
10.685(3)
11.769(3)
20.951(5)
90
93.25(3)
90
[
[
1] H. Hopf, J. Kubitschke, P. G. Jones, L. Ernst, Eur. J. Org.
Chem. 2008, 548–554.
b [Å]
c [Å]
2] Reviews: a) B. H. Smith, Bridged Aromatic Compounds, Aca-
demic Press, New York, 1964; b) P. M. Keehn, S. M. Rosenfeld
(Eds.), Cyclophanes, Academic Press, 1983, vol. I and II; c) F.
Diederich, Cyclophanes, The Royal Society of Chemistry, Cam-
bridge, 1991; d) H. Takemura (Ed.), Cyclophane Chemistry for
α [°]
β [°]
γ [°] 3
V [Å ]
1964.8(4)
4
2630.4
4
Z
–3
st
D
x
[mgm ]
1.354
0.08
1.327
0.08
the 21 Century, Research Signpost, Trivandrum, 2002; e) R.
–1
µ [mm ]
F(000)
Gleiter, H. Hopf (Eds.), Modern Cyclophane Chemistry, Wiley-
VCH, Weinheim, 2004.
3] For a review, see: S. Ito, Y. Fujise, Y. Fukazawa in Cyclophanes
840
1088
T [°C]
–100
–120
[
2θ
max
50
50
(
Eds.: P. M. Keehn, S. M. Rosenfeld), Academic Press, New
No. of reflections
York, 1983, vol. II, ch. 8, pp. 485–520.
Measured
4135
3447
0.015
280
0.098
0.039
0.97
7730
4634
0.058
355
0.149
0.062
1.03
[4] a) R. Gleiter, M. Merger, Synthesis 1995, 969–972; b) R. Glei-
ter, M. Merger, A. Altreuther, H. Irngartinger, J. Org. Chem.
Independent
R
int
1
995, 60, 4692–4696.
5] S. Bradamante, A. Marchesini, G. Pagani, Tetrahedron Lett.
971, 12, 4621–4622.
Parameters
[
[
2
wR (F , all refl.)
1
R [F, Ͼ4σ(F)]
6] a) T. Hiyama, Y. Ozaki, H. Nozaki, Chem. Lett. 1972, 963–
964; b) T. Hiyama, Y. Ozaki, H. Nozaki, Tetrahedron 1974, 30,
S
–3
max. ∆ρ [eÅ ]
0.18
0.30
2
661–2668; c) R. Noyori, S. Makino, H. Takaya, Tetrahedron
Lett. 1973, 14, 1745–1746; d) S. Hirano, T. Hiyama, H. Nozaki,
Tetrahedron Lett. 1973, 14, 1331–1332; e) S. Hirano, T. Hi-
yama, H. Nozaki, Tetrahedron 1976, 32, 2381–2383; f) Y. Fuj-
ise, T. Shiokawa, Y. Mazaki, Y. Fukazawa, M. Fujii, S. Ito,
Tetrahedron Lett. 1982, 23, 1601–1604.
stability of refinement, restraints (SIMU; DELU) to displacement
parameters were employed (applies also to 29). For 26b, the Flack
parameter refined to –0.1(2). For 29, which crystallized as a deuter-
2958
www.eurjoc.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 2948–2959

Annulation of Seven-Membered Rings to [2.2]Paracyclophane
[
7] a) H. Horita, T. Otsubo, S. Misumi, Chem. Lett. 1977, 1309–
[16] Compare the preparation of benzosuberenone from benzosu-
berone by a similar approach: A. B. Smith III, J. L. Wood, T. P.
Keenan, N. Liverton, M. Visnick, J. Org. Chem. 1994, 59,
6652–6666.
1
8
312; b) H. Horita, T. Otsubo, S. Misumi, Chem. Lett. 1978,
07–810; c) H. Horita, T. Otsubo, Y. Sakata, S. Misumi, Tetra-
hedron Lett. 1976, 17, 3899–3902; d) A. W. Hanson, Acta Crys-
tallogr., Sect. B 1977, 33, 2003–2007; e) J. G. O’Connor, P. M.
Keehn, Tetrahedron Lett. 1977, 18, 3711–3714; f) J. G.
O’Connor, P. M. Keehn, J. Am. Chem. Soc. 1976, 98, 8446–
8
2
[
17] R. F. Nystrom, W. G. Brown, J. Am. Chem. Soc. 1948, 70,
3738–3740.
[18] J. A. Pople, J. Chem. Phys. 1956, 24, 1111–1111.
450; g) N. Kato, Y. Fukazawa, S. Ito, Tetrahedron Lett. 1979,
0, 1113–1116; h) S. Ito, Pure Appl. Chem. 1982, 54, 957–974.
[
19] J. Jusélius, D. Sundholm, Phys. Chem. Chem. Phys. 1999, 1,
3429–3435.
[
8] R. Frim, F.-W. Raulfs, H. Hopf, M. Rabinovitz, Angew. Chem.
1
986, 98, 160–161; Angew. Chem. Int. Ed. Engl. 1986, 25, 174–
[20] I. D. Reingold, H. A. Trujillo, B. E. Kahr, J. Org. Chem. 1986,
51, 1627–1629.
1
75.
[
9] H. Hopf, F.-W. Raulfs, D. Schomburg, Tetrahedron 1986, 42,
[21]
a) B. Atasoy, M. Balci, Tetrahedron 1986, 42, 1461–1468; b) W.
Adam, M. Balci, Z. Ceylan, R. F. Hintze, Chem. Ber. 1991,
1655–1663.
[
10] Similar ideas have been discussed by Keehn in his classical pa-
pers on the preparation of tropyliophanes, but apparently such
a novel organic salt has never been prepared.[7f]
124, 383–386; c) J. Letich, G. Sprintschnik, Chem. Ber. 1986,
119, 1640–1660; d) I. Heise, J. Letich, Chem. Ber. 1985, 118,
332–339.
[
[
11] H. Hopf, F. W. Raulfs, Isr. J. Chem. 1985, 25, 210–216.
[22] a) Review: M. L. H. Green, D. K. P. Ng, Chem. Rev. 1995, 95,
12] M. J. Nugent, T. L. Vigo, J. Am. Chem. Soc. 1969, 91, 5483–
4
39–473; more recent literature: b) M. Tamm, A. Kunst, T.
5486.
Bannenberg, E. Herdtweck, R. Schmid, Organometallics 2005,
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Received: February 12, 2008
Published Online: April 23, 2008
786–787.
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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