Synthesis and Electronic Properties of Fluoreno[2,1-a]fluorenedione and Fluoreno[1,2-a]fluorenedione

Article abstract of DOI:10.1021/acs.joc.7b02699

The [2,1-a]- and [1,2-a]-isomers of fluorenofluorenedione have been synthesized via intramolecular Friedel-Crafts acylations. DFT calculations indicate that the [1,2-a]-isomer adopts a twisted, helical C₂-symmetric structure and that its proton

Full text of DOI:10.1021/acs.joc.7b02699

Note
pubs.acs.org/joc
Cite This: J. Org. Chem. XXXX, XXX, XXX−XXX
Synthesis and Electronic Properties of Fluoreno[2,1‑a]fluorenedione
and Fluoreno[1,2‑a]fluorenedione
Allison S. Hacker, Mauricio Pavano, James E. Wood, II, Chad E. Immoos, Hannah Hashimoto,
Sam P. Genis, and Derik K. Frantz*
Department of Chemistry and Biochemistry, California Polytechnic State University, 1 Grand Avenue, San Luis Obispo, California
93401, United States
S
* Supporting Information
ABSTRACT: The [2,1-a]- and [1,2-a]-isomers of fluorenofluor-
enedione have been synthesized via intramolecular Friedel−Crafts
acylations. DFT calculations indicate that the [1,2-a]-isomer adopts
a twisted, helical C2-symmetric structure and that its protonated
form is the thermodynamic product of the Friedel−Crafts acylation
in hot sulfuric acid. Absorption spectroscopy and cyclic voltammetry
measurements provide experimental estimations of frontier molec-
ular orbital energy levels, which are reported and discussed.
he synthesis of extended π-systems comprising polycyclic
conjugated hydrocarbons (PCHs) permits fundamental
Synthesis of IF- and FF-based diones relies primarily on two
strategies, which Haley categorizes as “inside-out” and “outside-
in” (Scheme 1).14d Both methods employ intramolecular
Friedel−Crafts acylation but differ in the locations of the
acylium electrophiles. In the inside-out strategy, acylium ions
T
investigations into concepts related to aromaticity and
antiaromaticity1 and enables applied research toward the
development of functional organic materials.2 In recent years,
PCHs bearing a variety of structural arrangements have been
featured in devices such as organic field-effect transistors3
(OFETs), organic light-emitting diodes (OLEDs),4 and organic
photovoltaics (OPVs).5 Strategies to access these extended
PCHs often rely on cyclic ketones as synthetic intermediates.
Ketones serve as direct precursors for π-extension via Wittig-
type reactions, particularly Ramirez dibromoolefinations6 and
fulvene formation7, and have been employed in the synthesis of
phenalenyl radicals8 and bisphenalenyl9 systems. PCH-based
diones are particularly useful as precursors to substituted π-
extended molecules via addition of organometallic reagents
followed by Sn-mediated reductive aromatization.10 This
methodology appears often in the chemical literature and has
been featured in the synthesis of archetypal PCHs such as
oligoacenes,11 zethrenes,12 and bisanthenes.13
Scheme 1. “Inside-Out” and “Outside-In” Strategies for IF-
Dione Synthesis ([1,2-b]-Isomer Shown) and the “Outside-
In” Approach to FF-Diones from Diones 1a and 1b
Over the past decade, the groups of Haley14−16 and
́
Tobe17−19 have generated a variety of Kekule diradicaloid20
indenofluorene (IF) isomers, all of which have been
synthesized from IF-dione precursors.21 Whereas isomers of
IF possess benzenoid rings as cores, isomers of fluoreno-
fluorene (FFs) contain central naphthalenoid groups. Three
examples of FF, each deriving from dione intermediates, have
been reported to date: Haley’s closed-shell [4,3-c]-22 and [3,2-
b]-isomers23 and Tobe’s substantially open-shell [2,3-b]-
isomer.24 Their usefulness as synthetic building blocks and as
organic materials25 motivates the synthesis and study of new
PCH-based diones.
Received: October 24, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.joc.7b02699
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Note
located on the central aromatic ring add to the exterior benzene
rings to form the polycylic dione. Conversely, in the outside-in
strategy, acylium ions located on the outer rings add to the
central aromatic ring. Haley’s syntheses of [4,3-c]- and [3,2-b]-
FF-diones23 and Tobe’s synthesis of [2,3-b]-FF-dione24 all
make use of an inside-out strategy. Note that Haley used a Pd-
catalyzed aryl−aryl cyclization developed by Scherf26 in his
original synthesis of [4,3-c]-FF-dione.22 In the present study,
we set out to synthesize and study fluorenofluorenediones via
the outside-in strategy from diphenylnaphthalene-based die-
sters 1a and 1b.
structure to accommodate steric clashing, and likely electro-
static repulsion, of the two oxygen atoms (Figure 1a).
Diesters 1a and 1b were synthesized from commercially
available diols 2a and 2b, respectively (Scheme 2). Triflation
Scheme 2. Synthesis of FF-Diones 4a (Top) and 4b
(Bottom)
Figure 1. (a) Calculated structures of 4b in C2- and C2v-symmetric
conformations. (b) Calculated ground state energies for diones 4b, 4c,
and 4d and their protonated derivatives 4b-H+, 4c-H+, and 4d-H+.
Lowest-energy protonated isomers are shown. (c) Calculated structure
of 4b-H+, indicating the location of proton wedged between both
ketones. All calculations were performed at the B3LYP-6-31G* level of
theory.
and subsequent Suzuki cross-coupling27 reactions with 2-
ethoxycarbonylbenzeneboronic acid (3) afforded 1a and 1b in
gram quantities following a known procedure to diester 1a.28
Outside-in Friedel−Crafts acylation of 1a generated dione 4a
(the [2,1-a]-isomer) in a high yield, a result that was
unsurprising due to the higher nucleophilicity of naphthalene’s
1- and 5-positions compared to its 3- and 7-positions. Although
a dithieno analogue of 4a has been recently described,29 dione
4a is reported only once in the chemical literature in a German
patent from 1932. The patent describes the appearance of the
According to the calculations, the planar C2v structure lies 7.2
kcal/mol higher in energy, suggesting that enantiomeric, C2-
symmetric structures of 4b interconvert quickly by structural
flipping at room temperature. We attribute dione 4b’s high
solubility relative to 4a to its twisted molecular structure, which
likely weakens intermolecular π-stacking interactions in the
solid state,31 and its substantial dipole moment, calculated to be
4.2 debye in the gas-phase ground state.
The calculations also predict that the ground state energy of
dione 4b is >13 kcal/mol higher in energy than those of the
other two isomers (the [3,2-a]-isomer 4c and the [2,3-b]-
isomer 4d) that could result from a rearrangement-free,
intramolecular Friedel−Crafts acylation of 1b (Figure 1b,
top). The higher nucleophilicity of the 1- and 8-positions of the
naphthalene core of 1b could explain this result. Nucleophil-
icity is, however, a kinetic phenomenon, and the reaction in hot
H2SO4 is hardly under “kinetic control.” We propose that an
intramolecular hydrogen-bonding interaction between the
proximal oxygen atoms stabilizes the protonated structure of
4b (Figure 1c) during the reaction. Calculations predict that
the protonated [1,2-a]-isomer 4b-H+ lies 6.7 and 8.4 kcal/mol
lower in energy than 4c-H+ and 4d-H+, respectively (Figure 1b,
bottom). This result suggests that 4b-H+ is indeed the
compound in passing as “weinrot gefarbte, metallisch
̈
glanzende, schon ausgebildete Blatter” (red wine-colored,
̈
̈
̈
metallically shiny, beautifully shaped leaves).30 We found that
microcrystalline flakes and films of 4a match the patent’s
description and that the fine powder form exhibits a lighter,
bright-red color. The dione is sparingly soluble, a common
characteristic for planar PCH-bearing diones.25 Saturated, yet
intrinsically highly dilute, solutions in CH2Cl2 and acetone are
faintly peach-colored, and slightly higher concentrations in
refluxing toluene are yellow.
Remarkably, intramolecular Friedel−Crafts acylation of 1b
affords dione isomer 4b (the [1,2-a]-isomer) exclusively in a
high yield (Scheme 2, bottom). Compound 4b is a bright-
orange solid that, unlike compound 4a, is moderately soluble as
a bright-yellow solution in polar aprotic organic solvents.
Computational models (B3LYP-6-31G*) indicate that the
ground state of molecule 4b adopts a helical, C2-symmetric
B
DOI: 10.1021/acs.joc.7b02699
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Note
thermodynamic product of the reaction and affords 4b after
neutralization.
Absorption spectra of diones 4a and 4b reveal that both
compounds exhibit weakly absorbing, low-energy S0 → S1
transitions in the visible region and strongly absorbing
transitions in the UV range (Figure 2). As Haley and co-
Figure 3. Cyclic voltammograms of dione 4a (top) and dione 4b
(bottom). Measurements were performed in a 0.1 M solution of
Bu4NPF6 in CH2Cl2 under N2 using a Ag/AgNO3 reference electrode,
a Pt disk working electrode, and a Pt wire counter electrode. Dione 4a
is sparingly soluble and was measured as a saturated, yet dilute,
solution. Dione 4b was measured as a 1 mM solution.
Figure 2. Absorption spectra of 4a (solid line) and 4b (dashed line) in
CH2Cl2. Shaded area shows molar absorptivity (ε) multiplied by 5
over the range 350−600 nm.
workers point out,25 the visible-range absorbances in IF-diones
had been originally attributed to n → π* transitions;32 TD-
DFT calculations, however, predict that this absorbance arises
from a π → π* transition. Given the structural and
spectroscopic similarities between IF-diones and these FF-
diones, it is likely that the visible transitions in 4a and 4b are
also π → π* in nature. In the UV region, dione 4a exhibits
stronger and sharper absorptions with higher vibrational
structure compared to dione 4b. This result may arise from
dione 4b’s higher flexibility and reduced conjugation: the
peripheral benzene rings in dione 4b are nonconjugated, as
they connect to the naphthalene core at the 2- and 7- positions
in a meta-configuration.
Scheme 3. Structures of Dianions of 4a (Top) and 4b
(Bottom)
The electrochemical properties of diones 4a and 4b were
probed by cyclic voltammetry experiments (Figure 3). Both
diones exhibit two reductions and no observable oxidations.
Whereas 4a exhibits two reversible reductions, the second
reduction of 4b is not completely reversible. The first reduction
(Ered1) occurs at nearly the same half-wave potential for both
diones (Ered1 = −1.43 V for 4a and −1.44 V for 4b). The
second reduction (Ered2) requires a substantially more negative
potential for dione 4b (−1.92 V) compared to dione 4a (−1.72
V). The dianion of 4a possesses a 1,8-napthoquinodimethane
core that can access both open- and closed-shell resonance
forms (Scheme 3, top). The dianion of 4b, however, is
fundamentally diradical in nature and holds two oxygen atoms
with a substantial negative charge in close proximity (Scheme 3,
bottom). Negative charge repulsion likely increases the second
reduction potential of 4b compared to 4a, and the diradical
nature of 4b2− renders it less stable than 4a2−. The difference in
potential between Ered1 and Ered2 in dione 4b (0.48 V) closely
matches that of indeno[2,1-b]fluorenedione (0.47 V),33 an IF-
dione whose dianion is also fundamentally diradical in nature.
Calculated structures of frontier molecular orbitals of 4a and
4b, and their experimentally determined energy levels, are
presented in Figure 4. Based on onset potentials for their first
reductions, LUMO energies for 4a and 4b are estimated to be
−3.56 eV and −3.53 eV, respectively. Onset wavelengths for
absorbance transitions estimate that the HOMO−LUMO
energy gap (EH−L) of dione 4a is 2.30 eV (540 nm) and that
of dione 4b is higher in energy at 2.46 eV (505 nm). Thus,
HOMO energies lie at −5.86 eV for 4a and −5.99 eV for 4b.
In conclusion, we have used the outside-in Friedel−Crafts
acylation strategy to generate the [2,1-a]- and [1,2-a]-isomers
of fluorenofluorenedione selectively and in high yields from
appropriately substituted diester precursors. Dione 4a is red
and sparingly soluble, and dione 4b is orange and moderately
soluble in polar aprotic organic solvents. Both molecules
undergo two reductions in their cyclic voltammograms, and the
potential and shape of the second reduction of 4b reveals the
instability of its dianion. The diones exhibit electronic
absorptions in the visible and UV ranges. Current work is
directed at employing these diones as synthetic building blocks
for the generation of novel extended π-systems.
C
DOI: 10.1021/acs.joc.7b02699
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Note
matched the literature spectra.28,34 1H NMR (400 MHz, CDCl3, δ):
7.98 (d, 2H, J = 8.9 Hz), 7.82 (d, 2H, J = 2.5 Hz), 7.49 (dd, 2H, J =
8.9, 2.4 Hz).
2,6-Bis[2-(ethoxycarbonyl)phenyl]naphthalene (1a). In a 250 mL,
3-neck round-bottom flask affixed with a condenser and two septa, 2,6-
bis(trifloromethylsulfonyloxy)naphthalene (3.00 g, 7.07 mmol), Pd-
(PPh3)4 (0.654 g, 0.57 mmol), and o-ethoxycarbonylbenzoic acid (4.39
g, 22.6 mmol) were degassed with N2 (evacuation/refill). A solution of
20% Na2CO3 (aq) (20 mL) and DME (50 mL) (separately degassed
by the freeze−pump−thaw method) were added to the mixture, which
was then stirred at 80 °C for 2.5 h. The resulting brown solution was
allowed to cool to room temperature, and then H2O (∼10 mL) and
EtOAc (∼10 mL) were added to separate the phases. The aqueous
phase was extracted with EtOAc, and the combined organic phase was
dried over MgSO4 and concentrated in vacuo. The resulting brown oil
was purified by column chromatography (silica, CH2Cl2/heptane 1:9).
The fractions containing product were concentrated in vacuo, yielding
a colorless solid (1.98 g, 66% yield). The obtained spectra matched the
literature spectra.28 1H NMR (400 MHz, CDCl3, δ): 7.89 (dd, 2H, J =
7.8, 1.1 Hz), 7.86 (d, 2H, J = 8.4 Hz), 7.82 (d, 2H, J = 1.6 Hz), 7.58
(td, 2H, J = 7.5, 1.4 Hz), 7.51−7.42 (m, 6H), 4.08 (q, 4H, J = 7.1 Hz),
0.92 (t, 6H, J = 7.1 Hz).
7H,14H-Dihydrofluoreno[2,1-a]fluorene-7,14-dione (4a). Com-
pound 1a (965 mg, 2.22 mmol) was added to a 25 mL, 1-neck
round-bottom flask. Concentrated sulfuric acid (8 mL) was then
added, and the reaction was stirred at 90 °C for 35 min. The resulting
dark green, acidic solution was neutralized with saturated, aqueous
NaHCO3 in an ice bath, generating a dark purple-red precipitate. The
precipitate was filtered and washed with H2O and then washed with
acetone to remove side products. After the acetone wash, the purple-
red solid was triturated with hot toluene and allowed to cool to room
temperature. Filtration afforded purple-red plates (623 mg, 84% yield).
Figure 4. Experimentally determined HOMO and LUMO energies for
diones 4a (left) and 4b (right) and their calculated (B3LYP-6-31G*)
orbital structures.
EXPERIMENTAL SECTION
■
General Information. Synthetic procedures were performed open
to air unless otherwise noted. Anhydrous THF was dried and stored
over activated 3 Å molecular sieves. Other solvents and commercially
available reagents were used as received without further purification.
Analytical thin-layer chromatography was performed on Agela
Technologies silica gel plates and visualized by 254 nm radiation.
Column chromatography was performed with Sorbtech silica gel (60
Å, pH range 6.0−7.0). Melting ranges were recorded on a Vernier
Melting Station apparatus. Nuclear magnetic resonance (NMR)
spectra were recorded on a Bruker AVANCE II HD spectrometer at
400 MHz (100 MHz for 13C). Chemical shifts for 1H NMR and
13C{1H} NMR are reported in ppm (δ) relative to tetramethylsilane
(0.00 ppm) or residual solvent (dichloromethane-d2 5.33 ppm [for 1H
NMR]). Multiplicity is indicated by one or more of the following: s
(singlet); d (doublet); dd (doublet of doublets); td (triplet of
doublets); dt (doublet of triplets). Broad signals are indicated with the
abbreviation (br). Coupling constants (J) are reported in hertz (Hz).
Infrared spectra were recorded on a Thermo Scientific Nicolet iS5
Fourier transform infrared spectrometer (FTIR) using the attenuated
total reflectance (ATR) technique on a diamond surface. Only peaks
that are diagnostic of functional groups are reported. Percent
transmittance of peaks is indicated relative to that of the strongest
peak (normalized to 0%): s (0−33%); m (33−67%); w (67−100%).
High-resolution mass spectra (HRMS) were measured at the Mass
Spectrometry Laboratory in the School of Chemical Sciences,
University of Illinois, Urbana−Champaign; ESI/Q-TOF measure-
ments were performed on a Waters Q-TOF Ultima ESI instrument,
and EI measurements were performed on a Waters 70-VSE
instrument.
1
Mp >300 °C. H NMR (400 MHz, CD2Cl2, δ): 9.09 (d, 2H, J = 8.3
Hz), 7.76 (d, 2H, J = 8.3 Hz), 7.53 (dt-like d, 2H, J = 7.4 Hz), 7.50
(dt-like d, 2H, J = 7.4 Hz), 7.44 (td, 2H, J = 7.4, 1.1 Hz), 7.24 (td, 2H,
J = 7.4, 1.0 Hz). 13C NMR not measured due to sparing solubility of
compound. HRMS (ESI/Q-TOF, m/z): calcd for C24H12O2,
332.0837; found, 332.0838. FTIR (neat, cm−1): selected absorptions
1696s, 1601m.
2,7-Bis(trifluoromethylsulfonyloxy)naphthalene. In a 500 mL
round-bottom flask, a solution of 2,7-dihydroxynaphthalene (3.00 g,
18.8 mmol) in CH2Cl2 (50 mL) and Et3N (10 mL) was cooled to 0
°C. Triflic anhydride (7.6 mL, 45 mmol) was added steadily over 5
min while stirring. The dark reaction mixture was allowed to warm to
room temperature and stirred for 3.5 h. H2O (∼10 mL) and CH2Cl2
(∼10 mL) were then added to the mixture, and the aqueous phase was
extracted with CH2Cl2. The combined organic phase was dried over
MgSO4 and concentrated in vacuo. The resulting dark brown oil was
purified by column chromatography (CH2Cl2/heptane 2:8) to afford
2,7-bis(trifloromethylsulfonyloxy)naphthalene as a colorless solid
(6.50 g, 81% yield). The obtained spectra matched the literature
spectra.34,35 1H NMR (400 MHz, CDCl3, δ): 8.00 (d, 2H, J = 9.1 Hz),
7.81 (d, 2H, J = 2.4 Hz), 7.48 (dd, 2H, J = 9.1, 2.4 Hz).
2,7-Bis[2-(ethoxycarbonyl)phenyl]naphthalene (1b). In a 250 mL,
3-neck round-bottom flask affixed with a condenser and two septa, 2,7-
bis(trifloromethylsulfonyloxy)naphthalene (3.00 g, 7.07 mmol), Pd-
(PPh3)4 (656 mg, 0.57 mmol), and o-ethoxycarbonylbenzoic acid
(4.39 g, 22.6 mmol) were degassed with N2 (evacuation/refill). A
solution of 20% Na2CO3 (aq) (20 mL) and DME (50 mL) (each
separately degassed using the freeze−pump−thaw method with N2)
were added to the reagent mixture via cannula. The resulting reaction
mixture was stirred at 80 °C for 2.5 h. The resulting brown solution
was cooled to rt, and then H2O (∼10 mL) and EtOAc (∼10 mL) were
added to separate the phases. The aqueous phase was extracted with
EtOAc, and the combined organic phase was dried over MgSO4 and
concentrated in vacuo. The resulting brown oil was purified by column
chromatography (CH2Cl2/heptane 2:3), affording compound 1b as a
Synthesis. 2,6-Bis(trifluoromethylsulfonyloxy)naphthalene. In a
250 mL, 1-neck round-bottom flask, a solution of 2,6-dihydroxynaph-
thalene (2.00 g, 12.5 mmol) in CH2Cl2 (40 mL) and Et3N (8 mL) was
cooled to 0 °C over an ice bath. Triflic anhydride (5.0 mL, 30 mmol)
was added steadily over 5 min while stirring. The dark reaction mixture
was allowed to warm to room temperature and stirred for 20 h, after
which H2O (∼10 mL) and CH2Cl2 (∼10 mL) were added to the
mixture. The aqueous phase was extracted with CH2Cl2, and the
combined organic phase was dried over MgSO4 and concentrated in
vacuo. The dark brown oil was then purified by column
chromatography (graduated from heptane to 8:2 heptane/CH2Cl2),
affording 2,6-bis(trifluoromethylsulfonyloxy)naphthalene as a color-
less, crystalline solid (3.82 g, 72% yield). The obtained spectra
1
light yellow oil (2.45 g, 82% yield). H NMR (400 MHz, CDCl3, δ):
7.90−7.85 (m, 4H), 7.80 (br s, 2H), 7.57 (td, 2H, J = 7.52, 1.3 Hz),
7.49−7.43 (m, 6H), 4.08 (q, 4H, J = 7.1 Hz), 0.92 (t, 6H, J = 7.1 Hz).
D
DOI: 10.1021/acs.joc.7b02699
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Note
13C NMR (100 MHz, acetone-d6, δ): 168.8, 142.7, 140.2, 133.9, 132.6,
132.3, 132.0, 131.6, 130.4, 128.1, 128.0, 127.9, 127.8, 61.2, 14.0.
HRMS (ESI/Q-TOF, m/z) calcd for C28H25O4 [M + H]+, 425.1747;
found, 425.1745. Rf: 0.48 (silica, CH2Cl2/heptane 1:1). FTIR (neat,
cm−1): selected absorptions 2980w, 1709s, 1597m.
ORCID
Derik K. Frantz: 0000-0002-7712-0479
Notes
The authors declare no competing financial interest.
13H,14H-Dihydrofluoreno[1,2-a]fluorene-13,14-dione (4b). Com-
pound 1b (1.12 g, 2.65 mmol) was added to a 25 mL round-bottom
flask. Concentrated sulfuric acid (8 mL) was then added, and the
reaction was stirred at 90 °C for 40 min. The resulting dark mixture
was added dropwise to a saturated solution of NaHCO3 to produce a
bright orange precipitate, which was filtered, washed with H2O, and
allowed to dry, affording compound 4b as a bright orange solid (780
ACKNOWLEDGMENTS
■
We acknowledge Cal Poly’s Research, Scholarly, and Creative
Activities (RSCA) Grant Program and the Frost Summer
Research Program for financial support of this work. We thank
Professor Michael M. Haley (University of Oregon) for helpful
discussions. We thank the Mass Spectrometry Facility at the
University of Illinois at Urbana−Champaign for measuring the
mass spectra of new compounds.
1
mg, 89% yield). Mp 265−270 °C dec. H NMR (400 MHz, CDCl3,
δ): 7.95 (d, 2H, J = 8.3 Hz), 7.67 (d, 2H, J = 7.3 Hz), 7.63 (d, 2H, J =
8.3 Hz), 7.52 (d, 2H, J = 7.3 Hz), 7.44 (td, 2H, J = 7.3, 1.1 Hz), 7.32
(td, 2H, J = 7.3, 0.9 Hz). 13C NMR (100 MHz, CDCl3, δ): 191.9,
149.4, 142.9, 137.2, 136.6, 135.5, 134.1, 130.5, 130.1, 124.80, 124.75,
120.7, 119.3. HRMS (EI, m/z) calcd for C24H12O2, 332.08373; found,
332.08345. Rf: 0.35 (silica, CH2Cl2/heptane 1:1). FTIR (neat, cm−1):
selected absorptions 3041w, 1675s, 1605m.
REFERENCES
■
(1) Randic,
́
M. Chem. Rev. 2003, 103, 3449−3606.
(2) (a) Watson, M. D.; Fechtenkotter, A.; Mullen, K. Chem. Rev.
̈
̈
2001, 101, 1267−1300. (b) Wu, J.; Pisula, W.; Mullen, K. Chem. Rev.
2007, 107, 718−747.
(3) (a) Zaumseil, J.; Sirringhaus, H. Chem. Rev. 2007, 107, 1296−
1323. (b) Di, C.; Zhang, F.; Zhu, D. Adv. Mater. 2013, 25, 313−330.
(4) Xiao, L.; Chen, Z.; Qu, B.; Luo, J.; Kong, S.; Gong, Q.; Kido, J.
Adv. Mater. 2011, 23, 926−952.
(5) Schlenker, C. W.; Thompson, M. E. Top. Curr. Chem. 2011, 312,
175−212.
(6) Desai, N. B.; McKelvie, N.; Ramirez, F. J. Am. Chem. Soc. 1962,
84, 1745−1747.
(7) (a) Mills, N. J. Org. Chem. 2013, 78, 4629−4641. (b) Usta, H.;
Risko, C.; Wang, Z.; Huang, H.; Deliomeroglu, M. K.; Zhukhovitskiy,
A.; Facchetti, A.; Marks, T. J. J. Am. Chem. Soc. 2009, 131, 5586−5608.
(c) Andrew, T. L.; Cox, J. R.; Swager, T. M. Org. Lett. 2010, 12, 5302−
5305.
(8) (a) Goto, K.; Kubo, T.; Yamamoto, K.; Nakasuji, K.; Sato, K.;
Shiomi, D.; Takui, T.; Kubota, K.; Kobayashi, T.; Yakusi, K.; Ouyang,
J. J. Am. Chem. Soc. 1999, 121, 1619−1620. (b) Uchida, K.; Ito, S.;
Nakano, M.; Abe, M.; Kubo, T. J. Am. Chem. Soc. 2016, 138, 2399−
2410.
̈
Absorption Spectra. Absorption spectra were measured on an
Agilent Technologies Cary Series UV−vis spectrophotometer using 10
mm quartz cuvettes in spectroscopic grade CH2Cl2. Molar
absorptivities (ε) were measured according to the Beer−Lambert
equation (ε = Acl). The reported spectra show the average ε for each
wavelength from three freshly prepared solutions of 4a and 4b (9.30 ×
10−6, 1.23 × 10−5, and 1.25 × 10−5 for 4a; 1.17 × 10−5, 1.25 × 10−5,
1.36 × 10−5 for 4b).
Cyclic Voltammetry. Cyclic voltammetry (CV) measurements
were performed under N2 on a CH Instruments potentiostat (Model
760B) using a Ag/AgNO3 reference electrode (containing a 0.01 M
solution of AgNO3 in CH3CN), a Pt disk working electrode, and a Pt
wire counter electrode. Measurements were performed at a sweep rate
of 100 mV/s in dry, degassed CH2Cl2 containing Bu4NPF6 (0.1 M) as
a supporting electrolyte. The ferrocene/ferrocenium (Fc/Fc+)
reversible oxidation was used as an internal standard; Fc was added
to the samples and measured directly after measurements of pure 4a
and 4b. The LUMO energy levels of 4a and 4b were estimated using
the following equation:
E
LUMO(eV) = −[Eonset − Eonset(Fc/Fc+)] − 4.80 eV
(9) Ohashi, K.; Kubo, T.; Masui, T.; Yamamoto, K.; Nakasuji, K.;
Takui, T.; Kai, Y.; Murata, I. J. Am. Chem. Soc. 1998, 120, 2018−2027.
(10) (a) Marshall, J. L.; Lehnherr, D.; Lindner, B. D.; Tykwinski, R.
R. ChemPlusChem 2017, 82, 967−1001.
where Eonset is the onset potential for the first reductions of 4a or 4a
and Eonset(Fc/Fc+) is the onset potential for the oxidation of the Fc/
Fc+. The value −4.80 eV is the HOMO energy of ferrocene compared
to the vacuum level. The plots shown in Figure 3 are referenced
against Fc/Fc+ (half-wave potential = 0 V). The value for Eonset(Fc/
Fc+) was determined to be −0.09 V. The value for Eonset was
determined to be 1.33 V for 4a and 1.36 V for 4b. Using the equation
above, the LUMO energies for 4a and 4b were estimated to be −3.56
eV and −3.53 eV, respectively.
Calculations. Density functional calculations were performed using
the B3LYP method in the 6-31G* basis set. Calculations were
performed using the Spartan 14 software package (Wavefunction, Inc.
Irvine, CA, USA).36
(11) (a) Anthony, J. E. Chem. Rev. 2006, 106, 5028−5048. (b) Miao,
Q. Adv. Mater. 2014, 26, 5541−5549.
(12) (a) Sun, Z.; Zeng, Z.; Wu, J. Acc. Chem. Res. 2014, 47, 2582−
2591. (b) Li, Y.; Heng, W.-K.; Lee, B. S.; Aratani, N.; Zafra, J. L.; Bao,
́
N.; Lee, R.; Sung, Y. M.; Sun, Z.; Huang, K.-W.; Webster, R. D.; Lopez
Navarrete, J. T.; Kim, D.; Osuka, A.; Casado, J.; Ding, J.; Wu, J. J. Am.
Chem. Soc. 2012, 134, 14913−14922. (c) Sun, Z.; Lee, S.; Park, K.;
Zhu, X.; Zhang, W.; Zheng, B.; Hu, P.; Zeng, Z.; Das, S.; Li, Y.; Chi,
C.; Li, R.; Huang, K.; Ding, J.; Kim, D.; Wu, J. J. Am. Chem. Soc. 2013,
135, 18229−18236.
(13) (a) Li, J.; Zhang, K.; Zhang, X.; Huang, K.-W.; Chi, C.; Wu, J. J.
Org. Chem. 2010, 75, 856−863. (b) Li, J.; Jiao, C.; Huang, K.-W.; Wu,
J. Chem. - Eur. J. 2011, 17, 14672−14680.
ASSOCIATED CONTENT
■
(14) For indeno[1,2-b]fluorene and derivatives, see: (a) Chase, D. T.;
Rose, B. D.; McClintock, S. P.; Zakharov, L. N.; Haley, M. M. Angew.
Chem., Int. Ed. 2011, 50, 1127−1130. (b) Chase, D. T.; Fix, A. G.;
Rose, B. D.; Weber, C. D.; Nobusue, S.; Stockwell, C. E.; Zakharov, L.
N.; Lonergan, M. C.; Haley, M. M. Angew. Chem., Int. Ed. 2011, 50,
11103−11106. (c) Chase, D. T.; Fix, A. G.; Kang, S. J.; Rose, B. T.;
Weber, C. D.; Zhong, Y.; Zakharov, L. V.; Lonergan, M. C.; Nuckolls,
C.; Haley, M. M. J. Am. Chem. Soc. 2012, 134, 10349−10352.
(d) Frederickson, C. K.; Zakharov, L. N.; Haley, M. H. J. Am. Chem.
Soc. 2016, 138, 16827−16838.
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.joc.7b02699.
NMR and IR spectra of compounds 1b, 4a, and 4b and
Cartesian coordinates of DFT-calculated structures
(PDF)
AUTHOR INFORMATION
■
(15) For indeno[2,1-c]fluorene, see: Fix, A. G.; Deal, P. E.; Vonnegut,
C. L.; Rose, B. D.; Zakharov, L. N.; Haley, M. M. Org. Lett. 2013, 15,
1362−1365.
Corresponding Author
*E-mail: dfrantz@calpoly.edu.
E
DOI: 10.1021/acs.joc.7b02699
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Note
(16) For accounts of Haley’s indenofluorenes and other quinoidal
systems, see: (a) Frederickson, C. K.; Rose, B. D.; Haley, M. M. Acc.
Chem. Res. 2017, 50, 977−987. (b) Haley, M. M. Chem. Rec. 2015, 15,
1140−1143.
(17) For indeno[2,1-a]fluorene, see: Shimizu, A.; Tobe, Y. Angew.
Chem., Int. Ed. 2011, 50, 6906−6910.
(18) For indeno[2,1-b]fluorene, see: Shimizu, A.; Kishi, R.; Nakano,
M.; Shiomi, D.; Sato, K.; Takui, T.; Hisaki, I.; Miyata, M.; Tobe, Y.
Angew. Chem., Int. Ed. 2013, 52, 6076−6079.
(19) For a review/perspective of non-alternant non-benzenoid
aromatic compounds, including indenofluorenes, see: Tobe, Y.
Chem. Rec. 2015, 15, 86−96.
(20) Abe, M. Chem. Rev. 2013, 113, 7011−7088.
(21) Although not an indenofluorene, it is worth mentioning that
Haley’s extended diindenoanthracene was synthesized by another
strategy using DDQ oxidation: Rudebusch, G. E.; Zafra, J. L.; Jorner,
K.; Fukuda, K.; Marshall, J. L.; Arrechea-Marcos, I.; Espejo, G. L.;
Ponce Ortiz, R.; Gomez-García, C. J.; Zakharov, L. N.; Nakano, M.;
Ottosson, H.; Casado, J.; Haley, M. M. Nat. Chem. 2016, 8, 753−759.
(22) Rose, B. D.; Vonnegut, C. L.; Zakharov, L. N.; Haley, M. M.
Org. Lett. 2012, 14, 2426−2429.
(23) Barker, J. E.; Frederickson, C. K.; Jones, M. H.; Zakharov, L. N.;
Haley, M. M. Org. Lett. 2017, 19, 5312−5315.
(24) Miyoshi, H.; Miki, M.; Hirano, S.; Shimizu, A.; Kishi, R.;
Fukuda, K.; Shiomi, D.; Sato, K.; Takui, T.; Hisaki, I.; Nakano, M.;
Tobe, Y. J. Org. Chem. 2017, 82, 1380−1388.
(25) Rose, B. D.; Santa Maria, P. J.; Fix, A. G.; Vonnegut, C. L.;
Zakharov, L. N.; Parkin, S. R.; Haley, M. M. Beilstein J. Org. Chem.
2014, 10, 2122−2130.
(26) Preis, E.; Scherf, U. Macromol. Rapid Commun. 2006, 27, 1105−
1109.
(27) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457−2483.
(28) Rao, R.; Desmecht, A.; Perepichka, D. F. Chem. - Eur. J. 2015,
21, 6193−6201.
(29) Ma, Y.; Zheng, Q.; Yin, Z.; Cai, D.; Chen, S.-C.; Tang, C.
Macromolecules 2013, 46, 4813−4821.
(30) Kranzlein, G.; Wolfram, A.; Hausdorfer, E. Verfahren zur
̈
̈
Darstellung von cyclischen Diketonen. German Patent 546226, March
10, 1932.
(31) (a) Smyth, N.; Van Engen, D.; Pascal, R. A., Jr. J. Org. Chem.
1990, 55, 1937−1940. (b) Shen, Y.; Chen, C.-F. Chem. Rev. 2012, 112,
1463−1535. (c) Fujikawa, T.; Segawa, Y.; Itami, K. J. Am. Chem. Soc.
2015, 137, 7763−7768.
(32) Rose, B. D.; Chase, D. T.; Weber, C. D.; Zakharov, L. N.;
Lonergan, M.C.; Haley, M. M. Org. Lett. 2011, 13, 2106−2109.
(33) Romain, M.; Chevrier, M.; Bebiche, S.; Mohammed-Brahim, T.;
Rault-Berthelot, J.; Jacques, E.; Poriel, C. J. Mater. Chem. C 2015, 3,
5742−5753.
(34) Frigoli, M.; Moustrou, C.; Samat, A.; Guglielmetti, R. Eur. J. Org.
Chem. 2003, 2003, 2799−2812.
(35) Lombardo, C. M.; Welsh, S. J.; Strauss, S. J.; Dale, A. G.; Todd,
A. K.; Nanjunda, R.; Wilson, W. D.; Neidle, S. Bioorg. Med. Chem. Lett.
2012, 22, 5984−5988.
(36) Shao, Y.; Molnar, L. F.; Jung, Y.; Kussmann, J.; Ochsenfeld, C.;
Brown, S. T.; Gilbert, A. T. B.; Slipchenko, L. V.; Levchenko, S. V.;
O’Neill, D. P.; DiStasio, R. A., Jr.; Lochan, R. C.; Wang, T.; Beran, G.
T. O.; Besley, N. A.; Herbert, J. M.; Lin, C. Y.; Van Voorhis, T.; Chien,
S. H.; Sodt, A.; Steele, R. P.; Rassolov, V. A.; Maslen, P. E.;
Korambath, P. P.; Adamson, R. D.; Austin, B.; Baker, J.; Byrd, E. F. C.;
Dachsel, H.; Doerksen, R. J.; Dreuw, A.; Dunietz, B. D.; Dutoi, A. D.;
Furlani, T. R.; Gwaltney, S. R.; Heyden, A.; Hirata, S.; Hsu, C.-P.;
Kedziora, G.; Khalliulin, R. Z.; Klunzinger, P.; Lee, A. M.; Lee, A. S.;
Liang, W. Z.; Lotan, I.; Nair, N.; Peters, B.; Proynov, E. I.; Pieniazek,
P. A.; Rhee, Y. M.; Ritchie, J.; Rosta, E.; Sherrill, C. D.; Simmonett, A.
C.; Subotnik, J. E.; Woodcock, H. L., III; Zhang, W.; Bell, A. T.;
Chakraborty, A. T.; Chipman, D. M.; Keil, F. J.; Warshel, A.; Hehre,
W. J.; Schaefer, J. F.; Kong, J.; Krylov, A. I.; Gill, P. M. W.; Head-
Gordon, M. Phys. Chem. Chem. Phys. 2006, 8, 3172−3191.
F
DOI: 10.1021/acs.joc.7b02699
J. Org. Chem. XXXX, XXX, XXX−XXX