Sequential formation of yellow, red, and orange 1-phenyl-3,3-biphenylene- allene dimers prior to blue tetracene formation: Helicity reversal in trans-3,4-diphenyl-1,2-bis(fluorenylidene)cyclobutane

Article abstract of DOI:10.1002/chem.200501169

1-Phenyl-3,3-biphenylene-allene (2), the base-catalyzed rearrangement product of 9-phenylethynylfluorene (1) yields a yellow, head-to-tail dimer 6 that, upon gentle warming, is converted to the red tail-to-tail isomer trans-3,4-diphenyl-1,2-bis(fluorenylidene)cyclobutane (7), in which the two fluorenylidene moieties severely overlap. The helical sense of the fluorenylidene moieties in 7 matches that of the phenyl substituents, and the interplanar angle between the fluorenylidene moieties is 41°. At 80°C, 6 isomerizes to orange cis-3,4-diphenyl-1,2-bis(fluorenylidene)cyclobutane (8), which at 110°C is converted to orange trans diastereomer 9, whereby the helicity of the overlapping fluorenylidene moiet ies is reversed from that in 7 such that they are aligned with the ring hydrogen atoms, and the interplanar angle between the fluorenylidene moieties is now 60°. At 180°C. 6 rearranges to dispirodihydrotetracene 3 and blue, electroluminescent diindenotetracene 4, which is readily oxidized to peroxide 5. In the solid state, both 3 and 4 adopt structures with C_i, symmetry (only an inversion center) such that the central polycyclic framework is nonplanar. Deprotonation of yellow head-to-tail allene dimer 6 with tBuOK in DMSO and reprotonation with HOAc yields the [1.3]-hydrogen migration product 10, in which the proton originally on the cyclobutane ring is now sited at C9 on the exocyclic fluorenyl substituent. Analogously, deprotonation and reprotonation of orange dimer 9 furnishes [1,3]-hydrogen migration product 11. Side product 17, formed during the synthesis of 1 from 9-phenylethynylfluoren-9-ol, BF3 and Et₃SiH, was shown to be a silyl-indene spiro-linked to C9 of fluorene. All products were characterized by NMR spectroscopy and X-ray crystallography, and the mechanisms of these interconversions are discussed.

Full text of DOI:10.1002/chem.200501169

FULL PAPER
DOI: 10.1002/chem.200501169
Sequential Formation of Yellow, Red, and Orange 1-Phenyl-3,3-Biphenylene-
Allene Dimers Prior to Blue Tetracene Formation: Helicity Reversal in trans-
3,4-Diphenyl-1,2-bis(fluorenylidene)cyclobutane
Emilie V. Banide,[a] Yannick Ortin,[a] Corey M. Seward,[a] Laura E. Harrington,[b]
Helge Müller-Bunz,[a] and Michael J. McGlinchey*[a]
Abstract:
1-Phenyl-3,3-biphenylene-
ies is reversed from that in 7 such that
they are aligned with the ring hydrogen
atoms, and the interplanar angle be-
tween the fluorenylidene moieties is
now 608. At 1808C, 6 rearranges to di-
spirodihydrotetracene 3 and blue, elec-
troluminescent diindenotetracene 4,
which is readily oxidized to peroxide 5.
In the solid state, both 3 and 4 adopt
structures with Ci symmetry (only an
inversion center) such that the central
polycyclic framework is nonplanar. De-
protonation of yellow head-to-tail
allene dimer 6 with tBuOK in DMSO
and reprotonation with HOAc yields
the [1,3]-hydrogen migration product
10, in which the proton originally on
the cyclobutane ring is now sited at C9
on the exocyclic fluorenyl substituent.
Analogously, deprotonation and repro-
tonation of orange dimer 9 furnishes
[1,3]-hydrogen migration product 11.
Side product 17, formed during the
synthesis of 1 from 9-phenylethynyl-
fluoren-9-ol, BF3 and Et3SiH, was
shown to be a silyl-indene spiro-linked
to C9 of fluorene. All products were
characterized by NMR spectroscopy
and X-ray crystallography, and the
mechanisms of these interconversions
are discussed.
allene (2), the base-catalyzed rearrange-
ment product of 9-phenylethynylfluor-
ene (1) yields a yellow, head-to-tail
dimer 6 that, upon gentle warming, is
converted to the red tail-to-tail isomer
trans-3,4-diphenyl-1,2-bis(fluorenyl-
idene)cyclobutane (7), in which the two
fluorenylidene moieties severely over-
lap. The helical sense of the fluorenyl-
idene moieties in 7 matches that of the
phenyl substituents, and the interplanar
angle between the fluorenylidene moi-
eties is 418. At 808C, 6 isomerizes to
orange cis-3,4-diphenyl-1,2-bis(fluore-
nylidene)cyclobutane (8), which at
1108C is converted to orange trans dia-
stereomer 9, whereby the helicity of
the overlapping fluorenylidene moiet-
Keywords: allenes · dimerization ·
helical structures · isomerization ·
tetracenes
Introduction
tracene 3 and peroxide 5 were all unambiguously character-
ized by X-ray crystallography.[1,2]
In a recent communication,[1] we reported that, upon heat-
ing, 9-phenylethynylfluorene (1) rearranges to the corre-
sponding allene 2, which dimerizes and subsequently yields
In 1965, Kuhn and Rewicki observed that, when allene 2
is heated in refluxing heptane, yellow and red dimers are
formed.[3] The yellow product was subsequently identified as
head-to-tail dimer 6,[4] but the identity of the red product 7
remained unresolved. We now describe the sequential for-
mation and X-ray crystallographic characterization of six
dimers of allene 2, which are yellow (6), red (7), orange (8),
orange (9), pale yellow (10) and pale yellow (11), as well as
the structure of blue tetracene 4. Moreover, we offer a ra-
tionalization of the processes leading to successive isomeric
allene dimers, and ultimately to the tetracenes.
the dispirofluorenyldihydrotetracene
3 and the diinde-
no[1,2,3-de:1’,2’,3’-mn]tetracene 4. In air, the latter com-
pound is readily oxidized to peroxide 5. Alkyne 1, dispirote-
[a] E. V. Banide, Dr. Y. Ortin, Dr. C. M. Seward, Dr. H. Müller-Bunz,
Prof. Dr. M. J. McGlinchey
UCD School of Chemistry and Chemical Biology
University College Dublin, Belfield, Dublin 4 (Ireland)
Fax : (+353)1-716-1185
E-mail: michael.mcglinchey@ucd.ie
[b] Dr. L. E. Harrington
Department of Chemistry, McMaster University
Hamilton, ON, L8S4M1 (Canada)
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3-(9-fluorenylidene)-2-phenyl-4-
phenylmethylenespiro[cyclobu-
tane-1,9’-fluorene] (6) has
a
head-to-tail 1,2-dialkylidenecy-
clobutane structure in which
one spiro-bonded fluorenyl-
idene moiety is linked through
ꢀ
a long (1.605 Š) C3 C4 bond
Results and Discussion
to a benzylidene unit. In the
exocyclic phenylmethylene substituent the phenyl group is
positioned exo and the interplanar angle C5-C1-C2-C18 be-
tween the two exocyclic double-bonded fragments is 388.
In contrast, when the same reaction was performed at
room temperature, 6 was again the major product, but
traces of the previously unidentified red compound 7 were
found. However, when alkyne 1 and triethylamine were
heated together in refluxing dichloromethane at 408C, red
dimer 7 was more abundant and could be separated from
yellow isomer 6 by chromatography on silica. Recrystalliza-
tion from dichloromethane/pentane furnished crystals suita-
ble for an X-ray diffraction study, and the identity of 7 was
When alkyne 1 is stirred in pentane at 08C for 5–7 h in the
presence of triethylamine, a yellow precipitate of 6 gradually
forms. X-ray quality crystals of 6 were obtained from diethyl
ether/hexane; the structure (Figure 1) confirms the original
assignment.[4a] As shown in Scheme 1, the yellow dimer,
revealed as trans-3,4-diphenyl-1,2-bis(fluorenylidene)cyclo-
[5]
butane. Figure 2depicts the palindromic
helical molecule
of pseudo-C2 symmetry such that the two phenyl substitu-
ents in the cyclobutane ring adopt a trans configuration; the
two exocyclic fluorenylidene fragments overlap considerably
and are twisted out of the ring plane and in the same helical
sense as the phenyl groups. Thus, for the enantiomer of 7
depicted in Scheme 1 and Figure 2, the fluorenylidene moi-
eties at C1 and C2, when viewed along the twofold axis
ꢀ
ꢀ
passing through the midpoints of C1 C2and C3 C4 succes-
sively, give rise to a P helix[6] while C3 and C4 each have R
configurations. The four-membered ring is almost flat, and
3
ꢀ
the length of the C3 C4 bond linking the two sp ring
Figure 1. Molecular structure of yellow head-to-tail dimer 6; thermal el-
lipsoids are drawn at the 50% probability level.
carbon atoms is now only 1.587 Š. The dihedral angle be-
tween the fluorenylidene planes
is 418.
In a subsequent experiment,
yellow head-to-tail dimer 6 was
held at 808C overnight to yield,
after chromatographic separa-
tion, orange dimer 8, which was
identified by NMR spectrosco-
py as cis-3,4-diphenyl-1,2-bis-
(fluorenylidene)cyclobutane. In
this case, each of the exocyclic
fluorenylidene moieties exhibit-
1
ed eight H NMR signals, which
clearly shows that the molecule
is no longer C2-symmetric; like-
wise, the methyne protons in
the cyclobutane ring appeared
as doublets (J=8.4 Hz) at 5.40
and 5.29 ppm. These data were
paralleled in the 13C NMR spec-
trum, which again indicated the
reduced symmetry of the mole-
Scheme 1. Sequential formation of allene dimers and tetracenes.
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Allenes
FULL PAPER
Figure 2. a) Molecular structure of red trans dimer 7; thermal ellipsoids
are drawn at the 50% probability level. b) Space-filling view of red trans
dimer 7, emphasizing the overlap of the fluorenylidene moieties.
Figure 3. a) Molecular structure of orange cis-3,4-diphenyl-1,2-bis(fluore-
nylidene)cyclobutane (8). Only one of the four independent molecules in
the unit cell is shown. b) Space-filling view of orange cis dimer 8, empha-
sizing the severe overlap of the fluorenylidene moieties.
cule, whose structure was unequivocally confirmed by X-ray
crystallography (Figure 3). The monoclinic unit cell (Z=8)
contains four independent molecules, and the dihedral angle
between the fluorenylidene planes is now 62ꢁ28.
of the two trans diastereomers was observed with an equili-
brium ratio for 7:9 of approximately 1:6, as determined by
NMR spectroscopy. Clearly, orange isomer 9, in which the
dihedral angle between the bulky fluorenylidene groups is
now 608, is markedly favored over its red trans counterpart
7 and cis isomer 8.
Finally, thermolysis of yellow head-to-tail dimer 6 in re-
fluxing toluene at 1108C yields yet a fourth allene dimer,
namely, 9, an orange material that is relatively insoluble in
diethyl ether and thus readily separable from the small
quantity of red dimer 7 that is also formed. Recrystallization
from dichloromethane/diethyl ether/hexane gave crystals of
X-ray quality, and the resulting structure is depicted in
Figure 4. The molecule of 9 has almost perfect C2 symmetry,
with atom connectivity identical to that found in red dimer
7, but the helicity of the two exocyclic fluorenylidene frag-
ments has now been reversed. Thus, for the structure depict-
ed in Scheme 1 and Figure 4, the fluorenylidene moieties in
9 now give rise to an M helix while C3 and C4 maintain
their R configurations. That is, the fluorenylidene moieties
are now oriented such that they are aligned with the hydro-
gen atoms in the cyclobutane ring, which adopts a markedly
As noted at the outset, we had previously proposed that
the blue diphenyldiindeno[1,2,3-de:1’,2’,3’-mn]tetracene (4)
arose via rearrangement of an allene dimer,[1] and this has
now been confirmed by thermolysis of yellow head-to-tail
dimer 6 in dimethyl sulfoxide at 1808C for 6 h. The dark
blue crystals thus obtained were characterized by X-ray dif-
fraction, and the structure is illustrated in Figure 5a. In the
solid state, the molecule is not fully planar but rather adopts
a centrosymmetric (Ci) conformation such that the indenyl
moieties are curved away from the central tetracene frame-
work by 188; the phenyl substituents each make a dihedral
angle of 578 with the planar tetracene unit. This places one
hydrogen atom (H12) in each of the exterior six-membered
rings of the fluorenyl units almost directly above a peripher-
ꢀ
nonplanar “butterfly-type” conformation in which the C3
C4 bond length is now 1.594 Š (average of three independ-
ent molecules in the unit cell). When a pure sample of
orange dimer 9 was held at 1108C for 8 h, interconversion
1
al phenyl substituent, which results in a H NMR shielding
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M. J. McGlinchey et al.
Figure 4. a) Molecular structure of orange trans dimer 9; thermal ellip-
soids are drawn at the 50% probability level. b) Space-filling view of
orange trans dimer 9, emphasizing the inversion of helicity of the fluore-
nylidene moieties relative to that in the structure of red trans dimer 7.
of 1.3 ppm relative to its para-situated counterpart (H9) in
the same ring.[1] In the solid state, p stacking between tetra-
cenes is evident (Figure 5b).
Figure 5. a) Top view of the molecular structure of blue tetracene 4; ther-
mal ellipsoids are drawn at the 50% probability level. b) Front and side
views showing the p stacking of blue tetracene 4.
The blue tetracene 4 can be kept in the dark under a ni-
trogen atmosphere for an extended period; however, when
exposed to oxygen and sunlight, it is gradually converted to
the pale yellow peroxide 5, whose structure is shown in
Figure 6. It has long been known that linear polyaromatics
such as naphthacene and pentacene readily undergo addi-
tion of dioxygen,[7] perhaps via excitation to the triplet state,
which facilitates reaction with ground-state triplet dioxygen.
However, a recent report[8] describes the reaction of a tetra-
kis(trimethylsilyl)pentacene with oxygen when exposed to
sunlight, and the possible involvement of a radical cation
was discussed. One could also envisage a third possibility,
namely, formation of singlet oxygen through sensitization by
4 followed by a [4+2] cycloaddition.
conformation (Figure 7b), whereby the spiro-bonded fluo-
renyl moieties are each folded to the same side of the tetra-
cene framework by about 178. However, as a single com-
pound, 3 adopts Ci symmetry (as does 4) such that the tetra-
cene skeleton resembles a chaise-longue in which the termi-
nal rings are bent in opposite directions out of the central
plane through 148, and the spiro-bonded fluorenyl units are
also folded out of this plane, by 188, but now lie on opposite
sides of this central framework. Although both tetracenes 3
and 4 adopt Ci conformations in the solid state, they have
considerable flexibility, since their NMR spectra are entirely
consistent with time-averaged C2h symmetry.
In a preliminary communication,[1] we reported the struc-
ture of dispirodihydrotetracene 3 as a cocrystal with perox-
ide 5. We have now obtained single crystals of 3, and the
structure appears in Figure 7a. In the previous determina-
tion,[1] the molecule exhibited a “twisted-saddle” C2-type
In their 1965 paper,[3] Kuhn and Rewicki also noted that
deprotonation of yellow head-to-tail dimer 6 with potassium
tert-butoxide in DMSO immediately produced a blue anion-
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Allenes
FULL PAPER
ic species; subsequent reprotonation with acetic acid yielded
isomeric, but unidentified, pale yellow product 10. Upon re-
peating this procedure, a sample of 10 was obtained, the
structure of which was elucidated by NMR spectroscopy
and confirmed by X-ray crystallography. In the 1H NMR
spectrum of 6, all eight protons in each of the fluorenyl moi-
eties were distinguishable, as anticipated for a molecule of
such low symmetry. However, after the deprotonation/repro-
tonation sequence, each of the fluorenyl groups exhibited
only four proton environments, which implies the existence
of a time-averaged molecular mirror plane; likewise, the
1
13C NMR spectra of 6 and 10 paralleled the H NMR results.
These observations suggested that the intermediate blue
species was best represented as a 14p fluorenide anion, and
that reprotonation had occurred at the C9 position of the
exocyclic fluorenyl substituent to give 1-(9-fluorenyl)-2-
phenyl-4-phenylmethylenespiro[cyclobutene-3,9’-fluorene]
(Scheme 1). The X-ray crystallographic structure of 10
(Figure 8) clearly reveals the formation of a cyclobutene
ring bearing a 9-fluorenyl substituent in the rearranged
product.
Figure 6. Molecular structure of tetracene peroxide 5.
Figure 8. Molecular structure of [1,3]-hydrogen migration product 10;
thermal ellipsoids are drawn at the 50% probability level.
Moreover, Rewicki and Kuhn[3] reported that they were
unable to deprotonate the unidentified red allene dimer,
now known to be trans-3,4-diphenyl-1,2-bis(fluorenylidene)-
cyclobutane (7). However, we found that when orange
isomer 9 was allowed to react with potassium tert-butoxide
in DMSO for an extended time (1–3 h), a greenish blue
anionic species was formed; subsequent reprotonation with
acetic acid yielded the [1,3]-hydrogen migration product 1-
(9-fluorenyl)-2,3-diphenyl-4-fluorenylidenecyclobutene (11),
analogous to that produced from yellow dimer 6. The struc-
ture of 11 appears as Figure 9. Apparently, deprotonation of
9 is sterically hindered relative to the situation in head-to-
tail isomer 6, and thus anion formation is a much slower
process. Red dimer 7 behaves similarly when treated with
potassium tert-butoxide in DMSO for 1 h; moreover, repro-
Figure 7. a) Top and side views of spirotetracene 3; thermal ellipsoids are
drawn at the 50% probability level. b) Molecular structure of the dispiro-
tetracene 3 when cocrystallized with 5.
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M. J. McGlinchey et al.
Further heating converts 6 to red dimer 7, in which both
fluorenylidene units are now exocyclic. One can readily en-
ꢀ
visage cleavage of the long C3 C4 bond (1.605 Š) in 6 to re-
generate the tetramethylene ethane diradical having a
phenyl and a biphenylene group, which can exist in three
isomeric forms: endo,endo (12), endo,exo (13) and exo,exo
(14). Now, following the allene dimerization mechanism pro-
posed by Christl,[13] conrotatory ring closure of endo,endo
form 13 leads to red trans dimer 7, while, at successively
higher temperatures endo,exo and exo,exo isomers 13 and 14
lead to the orange cis and orange trans products 8 and 9, re-
spectively.
Experiments are currently in progress on analogous mole-
cules having trifluoromethyl substituents in the phenyl rings,
which will allow rate data to be conveniently obtained
through 19F NMR measurements. These studies are aimed at
elucidating the kinetic parameters for this series of isomeri-
zations, and may help to further clarify the situation.
Figure 9. Molecular structure of [1,3]-hydrogen migration product, 11;
thermal ellipsoids are drawn at the 50% probability level.
tonation with acetic acid yield-
ed not only the [1,3]-hydrogen
migration product 11, but also
small quantities of orange
dimer 9, as befitting its status as
the thermodynamically more
stable atropisomer of trans-3,4-
diphenyl-1,2-bis(fluorenylidene)-
cyclobutane.
Mechanistic
considerations:
Having established not only the
molecular structures of the four
allene dimers 6–9, but also the
fact that they are sequentially
produced, one must offer a ra-
tionale for these observations.
Evidently, the initial yellow
head-to-tail dimer 6 is the ki-
netic product, and so must arise
Scheme 2. Proposed mechanism for the formation of allene dimers 6–9.
from the allene starting materi-
al 2 via a low-energy pathway
that does not involve extensive molecular reorganization.
Although a [p2s+p2a] cycloaddition mechanism for allene di-
merization is orbital-symmetry-allowed, a stepwise process
involving a diallylic diradical intermediate is more common-
ly invoked.[9–12] The orthogonal arrangement of substituents
in allenes, together with the obvious preference of large
groups to minimise steric hindrance, suggests that the initial
geometry of approach of two molecules of 2 is favored by a
C2-type trajectory, as depicted in Scheme 2.[13] Thus, at the
moment of generation, the most favorably oriented p orbi-
tals through which radical coupling can occur are located on
unlike termini, and a least-motion rotation about the central
bond suffices to bring these centers close enough for bond
formation to occur, and leads directly to the initially ob-
served yellow dimer 6.
As noted above, prolonged thermolysis of yellow allene
dimer 6 yields the dispirodihydrotetracene 3 and diindenote-
tracene 4. It is relevant to note the important studies by
Capdeveille and Rigaudy,[11] and also by Christl and co-
workers,[12] who demonstrated the intermediacy of biallyl
diradicals that can be delocalized onto the ortho positions of
neighboring aromatic rings and thus allow formation of six-
membered rings.
In Scheme 3, we show how these ideas can account for
the generation of the observed products 3–5. Cleavage of
ꢀ
the long C3 C4 bond (1.605 Š) of initially formed [2+2]
dimer 6 leads ultimately to diradical 14, from which one can
envisage coupling either between an ortho-phenyl site and
the C9 position of a neighboring fluorenyl ring (to give 15),
or between an ortho-fluorenyl position and the benzylic site
(leading to 16). Subsequent disrotatory electrocyclization of
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Allenes
FULL PAPER
there is always a side product
1
that, according to the H NMR
spectrum, contains a fluorenyl
group, a disubstituted phenyl
fragment and a triethylsilyl sub-
stituent. The identity of this
material was resolved unequiv-
ocally by X-ray crystallography
(Figure 11), which revealed the
it to be 2’-triethylsilylspiro-
[fluorene-9,1’-1H-indene] (17),
in which the fluorenyl moiety is
spiro-linked to a triethylsilyl-
substituted indenyl ring. One
might venture to suggest that
the Et3SiF now present in the
system might react with some
already formed allene 2 (by re-
arrangement of alkyne 1) to
Scheme 3. Proposed mechanism for the formation of tetracenes 3 and 4.
the 6p system in 15 and 16 generates the required molecular
frameworks, and aerial oxidation yields the observed prod-
ucts 3 and 4 and, eventually, 5.
Spectroscopic data: The striking color change (red to
orange-yellow) observed during the transformation of 7 via
8 into 9 is an interesting phenomenon. In the visible region,
the spectra of these compounds show strong absorptions at
457 (e=11300), 446 (e=25000) and 431 nm (e=27000), re-
spectively. Thus, dimer 7 absorbs mainly in the blue and
green regions, and thus appears red; in contrast, 8 and 9
absorb primarily in the blue and violet regions, and thus
appear orange-yellow. One can perhaps relate these colors
to the different degrees of conjugation between the two flu-
orenylidene moieties. In red isomer 7, the dihedral angle
C5-C1-C2-C18 between these substituents is 418, but this
opens up to 628 in 8, and 608 in 9. Assuming that a greater
deviation from coplanarity increases the HOMO–LUMO
gap, one would anticipate absorption at higher energy in 8
and 9, and this is indeed the case.
Figure 10. Luminescence data for blue tetracene 4 (10ꢀ4 m, THF). UV/Vis
absorption (solid line), fluorescent excitation (broken line), and fluores-
cent emission (&) spectra.
One of our original goals was to investigate the lumines-
cence behaviour of diindenotetracene 4, and the relevant
data are shown in Figure 10. This compound absorbs strong-
ly in red and yellow regions, and thus appears blue; in con-
trast, intense emission is observed in the red region at
665 nm.
An interesting final observation concerns the synthesis of
9-phenylethynylfluorene (1) from 9-phenylethynylfluoren-9-
ol by treatment with boron trifluoride and triethylsilane.[14]
The mechanism presumably involves coordination of the hy-
droxyl group to boron, transfer of fluorine from boron to sil-
icon and delivery of a hydride from silicon to carbon to fur-
nish the desired alkyne 1, possibly via single cyclic transition
state. In our hands, the reaction works reasonably satisfacto-
rily (50–60% yield of isolated product) and the alkyne has
been characterized by X-ray crystallography.[2] However,
Figure 11. Molecular structure of spiro-cyclized product 17; thermal ellip-
soids are drawn at the 50% probability level.
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M. J. McGlinchey et al.
by chromatography on silica gel with dichloromethane/pentane (1/9) as
eluent. 9-Phenylethynylfluorene (1) was isolated as a yellow solid (4.1 g,
15.4 mmol; 51%), m.p. 127–1308C, lit.: 129–1318C.[3] A second product,
9H-fluorene-9-spiro-1’-[2’-triethylsilylindene] (17), m.p. 89–948C, was
also obtained (300 mg, 0.8 mmol; 2.7%). A sample suitable for an X-ray
crystal structure determination was obtained by recrystallization from di-
chloromethane/hexane.
generate a b-silyl stabilized cation, as depicted in Scheme 4.
Subsequent Nazarov-type cyclization would lead directly to
the observed product 17. Related structures having spiro-
Data for 1: 1H NMR (500 MHz, CDCl3): d=7.83 (d, 2H, J=7.5 Hz, H4,
H5), 7.81 (d, 1H, J=7.5 Hz, H1, H8), 7.50 (d, 2H, 7.5 Hz, phenyl o-H),
7.48 (t, 2H, J=7.5 Hz, H3, H6), 7.44 (t, 2H, J=8.0 Hz, H2, H7), 7.34–
7.32(m, 3H, phenyl m-H, p-H), 5.02ppm (s, 1H, H9); 13C NMR
(125 MHz, CDCl3): d=144.1 (C8a, C9a), 140.6 (C4a, C4b), 131.9 (phenyl
o-C), 128.3 (phenyl m-C), 128.1 (phenyl p-C), 128.0 (C3, C6), 127.7 (C2,
C7), 125.2 (C1, C8), 123.6 (C3’a), 120.2 (C4, C5), 87.3 (C2’), 82.2 (C3’),
40.0 ppm (C9); elemental analysis calcd (%) for C21H14: C 94.70, H 5.30;
found: C 94.37, H 5.53.
Data for 17: 1H NMR (500 MHz,
CDCl3): d=7.79 (d, 2H, J=7.5 Hz,
H4, H5), 7.40 (d, 1H, J=7.5 Hz, H4’),
7.35 (s, 1H, H3’), 7.35 (td, 2H, J=7.5,
1.0 Hz, H3, H6), 7.22 (t, 1H, J=
7.5 Hz, H5’), 7.11 (t, 2H, J=7.5 Hz,
Scheme 4. Proposed Nazarov cyclization mechanism to form the spiro
product 17.
H2, H7), 6.96 (t, 1H, J=7.5 Hz, H6’),
6.82(dd, 2H, J=7.5, 1.0 Hz, H1, H8),
bonded fluorenyl and indenyl fragments include the 3’-
phenyl analogue that arises upon acidification of 9-(2,2-di-
phenylvinyl)fluoren-9-ol.[15] Moreover, we note that treat-
ment of 1,1-diphenyl-3,3-biphenyleneallene with bromine in
6.57 (d, 1H, J=7.5 Hz, H7’), 0.66 (t,
9H, J=8.0 Hz, CH3), 0.09 ppm (q, 6H,
J=8.0 Hz, CH2); 13C NMR (125 MHz,
CDCl3): d=152.1 (C7a’), 151.9 (C2’),
146.1 (C8a, C9a), 145.2(C3a ’), 144.0
CCl4
gives
2’-bromo-3’-phenylspiro[fluorene-9,1’-1H-
(C3’), 142.3 (C4a, C4b), 127.7 (C3, C6), 127.4 (C2, C7), 127.1 (C5’), 126.1
(C6’), 124.1 (C1, C8), 122.3 (C7’), 120.8 (C4’), 120.1 (C4, C5), 72.4 (C9),
7.2(CH 3), 2.9 ppm (CH2); elemental analysis calcd (%) for C27H28Si: C
85.21, H 7.42; found: C 84.99, H 7.67.
indene].[16]
To conclude, it has been established that dimerization of
allene 2 proceeds in several steps, the products of each of
which can be isolated and fully characterized. At higher
temperatures, expansion of the four-membered ring to a six-
membered ring, subsequent electrocyclization and, finally,
elimination of hydrogen leads to tetracene formation. The
generality of this process and the optical properties of a
wide variety of tetracenes are currently being explored. We
have also synthesized push–pull allene dimers[17] bearing fer-
rocenyl and other organometallic fragments, and the struc-
tures, dynamics and reactivity of these compounds will be
the subject of a future report.
Synthesis of 6: Triethylamine (200 mL, 0.29 mmol) was added to a suspen-
sion of 9-phenylethynylfluorene (1; 1.31 g, 4.92mmol) in pentane
(25 mL) at 08C, and the suspension was stirred for 5 h at 08C and then
overnight in a cold water bath. The precipitate was collected by filtration,
washed with cold pentane and dried to give 3-(9-fluorenylidene)-2-
phenyl-4-phenylmethylenespiro[cyclobutane-1,9’-fluorene] (6; 956 mg,
1.80 mmol; 73%) as a yellow powder, m.p. 175–1788C, lit.: 184–1868C.[3]
A sample suitable for an X-ray crystal structure determination was ob-
tained by recrystallization from dichloromethane/pentane.
1
Data for 6: H NMR (500 MHz, CDCl3); numbering is in accord with the
crystal structure: d=8.65 (d, 1H, J=8.0 Hz, H16), 7.85 (d, 1H, J=
Experimental Section
1H and 13C NMR spectra were recorded on a Varian Inova 300 MHz or
500 MHz spectrometer. Assignments were based on standard 2D NMR
techniques (1H–1H COSY, 1H–13C HSQC, and HMBC, NOESY). Elec-
trospray mass spectrometry was performed on a Micromass Quattro
micro instrument. Infrared spectra were recorded on a Perkin-Elmer Par-
agon 1000 FTIR spectrometer and were calibrated with polystyrene.
Merck silica gel 60 (230–400 mesh) was used for flash chromatography.
Melting points were determined on an Electrothermal ENG. instrument
and are uncorrected. Elemental analyses were carried out by the Micro-
analytical Laboratory at University College Dublin.
Syntheses of 1 and 17: Triethylsilane (5.7 mL, 36.1 mmol) was added
slowly to 9-phenylethynylfluoren-9-ol (8.5 g, 30.1 mmol) in dry dichloro-
methane (250 mL) at 08C. BF3·OEt2 (4.4 mL, 36.1 mmol) was added
dropwise, and the solution became green-brown. After stirring for 30 min
at 08C, the reaction was quenched with distilled water (100 mL), and the
mixture was extracted with diethyl ether several times. The organic
layers were washed with water and with brine successively, dried over
MgSO4, filtered and concentrated to give a brown solid that was purified
7.5 Hz, H13), 7.81 (d, 1H, J=7.5 Hz, H29), 7.78 (d, 1H, J=7.5 Hz, H10),
7.71 (d, 1H, J=7.5 Hz, H26), 7.69 (s, 1H, H18), 7.67 (d, 1H, J=7.5 Hz,
H32), 7.56 (brs, 1H, H38 or H42), 7.43 (td, 1H, J=7.5, 1.0 Hz, H14),
7.40 (td, 1H, J=7.5, 1.0 Hz, H27), 7.34 (td, 1H, J=7.5, 1.0 Hz, H15),
7.27 (td, 1H, J=7.5, 1.0 Hz, H9), 7.25 (td, 1H, J=7.5, 1.0 Hz, H28), 7.21
(brs, 1H, H39 or H41), 7.20 (d, 1H, J=8.0 Hz, H7), 7.12(t, 1H, J=
3282
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Chem. Eur. J. 2006, 12, 3275 – 3286

Allenes
FULL PAPER
7.5 Hz, H40), 7.09 (td, 1H, J=7.5, 1.0 Hz, H33), 7.03 (brs, 1H, H39 or
H41), 6.99 (td, 1H, J=7.5, 1.0 Hz, H8), 6.89 (t, 1H, J=7.5 Hz, H22), 6.79
(t, 2H, J=7.5 Hz, H21, H23), 6.55 (d, 2H, 7.5 Hz, H20, H24), 6.52 (td,
1H, J=7.5, 1.0 Hz, H34), 6.49 (brs, 1H, H38 or H42), 6.09 (d, 1H, J=
8.0 Hz, H35), 5.16 ppm (s, 1H, H4); 13C NMR (125 MHz, CDCl3): d=
150.1 (C25), 144.2 (C2), 143.9 (C1), 141.7 (C36), 141.4 (C31), 140.6
(C12), 140.0 (C11), 139.8 (C30), 138.4 (C6), 137.9 (C17), 137.8 (C37),
134.7 (C19), 131.5 (C5), 130.3 (C38, C42), 128.8 (C20, C24), 128.4 (C14),
128.1 (C18), 128.0 (C28), 127.8 (C9), 127.8 (C27), 127.6 (C22), 127.5
(C15), 127.4 (C21, C23), 127.4 (C33), 127.2 (C8), 127.1 (C40), 126.5
(C35), 126.1 (C34), 125.2 (C7), 124.1 (C16), 122.8 (C26), 120.1 (C13),
119.9 (C29), 119.7 (C22), 119.4 (C32), 63.4 (C3), 61.7 ppm (C4).
Syntheses of 7 and 9: When yellow dimer 6 was dissolved in dichlorome-
thane and heated at reflux for 1.5 h, the presence of a red product was
evident. After removal of solvent and redissolution in cyclohexane
(3 mL), 6 (55 mg, 0.10 mmol) was heated at reflux overnight. After re-
moving the solvent, NMR examination of the crude material indicated a
13:1 ratio of yellow dimer to red dimer. Chromatographic separation and
recrystallization from dichloromethane/pentane (1/9) gave X-ray quality
crystals of trans-3,4-diphenyl-1,2-bis(fluorenylidene)cyclobutane (7), m.p.
62.5 ppm (C3, C4); elemental analysis calcd (%) for C42H28: C 94.70 H
5.30; found: C 93.98, H 5.57.
Synthesis of 8: Yellow dimer 6 (330 mg, 0.62mmol) suspended in toluene
(5 mL) was heated at 858C for 30 h. After removing the solvent, the
crude product was purified by chromatography on alumina with dichloro-
methane/cyclohexane (1/9) as eluent. cis-3,4-Diphenyl-1,2-bis(fluorenyl-
idene)cyclobutane (8) was isolated as an orange solid (33.9 mg,
0.06 mmol; 10%), m.p. 214–2188C (decomp). A sample suitable for an
X-ray crystal structure determination was obtained by recrystallization
from dichloromethane/diethyl ether.
223–2268C, lit.: 227–2298C.[3] Analogously, yellow dimer
6 (100 mg,
0.19 mmol) suspended in toluene (5 mL) was heated at reflux for 3 d, and
the product was concentrated to give a brown oil and triturated with di-
ethyl ether to give orange dimer 9 (52mg, 0.1 mmol; 52%), m.p. 196–
2008C. A sample suitable for an X-ray crystal structure determination
was obtained by recrystallization from dichloromethane/diethyl ether/
hexane.
1
Data for 8: H NMR (500 MHz, CDCl3): d=7.75 (d, 1H, J=7.5 Hz), 7.72
(d, 2H, J=7.5 Hz), 7.66 (d, 1H, 7.5 Hz), 7.63 (dd, 1H, J=7.0, 1.0 Hz),
7.38 (d, 1H, J=7.5 Hz), 7.38 (brs, 1H), 7.34–7.10 (m), 7.13 (td, 1H, J=
7.5, 0.5 Hz), 7.08–6.95 (m, 5H), 6.94–6.85 (m, 2H), 6.77 (td, 1H, J=7.5,
1.0 Hz), 6.65 (brs, 0.5H), 6.45 (brs, 1H), 6.18 (brs, 1H), 5.42(d, 1H, J=
8.5 Hz), 5.31 ppm (d, 1H, J=8.5 Hz); 13C NMR (125 MHz, CDCl3): d=
145.6, 141.4, 140.6, 140.3, 140.3, 140.2, 138.7, 138.3, 137.4, 137.4, 137.1,
136.3, 135.2, 134.8, 129.7 (brs), 129.0 (brs), 128.7, 128.6, 128.4 (brs),
128.3, 127.9, 127.8 (brs), 127.5, 127.5, 127.2 (brs), 127.2, 126.8, 126.6,
126.5, 126.4, 126.3, 125.6, 125.2, 120.0, 119.5, 119.4, 119.4, 58.2, 56.3 ppm;
elemental analysis calcd (%) for C42H28·0.25CH2Cl2·0.5Et2O: C 89.62, H
5.89; found: C 89.89, H 5.62.
1
Data for 7: H NMR (500 MHz, CDCl3); numbering is in accord with the
crystal structure: d=7.68 (d, 2H, J=7.5 Hz, H10, H26), 7.62 (d, 2H, J=
7.0 Hz, H13, H23), 7.29 (d, 2H, J=8.0 Hz, H7, H29), 7.24 (t, 2H, J=
7.5 Hz, H9, H27), 7.22 (d, 4H, J=7.5 Hz, phenyl o-H), 7.18 (t, 4H, J=
Synthesis of 10: Potassium tert-butoxide (126 mg, 1.13 mmol) was added
portionwise to a solution of yellow dimer 6 (500 mg, 0.94 mmol) in di-
methyl sulfoxide (10 mL), and the solution turned dark blue. After stir-
ring at room temperature for 1 h, the reaction was quenched with a solu-
tion of acetic acid (20 mL; 2 mL acetic acid in 50 mL water) and extract-
ed twice with diethyl ether. The organic phases were combined, washed
with brine, dried over MgSO4, filtered and concentrated to give a yellow
solid. The crude material was triturated with diethyl ether to give 9
(343 mg, 0.64 mmol; 68%) as a pale yellow solid, m.p. 194–1968C, lit.:
233–2358C (with sintering at 1908C).[3] A sample suitable for an X-ray
crystal structure determination was obtained by recrystallization from di-
chloromethane/diethyl ether/hexane.
7.5 Hz, phenyl m-H), 7.14 (t, 4H, J=7.0 Hz, H14, H22, phenyl p-H), 7.09
(d, 2H, J=7.5 Hz, H20, H16), 6.87 (td, 2H, J=7.5 Hz, H8, H28), 6.86
(td, 2H, J=7.5 Hz, H15, H21), 4.73 ppm (s, 2H, H3, H4); 13C NMR
(125 MHz, CDCl3): d=143.9 (C1, C2), 141.2 (C31, C37), 140.5 (C12,
C24), 140.4 (C11, C25), 138.0 (C17, C19), 136.7 (C6, C30), 135.9 (C5,
C18), 128.8 (phenyl m-C), 128.7 (C9, C27), 128.0 (C14, C22), 127.5
(phenyl o-C), 127.0 (C8, C28, phenyl p-H), 126.5 (C15, C21, C16, C20),
126.3 (C7, C29), 119.6 (C13, C23), 119.3 (C10, C26), 61.2 ppm (C3, C4);
elemental analysis calcd (%) for C42H28·0.5 CH2Cl2: C 88.75 H 5.08;
found: C 88.11, H 5.57.
Data for 10: 1H NMR (500 MHz, CDCl3): d=7.95 (d, 2H, J=7.5 Hz),
7.89 (d, 2H, J=7.5 Hz), 7.83 (d, 2H, J=7.5 Hz), 7.52(t, 2H, J=7.5 Hz),
7.46 (d, 2H, J=7.5 Hz, H), 7.43 (td, 2H, J=7.5 Hz), 7.38 (td, 2H, J=
7.5 Hz), 7.22 (td, 2H, J=7.5 Hz), 7.15–6.95 (m, 5H), 6.80–6.65 (m, 4H),
1
Data for 9: H NMR (500 MHz, CDCl3); numbering is in accord with the
crystal structure: d=7.75 (d, 2H, J=7.5 Hz, H13, H23), 7.74 (dd, 2H, J=
8.0, 1.5 Hz, H10, H26), 7.52 (d, 2H, J=8.0 Hz, H16, H20), 7.49 (d, 4H,
J=7.0 Hz, phenyl o-H), 7.32(t, 6H, J=7.5 Hz, H14, H22, phenyl m-H),
7.29 (t, 2H, J=7.5 Hz, H9, H27), 7.27 (d, 2H, J=7.0 Hz, H7, H29), 7.24
(t, 2H, J=7.5 Hz, phenyl p-H), 7.05 (td, 2H, J=7.5, 0.5 Hz, H8, H28),
7.03 (td, 2H, J=7.5, 1.0 Hz, H15, H21), 4.80 ppm (s, 2H, H3, H4);
13C NMR (125 MHz, CDCl3) 143.0 (C1, C2), 142.0 (C31, C37), 140.6
(C11, C25), 140.3 (C12, C24), 138.6 (C6, C30), 136.8 (C17, C19), 134.8
(C5, C18), 129.5 (phenyl m-C), 128.7 (C14, C22), 128.4 (C7, C29), 127.5
(C15, C21), 127.4 (C8, C28), 127.3 (phenyl o-C), 127.2 (phenyl p-C),
126.3 (C16, C20), 124.8 (C9, C27), 120.1 (C10, C26), 119.6 (C13, C23),
Chem. Eur. J. 2006, 12, 3275 – 3286
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3283

M. J. McGlinchey et al.
6.25–6.10 (m, 2H), 5.70 ppm (s, 1H); 13C NMR (125 MHz, CDCl3): d=
150.6 (brs), 146.3, 145.9 (C5, C16), 144.8 (C24, C35), 141.5 (C29, C30),
141.1 (C10, C11), 135.3, 132.6 (brs), 128.6 (Cphenyl), 128.1 (C8, C13,
13C NMR (125 MHz, CD2Cl2): d=141.3, 140.9, 138.4, 138.2, 130.5, 128.2
(C), 134.5, 128.7 (phenyl CH), 128.6 (C2), 127.4 (C1), 127.3 (C6), 126.5
(C7), 125.8 (C5), 120.9 (C4), 120.0 ppm (C3); HRMS: m/z: calcd for
C42H24 [M+]: 528.1878; found: 528.1873.
C
phenyl), 128.0 (C27, C32), 127.9, 127.9 (C7, C14, C26, C33), 127.8 (Cphenyl),
Data for 5: 1H NMR (600 MHz, CD2Cl2); numbering is in accord with
the crystal structure: d=8.42(1H, d, J=8.4 Hz, phenyl p-H), 8.20 (1H,
d, J=7.7 Hz, H1), 8.15 (1H, d, J=7.8 Hz, H4), 8.06 (1H, d, J=7.8 Hz,
H12), 7.96 (2H, d, J=7.0 Hz, phenyl o-H), 7.89 (1H, d, J=7.7 Hz, H9),
7.67 (1H, d, J=7.0 Hz, H11), 7.64 (2H, dd, J=7.1, 7.6 Hz, phenyl m-H),
7.62(1H, dd, J=7.6, 7.6 Hz, H5), 7.51 (1H, dd, J=7.9, 7.6 Hz, H13), 7.40
(1H, dd, J=7.9, 7.5 Hz, H2), 7.29–7.27 (2H, m, H6, H10), 7.21 (1H, dd,
J=7.6, 7.6 Hz, H14), 7.13–7.10 (2H, m, H3, H7), 6.96 (2H, d, J=7.1 Hz,
phenyl o-H), 6.82(1H, d, J=7.5 Hz, H15), 6.69 (1H, d, J=8.0 Hz,
phenyl p-H), 6.58 ppm (2H, dd, J=7.8, 7.7 Hz, phenyl m-H). The num-
bering for protons 1–3 and 9–11, as well as 4–7 and 12–15 may be inter-
changed. 13C NMR (150 MHz, CD2Cl2): d=144.3, 142.5, 141.0, 138.7,
136.6, 134.6, 133.6, 132.1 (C), 132.5, 129.7, 129.4, 129.3, 128.8, 128.0,
127.9, 127.3, 124.4, 123.8, 123.6, 122.9, 122.4, 121.6, 121.0 (CH), 128.9,
127.5, 126.5, 123.9 ppm (2CH); HRMS: m/z: calcd for C42H24O2 [M+]:
560.1776; found: 560.1776.
127.6, 125.8 (C36, Cphenyl), 126.6, 125.2 (C25, C34), 124.1 (C6, C15), 120.4
(C28, C31), 120.3 (C9, C12), 113.6 (brs), 65.8 (C1), 46.9 ppm (C23); ele-
mental analysis calcd (%) for C42H28·0.5CH2Cl2: C 88.75, H 5.08; found:
C 88.31, H 5.33.
Synthesis of 11: Potassium tert-butoxide (101 mg, 0.90 mmol) was added
portionwise to a solution of orange dimer 9 (300 mg, 0.56 mmol) in di-
methyl sulfoxide (6 mL), and the solution turned dark green-blue. After
stirring at room temperature for 3 h, the reaction was quenched with a
solution of acetic acid (10 mL; 2mL acetic acid in 50 mL water), and ex-
tracted twice with diethyl ether and dichloromethane. The organic phases
were combined, washed with brine, dried over MgSO4, filtered and con-
centrated to give a yellow solid. The crude material was triturated with
diethyl ether to give 11 (286 mg, 0.53 mmol; 95%) as a pale yellow solid,
m.p. 132–1358C (decomp). A sample suitable for an X-ray crystal struc-
ture determination was obtained by recrystallization from dichlorome-
thane/diethyl ether/hexane.
Data for 11: 1H NMR (500 MHz, CDCl3): d=8.40 (d, 1H, J=8.0 Hz),
7.97 (d, 1H, J=7.5 Hz), 7.92(d, 1H, J=8.0 Hz), 7.89 (d, 1H, J=8.0 Hz),
7.81 (d, 1H, J=7.5 Hz), 7.74 (d, 1H, J=7.0 Hz), 7.73 (d, 1H, J=7.5 Hz),
7.59 (d, 2H, J=8.0 Hz), 7.51 (t, 1H, J=7.5 Hz), 7.41 (t, 1H, J=7.5 Hz),
X-ray measurements for 3, 4, 6–10, 11, and 17: X-ray crystallographic
data (Table 1) were in each case collected from a suitable sample mount-
ed with grease on the end of a thin glass fiber. Data were collected on a
D8 Bruker diffractometer equipped with a Bruker SMART APEX CCD
area detector (employing the program SMART)[18] and an X-ray tube uti-
lizing graphite-monochromated MoKa radiation (l=0.71073 Š). A full
sphere of the reciprocal space was scanned by phi-omega scans. Data
processing was carried out by use of the program SAINT,[19] while the
program SADABS[20] was utilized for scaling of diffraction data and an
empirical absorption correction based on redundant reflections. Struc-
tures were solved by using the direct-methods procedure in the Bruker
SHELXL[21] program library and refined by full-matrix least-squares
methods on F2. In 4 and 6 all hydrogen atoms were located in the differ-
ence Fourier map and allowed to refine freely with isotropic temperature
factors, as were the hydrogen atoms in the main molecule of 11, where
the solvent hydrogen atoms were added at calculated positions, and re-
fined using a riding model. In the remaining structures all hydrogen
atoms were treated in this way. Anisotropic temperature factors were
used for all non-hydrogen atoms, except in 8 where the carbon atoms
could only be refined with isotropic temperature factors.
7.38–7.32(m, 4H), 7.31–7.21 (m, 2H), 7.16–7.09 (m, 2H), 6.91 (t, 1H,
J=
7.5 Hz), 6.80 (t, 2H, J=7.5 Hz), 6.48 (d, 2H, J=7.5 Hz), 5.96 (s, 1H),
5.37 ppm (s, 1H); 13C NMR (125 MHz, CDCl3): d=156.2, 147.8, 144.9,
144.3, 142.5, 141.5, 141.4, 140.8, 140.1, 139.1, 137.8, 131.7, 128.8, 128.5,
128.3, 128.3, 128.0, 128.0, 127.6, 127.5, 127.1, 126.9, 126.6, 126.6, 125.5,
125.3, 124.8, 124.6, 120.5, 120.1, 120.0, 119.4, 53.9, 49.3 ppm; elemental
analysis calcd (%) for C42H28·1.5Et2O: C 89.58, H 6.68; found: C 90.33,
H 6.24.
Syntheses of 3, 4 and 5: 9-Phenylethynylfluorene (636 mg, 2.39 mmol)
and tetracyclone (963 mg, 2.51 mmol) were added together, and the mix-
ture was heated over a free flame with an air condenser attached for
30 min. The solution was cooled, and 5 mL of benzene was added to pre-
vent solidification of the tetracyclone. The mixture was subjected to
column chromatography (100% hexanes to 100% CH2Cl2), which result-
ed in the recovery of tetracyclone and isolation of two major fractions:
pale yellow dispiro[fluorene-9,5’-11’H-naphthacene-11’,9’’-fluorene] (3;
164 mg, 0.31 mmol, 13%), m.p. 250–2538C, and deep blue 8,16-diphenyl-
diindeno[1,2,3-de:1’,2’,3’-mn]naphthacene (4; 570 mg, 1.1 mmol, 45%),
m.p. 167–1708C (decomp).
After completing the initial structure solution for 7, it was found that
27% of the total cell volume was filled with disordered solvent, which
could not be modelled in terms of atomic sites. From this point on, resid-
ual peaks were removed and the solvent region was refined as a diffuse
contribution without specific atom positions by using the PLATON
module SQUEEZE,[22] which subtracts electron density from the void re-
gions by appropriately modifying the diffraction intensities of the overall
structure. An electron count over the solvent region provides an estimate
for the number of solvent molecules removed from the cell. The number
of electrons thus located, 1474 per unit cell, was included in the formula,
formula weight, calculated density, m and F(000). This residual electron
density was assigned to two molecules of diethyl ether per molecule of 7
(1474/18=81.89 electrons per molecule of 7; two molecules of diethyl
ether would give 84 electrons). A dramatic improvement was observed in
all refinement parameters and residuals when this procedure was applied.
SQUEEZE was also used to treat disordered solvent in the structures of
8 and 10.
Alternatively, yellow dimer 6 (1.0 g, 1.88 mmol) suspended in dimethyl
sulfoxide (20 mL) was heated at reflux for 5 h, during which time a blue
coloration of the solution was observed. The solution was cooled, water
(20 mL) was added and the mixture was extracted with diethyl ether and
dichloromethane. The organic phases were combined, washed with brine,
dried over MgSO4, filtered and concentrated to give a dark oil. Chroma-
tographic separation with toluene/cyclohexane (1/9) and recrystallization
from dichloromethane/pentane, gave X-ray quality crystals of dispiro-
fluorenyldihydrotetracene 3 and diindeno[1,2,3-de:1’,2’,3’-mn]tetracene 4.
When 4 was left in air and exposed to daylight for several hours, it was
gradually oxidized to give pale yellow 8,16-diphenyl-8H-8,16b-epidioxy-
diindeno[1,2,3-de:1’,2’,3’-mn]naphthacene (5), m.p. 261–2648C.
Data for 3: 1H NMR (500 MHz, CD2Cl2); numbering is in accord with
the crystal structure: d=7.87 (4H, d, J=7.5 Hz, H16), 7.43 (4H, dd, J=
7.4, 7.4 Hz, H15), 7.20 (4H, dd, J=7.5, 7.4 Hz, H14), 7.16 (4H, d, J=
7.4 Hz, H13), 6.97 (2H, dd, J=7.5, 7.6 Hz, H2), 6.86 (2H, d, J=8.2Hz,
H1), 6.76 (2H, dd, J=7.5, 7.5 Hz, H3), 6.28 (2H, d, J=7.7 Hz, H4),
5.95 ppm (2H, H6); 13C NMR (125 MHz, CD2Cl2): d=153.5, 142.6, 140.6,
128.1, 127.9, 126.7 (C), 128.7 (C14), 128.4 (C15), 128.1 (C1), 127.8 (C3),
127.6 (C2), 126.5 (C4), 125.9 (C13), 120.8 (C16), 69.0 ppm (C6); HRMS:
m/z: calcd for C42H26 [M+]: 530.2035; found: 530.2010.
CCDC-273672 (6), CCDC-273673 (7), CCDC-273674 (9), CCDC-273675
(3), CCDC-273676 (10), CCDC-273677 (17), CCDC-273678 (4), CCDC-
273679 (11) and CCDC-273680 (8) contain the supplementary crystallo-
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.
Data for 4: 1H NMR (500 MHz, CD2Cl2): d=7.96 (4H, d, J=8.0, 6.3 Hz,
H1, H3), 7.86 (2H, d, J=7.4 Hz, H4), 7.67 (4H, brs, Ph), 7.61 (2H, dd,
J=7.6, 6.8 Hz, H2), 7.46 (6H, brs, Ph), 7.10 (2H, dd, J=7.2, 7.2 Hz, H5),
6.77 (2H, dd, J=7.6, 7.5 Hz, H6), 6.57 ppm (2H, d, J=8.0 Hz, H7);
3284
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ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 3275 – 3286

Allenes
FULL PAPER
Table 1. Crystallographic data.
3
4
6
7
8
9
10
11
17
formula
M
C42H26·2C4H10O C42H24
C42H28
532.64
C42H28·2C4H10O[c] C42H28
C42H28·1= C4H10O[c] C42H28·1= C4H10O[c] C42H28·C4H10O C27H28Si
2
3
678.87
528.61
670.80
532.64
569.70
557.33
606.76
380.58
crystal
system
space
Group
a [Š]
b [Š]
c [Š]
a [8]
triclinic
triclinic
monoclinic
trigonal
monoclinic orthorhombic
monoclinic
triclinic
triclinic
¯
¯
¯
¯
¯
P1
P1
Cc
R3
P21
Pbcn
P21/c
P1
P1
9.7183(17)
11.473(2)
18.316(3)
93.463(3)
97.648(4)
113.730(3)
1838.2(6)
21
6.2886(9)
18.2159(16) 44.0683(19)
15.233(6)
8.987(4)
38.173(3)
16.7503(11)
8.5223(9)
17.7609(19)
20.117(2)
90
99.502(2)
90
8.8824(12)
11.3304(15)
16.048(2)
86.752(2)
84.894(2)
88.268(2)
1605.6(4)
9.7574(15)
10.3304(16)
21.297(3)
95.133(3)
92.099(3)
97.908(3)
2115.1(6)
7.7305(11) 19.8116(17) 44.0683(19)
13.2639(19) 8.5724(7)
9.6514(9)
90
41.163(16) 28.754(2)
90 90
100.163(7) 90
93.099(2)
98.409(2)
100.014(2) 90
626.07(15) 2896.4(4)
18
90
b [8]
g [8]
110.5690(10) 90
120
16232.1(18)
90
90
V [Š3]
Z
1calcd
5547(4)
4
18386(2)
42
3003.3(5)
4
4
8
2
1.226
1.402
1.221
1.235
1.276
1.235
1.233
1.255
1.195
[gcmꢀ3
]
T [K]
100(2)
0.073
44.00
100(2)
0.080
52.22
4398
100(2)
0.069
52.00
100(2)
0.074
52.00
113(2)
0.0720.071
48.00
100(2)
100(2)
105(2)
100(2)
m [mmꢀ1
]
0.067
0.073
1
0.12
2qmax [8]
reflns meas- 16975
ured
45.00
101709
52.00
21816
52.00
11912
48.00
27278
22248
39446
23392
reflns used
(Rint
parameters 488
final R
4509 (0.0666)
2193
(0.0176)
238
2858
(0.0300)
491
6976 (0.0289)
379
14670
(0.0800)
674
12007 (0.0506)
1135
5759 (0.0256)
379
5916 (0.0197) 6614
(0.0489)
511
)
538
values
[I>2s(I)]:
R1[a]
0.0547
0.1140
0.0383
0.0987
0.0269
0.0671
0.0410
0.1035
0.1082
0.2623
0.0430
0.1008
0.0430
0.1108
0.0400
0.0921
0.0947
0.2545
wR2[b]
R values
(all data):
R1[a]
0.0838
0.1260
0.0444
0.1029
1.048
0.0276
0.0678
1.035
0.0521
0.1075
1.055
0.1400
0.2916
1.0321.041
0.0577
0.1064
0.0505
0.1146
0.0504
0.0981
1.178
0.1023
0.2570
wR2[b]
GOF on F2 1.059
1.070
6
1.02
[a] R1 =ꢀjjFo jꢀjFc jj/ꢀjFo j. [b] wR2 =[ꢀw(F2oꢀFc2)2/ꢀw(Fo2)2]1/2. [c] The diethyl ether molecule(s) could not be located in the unit cell. PLATON SQUEEZE
was used to compensate for the spread electron density.
ꢀ
[6] Taking the C1 C2bond axis as a locant, the relative orientations of
Acknowledgement
the fluorenylidene moieties can be defined as being clockwise (R)
or counterclockwise (S). Thus, the enantiomer of 7 depicted in
Figure 2could be labelled (3 R,4R)-trans-3,4-diphenyl-(1:2R)-bis-
(fluorenylidene)cyclobutane. See, for example, K. C. Nicolaou,
We thank Science Foundation Ireland and University College Dublin for
generous financial support, Dr. Nol Lugan, Laboratoire de Chimie de
Coordination, Toulouse, for advice on the use of the program SQUEEZE
C. N. C. Boddy, J. S. Siegel, Angew. Chem. 2001, 113, 723–726;
to resolve solvent disorder in crystal structures, and our colleagues Dr.
Angew. Chem. Int. Ed. 2001, 40, 701–704.
Mike Casey and Dr. Declan Gilheany for useful discussions. We are espe-
[7] L. F. Fieser, M. Fieser, Organic Chemistry, 3rd ed., Reinhold, New
cially grateful to Professor Manfred Christl (Universität Wurzbürg) for
York, NY, 1956, pp. 774–775.
very helpful comments on the manuscript. C.M.S. is the recipient of a
[8] S. H. Chan, H. K. Lee, Y. M. Wang, N. Y. Fu, X. M. Chen, Z. W. Cai,
post-doctoral fellowship from the Natural Sciences and Engineering Re-
H. N. C. Wong, Chem. Commun. 2005, 66–68.
search Council of Canada.
[9] L. Jacobs, J. R. McLenon, O. J. Muscio Jr., J. Am. Chem. Soc. 1969,
91, 6038–6041.
[10] F. Toda, H. Motomura, H. Oshima, Bull. Chem. Soc. Jpn. 1974, 47,
467–470.
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Received: September 23, 2005
Revised: December 11, 2005
Published online: February 10, 2006
3286
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Chem. Eur. J. 2006, 12, 3275 – 3286