Synthesis of 1,3-diphenyl-6-alkyl/aryl-substituted fulvene chromophores: Observation of π-π Interactions in a 6-pyrene-substituted 1,3-diphenylfulvene

Article abstract of DOI:10.1021/jo301101x

The synthesis, structural, and electronic properties of nine 1,3-diphenyl-6-alkyl/aryl substituted pentafulvenes were studied. Pyrene ring π-π interactions were revealed from analysis of the experimental crystal packing of 1,3-diphenyl-6-(1-pyrene)fulvene and supporting DFT calculations. Photophysical properties derived from UV-vis and fluorescence emission measurements demonstrated tunable and low HOMO-LUMO band gaps for the series. The presented results point to a model synthetic approach for incorporation of extended π systems and donor-π-acceptor groups for fulvene-based electronic materials.

Full text of DOI:10.1021/jo301101x

Note
pubs.acs.org/joc
Synthesis of 1,3-Diphenyl-6-alkyl/aryl-Substituted Fulvene
Chromophores: Observation of π−π Interactions in a 6-Pyrene-
Substituted 1,3-Diphenylfulvene
Andrew J. Peloquin,† Rebecca L. Stone,† Sarah E. Avila,† Erlyn R. Rudico,† Christopher B. Horn,†
Kim A. Gardner,† David W. Ball,‡ Jane E. B. Johnson,† Scott T. Iacono,† and Gary J. Balaich*,†
†Department of Chemistry, United States Air Force Academy, USAF Academy, Colorado 80840, United States
‡Department of Chemistry, Cleveland State University, Cleveland, Ohio 44115, United States
S
* Supporting Information
ABSTRACT: The synthesis, structural, and electronic proper-
ties of nine 1,3-diphenyl-6-alkyl/aryl substituted pentafulvenes
were studied. Pyrene ring π−π interactions were revealed from
analysis of the experimental crystal packing of 1,3-diphenyl-6-
(1-pyrene)fulvene and supporting DFT calculations. Photo-
physical properties derived from UV−vis and fluorescence
emission measurements demonstrated tunable and low
HOMO−LUMO band gaps for the series. The presented
results point to a model synthetic approach for incorporation of extended π systems and donor-π-acceptor groups for fulvene-
based electronic materials.
entafulvenes have been investigated as important structural
units in synthesis areas spanning natural products1 and
promoted cyclization. The Grignard addition of PhMgCl to 2,
with ensuing dehydration, afforded 1,3-diphenyl-1,3-cyclo-
pentadiene 3, which was purified by crystallization from hot
EtOH.13 The final, key step14 is the reaction of 3 with
numerous functionalized aldehydes producing a diverse fulvene
substrate pool 4−12. The overall procedure is high-yielding and
operationally simple, requires no chromatography, and is easily
amenable to scale up to multigram quantities of fulvenes. The
fulvenes produced in the reaction of 3 with functionalized
aldehydes crystallize from the ethanol and can be obtained as
pure crystalline solids by recrystallization from common
organic solvents. Structure elucidation and purity of fulvenes
4−12 were confirmed using a combination of spectroscopic
techniques, including single crystal X-ray analysis for fulvenes
4−6,15 8, and 11 (see Supporting Information).
Organic materials incorporating pyrene in the molecular
architecture are of current interest,16,17 and herein, we highlight
the molecular and crystal structure of the 6-(1-pyrene)-
substituted fulvene 11 (Figure 1). Dark prismatic crystals of
11 were obtained from THF layered with MeCN. Molecules of
11 crystallized out in the centrosymmetric space group, Pbca,
with one molecule per asymmetric unit.18 Alternating short and
long bond distances as well as alternating intraring bond angles
for the fulvene ring of 11 were observed and are consistent with
data for other substituted pentafulvenes reported previously
(Figure 1).7−10,19−21 The pyrene ring of 11 is tilted out of the
fulvene ring plane by the largest angle [50.51°(4)] compared to
the other aromatic ring 6-substituted fulvenes in this series [6,
P
medicine,2,3 cyclic conjugated systems,4,5 and organometallic
complexes with catalytic and other properties.6 Ring and
exocyclic C6-substituted pentafulvenes are receiving increased
research attention in the design of materials with electronic
properties such as donor-π-acceptor systems and n-type
semiconductors.7−9 The synthesis of pentafulvene-based
polymers and supramolecular architectures, some of which
exhibit luminescent properties, has been reported.10 Important
in this type of work are synthetic methods that give entry into
substitutional variability for tuning of electronic properties
while maintaining a framework that will allow for incorporation
of the pentafulvene structural unit into polymers or extended
networks. In the course of our research on the synthesis of C2-
symmetric ansa-metallocenes,11,12 the crystallinity and intense
color of some of the pentafulvene precursors prompted us to
consider more carefully their absorption properties and a
possible synthetic design for their incorporation into electronic
materials. Herein, we report the synthesis, spectroscopic
properties, and select single crystal X-ray structures of several
new 1,3-diphenyl-6-alkyl/aryl fulvenes. This work represents a
modular approach to the selective and stepwise attachment of
electronically functional substituents in positions favorable for
applications as monomeric units or for incorporation into
polymers and supramolecular assemblies.
Fulvenes 4−12 were obtained using an overall four-step
reaction sequence (Scheme 1). Stetter coupling of benzalde-
hyde with methyl vinyl ketone gave 1-phenyl-1,4-pentanedione
1, which was purified by vacuum distillation. Conversion of 1 to
3-phenyl-cyclopenten-1-one 2 was carried out employing base-
Received: May 29, 2012
© XXXX American Chemical Society
A
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head to tail to their complementary pyrene rings in the top of
the bilayer, forming π−π-stacked dimers. A tetrameric packing
motif results in which the space between π-stacked pyrene rings
is shrouded by 1,3-diphenylfulvene rings from the top and
bottom of the bilayer. The closest contacts between pyrene ring
C atoms of adjacent molecules (see packing motif, Figure 1)
range from 3.629 to 3.664 Å which gives an average centroid-
to-centroid distance of 3.64 Å. However, the centroids of the
pyrene rings of π-stacked dimers of 11 are slipped 1.15 Å end
to end and 0.51 Å edge to edge when viewed down the normals
of pyrene rings (Figure 1). The angles between pyrene ring
normals and centroid-to-centroid vectors are 18.4° in the end-
to-end direction and 8.1° in the edge-to-edge direction. This
results in a somewhat slipped π−π interaction between
coplanar pyrene rings with an interplane contact distance of
3.46 Å, well within the distance expected for a noncovalent π−π
interaction.24 In the crystal structure of fulvene 11, the pyrene
ring overlap is intermediate between perfect face-to-face
alignment and fully slipped alignment where some of the ring
atoms are positioned directly above or below the centroid of
the opposite ring.
Scheme 1. Synthesis of 1,3,6-Substituted Fulvenes
In an effort to better understand the π−π stacking, density
functional theory (DFT) calculations were performed on 11.
The calculations were performed with Gaussian 0932 using
Grimme’s generalized gradient approximation functional (key-
word B97D)33 and the standard 6-31G(d,p) basis set.34 This
functional has been shown in the past35 to be an appropriate
selection for π-stacked systems. No basis set superposition error
correction was performed, so the targeted energy value, the
energy of interaction of the dimer of 11, should be considered
an upper limit. The resultant energy-minimized dimer was
found to be 93.7 kJ mol−1 more stable than isolated molecules
of 11. Although this should be regarded as an upper limit,
because of the relative simplicity of the calculation, it does point
to a significant energetic tendency for the dimer to form, at
least in the gas phase. Significant differenes in the calculated
dimer structure were observed and include fully slipped π-
stacked pyrene rings, non-coplanar pyrene rings, and different
relative orientations for the 1,3-diphenylfulvene rings (see
Supporting Information for pictorial representations of
calculated versus observed dimers). Although slipped, face-to-
face π−π interactions exist in the solid state structure of 11, no
such face-to-face interactions were observed in the reported
crystal structure of 1,2,3,4-tetramethyl-6-(1-pyrene)fulvene.22
The noted differences between the calculated and observed
dimer structures of 11 as well as the lack of any π−π stacking
interactions in the crystal structure of 6-(pyrene)-1,2,3,4-
tetramethylfulvene could point to a directing influence of 1,3-
diaryl substituents in enforcing dimeric π−π stacking
interactions for these types of fulvenes, which is one focus of
ongoing research.
The fulvene series 4−12 produced intensely colored, high-
melting point solids ranging across the visible spectrum from
orange and red to black based on the nature of substitution on
the exocyclic C6 position on the fulvene core. In order to
understand electronic-structure property relationships for 4−
12, solution studies including ultraviolet−visible excitation with
complementary fluorescence emission were performed in THF
with concentrations ranging from 0.4 to 0.6 mmol L−1.
Absorbance studies on the fulvene series are compiled
graphically in Figure 2, and selected optical properties are
also shown in Table 1. All fulvenes produced more than two
strong, distinct absorptions due to π−π* transitions from their
44.60°(5); and 8, 45.75°(4)], and it is significantly larger than
this angle reported for 1,2,3,4-tetramethyl-6-(1-pyrene)fulvene
(13.68°).22 Pyrene rings have been observed to form π−π
interactions in the solid state as well as in organic and
organometallic compounds with attached pyrene units.23−26
These interactions play an important role in supramolecular
chemistry and in organic- and organometallic-based molecular
electronics.27−31 One of the most notable features in the crystal
structure of 11 is the organization of molecules into layers in
which all pyrene rings adopt a head-to-tail19 π−π-stacked
arrangement (Figure 1). In the c direction, molecules of 11 are
arranged in a H-TT-HH-TT-H bilayer-type repeating
sequence [head (H) = pyrene ring (red), tail (T) = 1,3-
diphenylfulvene rings (blue), Figure 1]. Adjacent fulvene
molecules running along the b direction are packed such that
the planes from attached pyrene rings are oriented nearly
perpendicular (87.2°) to each other giving a herringbone
appearance to the pattern. In the HH region, pyrene rings in
the bottom of the bilayer are aligned almost face to face and
B
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Figure 1. Crystal and molecular structure of fulvene 11, showing the ORTEP view (upper left, viewed normal to and with numbering scheme for the
fulvene ring), crystal packing viewed along the b direction (upper right), and the slipped π−π stacking arrangement of pyrene rings viewed normal to
the pyrene ring planes (lower left), and in the plane of pyrene rings (lower right). Thermal ellipsoids are shown at the 50% probability level.
Hydrogen atoms were omitted for clarity. Selected bond distances (Å): C1−C2 1.353(2), C2−C3 1.467(2), C3−C4 1.363(2), C4−C5 1.459(2),
C5−C6 1.357(2). Selected bond angles (deg): C5−C1−C2 107.09(12), C1−C2−C3 110.06(12), C2−C3−C4 108.07(12), C3−C4−C5
108.74(12), C4−C5−C1 106.00(11).
Table 1. Selected Solution Electronic Properties of Fulvenes
4−12
excitation
a
b
c
entry λmax (nm) log(ε) emission λmax (nm) Δλmax (nm) ΔE (eV)
4
400
365
438
450
436
440
439
422
384
3.11
3.03
3.10
2.98
3.04
3.03
4.36
3.87
4.06
460
420
500
516
509
506
503
480
451
60
55
62
66
73
66
64
58
67
2.32
2.36
2.04
2.01
2.07
2.06
2.34
2.45
2.73
5
6
7
8
9
10
11
12
a
b
ε reported in L mol−1 cm−1. λmax reported in nm based on λmax
c
excitiation. Estimated by onset of absorption.
tronics. Extended fused ring fulvenes 11 and 12 produced the
largest band gaps among the series, with absorption onsets
slightly less than 500 nm. The maximum absorption wavelength
(λmax) was employed to excite each of the fulvenes in the series.
All fulvenes in this study possessed weak emission signals,
indicating most of the excitation energy is lost to primarily
nonradiative-decay processes such as structural, translational, or
rotational molecular vibrations. Overall, emission bathochromic
shifts upon excitation appear within a narrow range of 55−73
nm with no direct correlation with fulvene structure. These
small Stokes shifts indicate negligible intramolecular charge
transfer.
Figure 2. Solution absorbance spectra of fulvene compounds 4−12 in
THF.
structural contributions. Nonaromatic substituted fulvenes 4
and 5 produced the most intense absorption bands at only 260
and 280 nm, respectively. For fulvenes 6−12, absorptions
beyond 300 nm are a consequence of through-space aromatic
conjugation with the fulvene core.
The lowest-energy onset absorption extended to nearly 600
nm for the series, indicating that these fulvenes overall possess
low HOMO−LUMO band gaps (ΔE ranging from 2.01 to 2.73
eV) making them attractive precursory organic-based elec-
C
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M) was added until the mixture was acidic to pH paper. The resulting
brown precipitate was vacuum filtered and washed with water (200
mL). The brown solid was air dried and subsequently dried in a
vacuum desiccator giving 3-phenylcyclopent-2-en-1-one 2 as a crude,
brown solid (25.2 g, 92%). The crude product was recrystallized by
dissolving in boiling hot absolute EtOH (110 mL) and cooling (−5
°C). Vacuum filtration, washing with cold absolute EtOH (30 mL),
and vacuum drying afforded 2 as a yellow crystalline solid (14.3 g,
52%). An additional crystalline crop of product was obtained by
concentration of the filtrate to 50 mL, cooling (−5 °C), and seeding
with crystals from the first crop (2.7 g, total combined yield 17.0 g,
62%). 1H NMR (300 MHz, CDCl3): δ 7.66, 7.46 (m, 5H, Ph), 6.57 (t,
1H, CH), 3.05, 2.59 (m, 4H, CH2). 13C NMR (75 MHz, CDCl3): δ
209.2 (CO), 173.8, 134.1 (Ph ipso-C and Ph-C), 131.2, 128.9, 127.5,
126.8 (CH), 35.3, 28.6 (CH2). MS (EI, 70 eV): m/z 158 (M+), 129,
115, 102, 91, 77, 64.
Trifunctional 1,3,6-aryl and 1,3,6-alkyl/aryl pentafulvenes can
be obtained using a modular approach based on the synthetic
scheme for 1,3-diphenylcyclopentadiene and a subsequent
fulvene synthesis step. The ability to tailor the synthesis
provided a diverse pool of functionalized fulvene compounds.
The commercial availability of alkyl and aryl aldehydes as well
as various Grignard reagents makes this synthetic approach an
attractive one for the design of new electronic materials and
ligands containing or derived from a conjugated pentafulvene
core. Incorporation of polyaromatic hydrocarbons, alkynes, and
other heteroalkyl- and heteroaromatic-based functional groups
may lead to highly conjugated and processable organic and
organometallic materials. It is anticipated that the correct
choice and placement of functional groups could result in
materials with properties including donor-π-acceptor behavior,
intense absorption in the visible and near-infrared (low band
gap) regions, and fluorescence. Electronic-structure property
relationships suggest that these fulvene-based compounds could
also serve as valuable repeat structures for extended macro-
molecular systems possessing one or more of these properties.
1,3-Diphenylcyclopentadiene 3. A solution of 3-phenylcyclo-
pent-2-en-1-one 2 (8.42 g, 53.2 mmol) in THF (80 mL) under N2 was
added dropwise over 15 min to vigorously stirred PhMgCl in THF (2
M, 35 mL, 70 mmol) under N2. The resulting brown reaction mixture
was allowed to stir at room temperature for 16 h under N2 exposed to
air, and THF was removed by rotary vacuum to give a brown residue.
The brown residue was taken up and vigorously stirred in a mixture of
water (300 mL) and Et2O (300 mL). Addition of 6 M H2SO4 (15 mL,
90 mmol) resulted in a brown Et2O layer and a clear water layer, which
was stirred for an additional 5 min. The brown Et2O layer was
separated and washed sequentially with saturated NaHCO3 (3 × 200
mL), water (2 × 200 mL), and saturated brine (1 × 200 mL). The
organic layer was dried over anhydrous Na2SO4, filtered, and
concentrated under vacuum to afford a golden-colored oil, which
was recrystallized by dissolving in boiling hot absolute EtOH (300
mL) and cooling (−5 °C). Vacuum filtration, washing with cold
absolute EtOH (20 mL), and vacuum drying afforded 3 as colorless
EXPERIMENTAL SECTION
■
Syntheses of compounds 1, 2, and 3 were carried out using modified
literature procedures.13 The procedures are outlined below and
include spectroscopic data that were not available in the original
reports. Fulvene syntheses using 3 as the cyclopentadiene starting
material were carried out using the method of Stone and Little.14
Reactions were carried out under an atmosphere of nitrogen unless
otherwise noted. All glassware was oven-dried prior to use. 1H,
13C{1H}, and 19F NMR data were obtained under ambient
temperature conditions, and chemical shifts were reported in parts
per million (δ). Chemical shifts were referenced using the peak for
1
crystalline flakes that appear golden in bulk (9.16 g, 79%). H NMR
(300 MHz, CDCl3): δ 7.18−7.66 (m, 11H, Ph and PhCHCPh), 6.63
(m, 1H, PhCCHCH2), 3.58 (m, 2H, CH2). 13C NMR (75 MHz,
CDCl3): δ 147.8, 146.6, 136.1, 135.6 (C), 128.7, 128.6, 127.4, 127.0,
126.9, 126.1, 125.9, 125.1 (CH), 41.8 (CH2). MS (EI, 70 eV): m/z
218 (M+), 202, 189, 165, 141, 139, 115, 101.
1
residual CHCl3 (δ 7.25) or TMS (δ 0.00) for H NMR and the peak
for CDCl3 (δ 77.0) for 13C NMR. 19F NMR was referenced to CFCl3
(δ 0.00). Coupling constants for all spectra are reported in hertz.
Samples for absorbance and emission spectra were collected in THF
using a path length of 1 cm in Spectrosil quartz cuvettes (3 mL).
HRMS data were obtained using a double focusing sector instrument
operating in EI mode.
1,3-Diphenyl-6-(tert-butyl)fulvene 4. To a vigorously stirred
mixture of 1,3-diphenylcyclopentadiene (3.86 g, 17.7 mmol) in
absolute EtOH (30 mL) under N2 were added pivaldehyde (2.20
mL, 20.3 mmol) and pyrrolidine (2.20 mL, 26.4 mmol), and the
reaction mixture was maintained at room temperature for 26 h. After
20 h, GC−MS analysis of the reaction mixture showed less than 1%
1,3-diphenylcyclopentadiene remaining. The precipitate from the
reaction mixture was vacuum filtered, washed with cold absolute
EtOH (3 × 30 mL), and vacuum dried to give 4 as a bright orange,
microcrystalline solid (4.26 g, 84%). Crystals suitable for single-crystal
X-ray diffraction were obtained from EtOH by slow evaporation. Mp:
1-Phenyl-1,4-pentanedione 1. Freshly distilled benzaldehyde
(31.2 g, 294 mmol) in DMF (150 mL) was added dropwise over 10
min to a vigorously stirred suspension of NaCN (1.5 g, 30.6 mmol) in
DMF (100 mL) at 35 °C under N2. The color of the reaction mixture
turned yellow and faded to a dark orange as the addition of
benzaldehyde neared completion. The reaction mixture was allowed to
stir for 10 min, and freshly distilled methyl vinyl ketone (16.0 g, 228
mmol) in DMF (150 mL) was added dropwise over 20 min with
continued vigorous stirring at 35 °C under N2. The resulting dark
red−brown reaction mixture was allowed to stir for 4 h at 35 °C under
N2 exposed to air and combined with twice the volume of water. The
pale yellow suspension was extracted by vigorous stirring over two, 1 L
portions of CHCl3. The combined organic fractions were filtered
through a cotton plug and concentrated under a rotary vacuum.
Residual DMF was removed, by Kugelrohr vacuum distillation (100
°C, 2 Torr) followed by distillation of 1 (150 °C, 2 Torr), as a viscous
light yellow liquid (32.7 g, 81%), which was >95% pure (1H NMR,
1
96−97 °C. H NMR (300 MHz, CDCl3): δ 1.35 [s, 9H, C(Me)3],
6.86, 7.05, 6.49 (3H, fulvene ring and exocyclic CH), 7.26−7.71 (m,
10H, Ph). 13C NMR (75 MHz, CDCl3): δ 31.3 [C(Me)3], 36.0
[C(Me)3], 114.2, 126.1, 126.6, 126.8, 127.7, 128.2, 128.6, 129.6, 135.5,
136.4, 141.3, 142.3, 145.0, 154.3 (CH and ring-C). HRMS-EI: m/z
calcd for C22H22 [M]+, 286.17215; found, 286.17163.
1,3-Diphenyl-6-cyclohexylfulvene 5. Cyclohexane carboxalde-
hyde (1.88 mL, 15.6 mmol), pyrrolidine (1.75 mL, 21.3 mmol), and
1,3-diphenylcyclopentadiene (3.1 g, 14.2 mmol) were used employing
the procedure outlined for the preparation of 1,3-diphenyl-6-(tert-
butyl)fulvene 4 to obtain 5 as a bright orange, microcrystalline solid
(2.79 g, 63%). Crystals suitable for single-crystal X-ray diffraction were
1
GC−MS). H NMR (300 MHz, CDCl3): δ 7.97 (m, 2H, o-Ph), 7.49
(m, 3H, m- and p-Ph), 3.25, 2.86 (t, 4H, CH2), 2.23 (s, 3H, Me). 13
C
NMR (75 MHz, CDCl3): δ 206.8, 198.1 (CO), 136.4, 132.8, 128.2,
127.7 (Ph), 36.7, 32.1, 29.7 (CH2 and Me). MS (EI, 70 eV): m/z 176
1
obtained from THF layered with EtOH. Mp: 89−90 °C. H NMR
(M+), 161 (M+ − Me), 133 (M+ − COCH3), 105 [M+
−
(300 MHz, CDCl3): δ 1.18−1.88 (m, 10H, Cy-CH2), 2.83 (m, 1H,
Cy-CH), 7.28−7.72 (m, 10H, Ph), 6.94, 6.89 (2H, fulvene ring-CH),
(CH2)2COCH3], 77 (Ph+).
2
6.35 (d, 1H, fulvene exocyclic CHCy, J = 10 Hz). 13C NMR (75
3-Phenylcyclopent-2-en-1-one 2. A pale yellow suspension of 1-
phenyl-1,4-pentanedione 1 (30.7 g, 174 mmol) in 0.5 M NaOH (400
mL) was vigorously stirred under reflux conditions for 4 h resulting in
a brown-colored reaction mixture. The reaction mixture was cooled in
an ice bath with vigorous stirring, and hydrochloric acid (200 mL, 3
MHz, CDCl3): δ 25.6, 25.8, 33.2, 40.4 (Cy), 113.7, 126.0, 126.8, 127.6,
127.9, 128.3, 128.6, 129.2, 135.5, 136.2, 140.5, 142.7, 144.4, 148.9 (CH
and C). HRMS-EI: m/z calcd for C24H24 [M]+, 312.18780; found,
312.18685.
D
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1,3,6-Triphenylfulvene 6.15 Benzaldehyde (1.88 mL, 15.6
mmol), pyrrolidine (1.75 mL, 21.3 mmol), and 1,3-diphenylcyclo-
pentadiene (3.1 g, 14.2 mmol) were used employing the procedure
outlined for the preparation of 1,3-diphenyl-6-(tert-butyl)fulvene 4 to
obtain 6 as a cherry-red, microcrystalline solid (1.89 g, 65%). Crystals
suitable for single-crystal X-ray diffraction were obtained from 50:50
C6H6/MeOH at −5 °C. Mp: 121−22 °C. 1H NMR (300 MHz,
CDCl3): δ 7.26−7.74 (overlapping m, 16H, Ph, and fulvene exocyclic
CH-Ph), 7.00, 7.04 (2H, fulvene ring-CH). 13C NMR (75 MHz,
CDCl3): δ 114.6, 126.1, 127.1, 128.0, 128.1, 128.4, 128.6, 128.7, 129.1,
129.4, 131.0, 135.2, 136.0, 137.1, 138.5, 141.6, 144.3, 146.8 (CH and
C). HRMS-EI: m/z calcd for C24H18 [M]+, 306.14085; found,
306.14108.
butyl)fulvene 4 to obtain 11 as a black microcrystalline solid (1.45 g,
71%). Dark-red prismatic crystals of 11, suitable for single-crystal X-ray
diffraction, were obtained from THF layered with MeCN. Mp: 195−
1
196 °C. H NMR (300 MHz, CDCl3): δ 7.26−8.36 (overlapping m,
20H, Ph, fulvene exocyclic CH-pyrene, and pyrene CH), 7.11, 6.99
(2H, fulvene ring-CH). Selected 13C NMR (75 MHz, CDCl3): δ
115.8, 123.8, 124.7, 125.7, 125.8, 126.1, 126.2, 127.1, 127.4, 128.0,
128.25, 128.33, 128.34, 128.4, 128.6, 128.7, 129.4, 129.5, 130.1, 130.9,
131.3, 131.4, 131.9, 135.2, 136.1, 136.5, 141.1, 146.0, 146.9. HRMS-EI:
m/z calcd for C34H22 [M]+, 430.17215; found, 430.17145.
1,3-Diphenyl-6-(2-fluorenyl)fulvene 12. 2-Fluorenecarboxalde-
hyde (2.95 g, 15.2 mmol), pyrrolidine (1.71 mL, 20.9 mmol), and 1,3-
diphenylcyclopentadiene (3.01 g, 13.9 mmol) were used employing
the procedure outlined for the preparation of 1,3-diphenyl-6-(tert-
butyl)fulvene 4 to obtain 12 as a dark red−brown microcrystalline
solid (5.48 g, 93%). Mp: 179−180 °C. 1H NMR (300 MHz, CDCl3):
δ 7.30−7.88 (overlapping m, 18H, Ph, fulvene exocyclic CH-fluorene,
and fluorene CH), 7.00, 7.13 (2H, fulvene ring-CH), 3.98 (s, 2H,
CH2). 13C NMR (75 MHz, CDCl3): δ 36.9 (CH2), 114.6, 120.1,
120.4, 125.2, 126.1, 126.9, 127.0, 127.3, 127.4, 127.7, 127.9, 128.4,
128.7, 129.4, 130.1, 135.4, 135.7, 136.2, 139.2, 141.0, 141.8, 142.9,
143.6, 143.7, 143.9, 146.6 (CH and C). HRMS-EI m/z calcd for
C31H22 [M]+, 394.17215; found, 394.17395.
1,3-Diphenyl-6-(4-trifluoromethylphenyl)fulvene 7. 4-
(Trifluoromethyl)benzaldehyde (3.40 mL, 25.7 mmol), pyrrolidine
(2.30 mL, 27.5 mmol), and 1,3-diphenylcyclopentadiene (4.00 g, 18.3
mmol) were used employing the procedure outlined for the
preparation of 1,3-diphenyl-6-(tert-butyl)fulvene 4 to obtain 7 as a
1
maroon microcrystalline solid (2.60 g, 38%). Mp: 115−116 °C. H
NMR (300 MHz, CDCl3): δ 7.22−7.74 [overlapping m, 15H, Ph,
fulvene exocyclic CH-(p-(CF3)Ph, and p-(CF3)Ph CH], 7.02, 6.93
(2H, fulvene ring-CH). 13C NMR (75 MHz, CDCl3): δ 125.6 (q, CF3,
JCF = 3.9 Hz), 113.9, 126.2, 127.3, 128.3, 128.5, 128.8, 128.9, 129.4,
130.6, 134.8, 135.6, 135.9, 140.5, 141.6, 146.3, 147.8 (CH and C). 19
F
NMR (376 MHz, CDCl3): δ −62.6 (CF3). HRMS-EI: m/z calcd for
ASSOCIATED CONTENT
* Supporting Information
■
C25H17F3 [M]+, 374.12824; found, 374.12882.
S
1,3-Diphenyl-6-(3,5-dimethoxyphenyl)fulvene 8. 3,5-Dime-
thoxybenzaldehyde (1.88 mL, 15.6 mmol), pyrrolidine (1.75 mL,
21.3 mmol), and 1,3-diphenylcyclopentadiene (3.1 g, 14.2 mmol) were
used employing the procedure outlined for the preparation of 1,3-
diphenyl-6-(tert-butyl)fulvene 4 to obtain 8 as a dark red solid (2.79 g,
63%). Dark-red prismatic crystals suitable for single-crystal X-ray
diffraction were obtained by cooling (−5 °C) a concentrated solution
Figure of electronic absorption spectra and figures depicting
1H, 13C, and 19F NMR spectra, text describing crystallographic
details, tables of crystallographic data and cifs for fulvenes 4−6,
8, and 11, and text and data related to DFT calculations. This
material is available free of charge via the Internet at http://
pubs.acs.org.
1
of 8 in CH2Cl2. Mp: 124−125 °C. H NMR (300 MHz, CDCl3): δ
3.84 (s, 6H, OMe), 6.51 (t, 1H, MeOCCHCOMe), 6.77 (d, 2H,
MeOCCHCCHCOMe), 6.99, 7.04 (2H, fulvene ring-CH), 7.18−7.74
[overlapping m, 11H, Ph, and fulvene exocyclic CH-(3,5-dimethox-
yphenyl)]. 13C NMR (75 MHz, CDCl3): δ 55.4 (OMe), 101.4, 108.4,
114.6, 126.1, 127.0, 128.0, 128.2, 128.4, 128.7, 129.4, 135.1, 135.9,
138.4, 138.8, 141.6, 144.6, 146.7, 160.8 (CH and C). HRMS-EI: m/z
calcd for C26H22O2 [M]+, 366.16198; found, 366.16105.
AUTHOR INFORMATION
Corresponding Author
*E-mail: gary.balaich@usafa.edu.
Notes
■
The authors declare no competing financial interest.
1,3-Diphenyl-6-(3-phenoxyphenyl)fulvene 9. 3-Phenoxyben-
zaldehyde (1.09 g, 5.51 mmol), pyrrolidine (0.57 mL, 6.89 mmol), and
1,3-diphenylcyclopentadiene (1.03 g, 4.59 mmol) were used employ-
ing the procedure outlined for the preparation of 1,3-diphenyl-6-(tert-
butyl)fulvene 4 to obtain 9 as a dark-red microcrystalline solid (1.59 g,
ACKNOWLEDGMENTS
■
We dedicate this paper to Professor John S. Wilkes who
recently retired from his position as Director, Chemistry
Research Center, USAF Academy. John is a renowned ionic-
liquids chemist and will be deeply missed. It has been a great
experience working with him over the years. We acknowledge
the Air Force Office of Scientific Research and the Department
of Chemistry, USAF Academy, for funding.
1
87%). Mp: 132−133 °C. H NMR (300 MHz, CDCl3): δ 7.02−7.68
[overlapping m, 20H, Ph, fulvene exocyclic CH-(3-phenoxyphenyl),
and 3-phenoxyphenyl CH], 6.97, 6.93 (2H, fulvene ring-CH). 13C
NMR (75 MHz, CDCl3): δ 114.3, 119.3, 120.1, 123.7, 125.5, 126.1,
127.1, 128.0, 128.2, 128.4, 128.6, 129.3, 129.9, 130.0, 135.0, 135.8,
137.5, 138.6, 141.6, 144.7, 146.9, 156.8, 157.8 (CH, CO and C).
HRMS-EI: m/z calcd for C30H22O [M]+, 398.16707; found,
398.16659.
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E
dx.doi.org/10.1021/jo301101x | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
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dx.doi.org/10.1021/jo301101x | J. Org. Chem. XXXX, XXX, XXX−XXX