Syntheses, X-ray crystal structures and reactivity of fluorenylidene- and dibenzosuberenylidene-allenes: Convenient precursors to dispirotetracenes, di-indenotetracenes and 2-phenyl-11bH-dibenz[cd,h]azulene

Article abstract of DOI:10.1039/c004868b

3,3-(Biphenyl-2,2′-diyl)-1-α,α,α-trifluoro-p-tolyl- allene, 9, sequentially forms head-to-tail, 12, cis-tail-to-tail, 13, and trans tail-to-tail, 14, 1,2-dialkylidene-cyclobutane dimers, each of which has been characterised by X-ray crystallography. Thermolysis at 180°C yields the dispirotetracene, 15, and di-indenotetracene, 16; the latter compound forms an air-stable Diels-Alder adduct, 17, with N-methylmaleimide. In contrast, the dibenzo[a,d]cycloheptenylidene-allenes, (C₁₄H₁₀)CCC(Br)Ph, 20a, and (C₁₄H₁₀)CCC(H)Ph, 21a, do not dimerise under relatively mild conditions. However, protonation of the bromo-allene, 20a, and subsequent addition of hydride, provide a facile entry to the difficultly accessible bowl-shaped dibenz[cd,h]azulene framework, as in 30, that had not previously been structurally characterised. Among others, the X-ray crystal structures of 12, 13, 14, 17, 20a, 21a and 30 are reported.

Full text of DOI:10.1039/c004868b

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PAPER
www.rsc.org/obc | Organic & Biomolecular Chemistry
Syntheses, X-ray crystal structures and reactivity of fluorenylidene- and
dibenzosuberenylidene-allenes: convenient precursors to dispirotetracenes,
di-indenotetracenes and 2-phenyl-11bH-dibenz[cd,h]azulene†
Emilie V. Banide, Crystal O’Connor, Natasha Fortune, Yannick Ortin, Sandra Milosevic, Helge Mu¨ller-Bunz
and Michael J. McGlinchey*
Received 6th April 2010, Accepted 8th June 2010
First published as an Advance Article on the web 27th July 2010
DOI: 10.1039/c004868b
3,3-(Biphenyl-2,2¢-diyl)-1-a,a,a-trifluoro-p-tolyl-allene, 9, sequentially forms head-to-tail, 12,
cis-tail-to-tail, 13, and trans tail-to-tail, 14, 1,2-dialkylidene-cyclobutane dimers, each of which has been
characterised by X-ray crystallography. Thermolysis at 180 ◦C yields the dispirotetracene, 15, and
di-indenotetracene, 16; the latter compound forms an air-stable Diels–Alder adduct, 17, with
= =
N-methylmaleimide. In contrast, the dibenzo[a,d]cycloheptenylidene-allenes, (C14H10)C C C(Br)Ph,
= =
20a, and (C14H10)C C C(H)Ph, 21a, do not dimerise under relatively mild conditions. However,
protonation of the bromo-allene, 20a, and subsequent addition of hydride, provide a facile entry to the
difficultly accessible bowl-shaped dibenz[cd,h]azulene framework, as in 30, that had not previously been
structurally characterised. Among others, the X-ray crystal structures of 12, 13, 14, 17, 20a, 21a and 30
are reported.
formation of the head-to-tail dimer occurs only when the system
Introduction
is held at 65 ◦C for several hours.4 It is, of course, well-established
In continuation of our ongoing studies of the intermediates
involved in the dimerisation of fluorenylidene-allenes, 1, to yield,
ultimately, electroluminescent tetracenes, we recently reported
the syntheses, structures and rearrangements of a series of
1,2-bis(alkylidene)cyclobutanes.1 As shown in Scheme 1, two
molecules of the allene yield initially a head-to-tail dimer, 2, that
that a trimethylsilyl group stabilises an anion in the a-position,
but a cation only in a b-position.5
It is particularly tempting to invoke this situation with
the dimerisation of 3,3-(biphenyl-2,2¢-diyl)-1-chloro-1-ferrocenyl-
allene where the charge deficiency could be very readily alleviated
by donation of electron density from the iron atom, as depicted in
Scheme 3. Interestingly, however, the dimer produced in this case
is the head-to-head isomer that is very severely distorted towards
a pseudo-C2 symmetric butterfly-type geometry in which the link
isomerises sequentially to form a series of diastereomeric tail-to-
tail structures 3, 4 and 5; finally, at 180 ◦C, the dispiro-tetracene,
6, and a di-indenotetracene, 7, are formed. The latter molecules
undergo facile aerial oxidation to the corresponding peroxides, 8.2
between the two spiro-bonded fluorenyl centres is unusually long
6
The first step of this dimerisation process is thought to involve
the linking of the two central allene carbons which approach
in a mutually orthogonal fashion to form a bis-allyl diradical;3
this intermediate then undergoes ring-closure to the head-to-tail
isomer, 2, as in Scheme 2. However, one can readily envisage some
degree of charge separation whereby the fluorenide anion stabilises
the negative charge and the positive charge is delocalised onto the
aryl ring. Experimentally, the ease of allene dimerisation in these
systems is very sensitive to the nature of the substituents. Thus,
when R is a group that can stabilise a cation, e.g. phenyl, p-tolyl or
p-anisyl, head-to-tail dimer formation occurs readily, even below
˚
(C(3)–C(4) = 1.65 A).
The trans-3,4-diaryl-1,2-bis(fluorenylidene)cyclobutane tail-to-
tail dimers, 3 and 5, adopt C2-symmetric structures because of the
severe steric strain engendered by the overlapping fluorenylidene
moieties. With the aim of increasing the steric interactions between
the 1,2-bis(alkylidene) fragments, it was decided to attempt the
syntheses of the corresponding dibenzosuberenylidene systems
with their even larger wingspans. We here report the preparation,
X-ray crystallographic characterisation and reactivity of several
such allenes.
◦
0 C.2 Incorporation of an electron-withdrawing group, as in p-
Results and Discussion
= =
CF3–C6H4–C(H) C C13H8, 9, requires 24 h at room temperature
for complete dimerisation. Moreover, when R is trimethylsilyl,
Fluorenone-derived allenes
= =
As noted above, p-CF3–C6H4–C(H) C C13H8, 9, undergoes
initial head-to-tail dimerisation. As shown in Scheme 4, it is
School of Chemistry and Chemical Biology, University College Dublin,
Belfield, Dublin 4, Ireland. E-mail: michael.mcglinchey@ucd.ie; Fax: +353-
(1)-716-1178; Tel: +353-(1)-716-2880
† Electronic supplementary information (ESI) available: Synthetic details
and NMR data for molecules 20b, 20c, 21a, 21b, 23c and 24a. CCDC
reference numbers 769734 (12), 769736 (13), 769735 (14), 769744 (17),
769738 (20a), 769745 (20b), 769739 (21a), 769742 (23c), 769737 (24a),
769743 (30), 769740 (34) and 769741 (38). For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c004868b.
≡
conveniently prepared from p-CF3–C6H4–C CLi and fluorenone
to form the corresponding alkynol, 10; subsequent reaction with
BF3/Et3SiH furnishes the alkyne, 11, that is readily isomerised to
the desired allene, 9. The head-to-tail dimer, 12, and also the cis-
and trans-3,4-bis(a,a,a-trifluoro-p-tolyl)-1,2-bis(fluorenylidene)-
cyclobutanes, 13 and 14, respectively, have been characterised
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Scheme 1 Sequential formation of allene dimers leading ultimately to tetracenes.
Scheme 2 Head-to tail dimerisation of orthogonally oriented allenes.
Scheme 3 Head-to-head dimerisation of a ferrocenyl-allene.
X-ray crystallographically and their structures (including space-
fill views) appear in Fig. 1, 2 and 3 respectively. The cis and trans
isomers, 13 and 14, were also readily distinguishable by NMR;
in 13, the overlapping fluorenylidenes break the potential mirror
symmetry and make the protons at C(3) and C(4) inequivalent,
thus giving rise to a pair of 8.5 Hz doublets. In contrast, the
C2 symmetry of the trans isomer rendered them equivalent, thus
appearing as a singlet. Thermolysis at 180 ◦C yields the corre-
sponding a,a,a-trifluoro-p-tolyl-substituted dispirotetracene, 15,
as the major product (41%); di-indenotetracene, 16, is also formed
in minor quantities.7
˚
molecules: 1.611 A in the head-to-tail dimer, 12, 1.589 and 1.595
˚
A in the two independent molecules in the unit cell of the cis dimer,
13, but only 1.452 A in the trans dimer, 14.
˚
In an attempt to protect the di-indenotetracene, 16, from aerial
oxidation, it was dissolved in toluene and heated at reflux in the
presence of N-methylmaleimide for 24 h; the original blue-green
colour was discharged and, after chromatographic separation, the
Diels–Alder adduct, 17, was isolated as a colourless, air-stable
solid (Scheme 5). The structure is shown in Fig. 4 and reveals that
the N-methylmaleimide bridges the C(7b) and (C16) positions
analogous to the structure of the di-indenotetracene peroxide,
8. The N-methylmaleimide adduct adopts the endo orientation,
and one can clearly see a folding and twisting of the tetracene
The structures reveal that the length of the C(3)–C(4) linkage
is a sensitive measure of the strain in these sterically crowded
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Scheme 4 Synthesis of a,a,a-trifluoro-p-tolyl-substituted tetracenes, 15 and 16.
Fig. 1 Bird’s eye, and spacefill, view of the structure of 1-(9-fluorenylidene)-4-(a,a,a-trifluoro-p-tolyl)-2-[(a,a,a-trifluoro-p-tolyl)methylene]-
spiro[cyclobutane-3,9¢-[9H]-fluorene], 12; thermal ellipsoids are drawn at the 50% probability level.
Fig. 2 Bird’s eye, and spacefill, view of cis-1,2-di(fluorenylidene)-3,4-di(a,a,a-trifluoro-p-tolyl)cyclobutane, 13; thermal ellipsoids are at the 50%
probability level.
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Fig. 3 Bird’s eye, and spacefill, view of trans-1,2-di(fluorenylidene)-3,4-di(a,a,a-trifluoro-p-tolyl)cyclobutane, 14; thermal ellipsoids are at the 50%
probability level.
a retro-Diels–Alder to regenerate the tetracene, thus providing a
convenient method of storage.
Dibenzosuberenone-derived allenes
As noted above, the trans tail-to-tail dimers 3, 5 and 14 adopt
pseudo-C2 symmetrical conformations caused by the overlap of
the fluorenylidene rings with their large wingspans (approximately
˚
8.8 A). Moreover, the dihedral angle between the fluorenylidene
rings in these tail-to-tail dimers is highly dependent on the
identity of the substituents at C(3) and C(4). These interplanar
angles range from 41◦ in 3 (R = C6H5), to 44◦ in 14 (R =
p-CF3–C6H4), 58◦ in 5 (R = H), and 64◦ in 5 (R = p-CH3–
C6H4). With the aim of preparing analogous C2-symmetric dimers
containing dibenzosuberenylidene moieties, dibenzosuberenone,
18, was treated with a number of alkynyl-lithium reagents and
yielded the corresponding alkynols, 19a–c.
Fig. 4 X-ray crystal structure of 17, the endo Diels–Alder adduct of
N-methylmaleimide and the di-indenotetracene, 16; thermal ellipsoids are
drawn at the 50% probability level. Hydrogen atoms have been removed
for clarity.
As with the fluorenyl systems discussed above,4 the alkynols
19a (R = C6H5), 19b (R = (CH3)3Si), and 19c (R = p-CF3–
C6H4) reacted with HBr in acetic acid9 to form the corresponding
bromoallenes, 20a–c, in good yields (see Scheme 6). Subsequent
lithiation and hydrolysis with water furnished the allenes, 21a,b,
but in very poor yields. Instead, the major products are the
propargyl-allenes, 22a,b, presumably arising by attack of the
lithiated allene on unreacted bromoallene; such behaviour has also
been observed in the corresponding fluorenylidene systems.4,10,11
Moreover, the bromoallenes 20a–c were very sensitive to hydrolysis
framework◦such that the dihedral angle between the terminal rings
is now 124 , versus 116◦ in the case of the peroxide product.2 In
the anal◦ogous pentacene-maleimide adduct this dihedral angle
is 126.5 .8 In addition, the a,a,a-trifluoro-p-tolyl substituent
attached at C(8) is aligned parallel to the six-membered ring of the
adjacent fluorenyl group; this is particularly noticeable in the 1H
NMR spectrum whereby the fluorenyl-proton signals are markedly
shielded. Gratifyingly, upon heating in the solid state, 17 undergoes
Scheme 5 The Diels–Alder adduct, 17, of N-methylmaleimide and the di-indenotetracene, 16.
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Scheme 6 Routes to allenes derived from dibenzosuberenone.
at room temperature, and any trace of moisture and/or acid
brought about formation of the conjugated ketones, 23a–c.
Structures exemplifying the allenes 20 and 21 are shown in
Fig. 5 and in the ESI (Figures SI-1 and SI-2) which illustrate
clearly the non-planar character of the central cycloheptatriene
ring in each case. The conformation of the seven-membered
boat is defined by C(4a)–C(5a)–C(9a)–C(11a) [plane 1], C(4a)–
C(5)–C(5a) [plane 2] and C(9a)–C(10)–C(11)–C(11a) [plane 3].
In 20a (and 20b) the interplanar angles [plane 1]/[plane 2] and
[plane 1]/[plane 3] are 34.5◦ (and 39.0◦) and 13.3◦ (and 21.9◦),
respectively; the interplanar angles between the two benzo rings
are 152.7◦ (and 140.3◦). The allene double bonds are, of course,
shallower than those previously seen in 5-alkynyl-dibenzosuberen-
5-ols where the [plane 1]/[plane 2] and [plane 1]/[plane 3] angles
are approximately 55–60◦ and 25–30◦, respectively, and◦the angle
between the wingtip benzo rings is in the range 120–130 .12,13
The structure of a conjugated ketone, 23c, (R = p-CF3–C6H4) is
shown in ESI (Figure SI-3). As expected, the central ring adopts
a boat conformation, and the interplanar angles [plane 1]/[plane
2] and [plane 1]/[plane 3] are 49.2◦ and 25.5◦, respectively; the
angle between the two benzo rings is now 133.5◦. Moreover, the
ketonic moiety is twisted 38.4◦ out of planarity with the adjacent
double bond; this parallels the 36◦ out-of-plane bending of the
carbonyl substituent in the conjugated enones derived from the
Meyer–Schuster rearrangement of alkynyl-fluorenols.6
Nevertheless, the poor yields of allenes 21a,b mandated
that a more efficient synthesis be developed. To this end, 5-
phenylethynyl-5H-dibenzo[a,d]cyclohepten-5-ol, 19a, was treated
with boron trifluoride and triethylsilane so as to furnish the
corresponding alkyne, 24a, (shown in ESI as Figure SI-4). The
central cycloheptatriene adopts a boat conformation such that
the interplanar angles [plane 1]/[plane 2] and [plane 1]/[plane
3] are 58.5◦ and 30.7◦, respectively, and the two peripheral
benzo groups form a dihedral angle of 120.9◦. However, the
phenylethynyl group is now in a pseudo-equatorial position,
unlike that of the alkynol precursor, 19a, or of 5-ethynyl-5H-
dibenzo[a,d]cyclohepten-5-ol,12,13 in both of which the alkyne
occupies a pseudo-axial site. One possibility might be that,
after addition of the hydride and formation of the alkyne, the
dibenzocycloheptatriene boat undergoes a ring flip,14 thus placing
the alkyne in the pseudo-equatorial position. However, one must
also consider that, unlike the 9-alkynyl-9H-fluoren-9-ol situation
for which an intramolecular cyclic six-membered transition state
can be envisaged (as in Scheme 7), the dibenzosuberenylidene
system can readily exist as a 14p aromatic cation and so the
incoming hydride can attack on either face.
˚
=
orthogonal and the C(5) C(12) bonds, 1.321(3) (and 1.318(4)) A,
=
are significantly longer than C(12) C(13)–Br, 1.301(3) (and
˚
1.303(4) A), as was previously observed for 3,3-(biphenyl-2,2¢-
diyl)-1-bromo-1-phenyl-allene.4 In the parent allene, 21a, the inter-
planar angles [plane 1]/[plane 2] and [plane 1]/[plane 3] are 41.9◦
and 18.1◦, respectively, and the angle between the two benzo rings
is now 149.6◦. However, in contrast to its bromoallene precursor,
=
=
the bond lengths C(5) C(12) and C(12) C(13) are now equal
˚
(1.309(2) and 1.310(2) A). These dibenzo[a,d]cycloheptenylidene-
allene boats in which C(5) is trigonal planar are considerably
Not surprisingly, isomerisation of the alkyne 24a to the allene
21a is much more difficult than is the case for the corresponding
fluorenyl systems (11 → 9 in Scheme 4) since the tricyclic frame-
work in 24a favours formation of a 14p aromatic cation rather than
a 16p antiaromatic anion. Thus, treatment with triethylamine fails
to bring about this alkyne-to-allene rearrangement; however, this
transformation can be accomplished by use of a stronger base.
Fig. 5 X-ray crystal structure of bromoallene 20a; thermal ellipsoids are
drawn at the 50% probability level.
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10). The product was fully characterised by NMR spectroscopy
and X-ray crystallography. In contrast to the planar polycyclic
skeleton of 8-isopropyl-1-methyl-4-tert-butylbenz[cd]azulene, 25c,
whereby the only sp3-type carbon is a CH2 unit at position
C(2) in the 5-membered ring,18 the presence of the proton in
a pseudo-axial position at C(11b), a ring junction site, renders
the dibenz[cd,h]benzazulene, 30, non-planar. The structure is
depicted in Fig. 6 and reveals that the 7-membered ring adopts
a boat conformation such that the angles [plane 1]/[plane 2] and
[plane 1]/[plane 3] are 48.6◦ and 25.3◦, with a dihedral angle of
131.7◦ between the benzo rings. The indene fragment deviates
only 5.8◦ from planarity, and the 2-phenyl substituent is rotated
through 40.8◦ relative to the five-membered ring. The space-
filling representation shown in Fig. 7 emphasises the bowl-shaped
character of the molecule.
Scheme 7 Proposed mechanism for the conversion of a 9-alkynyl-
9H-fluoren-9-ol to the corresponding alkyne using BF3 and Et3SiH.
When the alkyne was dissolved in a methanol-tert-butanol 1 : 1
mixture, and stirred in the presence of potassium tert-butoxide15
for 24 h at room temperature, the allene 21a was isolated in 89%
yield.
Initial attempts to dimerise the allene 21a have so far been
unsuccessful, possibly because the system requires some degree
of charge separation, as indicated in Scheme 2. Since the diben-
zosuberenylidene moiety favours cation formation, it may be
necessary to incorporate strongly anion-stabilising substituents
(e.g. nitro or cyano) at the other terminus of the allene, and
experiments to explore this concept are continuing.
Synthesis of 2-phenyl-11bH-dibenz[cd,h]azulene
The availability of the bromoallene 20a raised the possibility
of developing a simple route to the benz[cd]azulene skeleton, a
hitherto relatively inaccessible ring system. The parent molecule,
25a, was prepared by Boekelheide and Smith in 1966 by means of a
difficult multistep route based on the carbene-mediated expansion
of the acenaphthene framework (see Scheme 8).16 Unfortunately,
the product is obtainable only in very low overall yield, is very
susceptible to polymerisation, and can only be handled at low
temperatures in dilute solution. Previously, in 1963, Hafner and
Schaum had reported the synthesis of 3,4,7,9-tetramethyl-2H-
benz[cd]azulene, 25b, but once again, the yields are low and
the product readily decomposes.17 More recently, in 2004, we
reported the synthesis and X-ray crystal structure of 26, the
Fig.
6 Bird’s eye view of the X-ray crystal structure of
2-phenyl-11bH-dibenz[cd,h]azulene, 30; thermal ellipsoids are drawn at
the 50% probability level.
6
h -tricarbonylchromium complex of 8-isopropyl-1-methyl-4-tert-
butylbenz[cd]azulene, 25c, starting from readily available guaiazu-
lene. In this latter case, the presence of the bulky substituents
renders the molecule reasonably stable but, upon prolonged
exposure to air, oxidative dehydrogenation leads to the formation
of 27.18
In 1966, Galantay reported the formation of 2H-
dibenz[cd,h]azulen-2-one, 28, via the Friedel–Crafts cyclisation of
the acid chloride, 29 (see Scheme 9). Moreover, it was suggested
that the favoured resonance structure would be zwitterionic
whereby the ring system behaved as a dibenz[cd,h]azulenium
cation.19 More recently, a series of 7H-naphth[3,2,1-cd]azulene-
7-ones have been prepared.20
In the light of these observations, it was thought that the
reaction of bromo-allene 20a with an acid followed by hydride
addition, would bring about formation of a phenyl-substituted
dibenz[cd,h]azulene. Indeed, when a THF solution of 20a and
HBF4 was held at 0◦ C for 1 h, heated at reflux for 24 h, treated with
triethylsilane at low temperature, and then hydrolysed, 2-phenyl-
11bH-dibenz[cd,h]azulene, 30, was isolated in 10% yield (Scheme
Fig. 7 Space-filling representation of the X-ray crystal structure of
2-phenyl-11bH-dibenz[cd,h]azulene, 30, emphasizing the bowl-shaped
character of the molecule.
One can speculate that the observed molecule with the addi-
tional hydrogen attached to C(11b) is favoured over the 2H-isomer
so as to maintain the aromatic character of the two benzo rings.
Interestingly, methyl substitution at the central carbon C(9b) of the
benz[cd]azulene system, as in 31, was reported by Hafner in 1986,21
but no X-ray crystallographic data are available. In that case, the
peripheral 12p framework renders the system antiaromatic, as
indicated by the NMR shielding of the exterior protons. To the
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Scheme 8 Structures and reactions of known benz[cd]azulenes.
Scheme 9 Formation of 2H-dibenz[cd,h]azulen-2-one, 28.
best of our knowledge, the most closely analogous molecule to
30 that has been structurally characterised is the palladium-
coupled bis-dibenzosuberene system, 32, which contains an al-
most flat dibenz[cd,h]azulene subunit: the angles between [plane
1]/[plane 2] and [plane 1]/[plane 3] are 13.1◦ and 9.7◦, with an
angle of 162.9◦ between the benzo rings. In contrast, the boat
conformation of the dibe◦nzosuberenylidene fragment in 32 is
normal with angles of 53.2 , 27.6◦ and 126.7◦, respectively.22
In terms of a proposed mechanism for the synthesis of 30, one
can visualise initial protonation by HBF4 at the central allene
carbon to form the allyl cation, 33, Nazarov cyclisation to form
the 5-membered ring, elimination of HBr to furnish the tropylium-
type cation, 34, and finally triethylsilane-mediated addition of
hydride.
Fig.
8
X-ray crystal structure of Z-5-(2-bromo-2-phenylethenyl)-
5H-dibenzo[a,d]cycloheptene, 35; thermal ellipsoids are drawn at the 50%
probability level.
the allyl cation 33: attack by the hydride at C(5) prior to cyclisation
yields the styrene derivative 35, and hydrolysis of the bromoallene
generates the “Meyer–Schuster type” conjugated ketone, 23a,
discussed above.
It is particularly informative to note that, when proto-
nation of the bromoallene 20a was carried out at room
temperature in diethyl ether for only
a
short period
of time, and then treated with triethylsilane, two other
species were isolated and fully characterised: Z-5-(2-bromo-2-
phenylethenyl)-5H-dibenzo[a,d]cycloheptene, 35, and 1-phenyl-
3-(dibenzo[a,d]cycloheptenylidene)-ethanone, 23a. The structure
of 35 was determined by X-ray crystallography and is shown in
Fig. 8. Once again, the central cycloheptatriene adopts a boat
conformation, whereby the interplanar angles [plane 1]/[plane 2]
and [plane 1]/[plane 3] are 50.4◦ and 28.1◦, and the angle between
the two benzo rings is now 126.1◦. We note that the proton at
C(5) is now pseudo-equatorial and the 2-bromo-2-phenylethenyl
substituent is in a pseudo-axial position. As shown in Scheme 10,
addition of HBF4 to bromoallene 20a brings about formation of
Attempt to prepare an indenyl-allene
The reaction of 2,3-diphenylindenone with phenylethynyllithium
yields, after hydrolysis, 2,3-diphenyl-1-(phenylethynyl)-inden-1-ol,
36. Subsequent treatment with boron trifluoride and triethylsilane
was expected to form 2,3-diphenyl-1-(phenylethynyl)-indene, 37,
that could be isomerised to the required allene, 38, as in Scheme 11.
However, X-ray crystallography revealed that the product was ac-
tually 1,2-diphenyl-3-(phenylethynyl)-1H-indene, 39, presumably
arising through consecutive symmetry-allowed [1,5]-suprafacial
sigmatropic hydrogen shifts via the iso-indene, 40.23 The structure
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Scheme 10 Formation of dibenz[cd,h]azulene, 30, from bromoallene 20a.
Scheme 11 Formation of 1,2-diphenyl-3-(phenylethynyl)-1H-indene, 39.
of the ene-yne, 39, appears in Fig. 9, and reveals that, as expected
for a conjugated system, the (phenylethynyl)indenyl fragment is
almost flat.
Scheme 12 Ring opening of 3-(phenylethynyl)-1,2,3-triphenylcyclopropene.
drogen migrations in substituted indenes have been extensively
studied.25
Conclusions
The relative ease of dimerisation of fluorenylidene-allenes is
markedly dependent on the identity of the substituent at
the other terminus. 3,3-(Biphenyl-2,2¢-diyl)-1-(a,a,a-trifluoro-
p-tolyl)-allene, 9, sequentially forms head-to-tail, 12, cis-tail-
to-tail, 13, and trans tail-to-tail, 14, dimers, each of which
has been characterised by X-ray crystallography. Finally, ther-
molysis at 180 ◦C yields the dispirotetracene, 15, and di-
indenotetracene, 16; the latter compound forms an air-stable
Diels–Alder adduct, 17, with N-methylmaleimide. In contrast,
the analogous dibenzosuberenylidene-allenes, 20a and 21a, do
not dimerise under relatively mild conditions, and this may be
a consequence of the inability of the substituents at opposite
allene termini to stabilise partial positive and negative charges.
Fig. 9 Molecular structure of 1,2-diphenyl-3-(phenylethynyl)-1H-indene,
39; thermal ellipsoids are drawn at the 50% probability level.
Interestingly, it has been reported24 that 1,2-diphenyl-3-
(phenylethynyl)-1H-indene, 39, was the preferentially formed
isomer during the thermolysis of 3-(phenylethynyl)-1,2,3-
triphenylcyclopropene (Scheme 12), and the energetics of hy-
4004 | Org. Biomol. Chem., 2010, 8, 3997–4010
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However, protonation of the bromo-allene 20a, and subsequent
addition of hydride provide a facile entry to the difficultly
accessible dibenz[cd,h]azulene framework that had not previously
been structurally characterised. The maximum width of the
mixture extracted with dichloromethane multiple times. The
organic layers were combined, washed successively with water
and with brine, dried over MgSO4, filtered and concentrated
to give a brown oil that was chromatographed on silica gel
using dichloromethane/pentane (1 : 9) as eluent to give 9-[(a,a,a-
trifluoro-p-tolyl)ethynyl]-9H-fluorene, 11, as a pale yellow solid
(2.45 g, 7.3 mmol; 64%) m.p. 167–170 ◦C (Found: C, 78.81; H,
4.13. C22H13F3 requires C, 79.03; H, 3.92); dH (500 MHz, CDCl3):
7.78 (d, J 7.5, 2H, H-4, H-5), 7.74 (d, J 7.5, 2H, H-1, H-8), 7.53 (m,
4H, phenyl m-H, o-H), 7.44 (t, J 7.5, 2H, H-3, H-6), 7.40 (td, J 7.5
and 1.0, 2H, H-2, H-7), 5.04 (s, 1H, H-9); dC (125 MHz, CDCl3):
143.6 (C-8a, C-9a), 140.6 (C-4a, C-4b), 132.2 (phenyl o-C), 129.9
(q, 2JCF 32.6, phenyl p-C), 128.3 (phenyl ipso-C), 128.2 (C-3, C-6),
127.8 (C-2, C-7), 126.3 (q, 1JCF 267, CF3), 125.2 (q, 3JCF 3.6, phenyl
m-C), 125.2 (C-4, C-5), 120.3 (C-1, C-8), 90.2 (C-10), 80.9 (C-11),
39.9 (C-9).
˚
planar fluorenyl fragment is ~8.8 A, whereas the corresponding
“wingspan” of the dibenzo[a,d]cycloheptenyl moiety can vary
˚
˚
from 9.0 A to 9.5 A depending on the degree of folding of
the central seven-membered boat, which in turn controls the
interplanar angle between the benzo rings. An attempt to prepare
an allene containing a 1,2-diphenylindenyl moiety led instead to
1,2-diphenyl-3-(phenylethynyl)-1H-indene, 39.
Experimental Section
1H, 13C and 19F NMR spectra were recorded on Varian 300,
400, 500 or 600 MHz spectrometers. Assignments were based
on standard 2-dimensional NMR techniques (1H–1H COSY,
1H–13C HSQC and HMBC, NOESY). Infrared spectra were
recorded on a Perkin–Elmer Paragon 1000 FT-IR spectrom-
eter and were calibrated with polystyrene. Merck silica gel
60 (230–400 mesh) was used for flash chromatography. Melt-
ing points were determined on an Electrothermal ENG in-
strument and are uncorrected. Elemental analyses were car-
ried out by the Microanalytical Laboratory at University Col-
lege Dublin. 5-Phenyl-5H-dibenzo[a,d]cyclohepten-5-ol (19a) and
5-(4-trimethylsilyl)phenyl-5H-dibenzo[a,d]cyclohepten-5-ol (19b)
were prepared as previously described.12,13
1-(9-Fluorenylidene)-4-(a,a,a-trifluoro-p-tolyl)-2-(a,a,a-trifluoro-
p-tolylmethylene)-spiro[cyclobutane-3,9¢-[9H]-fluorene] (12)
To 9-[(a,a,a-trifluoro-p-tolyl)ethynyl]-9H-fluorene, 11, (2.45
g, 7.3 mmol) suspended in pentane (35 mL) and cooled to
0
◦C, was added triethylamine (25 mL, 0.18 mmol), and the
suspension was stirred overnight in a cold water bath. The
precipitate was filtered, washed with cold pentane and dried to
give 1-(9H-fluorenylidene)-4-(a,a,a-trifluoro-p-tolyl)-2-(a,a,a-
trifluoro-p-tolylmethylene)-spiro[cyclobutane-3,9¢-[9H]fluorene],
12, (2.26 g, 3.38 mmol; 93%) as a yellow powder, m.p. 148–150 ◦C
(Found: C, 79.11; H, 4.39. C44H26F6 requires C, 79.03; H, 3.92); a
sample suitable for an X-ray crystal structure determination was
obtained by recrystallisation from dichloromethane/hexane; dH
(500 MHz, CDCl3): 8.58 (d, J 8.0, 1H), 7.85 (d, J 7.5, 1H), 7.82
(d, J 8.0, 1H), 7.78 (d, J 8.0, 1H), 7.71 (d, J 8.0, 1H), 7.69 (s, 1H),
7.68 (d, J 7.5, 1H), 7.65 (br s, 1H), 7.49 (br s, 1H), 7.46 (t, J 7.5,
1H), 7.43 (t, J 7.5, 1H), 7.35 (t, J 7.5, 1H), 7.30 (t, J7.5, 1H), 7.29
(brd s, 1H), 7.28 (t, J 7.5, 1H), 7.11 (t, J 7.5, 1H), 7.09 (d, J 8.0,
1H), 7.02 (d, J 8.5, 2H), 7.00 (t, J 8.0, 1H), 6.61 (d, J8.0, 2H), 6.55
(brd s, 1H), 6.52 (t, J 7.5, 1H), 5.97 (d, J 7.0, 1H), 5.22 (s, 1H);
dC (125 MHz, CDCl3): 149.3, 146.6, 141.7, 141.5, 141.5, 141.0,
140.9, 140.4, 139.7, 138.1, 138.0, 137.5, 131.1, 129.5 (q, 2JCF 32.1),
129.2 (q, 2JCF 36.0), 129.0, 128.7, 128.5, 128.3, 128.0, 127.7, 127.4,
126.5, 126.5, 126.1, 125.5 (brd s), 125.1, 124.3 (q, 3JCF 3.8), 124.3
(q, 1JCF 271), 124.2, 124.0 (q, 1JCF 268), 122.8, 120.3, 120.2, 120.0,
119.8, 65.7, 60.9; dF (282 MHz, CDCl3): -60.89, -61.22.
9-(a,a,a-Trifluoro-p-tolyl)-9H-fluoren-9-ol (10)
As previously described for a series of such molecules,4 nBuLi (3.12
mL of a 1.6 M hexane solution, 5 mmol) was added dropwise to a
solution of the alkyne (5 mmol) in tetrahydrofuran (50 mL) at 0 ◦C,
and the solution was allowed to warm to room◦temperature. After
15 min stirring, the solution was cooled to 0 C and fluorenone
(0.90 g, 5 mmol) was added portion by portion. The solution
was stirred at room temperature for 30 min, quenched with water
(2 mL) and the solvent was removed on a rotary evaporator.
Purification of the crude product by chromatography on alumina
using pentane/diethyl ether as eluent gave 9-(a,a,a-trifluoro-p-
tolyl)-9H-fluoren-9-ol, 10, (85%) m.p. 136-139 ◦C (Found: C,
75.46; H, 3.78. C22H13F3O requires C, 75.42 H, 3.74); dH (500 MHz,
CDCl3): 7.75 (dd, J 7.5 and 1.5, 2H, H-1, H-8), 7.62 (d, J 7.5, 2H,
H-4, H-5), 7.50 (m, 4H, phenyl m-H, o-H), 7.41 (td, J 7.5 and
1.0, 2H, H-3, H-6), 7.35 (td, J 7.5 and 1.5, 2H, H-2, H-7), 2.67 (s,
1H, OH); dC (125 MHz, CDCl3): 146.9 (C-8a, C-9a), 139.1 (C-4a,
C-4b), 132.2 (phenyl o-C), 130.3 (q, 2JCF 32.8, phenyl p-C), 129.9
(C-3, C-6), 128.7 (C-2, C-7), 126.3 (phenyl ipso-C), 125.2 (q, 3JCF
3.5, phenyl m-C), 123.9 (q, 1JCF 270, CF3), 124.4 (C-1, C-8), 120.3
(C-4, C-5), 91.5 (C-10), 81.7 (C-11), 75.2 (C–OH); IR (CH2Cl2):
Cis-3,4-bis-(a,a,a-trifluoro-p-tolyl)-1,2-
bis(fluorenylidene)cyclobutane (13)
The head-to-tail dimer, 1-(9-fluorenylidene)-4-(a,a,a-trifluoro-
p-tolyl)-2-(a,a,a-trifluoro-p-tolylmethylene)-spiro[cyclobutane-
3,9¢-[9H]-fluorene], 12, (450 mg, 0.67 mmol) suspended in toluene
(15 mL) was heated at 95 ◦C for 8 h. After removing the
solvent, the crude product was chromatographed on silica gel
using toluene/pentane (2 : 8) as eluent, and cis-3,4-di-(a,a,a-
trifluoro-p-tolyl)-1,2-bis(fluorenylidene)cyclobutane, 13, (87.4 mg,
0.13 mmol; 20%) was isolated as an orange solid, m.p. 202–
205 ◦C (Found: C, 77.27; H, 4.19. C44H26F6·(C2H5)2O requires
C, 77.62; H, 4.88); a sample of 13 suitable for an X-ray crystal
structure determination was obtained by recrystallisation from
3563 cm-1 (OH), 2230 cm-1 (C C).
≡
9-(a,a,a-Trifluoro-p-tolyl)ethynyl-9H-fluorene (11)
To 9-[(a,a,a-trifluoro-p-tolyl)ethynyl]-9H-fluoren-9-ol, 10, (4.0 g,
11.4 mmol) in dry dichloromethane (120 mL), and cooled to 0 ◦C,
triethylsilane (2.73 mL, 17.1 mmol) was added slowly. Boron
trifluoride-etherate (2.1 mL, 17.1 mmol) was added dropwise,
and the solution became dark blue. After stirring for 1 h at
0
◦C, the reaction was quenched with distilled water, and the
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pentane/diethyl ether; dH (500 MHz, CDCl3): 7.76 (d, J 7.5, 2H),
7.34 (d, J 7.0, 1H), 7.34 (d, J 7.0, 1H), 7.65 (d, J 7.5, 1H), 7.60 (d, J
8.0, 2H), 7.53 (brd s, 1H), 7.48 (brd s, 2H), 7.35 (t, J 7.5, 1H), 7.33
(td, J 7.0 and 1.0, 1H), 7.30 (d, J 7.5 Hz, 1H), 7.29 (td, J 7.5 and
1.0, 1H), 7.24 (d, J 7.5, 1H), 7.16 (td, J 7.5 and 1.0, 1H), 7.07 (td,
J 7.5 and0.5, 2H), 6.90 (td, J 7.5 and 1.0, 1H), 6.84 (td, J 8.0 and
1.0, 1H), 6.79 (td, J 7.5 and 1.0, 1H), 6.70 (brd s, 2H), 6.25 (brd s,
1H), 5.54 (d, J 8.5, 1H), 5.37 (d, J 8.5, 1H); dC (125 MHz, CDCl3):
143.0, 142.2, 142.2, 140.9, 140.8, 140.6, 140.4, 140.4, 139.10, 138.4,
137.0, 137.0, 135.8, 135.6, 129.4 (q, 2JCF 32.8), 129.2, 129.2 (q, 2JCF
32.3), 129.1, 128.8, 128.5, 127.7, 127.6, 127.4, 126.6, 126.5, 126.4,
125.6, 124.5 (brd s), 124.9, 124.25 (brd s), 124.1 (q, 1JCF 270), 124.1
(q, 1JCF 270), 120.3, 119.8, 119.8, 119.6, 57.8, 55.8; dF (282 MHz,
CDCl3): -61.07, -61.15.
(q, 3JCF 3.8, C-5¢), 124.2 (C-2¢), 124.0 (q, 1JCF 271, CF3), 123.1 (q,
3JCF 3.9, C-3¢), 120.7 (C-4, C-5), 60.4 (C-9).
Trans-3,4-bis-(a,a,a-trifluoro-p-tolyl)-1,2-bis(fluorenylidene)cyclo-
butane (14)
Analogously, when the head-to-tail dimer, 12, (250 mg, 0.37 mmol)
suspended in toluene (5 mL) was heated at reflux for 3 days, the or-
ange solid isolated, after removing the solvent and purification by
chromatography on silica gel using cyclohexane/toluene (9 : 1) as
eluent, was identified as trans-3,4-bis-(a,a,a-p-trifluorotolyl)-1,2-
bis-(fluorenylidene)cyclo-butane, 14, (165.3 mg, 0.25 mmol; 67%),
m.p. 201–204 ◦C (Found: C, 77.25; H, 4.78. C42H26F6·(C2H5)2O
requires C, 77.61; H, 4.85); a sample of 14 suitable for an X-ray
crystal structure determination was obtained by recrystallisation
from diethyl ether/hexane. dH (300 MHz, CDCl3): 7.79 (d, J 7.2,
2H), 7.78 (d, J 7.5, 2H), 7.63 (brd s, 8H), 7.52 (d, J 7.5, 2H), 7.38 (t,
J 7.5, 2H), 7.32 (t, J 7.5, 2H), 7.18 (d, J 7.8, 2H), 7.11 (t, J 7.8, 2H),
7.08 (t, J 7.5, 2H), 4.84 (s, 2H); dC (75 MHz, CDCl3): 145.5, 140.8,
Reaction of 8,16-bis(a,a,a-trifluoro-p-tolyl)diindeno[1,2,3-
de:1¢,2¢,3¢-mn]tetracene (16) with N-methylmaleimide
Under vacuum, the head-to-tail yellow dimer, 12, (435mg,
0.65 mmol) was heated in the solid state at 200 ◦C with a
heat gun for 30 min. After cooling to room temperature, the
blue residue was dissolved in degassed toluene (10 mL), and
heated at reflux under nitrogen for 2 h, in the presence of N-
methylmaleimide (289 mg, 2.6 mmol). When the solution became
colourless, the solvent was removed on a rotatory evaporator, and
the crude material was chromatographed on a silica gel column
using pentane/dichloromethane as eluent to give the Diels–Alder
adduct 17, (45.5 mg, 0.057mmol; 9%) as a white solid, dissociates
> 200 ◦C (Found: C, 76.01; H, 3.70; N, 1.67. C49H27F6NO2 requires
C, 75.87; H, 3.51; N, 1.81); a sample of 17 suitable for an X-ray
crystal structure determination was obtained by recrystallisation
from pentane/dichloromethane. dH (500 MHz, CDCl3): 8.66 (d, J
8.5, 1H, H-25), 8.09 (d, J 8.5, 1H, H-26), 7.82 (d, J 7.0, 1H, H-11),
7.75 (d, J 7.0, 1H, H-12), 7.70 (d, J 7.5, 1H, H-7), 7.69 (d, J 7.0,
2H, H-4, H-21), 7.59 (d, J 7.5, 1H, H-3), 7.51 (d, J 8.0, 1H, H-22),
7.45–7.41 (m, 3H, H-10, H-28, H-29), 7.24 (t, J 8.0, 1H, H-5), 7.18
(t, J 7.5, 2H, H-2, H-13), 6.99 (d, J 7.5 Hz, 1H, H-9), 6.90 (d, J
8.0, 1H, H-19), 6.78 (td, J 1.0 and 8.0, 1H, H-14), 6.76 (t, J 8.0 Hz,
1H, H-6), 6.32 (d, J 8.0, 1H, H-18), 6.29 (d, J 8.0, 1H, H-15), 6.15
(d, J 8.0, 1H, H-1), 4.26 (d, J 9.0 Hz, 1H, H-35), 3.11 (d, J 8.5 Hz,
1H, H-31), 2.57 (s, 3 H, H-33); dC (125 MHz, CDCl3): 175.9, 175.3
(C-32, C-34), 146.5 (C-16b), 145.9 (C-7a), 142.9 (C-16a), 142.1 (C-
16), 141.5 (C-17), 140.8 (C-3b), 140.0 (C-11b), 138.4 (C-7c), 137.9
(C-15a), 137.1 (C-15c), 136.9 (C-11a), 135.5 (C-15b), 135.3 (C-3a),
134.2 (C-8), 133.2 (C-29), 132.4 (C-8b), 131.7 (C-7), 131.6 (C-22),
131.3 (C-18), 130.3 (q, 2JCF 32.5, C-27), 129.7 (q, 2JCF 32.0, C-20),
129.3 (C-8a), 129.1 (C-25), 128.9 (C-15), 128.6 (C-10), 128.5 (C-2),
127.7 (C-13), 127.5 (C-6), 127.4 (C-5), 126.7 (C-14), 125.8 (C-9),
2
140.7, 140.4, 138.1, 136.4, 135.4, 129.8 (q, JCF 29.0, phenyl p-
C), 129.5, 128.9, 127.7, (fluorenyl–CH), 127.6 (phenyl o-C), 127.5,
126.6 (q, 3JCF 3.8, phenyl m-C), 126.2, 124.4, (fluorenyl–CH), 124.1
(q, 1JCF 276, CF3), 120.4, 119.9, (fluorenyl–CH), 62.0 (C-3, C-4);
dF (282 MHz, CDCl3): -60.95.
5,9-Dispirofluorenyl-2,8-bis(a,a,a-trifluoro-p-tolyl)-5H,9H-
dihydro-tetracene (15)
The head-to-tail dimer, 1-(9-fluorenylidene)-4-(a,a,a-trifluoro-
p-tolyl)-2-(a,a,a-trifluoro-p-tolylmethylene)-spiro[cyclobutane-
3,9¢-[9H]-fluorene], 12, (1.25 g, 1.87 mmol) dissolved in dimethyl
sulfoxide (25 mL) was heated at reflux for 24 h. The mixture
was cooled, water was added, and the mixture was extracted
with diethyl ether and dichloromethane. The organic phases were
combined, cooled to 0 ◦C for 1 h and filtered to give 15 (343.3 mg,
0.51 mmol; 28%) as a pale yellow solid m.p. 227–229 ◦C (Found:
C, 76.79; H, 3.62. C44H24F6·0.3CH2Cl2 requires C, 76.88; H, 3.58);
chromatographic separation of the filtrate using pentane/toluene
yielded additional 15 (162 mg, 0.24 mmol; 13%); dH (500 MHz,
CDCl3): 7.87 (d, J 7.5, H-4, H-5, 4H), 7.45 (td, J 7.5, J 1.0, 4H, H-
3, H-6), 7.23 (dd, J 8.0 and 0.5, 2H, H-5¢), 7.19 (td, J 7.5 and 1.0,
4H, H-2, H-7), 7.11 (dd, J 8.0 and 0.5, 4H, H-1, H-8), 6.98 (d, J
7.5, 2H, H-6¢), 6.55 (s, 2H, H-3¢), 6.01 (s, 2H, H-2¢); dC (125 MHz,
CDCl3): 151.5 (C-8a, C-9a), 140.1 (C-4a, C-4b), 139.8 (C-1a’, C-
1b’), 139.6 (C-2a’), 136.2 (C-6a’), 129.5 (q, 2JCF 32.3, C-4¢), 128.5
(C-3, C-6), 128.5 (C-2, C-7), 128.0 (C-6¢), 125.5 (C-1, C-8), 124.2
3
3
1
125.7 (q, JCF 3.8, C-26), 125.2 (q, JCF 3.6, C-28), 124.5 (q, JCF
1
271, CF3), 124.5 (q, JCF 271, CF3), 123.9-123.7 (m, C-1, C-21,
C-19), 120.5 (C-4), 120.3 (C-12), 119.4 (C-3), 119.2 (C-11), 57.3
(C-16), 55.8 (C-7b), 50.8 (C-31), 50.0 (C-35), 25.2 (CH3).
4006 | Org. Biomol. Chem., 2010, 8, 3997–4010
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5-(a,a,a-Trifluoro-p-tolyl)-5H-dibenzo[a,d]cyclohepten-5-ol (19c)
C-7), 128.5 (C-2, C-8), 128.5 (phenyl m-C) 128.5 (phenyl p-C),
127.6 (phenyl o-C), 117.6 (C-5), 95.5 (C-13); IR (CDCl3): 1926
To a solution of 1-ethynyl-4-trifluoromethyl-toluene (3.45 mL,
30 mmol) in dry THF (250 ◦mL), nBuLi (17.15 mL, 27.5 mmol)
cm-1 (C C C).
= =
◦
was added dropwise at -78 C. After stirring for 1 h at -78 C,
Z-5-(2-Bromo-2-phenylethenyl)-5H-dibenzo[a,d]cycloheptene (35)
and 1-phenyl-3-(dibenzo[a,d]cycloheptenylidene)ethanone (23a)
a solution of dibenzosuberenone (5.15 g, 25 mmol) in dry THF
(20 mL) was added dropwise. The reaction was stirred for 1 h,
quenched with distilled water (150 mL), and extracted with diethyl
ether several times. Theorganic layers were combined, washedwith
brine, dried over MgSO4, filtered and the solvent removed to give
a yellow oil. The crude product was purified by chromatography
on an alumina column using pentane/dichloromethane as eluent
to give 19c (4.36 g, 11.6 mmol; 45%) as a yellow solid, m. p. 79–82
◦C (Found: C, 76.23; H, 4.03. C24H15OF3 requires C, 76.59; H,
4.02; dH (500 MHz, CDCl3): 8.10 (d, J 8.0, 2H, H-4, H-6), 7.56 (d,
J 8.0, 2H, phenyl m-H), 7.51 (d, J 8.0, 2H, phenyl o-H), 7.47 (td,
J 7.0 and 1.5, 2H, H-3, H-7), 7.44 (d, J 8.0, 2H, H-1, H-9), 7.35
(td, J 7.0 and 1.5 Hz, 2H, H-2, H-8), 7.22 (s, 2H, H-10, H-11),
3.23 (s, 1H, OH); dC (125 MHz, CDCl3): 140.2 (C-4a, C-5a), 132.9
(C-9a, C-11a), 132.1 (phenyl o-C), 131.7 (C-10, C-11), 130.4 (q,
2JCF 32.9, phenyl p-C), 129.4 (C-1, C-9), 128.7 (C-3, C-7), 127.4
(C-2, C-8), 126.5 (phenyl ipso-C), 125.3 (q, 3JCF 3.9, phenyl m-C),
124.0 (q, 1JCF 271, CF3), 123.5 (C-4, C-6), 93.3 (C-12), 83.5 (C-13),
72.5 (C–OH).
To a solution of the bromo-allene 20a (1.10 g, 2.96 mmol) in
diethyl ether (30 mL) was added dropwise at 0 ◦C a solution
of boron trifluoride-etherate (488 mL, 3.56 mmol). Upon stirring
1 h at 0 ◦C, and 10 h at room temperature, triethylsilane
(615 mL, 3.85 mmol) was added dropwise. After stirring for
1 h, the mixture was quenched with water and extracted with
diethyl ether several times. The organic layers were combined,
washed with brine, dried over MgSO4, filtered and concen-
trated. The crude product was purified by chromatography on
silica using dichloromethane/pentane as eluent to give Z-5-(2-
bromo-2-phenylethenyl)-5H-dibenzo[a,d]-cycloheptene, 35, (391
mg, 1.05 mmol, 35%) as a white solid (Found: C, 73.65; H, 4.19;
Br, 21.23. C23H17Br requires C, 74.00; H, 4.59; Br. 21.41) m.p.
191–193 ◦C and 1-phenyl-3-(dibenzo[a,d]cycloheptenylidene)-
ethanone, 23a, (525 mg, 1.70 mmol, 58%) as a yellow solid
◦
m.p. 114–116 C (Found: C, 89.88; H, 5.36. C23H16O requires C,
89.58; H, 5.23); a sample of 35 suitable for an X-ray diffraction
structural determination was obtained by recrystallisation from
diethyl ether/pentane.
1-Bromo-1-phenyl-2-dibenzo[a,d]cycloheptenylidene-ethene (20a)
Data for 35. dH (500 MHz, CDCl3): 7.55 (dd, J 7.5 and 1.5,
2H, H-4, H-6), 7.47–7.35 (m, 6H, H-1, H-9, phenyl o-H, m-H),
7.33–7.24 (m, 5H, H-2, H-3, H-7, H-8, phenyl p-H), 7.07 (s, 2H,
H-10, H-11), 6.86 (d, 1H, H-12), 5.27 (d, 1H, H-13); dC (125 MHz,
CDCl3): 140.0 (C-13), 139.4 (C-4a, C-5a), 134.4 (C-9a, C-11a),
131.6 (C-10, C-11), 129.7 (C-1, C-9), 129.7 (phenyl ipso-C, C-12),
129.4 (brd s, C-4, C-6), 129.1 (phenyl m-C), 128.5 (phenyl p-C),
128.2 (C-3, C-7), 127.9 (phenyl o-C), 126.8 (C-2, C-8), 56.0 (C-5).
To
a
cooled solution of 5-phenylethynyl-5H-dibenzo-
[a,d]cyclohepten-5-ol, 19a, (300 mg, 0.97 mmol) in acetic
acid (5 mL) was added dropwise a solution of hydrobromic acid
(47%, 0.67 g, 3.90 mmol) in water (2.0 mL). Upon stirring for
1 h with cooling, the precipitate was filtered, washed with water
and dried. The product was dissolved in THF (5 mL), dried over
MgSO4, filtered and concentrated to give 20a (0.236 g, 0.64 mmol;
66%), as a yellow solid, m.p. 88–92 ◦C (Found: C, 74.25; H,
4.31. C23H15Br requires C, 74.41; H, 4.07); a sample suitable
for an X-ray diffraction structural determination was obtained
by recrystallisation from diethyl ether/pentane; dH (500 MHz,
CDCl3): 7.58 (d, J 7.0, 2H, H-4, H-6), 7.56 (dd, J 7.0 and 1.5, 2H,
phenyl o-H), 7.39 (td, J 6.8 and 2.5, 2H, H-3, H-7), 7.35 (td, J
7.5 and 1.5, 2H, H-2, H-8), 7.34–7.33 (m, 2H, H-1, H-9), 7.31 (t,
J 8.0, 2H, phenyl m-H), 7.25 (td, J 7.5 and 1.5, 1H, phenyl p-H),
6.85 (s, 2H, H-10, H-11); dC (125 MHz, CDCl3): 206.1 (C-12),
135.0 (C-9a, C-11a), 134.5 (C-4a, C-5a), 134.0 (phenyl ipso-C),
131.4 (C-10, C-11), 130.0 (C-1, C-9), 129.4 (C-4, C-6), 129.3 (C-3,
Data for 23a. dH (500 MHz, CDCl3): 7.74 (dd, J 7.0 and 1.4,
2H, phenyl o-H), 7.58 (d, J 7.7, 1H, H-6), 7.44 (td, J 6.9 and 1.8,
1H, H-7), 7.39–7.35 (m, 3H, H-8, H-9, phenyl p-H), 7.24 (td, J 8.4
and 1.2, 2H, phenyl m-H), 7.20 (dd, J 8.4 and 1.2, 1H, H-1), 7.18
(dd, J 7.2 and 1.2, 1H, H-4), 7.13 (td, J 7.2 and 1.2, 1H, H-2), 7.09
(td, J 7.2 and 1.2 Hz, 1H, H-3), 6.97 (d, J 12 Hz, 1H, H-10), 6.94 (d,
J 12.0, 1H, H-11), 6.55 (s, 1H, H-12); dC (125 MHz, CDCl3): 194.8
(C-13), 152.9 (C-5), 140.0 (C-5a), 137.9 (phenyl ipso-C), 136.6 (C-
4a), 133.9 (C-9a), 133.9 (C-11a), 132.6 (phenyl p-C), 131.4 (C-11),
131.2 (C-10), 129.5 (C-12), 129.2 (C-4), 129.2 (C-7), 128.6 (C-9),
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Table 1 Crystallographic data for 12, 13, 14 and 17
12
13
14
17
∑
∑
∑
(b)
Formula
M
(C44H26F6)2 C6H14
1423.47
(C44H26F6)4 CH2Cl2
2759.52
C44H26F6 C6H14
668.65
C49H27NO2F6
775.72
Crystal system
Space group
triclinic
triclinic
orthorhombic
Iba2 (#45)
10.154(3)
16.592(4)
23.131(6)
90
triclinic
¯
¯
¯
P1 (#2)
P1 (#2)
P1 (#2)
˚
a [A]
9.0486(15)
11.2654(19)
18.715(3)
91.991(3)
101.326(3)
109.783(3)
1749.6(5)
1
10.118(3)
16.177(4)
22.818(6)
110.541(4)
97.597(5)
94.218(5)
3437.7(16)
1
1.333
293(2)
0.137
1418
9.4052(11)
14.5518(17)
14.8501(17)
110.752(2)
107.181(2)
99.085(2)
1735.6(3)
2
1.484
100(2)
0.112
796
1.57 to 24.19
-10 ≤ h ≤ 10
-16 ≤ k ≤ 16
-17 ≤ l ≤ 17
12790
˚
b [A]
˚
c [A]
a [◦]
b [◦]
g [◦]
90
90
3
˚
V [A ]
3897.0(17)
4
Z
rcalcd [g.cm-3]
T [K]
1.351
100(2)
0.099
738
1.140
100(2)
0.085
1376
m mm-1
F(000)
q Range [◦]
Index ranges
1.93 to 26.00
-11 ≤ h ≤ 11
-13 ≤ k ≤ 13
-23 ≤ l ≤ 23
27144
1.91 to 24.00
-11 ≤ h ≤ 11
-18 ≤ k ≤ 18
-26 ≤ l ≤ 26
45731
1.76 to 26.00
-12 ≤ h ≤ 9
-20 ≤ k ≤ 20
-26 ≤ l ≤ 28
9426
Reflections measured
Reflections used
Rint
Data/restraints/parameters
6863
0.0285
6863/0/583
10807
1976
0.0581
1976/1/244
5529
0.0254
5529/0/524
0.0274
10807/2/1031(a)
Final R values [I>2s (I)]:
R1
0.0449
0.1150
0.0443
0.1086
0.0526
0.1311
0.0486
0.1290
wR2
R values (all data):
R1
wR2
0.0516
0.1203
1.026
0.708 and -0.456
0.0622
0.1205
1.008
0.471 and -0.255
0.0633
0.1361
1.031
0.0616
0.1363
1.056
0.440 and -0.280
GOF on F2
Largest diffraction peak and hole (e A )
-3
˚
0.792 and -0.513
a
Both C–Cl distances were restrained to be around 1.75 A. b The solvent could not be located. SQUEEZE was used to compensate for the spread electron
˚
density.
128.6 (C-1), 128.4 (C-3), 128.2 (C-2), 128.1 (phenyl m-C, C-8),
ipso-C), 132.8 (C-1), 132.5 (C-7), 132.2 (C-5a), 130.3 (C-6), 129.7
(C-8), 128.9 (C-10), 128.8 (phenyl m-C), 128.1 (phenyl p-C), 128.0
(phenyl o-C), 127.1 (C-4), 126.5 (C-9), 126.3 (C-11), 125.0 (C-5),
120.5 (C-3), 51.6 (C-11b).
127.2 (C-6); IR (CDCl3): 1648 cm-1 (C O).
=
2-Phenyl-11bH-dibenz[cd,h]azulene (30)
To a solution of 1-bromo-2-dibenzo[a,d]cyclo-heptenylidene-1-
phenyl-ethene, 20a, (1.0 g, 2.69 mmol) in THF (30 mL) was added
dropwise at 0 ◦C a solution 1 M of HBF4 in diethyl ether (740
mL, 5.4 mmol). Upon stirring 1 h at 0 ◦C and 12 h at reflux,
the mixture was cooled to room temperature and triethylsilane
(1.3 mL, 8.07 mmol) was added. After stirring 12 h at reflux,
the solvent was removed and the crude product was purified
by chromatography on silica using dichloromethane/pentane as
eluent to give 2-phenyl-11bH-dibenz[cd,h]azulene, 30, (96.1 mg,
0.33 mmol; 12%) as a white solid, m.p. 134–136 ◦C (Found: C.
94.66; H, 5.37. C23H16 requires C, 94.48; H, 5.52); a sample suitable
for an X-ray diffraction structural determination was obtained by
recrystallisation from diethyl ether/dichloromethane/hexane; dH
(500 MHz, CDCl3): 7.71 (d, J 7.0, 2H, phenyl o-H), 7.55 (d, J 7.5,
1H, H-3), 7.50 (t, J 7.5, 2H, phenyl m-H), 7.42 (t, J 7.5, 1H, phenyl
p-H), 7.38 (d, J 7.5 Hz, 1H, H-11), 7.33 (dd, J 7.5, and 1.0, 1H,
H-8), 7.32 (t, J 7.5, 1H, H-4), 7.28 (td, J 7.5 and 1.5, 1H, H-10),
7.23 (t, J 7.0, 1H, H-9), 7.21 (d, J 7.5, 1H, H-5), 7.10 (d, J 2.5,
1H, H-1), 7.05 (d, J 12.0, 1H, H-7), 7.02 (d, J 12.0, 1H, H-6), 4.48
(d, J 2.5, 1H, H-11b); dC (125 MHz, CDCl3): 146.4 (C-2), 145.1
(C-11c), 141.7 (C-2a), 136.1, 136.0, (C-7a, C-11a), 136.0 (phenyl
2,3-Diphenyl-1-(phenylethynyl)-inden-1-ol (36)
nBuLi (7.5 mL of a 1.6 M hexane solution, 12 mmol) was added
dropwise to a solution of phenylacetylene (1.10 mL, 10 mmol)
in THF (50 mL) at 0 ◦C. After stirring for 15 min at room
temperature, the solution was cooled to 0 ◦C and a solution of
2,3-diphenyl-1H-inden-1-one (2.82 g, 10 mmol) in THF (20 mL)
was added slowly. The solution was stirred at room temperature
for 30 min, quenched with a few drops of water and the solvent
evaporated. The crude product was chromatographed on alumina
gel using cyclohexane/dichloromethane as eluent to give 1-
(phenylethynyl)-2,3-diphenylinden-1-ol, 36, (3.64 g, 9.46 mmol,
94%) as a white solid, m.p. 134–137 ◦C (Found: C, 90.18; H, 5.08.
C29H20O requires C, 90.60; H, 5.24); dH (500 MHz, CDCl3): 7.84–
7.80 (m, 1H), 7.71–7.68 (m, 2H), 7.48–.28 (m, 16H), 2.67 (s, 1H,
OH); dC (125 MHz, CDCl3): 146.8, 144.3, 142.8, 140.3, 134.4,
133.8, 132.1, 129.9, 129.3, 129.3, 128.8, 128.7, 128.4, 128.3, 128.1,
127.9, 127.5, 123.2, 122.6, 121.4, 89.0, 84.2, 78.6; IR (CH2Cl2):
3561 cm-1 (OH), 2223 cm-1 (C C).
≡
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Table 2 Crystallographic data for 20a, 30, 34 and 38
20a
30
34
38
Formula
M
C23H15Br
371.26
C23H16
292.36
C23H17Br
373.28
C29H20
368.45
Crystal system
Space group
orthorhombic
P212121 (#19)
6.1828(8)
9.6681(12)
27.580(4)
90
90
90
1648.6(4)
4
1.496
100(2)
2.493
752
2.23 to 30.00
-8 ≤ h ≤ 8
-13 ≤ k ≤ 13
-38 ≤ l ≤ 38
34485
orthorhombic
Pccn (#56)
19.553(3)
28.605(5)
5.3564(9)
90
90
90
2995.9(9)
8
1.296
100(2)
0.073
1232
1.42 to 23.29
-21 ≤ h ≤ 21
-31≤ k ≤ 31
-5 ≤ l ≤ 5
16917
monoclinic
P21/n (#14)
10.3403(12)
15.2026(18)
11.2081(13)
90
106.127(2)
90
1692.6(3)
4
1.465
100(2)
2.428
760
2.32 to 27.00
-13 ≤ h ≤ 13
-19 ≤ k ≤ 19
-14 ≤ l ≤ 14
14572
monoclinic
C2/c (#15)
24.337(3)
5.7025(7)
28.668(3)
90
99.404(2)
90
3925.2(8)
8
1.247
100(2)
0.071
1552
1.44 to 26.00
-30 ≤ h ≤ 30
-7 ≤ k ≤ 7
-35 ≤ l ≤ 35
15216
˚
a [A]
˚
b [A]
˚
c [A]
a [◦]
b [◦]
g [◦]
3
˚
V [A ]
Z
rcalcd [g.cm-3]
T [K]
m mm-1
F(000)
q Range [◦]
Index ranges
Reflections measured
Reflections used
Rint
4803
0.0474
2135
0.0431
3684
0.0388
3836
0.0300
Data/restraints/parameters
4803/0/217
2135/0/208
3684/0/285
3836/53/343
Final R values [I>2s (I)]:
R1
0.0362
0.0897
0.0418
0.0956
0.0303
0.0748
0.0381
0.0865
wR2
R values (all data):
R1
wR2
0.0386
0.0914
0.0505
0.0991
0.0383
0.0801
0.0479
0.0922
GOF on F2
Largest diffraction peak and hole (e A )
1.110
1.905 and -0.365
1.128
0.200 and -0.135
1.030
0.519 and -0.356
1.041
0.219 and -0.155
-3
˚
1,2-diphenyl-3-(phenylethynyl)-1H-indene (39)
program SADABS.26 Crystal data of 20b were collected using an
Oxford Diffraction SuperNova A diffractometer fitted with an
Atlas detector. A twice redundant dataset was collected, assuming
that the Friedel pairs are not equivalent. An analytical absorption
correction based on the shape of the crystal was performed.27
The structures were solved by direct methods using SHELXS-9728
and refined by full matrix least-squares on F2 for all data using
SHELXL-97.28 Hydrogen atom treatment varied from compound
to compound, depending on the crystal quality. All hydrogen
atoms in 34, the ones of the main molecule in 12 and the ordered
ones in 24a were located in the difference fourier map and allowed
to refine freely. All other hydrogen atoms were added at calculated
positions and refined using a riding model. Their isotropic thermal
displacement parameters were fixed to 1.2 times (1.5 times for
methyl groups) the equivalent one of the parent atom. Anisotropic
thermal displacement parameters were used for all non-hydrogen
atoms.
To 1-(phenylethynyl)-2,3-diphenylinden-1-ol, 36, (3.0 g, 7.8 mmol)
in dry dichloromethane (80 mL), and cooled to 0 ◦C, triethylsilane
(1.5 mL, 9.36 mmol) was added slowly. Boron trifluoride-etherate
(1.2 mL, 9.36 mmol) was added dropwise and the solution became
green-black. After stirring for 30 min at 0 ◦C, the reaction
was quenched with distilled water (100 mL), and the mixture
was extracted with dichloromethane several times. The organic
layers were washed with brine, dried over MgSO4, filtered and
concentrated to give a brown oil that was chromatographed on
silica gel using dichloromethane/pentane as eluent to give 1,2-
diphenyl-3-(phenylethynyl)-1H-indene, 39, as a white solid (1.0
◦
g, 2.71 mmol; 35%), m.p. 148–149 C (lit.[24] 149 ◦C); a sample
suitable for an X-ray crystal structure determination was obtained
by recrystallisation from dichloromethane/pentane; dH (500 MHz,
CDCl3): 7.96 (dd, J 7.5 and 1.2 Hz, 2H), 7.70–7.60 (m, 3H), 7.43–
7.10 (m, 14H), 5.16 (s, 1H).
Crystal data
Acknowledgements
Crystal data for 12, 13, 14, 17, 20a, 21a, 23c, 24a, 30, 35 and 39
were collected using using Mo–Ka radiation on a Bruker SMART
APEX CCD area detector diffractometer. Data for 12, 13, 14, 17,
20a, 30, 35 and 39 are listed in Tables 1 and 2. Data for 20b, 21a,
23c and 24a are listed in ESI. A full sphere of the reciprocal space
was scanned by phi-omega scans. A semi-empirical absorption
correction based on redundant reflections was performed by the
We thank Science Foundation Ireland and University College
Dublin for generous financial support.
References
1 E. V. Banide, P. Oulie´ and M. J. McGlinchey, Pure Appl. Chem., 2009,
81(1), 1–17.
This journal is
The Royal Society of Chemistry 2010
Org. Biomol. Chem., 2010, 8, 3997–4010 | 4009
©

View Online
2 (a) L. E. Harrington, J. F. Britten and M. J. McGlinchey, Org. Lett.,
2004, 6, 787–790; (b) E. V. Banide, Y. Ortin, C. M. Seward, L. E.
Harrington, H. Mu¨ller-Bunz and M. J. McGlinchey, Chem.–Eur. J.,
2006, 12, 3275–3286.
13 E. V. Banide, H. Mu¨ller-Bunz, A. R. Manning, P. Evans and M. J.
McGlinchey, Angew. Chem., 2007, 119, 2965–2968, (Angew. Chem.,
Int. Ed., 2007, 46, 2907–2910).
14 A. Hjelmencrantz, A. Friberg and U. Berg, J. Chem. Soc., Perkin Trans.
2, 2000, 1293–1300.
15 (a) L. A. Paquette and G. V. Meehan, J. Am. Chem. Soc., 1970, 92,
3039–3044; (b) D. J. Cram, F. Willey, H. P. Fischer, H. M. Relles and
D. A. Scott, J. Am. Chem. Soc., 1966, 88, 2759–2766.
16 V. Boekelheide and C. D. Smith, J. Am. Chem. Soc., 1966, 88, 3950–
3958.
3 (a) L. Jacobs, J. R. McLennon and O. J. Muscio Jr., J. Am. Chem. Soc.,
1969, 91, 6038–6041; (b) F. Toda, H. Motomura and H. Oshima, Bull.
Chem. Soc. Jpn., 1974, 47, 467–470; (c) J. Rigaudy and P. Capdeveille,
Tetrahedron, 1977, 33, 767–773; (d) J. Rigaudy and P. Capdeveille,
Tetrahedron, 1979, 35, 2093–2100; (e) H. Jelinek-Fink, M. Christl,
E.-M. Peters, K. Peters and H. G. von Schnering, Chem. Ber., 1991,
124, 2569–2575; (f) M. Christl, M. Rudolph, E.-M. Peters, K. Peters
and H. G. von Schnering, Angew. Chem., 1995, 107, 2931–2934, (Angew.
Chem., Int. Ed. Engl., 1995, 34, 2730–2732); (g) M. Christl, S. Groetsch
and K. Gu¨nther, Angew. Chem., 2000, 112, 3395–3397, (Angew. Chem.
Int. Ed. Engl., 2000, 39, 3261–3263).
4 E. V. Banide, B. C. Molloy, Y. Ortin, H. Mu¨ller-Bunz and M. J.
McGlinchey, Eur. J. Org. Chem., 2007, 2611–2622.
5 H.-U. Siehl, F.-P. Kaufmann, Y. Apeloig, V. Braude, D. Danovich, A.
Berendt and N. Stamatis, Angew. Chem., 1991, 103, 1546–1549, (Angew.
Chem., Int. Ed. Engl., 1991, 30, 1479–1482).
17 K. Hafner and H. Schaum, Angew. Chem., 1963, 75, 90–91, (Angew.
Chem., Int. Ed. Engl., 1963, 2, 95–96).
18 S. Balduzzi, H. Mu¨ller-Bunz and M. J. McGlinchey, Chem.–Eur. J.,
2004, 10, 5398–5405.
19 E. Galantay, H. Agahigian and N. Paolella, J. Am. Chem. Soc., 1966,
88, 3875–3877.
20 N. Abe, H. Fujii, K. Takase and T. Morita, J. Chem. Soc., Perkin Trans.
1, 2001, 1353–1358.
21 K. Hafner and V. Ku¨hn, Angew. Chem., 1986, 98, 648–650, (Angew.
Chem., Int. Ed. Engl., 1986, 25, 632–633).
6 E. V. Banide, Y. Ortin, B. Chamiot, A. Cassidy, J. Niehaus, A. Moore, C.
M. Seward, H. Mu¨ller-Bunz and M. J. McGlinchey, Organometallics,
2008, 27, 4173–4182.
22 G. Dyker, F. Nerenz, P. Siemsen, P. Bubenitschek and P. G. Jones, Chem.
Ber., 1996, 129, 1265–1269.
23 M. Stradiotto and M. J. McGlinchey, Coord. Chem. Rev., 2001, 219–
221, 311–378 and references therein.
24 R. D. Gilbertson, H.-P. Wu, D. Gorman-Lewis, T. J. R. Weakley, H.-C.
Weiss, R. Boese and M. M. Haley, Tetrahedron, 2004, 60, 1215–1223.
25 S. S. Rigby, M. Stradiotto, S. Brydges, D. L. Pole, S. Top, A. D. Bain
and M. J. McGlinchey, J. Org. Chem., 1998, 63, 3735–3740.
26 G. M. Sheldrick, SADABS, Bruker AXS Inc., Madison, WI 53711,
2000.
7 The mechanism of formation of the dispirotetracenes and di-
indenotetracenes has been fully discussed previously.2b,4
.
8 D. B. Mitzi and A. Azali, Cryst. Growth Des., 2007, 7, 691–697.
9 H. Kollmar and H. Fischer, Tetrahedron Lett., 1968, 9, 4291–4294.
10 T. Toda, M. Kuwana, Y. Ohhashi and M. Yoshida, Chem. Lett., 1997,
21–22.
11 E. V. Banide, P. Oulie´, H. Mu¨ller-Bunz and M. J. McGlinchey,
Organometallics, 2008, 27, 5657–5664.
12 (a) T. Steiner, E. B. Starikov and M. Tamm, J. Chem. Soc., Perkin
Trans. 2, 1996, 67–71; (b) T. Steiner, S. A. Mason and M. Tamm, Acta
Crystallogr., Sect. B: Struct. Sci., 1997, 53, 843–848.
27 Program CrysalisPro Version 1.171.33.55, Oxford Diffraction Limited,
2010.
28 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr., 2008,
64, 112–122.
4010 | Org. Biomol. Chem., 2010, 8, 3997–4010
This journal is
The Royal Society of Chemistry 2010
©