Hairpin Furans and Giant Biaryls

Article abstract of DOI:10.1021/acs.joc.6b00492

The thermal reaction of two cyclopentadienones with 5,5′-binaphthoquinone or 6,6′-dimethoxy-5,5′-binaphthoquinone in refluxing nitrobenzene (210 °C) gives, in a single synthetic step that includes two Diels-Alder additions, two decarbonylations, and two d

Full text of DOI:10.1021/acs.joc.6b00492

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Article
Hairpin Furans and Giant Biaryls
Xin Geng, Joel T. Mague, James Patrick Donahue, and Robert Anthony Pascal
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.6b00492 • Publication Date (Web): 03 Apr 2016
Downloaded from http://pubs.acs.org on April 4, 2016
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Hairpin Furans and Giant Biaryls
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Xin Geng, Joel T. Mague, James P. Donahue, and Robert A. Pascal, Jr.*
Department of Chemistry, Tulane University, New Orleans, LA 70118, USA
E-mail: rpascal@tulane.edu
Abstract: The thermal reaction of two cyclopentadienones with 5,5'-binaphthoquinone or 6,6'-
dimethoxy-5,5'-binaphthoquinone in refluxing nitrobenzene (210 °C) gives, in a single synthetic
step that includes two Diels-Alder additions, two decarbonylations, and two dehydrogenations,
giant biaryl bisquinones (compounds 13, 14, 15, 18, and 21). However, when two
cyclopentadienones react with 6,6'-dimethoxy-5,5'-binaphthoquinone in nitrobenzene at higher
temperatures (250-260 °C), the resulting products are molecular ribbons composed of two
twisted aromatic systems fused to a heteropentahelicene (19, 20, and 22). These molecules are
representatives of a new class of chiral polycyclic aromatic compounds, the “hairpin furans”.
Interestingly, reheating a dimethoxy-substituted giant biaryl (e.g., 21) in nitrobenzene at 260 °C
does not yield the corresponding hairpin furan (22), and mechanistic studies indicate that some
intermediate or by-product of the synthesis of the giant biaryls is a reagent or catalyst necessary
for the conversion of the dimethoxybiaryl to the furan.
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Introduction
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Helical polycyclic aromatic hydrocarbons (PAHs) are not only topologically unusual, but
often possess remarkable chiroptical properties.1,2 For example, [13]helicene (1) is two full turns
of a molecular spring, and it has a reported [α]D ~ 8800.3 Similarly, the polyphenyl acene 2 is a
molecular ribbon with an end-to-end twist of 144°, and it has a reported [α]D ~ 7400.4,5 We ask
a simple question: might one combine the structural features of both classes of compounds to
yield molecules with more highly unusual shapes and extreme chiroptical properties?
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1
2
O
O
O
O
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
3
4
One method is simply to append twisted acenes to helicenes. For example, one might
construct the “hairpin acene” 3, in which two twisted 1,4-diphenyltriphenylene groups are fused
to [5]helicene to give a U-shaped conjugated molecule, whose preferred conformation is not
obvious, but for which planarity is not even a remote possibility. The configurational stability of
the [5]helicene would be increased by the bulky triphenylenes, and with luck the optical
activities of the helicene and the twisted triphenylenes would prove complementary. Indeed,
B3LYP/6-31G(d) calculations6 give [α]D ~ 7500 for compound 3 and [α]D ~ 4700 for its
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bisquinone analog 4. In this paper we explore possible syntheses of the hairpin acenes such as 3
and 4 (ultimately unsuccessful), and we report the preparation of closely related giant biaryls
(Schemes 1 and 2) and a series of heterocyclic hairpin acenes, the hairpin furans (Scheme 2),
which are formed in an unusual new reaction.8
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Results and Discussion
Syntheses and structures of giant biaryls and hairpin furans. One of the simplest ways to
construct the carbon skeletons of large polycyclic aromatic compounds is to employ Diels-Alder
additions of quinones to cyclopentadienones, a time-tested strategy with many successful
examples in the literature,9 including several of our own.10 For the preparation of the hairpin
acenes, Katz’ easily prepared pentahelicene bisquinone 511 (Scheme 1) would seem to be an
ideal precursor. A Diels-Alder reaction of compound 5 with two equivalents of phencyclone12
(6) in refluxing nitrobenzene, followed by decarbonylation and dehydrogenation of the double
adduct (the usual course of the reaction at high temperatures9,10), should give the hairpin acene
bisquinone 4 in a single step. Unfortunately, repeated attempts to perform this reaction failed to
yield any well-characterized single or double adducts. The MALDI-TOF mass spectra of the
reaction mixtures and partially purified products often showed peaks corresponding to the
desired double addition product, but no such compound was isolated in pure form, and the NMR
spectra of these materials suggested that any double adducts must be present in only very small
quantities, if at all. The result was the same when the reaction was carried out with di-tert-
butylphencyclone 7 (chosen to improve solubility, although this is not usually a problem at 210
°C), acecyclone12 (8), or tetraphenylcyclopentadienone. We therefore took a step back to
perform a few model reactions to test various aspects of this synthetic plan.
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Scheme 1
5
6
O
7
8
9
R
R
Ph
a
No products from
double addition
O
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or
+
O
O
O
Ph
8
6 R = Ph
7 R = 4-But-Ph
O
5
O
O
Ph
b
34%
O
O
Ph
Ph
O
O
Ph
10
9
Ph
Ph
O
O
13
b
d
O
29%
c
HO
O
O
R
R
8%,17%
OH
O
39%
R
R
O
O
O
11
12
14 R = Ph
15 R = 4-But-Ph
O
Conditions: (a) PhNO2, 210 °C, 24 h; (b) 8, PhNO2, 210 °C, 24 h; (c) O2, Co(salen)2, DMF, 4 h; (d) 6 or 7, PhNO2,
210 °C, 24 h.
We began with the simplest test, the reaction of naphthoquinone (9) and acecyclone (8), the
latter chosen because we find it to be more stable at high temperatures than other similar
cyclopentadienones. The expected Diels-Alder addition, decarbonylation, and dehydrogenation
proceeded without difficulty to give the polycyclic quinone 10 in modest yield. Do bisquinones
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perhaps pose a special problem? 5,5’-Binaphthoquinone (12) was prepared by oxygenation of
the known binaphthol 1113 with molecular oxygen and a cobalt catalyst, and it was heated with
two equivalents of acecyclone in nitrobenzene to give the giant biaryl 13 in 29% yield.
Furthermore, heating 11 with two equivalents of phencyclone (6) or di-tert-butylphencyclone 7
gave biaryls 14 and 15 in 8% yield and 17% yield, respectively. Thus, although the yields are
low, bisquinones can indeed undergo two Diels-Alder reactions with cyclopentadienones.
Both 10 and 13 are highly crystalline compounds; their X-ray structures were determined
as a matter of routine, and the molecular structures of both are illustrated in Figure 1.
Interestingly, compound 10 proved to be almost perfectly flat, but the quinones in compound 13
are significantly bent at the dicarbonyl rings, with the dihedral angle of ~160° between the mean
planes of the flanking benzene and fluoranthene rings. This bending is observed for both
quinones in each of the two crystallographically independent molecules of compound 13.
Polycyclic quinones are conformationally flexible, and ordinarily we would ascribe the
differences in the structures to packing forces, but surprisingly, HDFT calculations suggested
otherwise. When an initially bent structure of compound 10 was subjected to geometry
optimization at the B3LYP/6-31G(d) level, the result was a structure with a planar polycyclic
core, as observed in the X-ray structure of 10. However, when the X-ray structure of 13 was
optimized at this level, the bent structure remained; furthermore, the optimization of a structure
of 13 with initially planar quinones also yielded the bent geometry. We speculate that the
bending to some degree alleviates the repulsion of the electron clouds of the internal carbonyl
groups and the opposing benzene rings; i.e., between O2 and C37-C38-C57-C58-C59-C60, and
between O3 and C1-C2-C21-C22-C23-C24.
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Figure 1. Molecular structures of compounds 10 (above) and 13 (below). Thermal ellipsoids
are drawn at the 50% probability level.
Given that double Diels-Alder additions of cyclopentadienones to 5,5’-binaphthoquinone
proceeded smoothly, we returned to pentahelicene bisquinone 5, but all attempts to add
cyclopentadienones were unsuccessful, even when we employed a higher-boiling solvent
(diphenyl ether) or Lewis acid catalysts (BF3, FeCl3). Having no good alternate plan for the
direct preparation of the hairpin acenes, we decided to functionalize the giant biaryls in such a
way as to permit the eventual construction of the missing “middle” ring of the hairpin acenes.
Quite by chance, this scheme also provided a simple synthesis of heterocyclic hairpin acenes
containing a central furan rather than a central benzene ring. These reactions are illustrated in
Scheme 2.
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Scheme 2
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Ph
O
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Ph
O
O O
R
Ph
O
f
O
R
Ph
22
O O
O
Ph
R
29%
O
Ph
R
O
c
9%
19 R = Ph
20 R = 4-But-Ph
b
16%,
31%
O
Ph
MeO
O
Ph
a
MeO
O
OMe
OMe
4%
23
16
17
e
O
d
Ph
Ph
O
18%
13%
O
Ph
Ph
OMe
O
MeO
Ph
Ph
O
O
O
OMe
MeO
O
Ph
Ph
O
18
21
Conditions: (a) CrO3, HOAc, 10 min reflux; (b) 6 or 7, PhNO2, 260 °C, 24 h; (c) 8, PhNO2, 250 °C, 24 h; (d) 6,
PhNO2, 210 °C, 24 h; (e) 8, PhNO2, 210 °C, 24 h; (f) HI, HOAc, reflux 7 days.
The dimethoxybinaphthoquinone 17 was prepared initially by the method of Podlesny and
Kozlowski,14 but we found this procedure’s performance to be erratic. It proved much easier to
oxidize readily available 2,2’-dimethoxy-1,1’-binaphthalene15 (16) with CrO3 in acetic acid,
simply accepting a low yield of 17 (~ 4%) in exchange for the reliability of the reaction and the
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easy isolation of the product. When bisquinone 17 was heated with acecyclone (8) in refluxing
nitrobenzene, the giant biaryl 21 was formed as expected in 13% yield. Single crystals of 21
were obtained, and its X-ray structure is found in the Supporting Information. As in the case of
biaryl 13, both polycyclic quinones are bent at the carbonyl groups.
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It was our plan to remove the four carbonyl groups in 21 by reduction with HI in
HOAc10c,16 which would likely also convert the methoxy groups to hydroxy groups. The
resulting phenols would then be converted to bromides or triflates to provide the necessary
functionality for construction of the middle ring of the corresponding hairpin acene. However,
having accepted a dismal 4% yield in the first synthetic step, it was necessary to improve the
yield of biaryl 21 in order to have enough material for further elaboration of the ring system. For
this reason, the double Diels-Alder addition was carried out in a screw-capped tube at 250 °C.
The yield of double adduct (9%) was not improved, but, to our surprise, the product was no
longer 21, but instead the polycyclic furan 22! The structure was clearly evident from the
spectroscopic data: mass spectrometry showed a formal loss of dimethyl ether from 21, and the
1H and 13C NMR spectra of 22 contained no methoxy resonances. The relative simplicity of the
13C NMR spectrum also indicated that the molecule still retained the C2 symmetry of the starting
biaryl 21. We had thus prepared a heterocyclic hairpin polycycle in one step from a literature
starting material, and we named this class of compounds the “hairpin furans”, in the hope that
more examples could be made in a similar way.
Indeed, the reaction, if not completely general, is applicable to many cyclopentadienones.17
When compound 17 was heated with phencyclone (6) in nitrobenzene at 210 °C, once again the
product was the giant biaryl 18, but when the same reaction was performed at 260 °C, the sole
double adduct observed was the hairpin furan 19. Similarly, heating of 17 with di-tert-
butylphencyclone 7 at 260 °C gave the corresponding tetra-tert-butyl-substituted hairpin furan
20. The yield of this last reaction (31%) was considerably better than the others, suggesting that
solubilizing groups may have a positive effect.
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What is the shape of these hairpin furans? Computational studies of compound 19 at the
B3LYP/6-31G(d) level indicated that this molecule is a continuously twisted ribbon that bends
back upon itself. The lowest energy conformation possesses C2 symmetry and it contains three
components—a tetracenequinone, a heteropentahelicene, and a second tetracenequinone—all of
which display twists of the same sense. Thus, (M,M,M)-19 and (P,P,P)-19 are the preferred
conformations of a racemic sample of compound 19. The conformation of next lowest energy
appears to be a C1-symmetric structure in which the twist of one of the tetracenequinones is
reversed [e.g. (P,M,M)-19], a mere 3.3 kcal/mol higher in energy than the ground state. Single
crystals of compound 19 were obtained from CH2Cl2-toluene, and its X-ray structure was
determined. The molecular structure is approximately C2-symmetric, as expected, and closely
mimics the calculated geometry. The two terminal phenanthrene groups are roughly parallel,
and they enclose a chiral cleft approximately 4 Å wide between the van der Waals surfaces.
Interestingly, the crystal is centrosymmetric, and enantiomeric pairs of compound 19 surround
the centers of symmetry with a phenanthrene group of each molecule nested in the cleft of its
enantiomer (Figure 2).
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Figure 2. Stereoview of the packing of compound 19 in the crystal, showing the interleaving of
the phenanthrene groups of adjacent molecules.
Having prepared the tetraketo hairpins 19, 20, and 22, we planned to remove the carbonyl
groups. The only method that we have previously found to be effective for the reduction of such
hindered aromatic ketones is treatment with HI in refluxing acetic acid;16 even so, prolonged
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reaction times are required.10c When compound 22 was heated with HI/HOAc for a week, the
carbonyl groups were indeed removed, but the carbon skeleton also underwent rearrangement!
The product’s mass spectrum showed the expected replacement of four oxygen atoms with
hydrogen, but its complex 13C NMR spectrum clearly indicated that the C2 symmetry of the
starting material had been lost. The X-ray structure of the product, compound 23, is illustrated in
Figure 3. This “isohairpin furan” is nearly planar, and the new carbon skeleton is relieved of the
strain associated with the helical structure of the starting material. There was some question that
this structure might be due to an “anomalous crystal”, and that unrearranged or differently
rearranged material might be present in the bulk sample. However, the HF/6-31G(d)-calculated
13C NMR spectrum of 23 closely matches the observed spectrum (see Supporting Information);
23 is the principal product of the reduction. Reduction of compounds 19 and 20 was not
attempted; they are more strained that 22, and even more likely to rearrange.
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Figure 3. Molecular structure of compound 23; thermal ellipsoids are drawn at the 50%
probability level.
Mechanistic considerations. We were taken by surprise by both the formation of the
hairpin furans 19, 20, and 22, and the rearrangement of 22 to isohairpin 23; these reactions did
not follow any course that we had previously considered. After further thought, however, we
found that the isomerization of hairpin 22 to isohairpin 23 can be easily rationalized, even if the
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reaction mechanism is not easily tested. The first stage of the HI/HOAc reduction of the
quinones in compound 22 must yield the bis(hydroquinone) 24 (Scheme 3). This electron-rich
polycycle can certainly be protonated under the strongly acidic conditions, and a double
protonation of the furan to give structure 25 is plausible enough. Given the steric strain in the
molecule, 25 would undergo fragmentation as shown to give the diaryl ether 26, and rotation
about one of the ether bonds to give 27 would relieve any remaining steric conflict. At this
point, recyclization to the unstrained, isomeric bis(hydroquinone) 29 could occur (presumably
with acid catalysis), and continued reduction of the hydroquinones would give the observed
product 23.
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Scheme 3
O
HO
HO
H
O
H
HO
H
OH
O H
O
HO
HO
O
O
O
O
O
O
H
+ 2 H+
– 2 H+
4 HI
– 2 I2
O
HO
HO
HO
22
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rotate
HO
O
O
H
H
O
O
O
OH
OH
O
23
further
reduction
tautomerize
H
HO
OH
HO
O
HO
O
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27
28
Several variations of this sequence may be constructed, but all involve an acid-catalyzed
cleavage of the furan ring and its subsequent reformation by electrophilic substitution. It is
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plausible that the ether 26/27 might sometimes undergo the reduction of its quinone instead of
recyclization. If one could isolate the diaryl ether resulting from further reduction, then it would
go far to establish the proposed mechanism, but no such compound has yet been observed.
The mechanism of formation of the hairpin furans is a thornier problem. The synthesis of
the giant biaryls 18 and 21 is clearly due to double Diels-Alder addition of cyclopentadienones 6
and 8, respectively, to 17 followed by decarbonylation and dehydrogenation of the adducts. But
how can the giant biaryls be converted to the hairpin furans? The literature contains several
cases of the conversion o,o'-dihydroxybiaryls to dibenzofurans via Bronsted acid-catalyzed
dehydration20 or pyrolytic dehydration over zeolites, silica, or alumina,21-23 but we know of no
example where a dialkoxybiaryl is converted to a dibenzofuran, with or without acid catalysis.
The mystery deepened when we observed that re-heating compounds 18 and 21 at 260 °C
in nitrobenzene did not give the furans 19 and 22! Demethylation is not observed; only starting
material is recovered. It hardly seems likely that the biaryls are not the precursors of the hairpin
furans; something else must be present in the reaction mixtures that assist the furan formation.
These considerations led to a variety of test reactions (all performed in nitrobenzene24 at 260 °C),
most of which are illustrated in Scheme 4.
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Is trace acid responsible for the furan formation? Heating 21 with 2 mol% tosic acid gave
no conversion to 22. Is the process mediated by hydroquinones or semiquinone radicals that
might be present during the formation of the biaryls? Heating 21 with two equivalents of
hydroquinone gave no 22. Do residual starting materials somehow promote furan formation?
Heating 21 with phencyclone (6) or binaphthoquinone 17 individually gave no formation of 22,
but, astonishingly, when 6 and 17 were heated with 21, the latter was converted to hairpin furan
22 (along with the formation of biaryl 18 and furan 19, which are derived from phencyclone 6).
Interestingly, when 6 and 5,5’-binaphthoquinone (12) were heated with 21, furan 22 was formed
again, but when 6 and naphthoquinone (9) were heated with 21, there was no formation of
hairpin 22. Thus a binaphthoquinone appears to be required to drive the conversion of 21 to 22,
but the methoxy groups of 17 are not required.
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Scheme 4
O
O
O
5
6
7
8
O
O
SO3H
OH
Ph
Ph
MeO
O
O
O
O
O
OMe
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
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Me
OH
6
O
17
12
9
30
31
(a)
no additives
+ 30
Ph
(b)
(c)
(d)
(e)
(f)
O
O
Ph
+ 31
MeO
O
+ 6
Ph
Ph
O O
Ph
O
O
OMe
Ph
+ 17
+ 6 + 17
+ 6 + 12
+ 6 + 9
Ph O
(g)
(h)
O
21
Ph
22
Conditions: All rections were carried out at 260 °C in nitrobenzene with the indicated additives.
Most of these experiments were performed as simple tests for the presence or absence of
the indicated compounds, but experiment (f) (Scheme 4) was repeated with attention to the
yields. Accordingly, when compound 17 (20 µmol), 6 (80 µmol), and 21 (20 µmol) were heated
in nitrobenzene at 260 °C , furans 19 (0.4 µmol, 2%) and 22 (1.9 µmol, 10%), and biaryls 18 (1.2
µmol, 6%) and recovered 21 (6.8 µmol, 34%) were obtained. It thus appears that the yield of 22
from 21 (10%) was comparable to the yield of 22 from 8 and 17 (9%) in its normal synthesis, but
the yield of furan 19 (2%) was suppressed. From these experiments we conclude that some
intermediate or by-product of the synthesis of the giant biaryls is a reagent or catalyst necessary
for the conversion of the dimethoxybiaryl to the furan. However, there are dozens of possible
intermediates to consider for this role, none of which is an obvious choice, and we have so far
been unable to isolate any intermediates in the formation of the biaryls in pure form for further
testing.
As noted in the introduction, an early motivation for this work was to prepare compounds
with high optical rotations or other extreme chiroptical properties. Indeed, hairpin furans 19 and
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22 are calculated to have [α]D ~ 3500 and [α]D ~ 5100 at the B3LYP/6-31G(d) level of theory,
which we have found to give reasonable results for most compounds that exhibit large specific
rotations.6 Unfortunately, we have been unable to resolve any of the hairpin furans prepared so
far, despite the fact that the HDFT-calculated racemization pathway for compound 19 yields
ΔG‡rac = 23.7-25.3 kcal/mol at various levels of theory, barriers that imply a half-life for
racemization of 15 hours to 10 days at 20 °C.8 The calculated racemization pathway and the
attempted methods of resolution were described in out prior communication,8 and will not be
revisited here.
10
11
12
13
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15
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17
18
19
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60
Whether resolvable or not, the unique shapes of the hairpin furans lead one to consider
them as building blocks for a variety of larger, macrocyclic, twisted ribbons. The conceptually
simpler possibilities are illustrated in Scheme 5. If the two ends of hairpin furan 19 are
connected by a polycyclic belt, then the result (compound 30) is a molecular Moebius strip, but if
a planar polycyclic connection is employed, then the resulting structure (31) does not have a
Moebius topology; both compounds, however, are chiral polycycles with C2 symmetry. If a pair
of hairpins 22 of opposite chirality are coupled at the ends, the result (32) is an achiral twisted
belt with C2h symmetry, but if a homochiral pair of hairpins are coupled, then the result is a
chiral structure (33) with D2 symmetry. Of the four possibilities, the Moebius strip 30 presents
the greatest synthetic difficulties, and at present seems far from realization. On the other hand,
the coupling of a derivative of 22 substituted with iodine atoms at the four peri positions of the
terminal naphthalenes might well yield a mixture of 32 and 33, given that a mild, palladium-
catalyzed Ullmann coupling of 1,8-diiodonaphthalene to give perylene is well known and has a
reasonable yield.25 B3LYP/6-31G(d) calculations indicate that the achiral compound 32 is 13.6
kcal/mol more stable than the chiral 33; thus the former would be the expected dimer (if any) to
be formed in such a reaction. Of course, one need not restrict the connecting groups in hairpin
macrocycles to polycyclic aromatic substructures; any other link would still yield macrocycles
with well-defined chiral clefts.
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Scheme 5
5
6
7
O
Ph
8
9
Ph
10
11
12
13
14
15
16
17
18
19
20
21
22
23
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30
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60
O
O
O
Ph
O
Ph
30
O
O
Ph
Ph
O
O
Ph
O
Ph
31
O
Ph
Ph
O
O
Ph
Ph
O
O
O
O
O
Ph
Ph
O
O
Ph
Ph
32
O
Ph
Ph
O
O
Ph
Ph
O
O
O
O
O
Ph
Ph
O
Ph
Ph
O
33
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Experimental
The [5]helicene-bisquinone 5 was prepared by the method of Liu and Katz.11 Phencyclone
(6) and acecyclone (8) were prepared by the method of Dilthey et al.12 8,8’-Dihydroxy-1,1’-
binaphthalene (11) was prepared by the method of Artz et al.13 6,6’-Dimethoxy-5,5’-
binaphthoquinone (17) was initially prepared by the method of Podlesny and Kozlowski,14 but
later as described below. 2,2’-Dimethoxy-1,1’-binaphthalene (16) was prepared by the method
of Brenet et al.15
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
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22
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1,3-Bis(4-tert-butylphenyl)acetone. A solution of DCC (539 mg, 2.62 mmol) and DMAP
(84 mg, 0.69 mmol) in CH2Cl2 (5 mL) was stirred at room temperature under argon, and a
solution of p-tert-butylphenylacetic acid (494 mg, 2.57 mmol) in CH2Cl2 (5 mL) was added
dropwise. The resulting mixture was stirred at room temperature for 24 h. A that time, a white
precipitate was filtered away, and the filtrate was concentrated to dryness. The yellow residue
was purified by silica gel column chromatography (solvent, 5:1 hexanes-EtOAc) to obtain
yellow solid 1,3-bis(4-tert-butylphenyl)acetone (357 mg, 1.11 mmol, 86%). The preparation of
this compound has been reported on several occasions, but seemingly never with NMR data.26
We give its NMR spectra here: 1H NMR (300 MHz, CDCl3) δ 1.31 (s, 18 H), 3.69 (s, 4 H), 7.09
and 7.33 (AA’BB’ system, 8 H); 13C NMR (75 MHz, CDCl3) δ 31.3, 34.4, 48.6, 125.6, 129.1,
131.0, 149.9, 206.0 (8 of 8 expected resonances).
1,3-Bis(4-tert-butylphenyl)-2H-cyclopenta[l]phenanthren-2-one (7). 1,3-Bis(4-tert-
butylphenyl)acetone (1.60 g, 4.97 mmol) was dissolved in EtOH (25 mL) in a small Erlenmeyer
flask. Phenanthrenequinone (1.10 g, 5.29 mmol) was added, followed by the dropwise addition,
with stirring, of half of a solution of KOH (0.5 g) in EtOH (2 mL). At this point, the flask was
swirled in a 90 °C water bath, and the remaining KOH solution was added. Heating and swirling
was continued for 2 min, and then the mixture was immediately cooled, with continuous
swirling, in an ice bath for 7 min. Green-black solid compound 7 was collected by suction
filtration on a pre-chilled fritted funnel, washed with a small amount of chilled EtOH, and
immediately dried under vacuum (1.24 g, 2.51 mmol, 51%); mp 268-275 °C. Note: Derivatives
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of phencyclone (such as 7), of which we have made many,27 are often contaminated with the
6
7
8
9
hydrate but are difficult to purify; this sample was ~80% pure, and was used without further
1
purification. H NMR (500 MHz, CDCl3) δ 1.39 (s, 18 H), 6.99 (t, J = 7.5 Hz, 2 H), 7.30 (t, J =
10
11
12
13
14
15
16
17
18
19
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7.5 Hz, 2 H), 7.36 and 7.45 (AA’BB’ system, 8 H), 7.66 (dd, J = 8 Hz, 1 Hz, 2 H), 7.82 (d, J =
7.5 Hz, 2 H); HRMS (ESI-TOF) 495.2684 (M + H), calcd for C37H35O 495.2688.
7,14-Diphenylnaphtho[2,3-k]fluoranthene-8,13-dione (10). Naphthoquinone (159 mg,
1.00 mmol) and acecyclone (396 mg, 1.10 mmol) were dissolved in nitrobenzene (2 mL). The
dark solution was heated at reflux for 24 h. After cooling to room temperature, methanol (40
mL) was added to precipitate the crude product. This material was purified by silica gel column
chromatography (solvent: toluene) to yield compound 10 as a yellow solid (165 mg, 0.34 mmol,
1
34%); mp > 320 °C. H NMR (300 MHz, CDCl3) δ 6.35 (d, J = 7.5 Hz, 2 H), 7.35 (dd, J = 8 Hz,
7.5 Hz, 2 H), 7.46 (m, 4 H), 7.66 (m, 8 H), 7.82 (d, J = 8 Hz, 2 H), 8.09 (m, 2 H); 13C NMR (75
MHz, CDCl3) δ 126.0, 126.7, 127.4, 127.7, 128.0, 128.4, 129.0, 129.4, 131.0, 133.5, 133.8,
134.1, 134.8, 139.5, 141.0, 143.0, 184.4 (17 of 17 expected resonances); HRMS (ESI-TOF)
485.1538 (M + H), calcd for C36H21O2 485.1542. Single crystals, suitable for X-ray analysis,
were obtained from a solution in CHCl3-MeOH.
5,5’-Binaphthoquinone (12). Oxygen was bubbled into a solution of 8,8’-dihydroxy-1,1’-
binaphthalene (11, 102 mg, 0.357 mmol) in DMF (3 mL) for 10 min. Co(salen)2 (7.4 mg, 0.02
mmol) was added, and the solution darkened. The solution was stirred under oxygen for 4 h,
with the addition of two more portions of Co(salen)2 (7.4 mg each) after 1 and 2 h of stirring.
The resulting mixture was extracted with chloroform, and the extract was washed twice with
water, once with brine, and it was concentrated to dryness. The residue was purified by silica gel
column chromatography (solvent: CH2Cl2) to yield yellow solid compound 12 (44 mg, 0.14
1
mmol, 39%); mp 270-277 °C (sublimes). H NMR (300 MHz, CDCl3) δ 6.75 (d, J = 10.5 Hz, 2
H), 6.98 (d, J = 10.5 Hz, 2 H), 7.43 (dd, J = 7.5 Hz, 1.5 Hz, 2 H), 7.81 (t, J = 7.5 Hz, 2 H), 8.24
(dd, J = 7.5 Hz, 1.5 Hz, 2 H); 13C NMR (75 MHz, CDCl3) δ 126.4, 129.1, 132.8, 133.3, 134.9,
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137.7, 139.6, 142.4, 185.0, 185.3 (10 of 10 expected resonances); HRMS (ESI-TOF) 315.0651
(M + H), calcd for C20H11O4 315.0657.
8
9
9,9’-Bis(7,14-diphenylnaphtho[2,3-k]fluoranthene-8,13-dione) (13). 5,5’-
Binaphthoquinone (12, 100 mg, 0.318 mmol) and acecyclone (8, 251 mg, 0.701 mmol) were
dissolved in nitrobenzene (3.5 mL). The dark solution was heated at reflux for 24 h. After
cooling to room temperature, methanol (25 mL) was added to precipitate the crude product. This
brown material was fractionated by silica gel column chromatography (solvent, 10:1 toluene-
10
11
12
13
14
15
16
17
18
19
20
21
22
23
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32
33
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36
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43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
CH2Cl2) to obtain compound 13 as yellow solid (88 mg, 0.091 mmol, 29%); mp > 320 °C. H
NMR (500 MHz, CDCl3) δ 6.39 (d, J = 7.5 Hz, 2 H), 6.44 (d, J = 7.5 Hz, 2 H), 7.03 (t, J = 7.5
Hz, 2 H), 7.12 (d, J = 7.5 Hz, 2 H), 7.24 (m, 6 H), 7.38 (m, 6 H), 7.50 (m, 2 H), 7.56 (t, J = 7.5
Hz, 2 H), 7.62 (d, J = 7.5 Hz, 2 H), 7.71 (m, 4 H), 7.78 (m, 6 H), 8.02 (d, J = 7.5 Hz, 2 H); 13C
NMR (126 MHz, CDCl3) δ 125.3, 125.57, 125.61, 126.0, 127.1, 127.5, 127.8, 127.90, 127.91,
127.93, 127.99, 128.08, 128.12, 128.19, 128.21, 128.24, 128.4, 129.02, 129.04, 129.08, 129.4,
130.4, 131.8, 133.5, 133.7, 133.9, 134.6, 134.8, 134.9, 135.1, 138.1, 138.4, 139.3, 140.5, 140.6,
142.2, 142.5, 184.6, 186.2 (39 peaks; at most 36 are expected, but all are clearly visible and of
comparable intensity); MS (MALDI-TOF, DCTB + CF3CO2Na matrix), m/z 989 (M + Na, 100);
HRMS (ESI-TOF) 967.2847 (M + H), calcd for C72H39O4 967.2848. Single crystals, suitable for
X-ray analysis, were obtained from a solution in CHCl3.
11,11’-Bis(9,16-diphenylnaphtho[2,3-b]triphenylene-10,15-dione) (14). 5,5’-
Binaphthoquinone (12, 100 mg, 0.318 mmol) and phencyclone (267 mg, 0.699 mmol) were
dissolved in nitrobenzene (4 mL) in a screw-capped tube, and the tube was placed in a metal bath
at 210 °C for 24 h. After cooling to room temperature, methanol (25 mL) was added to
precipitate the crude product. This material was purified by silica gel column chromatography
(solvent, 10:1 toluene-CH2Cl2) to give compound 14 as yellow solid (27 mg, 0.027 mmol, 8%);
1
mp > 320 °C. H NMR (300 Mz, CDCl3) δ 6.96 (ddd, J = 8.5 Hz, 7.5 Hz, 1 Hz, 2 H), 7.06 (ddd,
J = 8.5 Hz, 7.5 Hz, 1 Hz, 2 H), 6.97-7.62 (broadened resonances underlying the remaining sharp
signals, ~20 H), 7.33 (dd, J = 8.5 Hz, 2 H), 7.47 (m, 6 H), 7.66 (t, J = 7.5 Hz, 2 H), 8.11 (dd, J =
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7.5 Hz, 1 Hz, 2 H), 8.36 (m, 6 H); 13C NMR (75 MHz, CDCl3) δ 123.3, 125.7, 125.8, 126.9,
127.3, 127.7, 127.8, 128.1, 128.7, 128.9 (br), 129.6, 129.9, 130.0, 130.1, 130.2, 131.1 (br), 132.0,
132.4, 132.5, 133.1, 135.1, 135.4, 136.2, 136.4, 137.0, 139.0, 139.9, 140.9, 141.1, 141.9, 183.5,
187.6 (32 of 34 expected resonances); MS (MALDI-TOF, DCTB + CF3CO2Na matrix) m/z 1041
(M + Na, 100); HRMS (MALDI-TOF, DCTB matrix) 1019.330, calcd for C76H43O4 1019.316.
Note: Three attempts to obtain HRMS data via ESI-TOF were unsuccessful due to the
insolubility of compound 14 in solvents appropriate for ESI mass spectrometry.
10
11
12
13
14
15
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11,11’-Bis{9,16-bis(4-tert-butylphenyl)naphtho[2,3-b]triphenylene-10,15-dione} (15).
5,5’-Binaphthoquinone (12, 81 mg, 0.26 mmol) and cyclopentadienone 7 (279 mg, 0.56 mmol)
were dissolved in nitrobenzene (3 mL), and the dark solution was heated at reflux for 24 h. After
cooling to room temperature, methanol (25 mL) was added to precipitate the crude product. This
material was purified by preparative TLC (solvent, 10:1 toluene-CH2Cl2) to yield compound 15
1
as a dark yellow solid (55 mg, 0.044 mmol, 17%); mp 261-262 °C. H NMR (400 MHz, CDCl3)
δ 1.34 (s, 18 H), 1.44 (s, 18 H), 6.94 (m, 4 H), 7.05-7.60 (broadened resonances underlying the
remaining sharp signals, ~18 H), 7.28 (m, 2 H), 7.40 (t, J = 7.5 Hz, 4 H), 7.52 (d, J = 7.5 Hz, 2
H), 7.62 (t, J = 7.5 Hz, 2 H), 8.09 (d, J = 7.5 Hz, 2 H), 8.32 (d, J = 7.5 Hz, 4 H); 13C NMR (101
MHz, CDCl3) δ 31.46, 31.52, 34.6, 34.7, 123.1, 123.2, 125.5, 125.7 (br), 126.8, 127.5, 127.9,
129.2, 129.7, 130.0, 130.1, 130.2, 130.6, 131.6, 132.2, 132.4, 133.6, 135.4, 135.6, 136.7, 136.9,
138.1, 138.6, 138.8, 140.0, 140.2, 150.2, 150.7, 183.1, 188.6 (34 of 38 expected resonances); MS
(MALDI-TOF, TCNQ matrix) m/z 1242 (M+, 100); HRMS (ESI-TOF) 1243.5664 (M + H),
calcd for C92H75O4 1243.5665.
6,6’-Dimethoxy-5,5’-binaphthoquinone (17). 2,2’-Dimethoxy-1,1’-binaphthalene (16)
(100 mg, 0.318 mmol) was dissolved in acetic acid (5 mL) by heating to reflux. A solution of
CrO3 (347 mg, 3.47 mmol) in water (4.6 mL) and acetic acid (27 mL) was added in one portion.
The resulting dark solution was heated at reflux for 10 min. After cooling to room temperature,
water was added and the mixture was extracted three times with CHCl3. The yellow extract was
washed with water and concentrated to give a red oil. The oil was fractionated by silica gel
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column chromatography (solvent, 1:1 hexanes-EtOAc) to give yellow solid 17 (4.2 mg, 0.011
1
mmol, 3.5%). H NMR (300 MHz, CDCl3) δ 3.75 (s, 6 H), 6.66 (d, J = 10 Hz, 2 H), 6.87 (d, J =
10 Hz, 2 H), 7.27 (d, J = 8.5 Hz, 2 H), 8.24 (d, J = 8.5 Hz, 2 H); 13C NMR (101 MHz, CDCl3) δ
56.3, 114.4, 126.3, 127.1, 129.0, 130.4, 137.9, 139.5, 161.5, 184.4, 185.6 (11 of 11 expected
resonances). The spectra are essentially identical to those reported previously.14 The yields of
compound 16 in nine consecutive oxidations were 3.2%, 3.5%, 2.7%, 3.0%, 2.4%, 3.3%, 3.5%,
4.7%, and 4.4%.
8
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11,11’-Bis(9,16-diphenyl-12-methoxynaphtho[2,3-b]triphenylene-10,15-dione) (18).
6,6’-Dimethoxy-5,5’-bisnaphthoquinone (17, 67 mg, 0.18 mmol) and phencyclone (6, 273 mg,
0.71 mmol) were dissolved in nitrobenzene (2 mL). The resulting dark solution was heated at
reflux for 24 h. After cooling to room temperature, methanol (20 ml) was added to precipitate the
crude product. This material was purified by column chromatography (solvent, 3:1 toluene-
CH2Cl2, then CH2Cl2) to give the compound 18 as yellow solid (35 mg, 0.032 mmol, 18%); mp
1
297-298 °C. H NMR (500 MHz, CDCl3) δ 3.90 (s, 6 H), 6.91 (ddd, J = 8 Hz, 7 Hz, 1 Hz, 2 H),
7.04 (ddd, J = 8 Hz, 7 Hz, 1 Hz, 2 H), 7.05 (br, 2 H), 7.17 (br, 2 H), 7.20 (d, J = 8.5 Hz, 2 H),
7.21 (m, 4 H), 7.27 (d, J = 8.5 Hz, 2 H), 7.33 (br d, J = 7.5 Hz, 2 H), 7.38 (ddd, J = 7.5 Hz, 7 Hz,
1 Hz, 2 H), 7.43 (ddd, J = 7.5 Hz, 7 Hz, 1 Hz, 2 H), 7.44 (br, 2 H), 7.78 (dd, J = 8.5 Hz, 1 Hz, 2
H), 7.51 (br, 6 H), 8.14 (d, J = 8.5 Hz, 2 H), 8.33 (m, 4 H); 13C NMR (126 MHz, CDCl3) δ 56.1,
114.4, 123.2, 123.3, 124.7, 125.5, 125.7, 127.2, 127.57, 127.63, 127.9, 128.3 (br), 128.6, 128.8,
129.5, 129.7, 130.0, 130.2, 130.8, 130.9, 131.5 (br), 132.3, 132.4, 134.9, 136.2, 136.6, 136.7,
138.6, 139.8, 141.2, 142.2, 161.1, 182.7, 188.2 (34 of 35 expected resonances; the presence of
some broadened resonances suggests slow phenyl rotation); UV (CHCl3) λmax (log ε) 254 (4.65),
282 (sh, 4.50), 336 (4.54), 416 (sh, 3.70); IR (KBr)νmax 1668 (s), 1575 (m), 1326 (s), 1269 (s);
755 (m), 745 (m), 723 (m), 700 (m); HRMS (ESI-TOF) 1079.3341 (M + H), calcd for C78H47O6
1079.3372; 1117.2900 (M + K), calcd for C78H46KO6 1117.2931.
12,12’-Epoxy-11,11’-bis(9,16-diphenylnaphtho[2,3-b]triphenylene-10,15-dione) (19).
6,6’-Dimethoxy-5,5’-binaphthoquinone (17, 60 mg, 0.16 mmol) and phencyclone (6, 250 mg,
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0.65 mmol) were dissolved in nitrobenzene (2 mL) in a screw-capped tube, and the tube was
placed in a metal bath at 260 °C for 24 h. After cooling to room temperature, methanol (10 mL)
was added to precipitate the crude product. This material was purified by silica gel column
chromatography (solvent, 3:1 toluene-CH2Cl2) to give compound 19 as a yellow solid (26 mg,
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0.025 mmol, 16%); mp > 320 °C. H NMR (300 MHz, CDCl3) δ 5.93 (t, J = 7.5 Hz, 2 H), 6.83
(m, 6 H), 7.14 (m, 6 H), 7.30 (d, J = 8 Hz, 2 H), 7.33-7.63 (m, 16 H), 7.78 (d, J = 8.5 Hz, 2 H),
8.22 (d, J = 8.5 Hz, 2 H), 8.33 (d, J = 8 Hz, 2 H), 8.36 (d, J = 8 Hz, 2 H); 13C NMR (75 MHz,
CDCl3) δ 115.8, 121.7, 123.3, 123.4, 125.6, 125.8, 127.1, 127.6, 127.76, 127.84, 127.9, 128.1,
129.0 (br), 129.5, 129.8, 129.9, 130.0, 130.1, 130.9, 131.0 (br), 132.1, 132.3, 132.4, 132.9, 135.4,
136.8, 137.0, 139.4, 139.8, 140.9, 141.8, 161.2, 181.0, 185.0 (34 of 34 expected resonances; the
presence of some broadened resonances suggests slow phenyl rotation); UV (CHCl3) λmax (log ε)
254 (4.70), 298 (sh, 4.57), 328 (4.51), 402 (sh, 3.92); IR (KBr)νmax 1670 (s), 1571 (m), 1321
(s), 1263 (m), 1239 (m), 1221 (m), 761 (s), 755 (s), 728 (m), 699 (m); MS (MALDI-TOF, TCNQ
matrix) m/z 1032 (M+, 100); HRMS (ESI-TOF) 1033.2948 (M + H), calcd for C76H41O5
1033.2954. Single crystals, suitable for X-ray analysis, were obtained from a solution in
CH2Cl2-toluene.
12,12’-Epoxy-11,11’-bis(9,16-bis(4-tert-butylphenyl)naphtho[2,3-b]triphenylene-10,15-
dione) (20). 6,6’-Dimethoxy-5,5’-binaphthoquinone (17, 58 mg, 0.155 mmol) and
cyclopentadienone 7 (302 mg, 0.610 mmol) were dissolved in nitrobenzene (2 mL) in a screw-
capped tube, and the tube was placed in a metal bath at 260 °C for 24 h. After cooling to room
temperature, methanol (10 mL) was added to precipitate the crude product. This material was
purified by preparative TLC (solvent, 3:1 toluene-CH2Cl2) to give compound 20 as yellow solid
1
(62 mg, 0.049 mmol, 31%); mp > 320 °C. H NMR (300 MHz, CDCl3) δ 0.85 (s, 18 H), 1.44 (s,
18 H), 6.41 (d, J = 8 Hz, 2 H), 6.85 (t, J = 7.5 Hz, 2 H), 7.00 (m, 4 H), 7.12 (br s, 4 H), 7.30-7.47
(m, 14 H), 7.69 (t, J = 7.5 Hz, 2 H), 7.81 (d, J = 8.5 Hz, 2 H), 8.31 (d, J = 8.5 Hz, 2 H), 8.34 (m,
4 H); 13C NMR (75 MHz, CDCl3) δ 31.0, 31.2, 34.1, 34.7, 115.9, 121.8, 123.1, 124.2, 124.7,
125.3, 125.6, 125.9, 127.5, 127.7, 127.9, 129.7, 129.9, 130.2, 130.3, 130.6, 130.8, 131.4, 131.5,
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131.7, 132.3, 132.4, 135.2, 137.0, 137.3, 138.0, 139.3, 139.8, 140.4, 150.3, 150.6, 161.2, 181.5,
184.9 (38 of 38 expected resonances); HRMS (ESI-TOF) 1257.5445 (M + H), calcd for
C92H73O5 1257.5457.
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9,9’-Bis(7,14-diphenyl-10-methoxynaphtho[2,3-k]fluoranthene-8,13-dione) (21). 6,6’-
Dimethoxy-5,5’-binaphthoquinone (17, 56 mg, 0.15 mmol) and acecyclone (8, 215 mg, 0.60
mmol) were dissolved in nitrobenzene (2 mL), and the resulting solution was heated at reflux for
24 h. After cooling to room temperature, methanol (20 mL) was added to precipitate the crude
product. This material was purified by preparative TLC (solvent, 3:1 toluene-CH2Cl2) to give
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compound 21 as a dark yellow solid (20 mg, 0.019 mmol, 13%); mp > 320 °C. H NMR (300
MHz, CDCl3) δ 3.74 (s, 6 H), 6.34 (d, J = 7 Hz, 2 H), 6.36 (d, J = 7 Hz, 2 H), 7.03 (d, J = 8.5 Hz,
2 H), 7.11 (m, 4 H), 7.15-7.35 (m, 12 H), 7.46 (m, 2 H), 7.55 (dd, J = 7 Hz, 1 Hz, 2 H), 7.65 (m,
4 H), 7.73 (m, 4 H), 8.02 (d, J = 8.5 Hz, 2 H); 13C NMR (101 MHz, CDCl3) δ 56.4, 114.2, 121.1,
124.8, 125.5, 125.6, 125.7, 127.2, 127.5, 127.97, 128.03, 128.16, 128.23, 128.4, 128.5, 128.7,
128.8, 129.18, 129.24, 129.6, 130.8, 133.8, 134.9, 135.1, 135.3, 138.2, 138.6, 139.6, 141.2,
142.2, 161.1, 184.0, 186.6 (33 of 33 expected resonances); UV (CHCl3) λmax (log ε) 284 (4.60),
318 (sh, 4.61), 400 (sh, 4.23), 418 (4.27); IR (KBr)νmax 1671 (s), 1577 (m), 1575 (m), 1426 (m),
1348 (m), 1324 (m), 1281 (s), 1271 (s), 1257 (m), 757 (s), 698 (m); MS (MALDI-TOF, TCNQ
matrix) m/z 1026 (M+, 100); HRMS (ESI-TOF) 1027.3063 (M + H), calcd for C74H43O6
1027.3060. Single crystals, suitable for X-ray analysis, were obtained from a solution in CHCl3-
benzene.
10,10’-Epoxy-9,9’-bis(7,14-diphenylnaphtho[2,3-k]fluoranthene-8,13-dione) (22). 6,6’-
Dimethoxy-5,5’-binaphthoquinone (17, 40 mg, 0.11 mmol) and acecyclone (8, 157 mg, 0.44
mmol) were dissolved in nitrobenzene (2 mL) in a screw-capped tube, and the tube was placed in
a metal bath at 250 °C for 24 h. After cooling to room temperature, methanol (25 mL) was
added to precipitate the crude product. This material was purified by preparative TLC (solvent,
3:1 toluene-CH2Cl2) to give compound 22 as a yellow solid (10 mg, 0.010 mmol, 9%); mp > 320
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°C. H NMR (300 MHz, CDCl3) δ 6.41 (d, J = 7.5 Hz, 2 H), 6.51 (d, J = 7.5 Hz, 2 H), 6.72 (t, J
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= 7.5 Hz, 2 H), 7.12 (m, 6 H), 7.25 (t, J = 7.5 Hz, 2 H), 7.30 (t, J = 7.5 Hz, 2 H), 7.39 (t, J = 7.5
Hz, 2 H), 7.53 (m, 4 H), 7.69 (m, 8 H), 7.79 (d, J = 8 Hz, 2 H), 7.84 (d, J = 8 Hz, 2 H), 8.22 (d, J
= 8 Hz, 2 H); 13C NMR (101 MHz, CDCl3) δ 115.7, 121.6, 125.8, 127.0, 127.5, 127.7, 127.8,
127.99, 128.05, 128.15, 128.21, 128.3, 128.8, 128.9, 129.0, 129.2, 129.5, 130.7, 131.0, 131.5,
133.7, 134.1, 135.0, 139.07, 139.14, 139.9, 140.8, 142.8, 161.1, 182.4, 183.8 (31 of 32 expected
resonances); UV (CHCl3) λmax (log ε) 280 (4.52), 310 (4.50), 424 (4.04); IR (KBr)νmax 1666 (s),
1426 (m), 1313 (s), 1284 (s), 1260 (m), 1251 (m), 1226 (m), 755 (s), 698 (m); MS (MALDI-
TOF, TCNQ matrix) m/z 980 (M+, 100); HRMS (ESI-TOF) 981.2629 (M + H), calcd for
C72H37O5 981.2641.
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10,11’-Epoxy-9,10’-bis(7,14-diphenylnaphtho[2,3-k]fluoranthene) (23). Hairpin furan
22 (11.3 mg, 0.012 mmol) was added to a solution of HI (5 mL) and acetic acid (20 mL). The
mixture was heated at reflux for one week under argon. After cooling to room temperature, water
was added and the mixture was extracted with CH2Cl2. The organic layer was collected, washed
twice with water, dried over Na2SO4, and concentrated. This crude product was purified by
preparative TLC (solvent, toluene). Extraction and concentration of the least polar yellow band
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gave compound 23 as yellow solid (3.2 mg, 0.0035 mmol, 29%); mp > 320 °C. H NMR (500
MHz, CDCl3) δ 6.60 (d, J = 7 Hz, 1 H), 6.63 (d, J = 7 Hz, 1 H), 6.64 (d, J = 7 Hz, 1 H), 7.03 (d,
J = 7 Hz, 1 H), 7.3-7.8 (m, 26H), 7.96 (m, 2H), 8.02 (m, 3H), 8.11 (s, 1H), 8.25 (s, 1H), 8.27 (s,
1H), 8.29 (s, 1H), 8.85 (s, 1H); 13C NMR (126 MHz, CDCl3) δ 106.4, 113.6, 115.8, 120.1, 121.5,
121.6, 121.7, 121.8, 121.9, 122.1, 125.4, 125.5, 125.6, 125.7, 125.9, 126.0, 126.7, 126.8, 127.0,
127.3, 127.8, 127.98, 128.05, 128.15, 128.22, 128.4, 128.5, 128.9, 129.2, 129.4, 129.47, 129.50,
129.6, 130.07, 130.19, 130.22, 130.37, 130.43, 130.51, 130.58, 130.9, 131.1, 131.6, 132.9, 134.1,
134.4, 134.6, 134.7, 135.0, 136.5, 136.68, 136.70, 136.75, 137.0, 138.7, 138.8, 139.0, 139.5,
155.0, 156.8 (60 of 64 expected resonances); MS (MALDI-TOF, α-cyano-4-hydroxycinnamic
acid matrix) m/z 921 (M + H, 100). Small crystals suitable for X-ray analysis were obtained
from a solution in CHCl3-toluene.
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Computational Methodology. HF/6-31G(d) and B3LYP/6-31G(d) calculations were
performed with GAUSSIAN 09;28 the built-in default thresholds for wave function and gradient
convergence were employed, and the potential minima were characterized by analytical
frequency calculations. The atomic coordinates and absolute energies for the calculated
structures mentioned in the text are found in the Supporting Information.
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Acknowledgment. This work was supported in part by National Science Foundation Grant
CHE-1265507, which is gratefully acknowledged. The X-ray diffractometer used in this work
was purchased with funds from National Science Foundation Grant MRI-1228232.
Supporting Information: NMR spectra of compounds 7, 10, 12-15, and 17-23; atomic
coordinates and energies of the calculated structures of compounds 10, 13, 19, 22, 23, 32, and
33; a summary of each of the X-ray structure determinations with an accompanying thermal
ellipsoid plot; and a crystallographic information file (CIF) for the structures of 10, 13, 19, 21,
and 23. This information is available free of charge via the Internet at http://pubs.acs.org/.
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References and Notes
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(1) For a review of helical organic compounds, especially the helicenes, see: Meurer, K. P.;
Vögtle, F. Top. Curr. Chem. 1985, 127, 1-76.
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(2) For a review of twisted acenes, see: Pascal, R. A., Jr. Chem. Rev. 2006, 106, 4809-4819.
(3) Martin, R. H.; Libert, V. J. Chem. Res. (S) 1980, 4, 130-131; J. Chem Res (M) 1980, 4,
1940-1950.
(4) (a) Lu, J.; Ho, D. M.; Vogelaar, N. J.; Kraml, C. M.; Pascal, R. A., Jr. J. Am. Chem.
Soc. 2004, 126, 11168-11169. (b) Lu, J.; Ho, D. M.; Vogelaar, N. J.; Kraml, C. M.; Bernhard,
S.; Byrne, N.; Kim, L.R.; Pascal, R. A., Jr. J. Am. Chem. Soc. 2006, 128, 17043-17050.
(5) Both [α]D’s are among the ten highest, reliably determined specific rotations.6 The
highest specific rotation belongs to a tetraketo heterohelicene with [α]D ~ 11,600.7
(6) Pascal, R. A., Jr.; West, A. P., Jr. Tetrahedron 2013, 69, 6108-6115.
(7) Fox, J. M.; Katz, T. J. J. Org. Chem. 1999, 64, 302-305.
(8) A portion of this work has been reported previously as a preliminary communication:
Geng, X.; Donahue, J. P.; Mague, J. T.; Pascal, R. A., Jr. Angew. Chem. Int. Ed. 2015, 54,
13957-13960.
(9) Ogliaruso, M. A.; Romanelli, M. G.; Becker, E. I. Chem. Rev. 1965, 65, 261-367.
(10) (a) Pascal, R. A., Jr.; Van Engen, D. Tetrahedron Lett. 1987, 28, 293-294. (b)
Watson, J. A.; Pascal, R. A., Jr.; Ho, D. M.; Kilway, K. V. Tetrahedron Lett. 2000, 41, 5005-
5008. (c) Lu, J.; Zhang, J.; Shen, X.; Ho, D. M.; Pascal, R. A., Jr. J. Am. Chem. Soc. 2002, 124,
8035-8041. (d) Qin, Q.; Ho, D. M.; Mague, J. T.; Pascal, R. A., Jr. Tetrahedron 2010, 66, 7933-
7938.
(11) Liu, L.; Katz, T. J. Tetrahedron Lett. 1990, 31, 3983-3986.
(12) Dilthey, W.; ter Horst, I.; Schommer, W. J. Prakt. Chem. 1935, 143, 189-210.
(13) Artz, S. P.; deGrandpre, M. P.; Cram, D. J. J. Org. Chem. 1985, 50, 1486-1496.
(14) Podlesny, E. E.; Kozlowski, M. C. Org. Lett. 2012, 14, 1408-1411.
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(15) Brenet, S.; Baptiste, B.; Philouze, C.; Berthiol, F.; Einhorn, J. Eur. J. Org. Chem.
6
7
2013, 1041-1045.
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9
(16) Konieczny, M.; Harvey, R. G. J. Org. Chem. 1979, 44, 4813-4816.
(17) In addition to the three hairpin furans illustrated in Scheme 2, we have also observed
their formation from the heating of compound 17 with aceanthrenecyclone (Ref. 12) and 5,7-
diphenyl-6H-benzo[h]cyclopenta[f]quinoline-6-one (Ref. 18) (an azaphencyclone). These two
reactions unambiguously give hairpin furans based on 1H NMR and MS data, but both give
inseparable mixtures of hairpin furan isomers because the starting cyclopentadienones are not
symmetric. Interestingly, the heating of 17 with tetraphenylcyclopentadienone (tetracyclone)
gives neither the furan nor a biaryl. Indeed, we once spent a great deal of time trying to make
1,2,3,4-tetraphenylanthraquinone by heating tetracyclone with naphthoquinone in nitrobenzene
(and other solvents) without success. It appears that tetracyclone can add to the naphthoquinone
at moderate temperatures, but at higher temperatures the adduct undergoes a retro-Diels-Alder
reaction in preference to decarbonylation; thus it is not surprising that we failed to observed
adducts with a binaphthoquinone. We have observed similar behavior for tetracyclone addition
to an azaaceanthrylene; in that case the X-ray structure of the pure adduct was obtained, and its
propensity to undergo retro-Diels-Alder reactions in preference to other reactions was
documented (Ref. 19). However, this is not a universal problem, because we have successfully
prepared octaphenylanthraquinone from benzoquinone and tetracyclone in nitrobenzene (Ref.
10c).
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(18) Walters, R. S.; Kraml, C. M.; Byrne, N.; Ho, D. M.; Qin, Q.; Coughlin, F. J.;
Bernhard, S.; Pascal, R. A., Jr. J. Am. Chem. Soc. 2008, 130, 16435-16441.
(19) West, A. P., Jr., Van Engen, D.; Pascal, R. A., Jr. J. Org. Chem. 1992, 57, 784-786.
(20) Areephong, J.; Ruangsupapichart, N.; Thongpanchang, T. Tetrahedron Lett. 2004, 45,
3067-3070.
(21) Arienti, A.; Bigi, F.; Maggi, R.; Moggi, P.; Rastelli, M.; Sartori, G.; Trere, A. J. Chem.
Soc., Perkin Trans. 1, 1997, 1391-1393.
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(22) Xie, X.; Zhang, T. Y.; Zhang, Z. J. Org. Chem. 2006, 71, 6522-6529.
(23) Shuklov, I. A.; Dubrovina, N. V.; Jiao, H.; Spannenberg, A.; Börner, A. Eur. J. Org.
Chem. 2010, 1669-1680.
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(24) There is a solvent effect: heating 6 and 17 in diphenyl ether at 260 °C gave a mixture
of biaryl 18 and furan 19, and heating 6 and 17 in 2-methylnaphthalene at 260 °C gave biaryl 18
with only a trace of furan 19. Nitrobenzene is so far the best solvent for furan formation, but it is
not absolutely required.
(25) Dyker, G. J. Org. Chem. 1993, 58, 234-238.
(26) (a) Draper, S. M.; Gregg, D. J.; Madathil, R. J. Am. Chem. Soc. 2002, 124, 3486-3487.
(b) Gregg, D. J.; Ollagnier, C. M. A.; Fitchett, C. M.; Draper, S. M. Chem. Eur. J. 2006, 12,
3043-3052. (c) Varughese, S.; Draper, S. M. Cryst. Growth Des. 2010, 10, 2298-2305.
(27) L’Esperance, R. P.; Van Engen, D.; Dayal, R.; Pascal, R. A., Jr. J. Org. Chem. 1991,
56, 688-694.
(28) Frisch, M. J., et al. Gaussian 09, revision A.02; Gaussian, Inc.; Wallingford CT, 2009.
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TOC Graphic
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Ph
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