4,7-Diphenylisobenzofuran: A useful intermediate for the construction of phenyl-substituted acenes

Article abstract of DOI:10.1021/jo062675b

(Chemical Equation Presented) The formation and subsequent reactivity of previously unknown 4,7-diphenylisobenzofuran, 5, is reported. The Diels-Alder reaction between 5 and p-benzoquinone in boiling glacial acetic acid yields an unprecedented exo,exo ant

Full text of DOI:10.1021/jo062675b

4,7-Diphenylisobenzofuran: A Useful Intermediate for the
Construction of Phenyl-Substituted Acenes
James Eric Rainbolt and Glen P. Miller*
Department of Chemistry and Material Science Program, UniVersity of New Hampshire,
Durham, New Hampshire 03824
glen.miller@unh.edu
ReceiVed December 29, 2006
The formation and subsequent reactivity of previously unknown 4,7-diphenylisobenzofuran, 5, is reported.
The Diels-Alder reaction between 5 and p-benzoquinone in boiling glacial acetic acid yields an
unprecedented exo,exo anti dual cycloaddition product, 16b, in excellent yield and with 100%
diastereoselectivity. Differences between the reactivities of 5 and the more common 1,3-diphenylisoben-
zofuran are highlighted. Reactive 5 is utilized to form new three-, four-, and five-ring acenes, and the
latter compound is reacted with [60]fullerene to produce new [60]fullerene-acene adducts.
Introduction
mentally verified as a transient species by Fieser and Haddadin6,7
via Diels-Alder trapping studies. More recently, isobenzofuran
and its substituted derivatives8 have been considered as inter-
mediates in natural product syntheses.9
As isobenzofurans are often reactive and unstable species,
save for some 1- and 1,3-substituted examples,10,11 the construc-
tion of stable precursors is essential. The 1-hydroxy and
1-alkoxyphthalans are well established as convenient precursors
to isobenzofurans.12-16 Here, we describe the syntheses of
compounds 1-3, precursors to previously unknown (()-4,7-
Our efforts to synthesize [60]fullerene-acene adducts1 typi-
cally begin with an acene synthesis. We are particularly
interested in phenyl-substituted acenes as the phenyl substituents
direct [60]fullerene cycloadditions to the desired rings along
the acene backbone and provide for enhanced solubility in
common organic solvents. One useful strategy to synthesize
phenyl-substituted pentacenes2 involves the Diels-Alder reac-
tion between phenyl-substituted isobenzofuran and p-benzo-
quinone.3 Isobenzofurans are long recognized as useful dienes
in Diels-Alder cycloadditions.4 The parent isobenzofuran was
first postulated by Wittig and Pohmer,5 and then later experi-
(5) Wittig, G.; Pohmer, L. Chem. Ber. 1956, 89, 1334.
(6) Fieser, L. F.; Haddadin, M. J. J. Am. Chem. Soc. 1964, 86, 2081.
(7) Fieser, L. F.; Haddadin, M. J. Can. J. Chem. 1965, 43, 1599.
(8) (a) Friedrichsen, W. AdV. Heterocycl. Chem. 1999, 73, 1. (b) Reck,
S.; Friedrichsen, W. Prog. Heterocycl. Chem. 1997, 9, 117. (c) Rodrigo,
R. Tetrahedron 1988, 44, 2093.
(9) Wege, D. AdV. Theor. Interesting Mol. 1998, 4, 1.
(10) Warrener, R. N.; Shang, M.; Butler, D. N. Chem. Commun. 2001,
17, 1550.
(1) (a) Miller, G. P.; Mack, J. Org. Lett. 2000, 2, 3979. (b) Miller, G.
P.; Mack, J.; Briggs, J. Org. Lett. 2000, 2, 3983. (c) Miller, G. P.; Briggs,
J.; Mack, J.; Lord, P. A.; Olmstead, M. M.; Blach, A. L. Org. Lett. 2003,
5, 4199. (d) Miller, G. P.; Briggs, J. Org. Lett. 2003, 5, 4203. (e) Miller,
G. P.; Briggs, J. Tetrahedron Lett. 2004, 45, 477.
(2) Miller, G. P.; Briggs, J. Proc. Electrochem. Soc. 2002, 2002-12,
(11) Rodrigo, R.; Knabe, S. M. J. Org. Chem. 1986, 51, 3973.
(12) Smith, J. G.; Kruger, G. J. Org. Chem. 1985, 50, 5759.
(13) Smith, J. G.; Sandborn, R. E.; Dibble, P. W. J. Org. Chem. 1986,
51, 3762.
(14) Naito, K.; Rickborn, B. J. Org. Chem. 1980, 45, 4061.
(15) Tu, N. P. W.; Yip, J. C.; Dibble, P. W. Synthesis 1996, 5, 77.
(16) Mikami, K.; Ohmura, H. Org. Lett. 2002, 4, 3355.
279.
(3) (a) Barnett, E. D. B. J. Chem. Soc. 1935, 1326. (b) Allen, C. F. H.;
Gates, J. W. J. Am. Chem. Soc. 1943, 65, 1502. (c) Oniciu, D. C.; Ghiviriga,
I.; Iordache, F.; Istrate, D.; Dinulescu, I. G. ReV. Roum. Chim. 1992, 37,
1285.
(4) Peters, O.; Friedrichsen, W. Trends Heterocycl. Chem. 1995, 4, 217.
10.1021/jo062675b CCC: $37.00 © 2007 American Chemical Society
Published on Web 03/21/2007
3020
J. Org. Chem. 2007, 72, 3020-3030

4,7-Diphenylisobenzofuran
SCHEME 1a
TABLE 1. Reactions between 5 and Maleic Anhydride
(()-4:maleic
anhydride
exp.
reagents/temp
time
endo 6a:exo 6ba
1
2
3
1:1.2
1:1.4
1:1.5
HOAc/118 °C
HOAc,Ac2O/50 °C
HOAc,Ac2O/35 °C
24 h
1 h
1 h
1:16.5
1:1
1:1
a Endo:exo ratios are calculated from 1H NMR integrations of crude
product mixtures.
SCHEME 2
a Reagents and conditions: (a) xylenes, 140 °C, 15 h; (b) DDQ, toluene,
111 °C, 18 h; (c) Zn, HOAc, 100 °C, 17 h; (d) DIBAL-H, dichloromethane,
-60 °C, 70 min.
diphenyl-1-hydroxyphthalan, (()-4. We further demonstrate that
compound (()-4 readily converts to 4,7-diphenylisobenzofuran,
5. We also show that reactive 5 is a versatile intermediate for
the synthesis of phenyl-substituted three-, four-, and five-ring
acene compounds. The reaction between 5 and p-benzoquinone
is especially interesting as it yields the unprecedented exo,exo
anti dual cycloaddition product 16b on the way to 1,4,8,11-
tetraphenylpentacene 21.
products precipitate cleanly and in good yield from this solution.
An E1 mechanism for the formation of isobenzofuran from
alkoxy precursors in acidic media has been reported24 and is
analogous to that shown in Scheme 2. Upon forming 5 in glacial
acetic acid, its reactivity with maleic anhydride was studied.
Both endo and exo products (Scheme 3) form under all
conditions tested (Table 1). While equal quantities of endo and
exo product are formed at 50 °C and below, the exo product,
6b, is highly favored in boiling acetic acid. Although a shift
toward exo selectivity at elevated temperatures is not unusual
for a Diels-Alder reaction, the magnitude of the change in
selectivity is quite large for this reaction. It is tempting to
conclude that the endo product is formed competitively under
kinetically controlled conditions (lower temperatures) while the
exo product is favored under reversible, thermodynamic condi-
tions (higher temperatures), but there is insufficient data to draw
this conclusion. Indeed, the high-temperature reactivity of 5 with
maleic anhydride mimics that of the parent isobenzofuran, which
forms nearly the same ratio of endo:exo products at similar
(∼130 °C) temperatures.25 Isobenzofuran itself should be more
reactive than 5 and less prone to undergo reversible cycload-
ditions at any temperature.
1H-1H NMR coupling, or lack thereof, between the methine
protons at the sites of cycloaddition (oxabicyclo substructure)
differentiates endo 6a from exo 6b.12,13,26,27 The aliphatic
methine protons of the oxabicyclo substructure of the endo
diastereomer produce an AA′XX′ pattern in the 1H NMR
spectrum. In the exo isomer 6b, the analogous protons possess
a dihedral angle that approaches 90°, thereby diminishing vicinal
1H-1H coupling. Consequently, the aliphatic methine protons
in 6b give rise to two singlets rather than two multiplets.
Results and Discussion
Synthesis of (()-4,7-Diphenyl-1-hydroxyphthalan ((()-4).
Lactol (()-4 is synthesized in four steps, each in 80% yield or
higher, starting from commercially available reactants (Scheme
1). Cycloaddition of 1,4-diphenyl-1,3-butadiene with maleic
anhydride is performed following the procedure of Kuhn and
Wagner-Jauregg17 to yield 3a,4,7,7a-tetrahydro-4,7-diphe-
nylphthalic anhydride, 1, in 80% yield. Subsequent aromatiza-
tion of 1 with a two-fold equivalent of 2,3-dichloro-5,6-dicyano-
p-benzoquinone (DDQ) in refluxing toluene gives the known
molecule18,19 4,7-diphenylphthalic anhydride, 2, in 87% yield.
Using a modified Yang-Zhu reduction,20 the diphenylphthalide
321 is synthesized in 89% yield. Conversion of 3 to the
previously unknown hydroxyphthalan (()-4 is performed in
80% yield using Rodrigo’s conditions.22
Lactol (()-4 is a stable white solid. Literature precedence
exists for solution-phase equilibria between similar hemiacetals
and their corresponding aldehyde-alcohol ring-opened tau-
tomers.23 In the case of (()-4, however, only the hemiacetal is
1
observed by H and 13C NMR spectroscopies.
In Situ Formation and Reactivity of 4,7-Diphenylisoben-
zofuran (5): Construction of Three- and Four-Ring Acene
Derivatives. Hydroxyphthalan (()-4 is a stable and convenient
precursor to 4,7-diphenylisobenzofuran 5. Glacial acetic acid
is an effective solvent/catalyst for the in situ generation of 5,
as is a mixture of p-TsOH in toluene. Glacial acetic acid is,
however, preferred as we observe that subsequent cycloaddition
Optimal conditions for the formation of 6a and 6b are
illustrated in Scheme 3. The mixture may be dehydrated using
p-TsOH to form anhydride 7,28 which is then subjected to
modified Cava conditions1d,29 to form keto-acid 8. Reducing 8
with borohydride produces racemic lactone (()-9 in modest
(17) Kuhn, R.; Wagner-Jauregg, Th. Chem. Ber. 1930, 63B, 2662.
(18) Bergmann, F. J. Am. Chem. Soc. 1942, 64, 176.
(19) Weizmann, C.; Bergmann, E.; Haskelberg, L. J. Chem. Soc. 1939,
391.
(20) Yang, C.-f.; Zhu, J.-l. Huaxue Shijie 2000, 41, 426.
(21) Murakoka, O.; Tanabe, G.; Yamamoto, E.; Ono, M.; Minematsu,
T.; Kimura, T. J. Chem. Soc., Perkin Trans. 1 1997, 2879.
(22) Keay, B. A.; Rodrigo, R. Can. J. Chem. 1985, 63, 735.
(23) Smith, J. G.; Deryn, E. F.; Munday, I. J.; Sandborn, R. E.; Dibble,
P. W. J. Org. Chem. 1988, 53, 2942.
(24) Mir-Mohamad-Sadeghy, B.; Rickborn, B. J. Org. Chem. 1983, 48,
2237.
(25) Fier, S.; Sullivan, R. W.; Rickborn, B. J. Org. Chem. 1988, 53,
2353.
(26) Wiersum, U. E.; Mijs, W. J. J. Chem. Soc., Chem. Commun. 1972,
347.
(27) Halton, B.; Evans, D. A.; Warrener, R. N. Aust. J. Chem. 1999, 52,
1123.
(28) Dufraisse, Ch.; Gigaudy, J.; Ricard, M. Tetrahedron Suppl. 1966,
8 (Part II), 491.
J. Org. Chem, Vol. 72, No. 8, 2007 3021

Rainbolt and Miller
SCHEME 3a
a Reagents and conditions: (a) maleic anhydride, HOAc, Ac2O, 118 °C, 2 h; (b) p-TsOH, toluene, Dean-Stark trap, 111 °C, 4 d; (c) PhH, AlCl3, 80 °C,
20 h; (d) NaBH4, NaOH, EtOH, H2O, 25 °C, 6 d; (e) PhMgBr, THF, 0 °C, 1 h; (f) maleic anhydride, p-TsOH, PhH, Dean-Stark trap, 80 °C, 24 h.
SCHEME 4a
a Reagents and conditions: (a) 1,4-naphthoquinone, HOAc, 60 °C, 2 h; (b) H2SO4, HOAc, 70 °C, 1 h; (c) HI, HOAc, 118 °C, N2, dark, 4 d; (d) 10% Pd/C,
1,2-dichlorobenzene, 180 °C, N2, dark, 3 d.
yield. Phenylation of (()-9 produces a mixture of lactols, which
and is trapped in situ with maleic anhydride to generate, after
further dehydration, 4,6,9,11-tetraphenylanthra[2,3-c]furan-1,3-
dione 11. Compound 11, a new acene derivative, is a stable
yellow solid that exhibits strong fluorescence.
1
coexist with their ring-opened keto-ol forms according to H
and 13C NMR spectra. Transient 1,3,5,8-tetraphenylisonaph-
thofuran, 10, is presumed to form upon dehydration of the lactol
The reaction between 5 and 1,4-naphthoquinone was also
studied (Scheme 4). Endo product 12a is favored at lower
(29) (a) Cava, M. P.; VanMeter, J. P. J. Am. Chem. Soc. 1962, 84, 2008.
(b) Cava, M. P.; VanMeter, J. P. J. Org. Chem. 1969, 34, 538.
3022 J. Org. Chem., Vol. 72, No. 8, 2007

4,7-Diphenylisobenzofuran
FIGURE 1. (Left) Side view of the MM2 geometry optimized endo,exo syn dual cycloaddition product arising from the known reaction2,3c between
2 equiv of 1,3-diphenylisobenzofuran and p-benzoquinone. (Right) ChemDraw structure of the same compound. Syn describes the relative positions
of the two oxygen bridges.
TABLE 2. Reactions between 5 and 1,4-Naphthoquinone
(()-4:
endo12a:
exo12ba
exp. 1,4-naphthoquinone
reagents/temp
time
4
5
6
7
8
1:1.2
1:1.1
1:1.1
1:1.1
1:1
HOAc/118 °C
18 h
5 h
2 h
2 h
1 h
N/Ab
HOAc,Ac2O/100 °C
HOAc,Ac2O/90 °C
HOAc,Ac2O/75 °C
HOAc,Ac2O/50 °C
1:3c
1.1:1
1.5:1
1.7:1
a Endo:exo ratios are calculated from 1H NMR integrations of crude
product mixtures. b Dehydration of 12a and 12b to form 13 is facile under
these reaction conditions. No 12a or 12b is observed by NMR. c Trace 13
is also observed.
temperatures, while exo product 12b is favored at elevated
temperatures (Table 2). The trend toward greater exo selectivity
at elevated temperatures is similar to that observed in the maleic
anhydride reaction (Table 1), although the change in selectivity
is not as dramatic. The mixture of 12a and 12b is readily
dehydrated to 1,4-diphenyltetracene-6,11-quinone, 13, which is
then transformed to a mixture of dihydrodiphenyltetracenes, 14a
and 14b, via an HI-HOAc reduction.1d Finally, a Pd/C
dehydrogenation produces previously unknown 1,4-diphenyltet-
racene, 15, in excellent yield.
FIGURE 2. Six possible diastereomers that can form in the dual
cycloaddition of 5 across p-benzoquinone.
Unusual Diastereoselectivity in the Reaction between 4,7-
Diphenylisobenzofuran (5) and p-Benzoquinone. Several two-
fold cycloaddition products are known for reactions where an
isobenzofuran or isonaphthofuran is reacted with p-benzo-
quinone. Isolated products have been reported for the reactions
involving 1,3-diphenylisobenzofuran (Figure 1),2,3c 5,6-ditrim-
ethylsilylisobenzofuran,30,31 and 1,3-diphenylisonaphthofuran.1d,e
In all cases, a single endo,exo syn diastereomer is reported, each
arising from consecutive endo and exo cycloadditions of two
isoacenofurans across opposite faces of the quinone. Parent
isobenzofuran and p-benzoquinone also form a two-fold cy-
cloaddition product32, but it was never isolated on the path
leading to pentacene-6,13-dione, a molecule more easily syn-
thesized via alternative routes.33,34
SCHEME 5a
Interestingly, there are a total of six different diastereomers
that could form upon the two-fold cycloaddition of 5 across
p-benzoquinone (Figure 2). These arise from two different
combinations each of either endo,endo or endo,exo or exo,exo
cycloadditions.
a Reagents and conditions: (a) HOAc, heat; see Table 3.
On the basis of literature precedence, we expected exclusive
formation of the endo,exo syn isomer 16c. However, when (()-4
and p-benzoquinone are reacted in glacial acetic acid (Scheme
5), we observe formation of both 16c as well as the exo,exo
anti diastereomer 16b. Isomer 16c is slightly favored at lower
temperatures, while 16b is dominant at higher temperatures
(Table 3). In fact, 16b forms in excellent yield and with 100%
diastereoselectivity in boiling glacial acetic acid. Neither 16b
(30) Yick, C.-Y.; Chan, S. H.; Wong, H. N. C. Tetrahedron Lett. 2000,
41, 5957.
(31) Yick, C.-Y.; Chan, S.-H.; Wong, H. N. C. Tetrahedron 2002, 58,
9413.
(32) Smith, J. G.; Dibble, P. W. J. Org. Chem. 1983, 48, 5361.
(33) Mack, J., II. Ph.D. dissertation, University of New Hampshire,
Durham, NH, 2000.
(34) Vets, N.; Smet, M.; Dehaen, W. Tetrahedron Lett. 2004, 45, 7287.
J. Org. Chem, Vol. 72, No. 8, 2007 3023

Rainbolt and Miller
FIGURE 3. Kinetically preferred approaches of a second equivalent of 5 to either the exo (top) or the endo (bottom) monoadduct of compound
5 and p-benzoquinone leading in both cases to endo,exo syn 16c. Ball and stick models of the exo and endo monoadducts and 16c are all AM1
geometry optimized structures. For clarity, the carbon atoms of p-benzoquinone are shown in green; those of 4,7-diphenylisobenzofuran are shown
in blue; oxygen atoms are shown in red.
FIGURE 4. Isolated dual cycloaddition product exo,exo anti 16b (left) and theoretical dual cycloaddition product exo,exo syn 16a (right). MMFF
optimized geometries.
TABLE 3. Reactions between 5 and p-Benzoquinone
exp. (()-4:p-benzoquinone reagents/temp time yield 16b:16ca
not especially helpful. Instead, it is instructive to consider the
possible paths leading from the first formed cycloadducts
between 4,7-diphenylisobenzofuran and p-benzoquinone (i.e.,
the endo and exo monoadducts) to the eventual endo,exo
product. As illustrated in Figure 3, the less hindered path from
either the exo or the endo monoadduct leads directly to the
endo,exo syn adduct 16c. Thus, we assign the endo,exo kinetic
product a syn stereochemistry, that is, 16c, based upon this
analysis as well as literature precedence involving other endo,-
exo isomers of this type.1d,e,2,3c,30,31
9
10
11
2.1:1
2.1:1
2.1:1
HOAc/118 °C
HOAc/90 °C
HOAc/70 °C
8 h 90% only 16bb
15 h 82%
5 h 89%
5:1
1:1.5
a Ratios of 16b:16c are calculated from 1H NMR integrations of
precipitate product mixtures. b Isomer 16c, if formed at all, is not detected
1
by H NMR spectroscopy.
nor 16c is especially soluble in acetic acid, as both readily
precipitate from cooled solutions.
Structural Analysis of 16b. Because 16b is formed with
100% diastereoselectivity in boiling glacial acetic acid, a
definitive stereochemical analysis is warranted for this molecule.
The lack of coupling between the protons on the oxabicyclo
moieties firmly establishes the exo,exo nature of 16b (see
analysis of 6a and 6b above) but does not distinguish between
syn and anti stereochemistries. Both the C2h symmetric exo,-
exo anti isomer 16b and the C2V symmetric exo,exo syn isomer
Structural Analysis of 16c. The existence of both endo and
exo stereochemistries on the oxabicyclo moieties of 16c is
clearly revealed by the presence of both coupled and non-
coupled aliphatic methine signals (see analysis of 6a and 6b
1
above). The H NMR data, however, do not distinguish syn
from anti stereochemistries (i.e., 16c from 16d). AM1 calcula-
tions reveal heats of formation for endo,exo syn isomer 16c
and endo,exo anti isomer 16d that are identical (94.7 kcal/mol)
within experimental error. However, because the endo,exo
product is formed under kinetically controlled conditions (Table
3), a comparison of ground-state energies for 16b and 16c is
1
16a (Figure 4) are consistent with the H NMR data. These
structures arise from dual exo cycloadditions across either the
opposite faces or the same face of p-benzoquinone, respectively.
There is no literature precedence involving a dual cycloaddition
3024 J. Org. Chem., Vol. 72, No. 8, 2007

4,7-Diphenylisobenzofuran
FIGURE 5. (Left) The three possible products arising from borohydride reduction of the hypothetical exo,exo syn 16a. (Right) The two products
formed during the borohydride reduction of exo,exo anti 16b. The time-averaged symmetries associated with each structure are identified.
1
TABLE 4. Expected H NMR Spectra for Compounds 17a-c and
18a,b
maximum number of
relationship
1H NMR signalsb
between
compound
boat formsa
fast inversionc
slow inversion
17a
17b
17c
18a
18b
CD
CD
CD
CD
CE
4
4
8
6
6
8 (2 × 4)
8 (2 × 4)
16 (2 × 8)
12 (2 × 6)
12 (1 × 12)
a CD, conformational diastereomers; CE, conformational enantiomers.
b The maximum number of 1H NMR signals in the aliphatic diagnostic
region (see text). c Inversion refers to boat-to-boat inversions of the central
cyclohexane ring. Fast and slow inversions are relative to the NMR time
scale.
FIGURE 6. The central aliphatic diagnostic region for hypothetical
structures 17a-c and isolated molecules 18a,b.
product of this type. To assign either syn or anti stereochemistry,
we attempted but failed to grow X-ray quality crystals. We
further attempted but failed to prepare both a 2,4-dinitrophe-
nylhydrazone derivative and a bis-dimethyl acetal. It was hoped
that a 2,4-dinitrophenylhydrazone derivative would readily
crystallize while the bis-dimethyl acetal would enable an NMR
elucidation of syn versus anti stereochemistry. Finally, we were
successful in converting the single exo,exo product into a
mixture of alcohols using a sodium borohydride reduction. This
conversion permitted the unambiguous assignment of anti
stereochemistry to the exo,exo product, that is, 16b, as described
below.
Analysis of Borohydride Reduction Products of 16b.
Reduction of hypothetical exo,exo syn isomer 16a would
produce up to three different diols (17a-c), while reduction of
exo,exo anti 16b produces two different diols (18a and 18b) as
illustrated in Figure 5. The expected 1H NMR signals associated
with each of the central aliphatic substructures (Figure 6) are
diagnostic. This diagnostic region possesses four types of
protons including three unique methine protons (HI, HII, HIII)
and one alcohol proton (HIV). The diagnostic region also
includes a central cyclohexane ring that prefers a boat confor-
mation in all cases due to constraining bicyclo addends. This
strong preference for boat conformations is corroborated by
molecular models and force-field calculations. For each of these
structures, the number of H NMR resonances expected in the
1
aliphatic diagnostic region is a function of both molecular
symmetry and the rate of boat-to-boat inversions (Table 4). As
1
such, H NMR spectroscopy alone can distinguish structures
17a-c from structures 18a,b.
The borohydride reduction of 16b yields a crude product that
is separated into two distinct bands on a silica preparative TLC
plate using chloroform and ethyl acetate (10:1) as eluent. Careful
characterization of these bands reveals each to be a single
product, one 18a and one 18b (Figures 5 and 7), isolated in an
1
approximate 1:1 ratio. The H NMR spectrum for the slow
eluting band is consistent with Cs symmetric 18a as a single
conformational diastereomer that is slow to invert on the NMR
1
timescale (Table 4). It exhibits two H NMR resonances for
the type HI protons, two resonances for the type HII protons,
one resonance for the type HIII protons, and one resonance for
the type HIV protons.35 This six resonance pattern is inconsistent
with structures 17a-c (Table 4), thereby confirming the
assignment of 16b. The observed preference of 18a for one of
two possible conformational diastereomers is suggested by
MMFF structures. In one boat form, both hydroxyl groups of
18a are pseudoaxial, enabling two distinct intramolecular
J. Org. Chem, Vol. 72, No. 8, 2007 3025

Rainbolt and Miller
FIGURE 7. Diols 18a (left) and 18b (right) shown in boat conformations as predicted by molecular models and MMFF. MMFF optimized geometries.
SCHEME 6a
a Reagents and conditions: (a) p-TsOH, PhH, Dean-Stark trap, 80 °C,
1 d; (b) HI, HOAc, CHCl3, 85 °C, N2, dark, 5 d; (c) DDQ, [60]fullerene,
PhH, 80 °C, N2, dark, 18 h.
hydrogen-bonding interactions (Figure 7). In the other boat form,
the hydroxyl groups are pseudo-equatorial and do not enjoy any
intramolecular hydrogen bonding.
1H NMR spectra for the fast eluting band on silica are
consistent with 18b as a mixture of indistinguishable confor-
mational enantiomers that are also slow to ring invert on the
NMR timescale (Table 4). At ambient temperature, the 1H NMR
spectrum of 18b reveals 12 unique resonances in the aliphatic
diagnostic region (four for the type HI protons, four for the type
HII protons, two for the type HIII protons, and two for the type
HIV protons35), each integrating for one proton. Likewise, 10
resonances are observed in the aliphatic diagnostic region of
the corresponding 13C NMR spectrum. Similar to 18a, the slow
inversion of 18b is likely due to an intramolecular hydrogen
bond that must be broken before interconverting the confor-
mational enantiomers.
Variable-temperature NMR spectroscopy corroborates our
analysis of 18b. Thus, diol 18b was dissolved in o-dichloroben-
zene-d4, and 400 MHz 1H NMR spectra were recorded at
progressively increasing temperatures. As illustrated in Figure
8, the type HI protons of 18b give rise to four 1H NMR singlets
betwen 5.3 and 6.0 ppm at or near room temperature. At elevated
temperatures, boat-to-boat interconversions become more rapid
1
FIGURE 8. Variable-temperature H NMR spectra for the type HI
protons of 18b.
on the NMR timescale, and consequently the two high field
and the two low field singlets are observed to coalesce at
(35) In the isolated products 18a and 18b, the assignments for the alcohol
proton resonances were confirmed by deuterium exchange with D2O.
3026 J. Org. Chem., Vol. 72, No. 8, 2007

4,7-Diphenylisobenzofuran
TABLE 5. Survey of Reactions between 24 and p-Benzoquinone
approximately 87 and 99 °C, respectively. These broadened
signals ultimately sharpen into two singlets at higher temper-
atures, at which point 18b exhibits Ci symmetry on the NMR
timescale. From the dynamic NMR data of 18b, we calculate
under Various Conditions
precipitate product ratiosb
exp. 24:BQa reagents/temp (°C)/time (h)
24
25
26
27c
‡
boat-to-boat inversion barriers of 18.1 ( 0.2 kcal/mol (∆Gc ,
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
2.1
2.0
2.3
2.1
2.2
2.0
2.1
2.1
2.0
2.0
2.1
2.0
2.0
2.1
2.1
HOAc/50/1
HOAc/70/1
HOAc/90/2
HOAc,Ac2O/118/16
EtOH/78/1
4 HOAc,EtOH/108/1
21 HOAc,EtOH/108/1
210 HOAc,EtOH/108/1
HOAc,CHCl3 (50:50 v/v)/50/1
HOAc,CHCl3 (50:50 v/v)/85/1
CHCl3/25/17
32 100 145
450 100 1580
0
0
0
0
0
‡
360 K) and 17.7 ( 0.2 kcal/mol (∆Gc , 372 K).
91
83
0
0
0
0
0
100
100
100
100
100
100
0
0
0
An alternative interpretation is possible in which the assign-
ments for 18a and 18b are switched, but this scenario is
considered unlikely. With this alternative interpretation, the fast
eluting band on silica would have to be assigned to the more
polar structure 18a, and the room-temperature 1H NMR
spectrum of this compound (consisting of 12 signals, each
with equal integration; see Table 4) would have to be
interpreted as due to a 50:50 mixture of conformational
diastereomers that are slow to invert on the NMR timescale. A
50:50 mixture of conformational diastereomers is neither
expected nor likely. The previously mentioned MMFF calcula-
tions indicate an energetic preference for one conformational
diastereomer of 18a, that which exhibits intramolecular hydro-
gen bonding.
trace
trace
trace
0
0
0
16 100
83
46
100
0
0
50 100
trace 100
trace 100
65 trace
10
10
CHCl3/61/1
CHCl3/61/17
toluene/111/18
xylenes/140/16
5
8
0
0
100
100
36 14
58
8
a BQ is p-benzoquinone. b Relative ratios of 24-27 present in precipitate.
If formed, dual cycloaddition adduct 25 is normalized to 100. c A single
1
mono addition adduct is observed by H NMR spectroscopy.
Construction of a New Five-Ring Acene from 16b: [60]-
Fullerene Trapping of 1,4,8,11-Tetraphenylpentacene. Di-
endoxide 16b is dehydrated using p-TsOH to give quinone
19, which is reduced to dihydropentacene 20 using HI
(Scheme 6). Quinone 19 exhibits exceptionally poor solubility,
SCHEME 7a
1
and its characterization is limited to H NMR spectroscopy.
Dihydropentacene 20, on the other hand, has vastly improved
solubility and has been fully characterized. Compound 20 is
aromatized in situ to produce 1,4,8,11-tetraphenylpentacene 21,
which is trapped with [60]fullerene to give a mixture of mono-
[60]fullerene adduct 22 and a single bis[60]fullerene adduct 23.
Compound 23 is presumed to be the cis-bis[60]fullerene adduct
shown in Scheme 6 based upon the known tendency for [60]-
fullerenes to cycloadd across acenes in a syn fashion.1a-d,33
a For reagents and conditions, see Table 5.
Although a separation was not achieved for the mixture of
22 and 23, the 1H and 13C NMR spectra obtained for this mixture
leave no doubt concerning the nature of the products formed.
As expected, the 1H NMR spectrum reveals two aliphatic
methine singlets between 5.7 and 6.2 ppm and two aromatic
singlets between 8 and 8.3 ppm. The signals at 5.73 and 8.24
integrate in a 1:2 ratio and are assigned to mono[60]fullerene
adduct 22. The singlets at 6.17 and 8.06 integrate in a 2:1 ratio
and are assigned to bis[60]fullerene adduct 23. The 13C NMR
spectrum reveals, as expected, a total of four signals due to sp3
carbons. Two signals between 54 and 58 ppm are assigned to
the methine carbons along the acene backbones of 22 and 23,
while two additional signals between 70 and 73 ppm are
assigned to the sp3 fullerene carbons on 22 and 23 that are
attached to their respective acenes at the sites of cycloaddition.
A total of 55 discernible 13C NMR signals is observed in the
product was reported.1d,e,2,3c,30,31 Surprisingly, there are only
three reports describing the dual cycloaddition of commercially
available 1,3-diphenylisobenzofuran, 24, across p-benzoquinone,
each conducted under a very limited set of conditions.36 We
sought to determine if alternative reaction conditions would
change the diastereoselectivity associated with the dual cy-
cloaddition between 24 and p-benzoquinone. As illustrated in
Table 5, we studied this reaction using a variety of solvent
systems and temperatures, most of which have never been
reported. Reactions were run in both protic and aprotic solvents
and at temperatures ranging from 25 to 140 °C.37 In all cases,
the only dual cycloaddition product observed is the known
endo,exo syn diastereomer 25 (Figure 1, Scheme 7, Table 5).
Because 4,7-diphenylisobenzofuran 5 shows greatest diastereo-
selectivity toward formation of exo,exo anti 16b in boiling acetic
acid (Table 3), we were especially interested to study the
corresponding reaction involving 1,3-diphenylisobenzofuran 24.
However, as illustrated in Table 5 (exps. 12-15), 24 degrades
to 1,2-dibenzoylbenzene, 26, in hot acetic acid. Thus, compound
24 with a 1,3-diphenyl substitution pattern is more prone to
degradation than is compound 5. In fact, the oxidation of 24 to
2
highly congested Csp region between 122 and 156 ppm where
a total of 65 signals is expected. There are numerous examples
of coincidental overlap in this region of the 13C NMR spectrum.
MALDI and LDI mass spectra of the mixture of 22 and 23
reveal separate signals at m/z 720 and 582 corresponding to
the retro-Diels-Alder products [60]fullerene and 21, respec-
tively.
Re-examination of the Reaction between 1,3-Diphenyl-
isobenzofuran (24) and p-Benzoquinone. The highly diaste-
reoselective formation of exo,exo anti 16b is unexpected because
in all previously studied dual cycloaddition reactions between
isoacenofurans and p-benzoquinone, a single endo,exo syn
(36) The reaction was run separately in ethanol, alcohol, and benzene.
See refs 2, 3b, and 3c. The endo,exo syn product invariably precipitates
from each of these solutions in high yields.
(37) It has been reported that the endo,exo syn product undergoes retro
Diels-Alder reactions under relatively mild conditions (see ref 2). At
elevated temperatures, the reactions are presumed to be reversible.
J. Org. Chem, Vol. 72, No. 8, 2007 3027

Rainbolt and Miller
4,7-Diphenyl-1-hydroxyphthalan ((()-4). Compound 3 (3.57
g, 12.5 mmol) was dissolved in dry methylene chloride (175 mL),
and the solution was cooled to -60 °C. Diisobutyl aluminum
hydride (15 mL of 1 M solution, 15 mmol) was added dropwise to
the stirring solution via syringe over 15 min. After 70 min, the
reaction was quenched with aqueous sodium hydroxide (5 mL, 10
wt % solution), and the solution was warmed to room temperature.
To the solution was added water (50 mL), and carbon dioxide was
bubbled through the solution until pH 7 was attained. The organic
layer was separated, and the aqueous layer was extracted with
dichloromethane (3 × 100 mL). The combined organic layers were
dried (CaCl2), and solvent was evaporated under ambient conditions
26 accompanies most of the reactions studied, to varying
degrees. While good yields of 25 could be achieved in
chloroform, toluene, and xylenes, the best solvent for the clean
formation of dual cycloaddition product 25 is ethanol.
Conclusion
The high yielding synthesis of 4,7-diphenyl-1-hydroxyph-
thalan ((()-4) has been achieved, and its facile conversion to
4,7-diphenylisobenzofuran (5) has been demonstrated. Separate
reactions between 5 and maleic anhydride, 1,4-napthoquinone,
and p-benzoquinone have been utilized to create novel three-,
four-, and five-ring acene derivatives. In boiling glacial acetic
acid, the reaction between 5 and p-benzoquinone produces an
unprecedented exo,exo anti dual cycloaddition product, 16b, in
high yield and with 100% diastereoselectivity. The exo,exo anti
structure of 16b has been elucidated using a combination of 1H
NMR spectroscopy and a stereochemical analysis of the
corresponding borohydride-reduced diol species 18a and 18b.
Elaboration of 16b generates 1,4,8,11-tetraphenylpentacene, 21,
which was successfully reacted with [60]fullerene to yield two
new [60]fullerene-acene adducts, 22 and 23. Finally, the
reactivity between commercially available 1,3-diphenylisoben-
zofuran, 24, and p-benzoquinone has been re-evaluated under
a variety of reaction conditions including those utilized in the
transformation of 5 to 16b. In all cases studied, however, the
only dual cycloaddition product formed was the known endo,-
exo syn adduct 25.
1
to yield (()-4 (2.90 g, 80%). mp ) 162 °C (dec). H NMR (500
MHz, CDCl3) δ (ppm): 2.84 (OH, d, 1H, J ) 6.35 Hz, disappears
with D2O), 5.08 (d, 1H, J ) 13.18 Hz), 5.51 (dd, 1H, J ) 13.18,
1.71 Hz), 6.63 (dd, 1H, J ) 6.35, 1.71 Hz, collapses to doublet
with D2O), 7.4-7.5 (m, 10H), 7.64 (m, 2H). 13C NMR (100 MHz,
CDCl3) δ (ppm): 71.9, 101.1, 127.89, 127.95, 128.1, 128.8, 129.03,
129.7, 130.0, 135.4, 137.2, 137.8, 138.4, 139.5, 139.7 (coincidental
overlap of two aromatic signals). HRMS (FAB) m/z ) 288.1137,
calcd m/z ) 288.11503.
Adducts of 4,7-Diphenylisobenzofuran and Maleic Anhy-
dride, 6a and 6b. Compound (()-4 (2.11 g, 7.33 mmol) and maleic
anhydride (0.81 g, 8.3 mmol) were heated to 118 °C in a solution
of acetic acid (20 mL) and acetic anhydride (2 mL) for 2 h. After
the mixture was cooled, water (2 mL) was added. The white
precipitate was filtered off, rinsed with acetic acid (10 mL), and
air-dried to yield a mixture of endo 6a and exo 6b (2.40 g, combined
1
89%). mp ) 258-260 °C. H NMR (500 MHz, CDCl3) δ (ppm):
3.52 (exo adduct 6b, s, 2H), 4.01 (endo adduct 6a, m, 2H), 6.01
(exo adduct 6b, s, 2H), 6.07 (endo adduct 6a, m, 2H), 7.43-7.57
(endo 6a and exo 6b, m, 24H). 13C NMR (125 MHz, CDCl3) δ
(ppm): 49.9, 50.5, 80.7, 82.6, 128.2, 128.3, 128.5, 128.8, 129.1,
129.5, 130.0, 134.8, 135.5, 138.3, 138.5, 140.0, 141.5, 167.4, 170.0
(coincidental overlap of two aromatic signals). HRMS (FAB) m/z
) 369.1120 (M + H+), calcd m/z ) 369.11268 (M + H+).
5,8-Diphenylnapthalene-2,3-dicarboxylic Anhydride (7). One-
Pot Synthesis from 4,7-Diphenyl-1-hydroxyphthalan ((()-4) and
Maleic Anhydride. Compound 4 (0.47 g, 1.6 mmol), maleic
anhydride (0.18 g, 1.9 mmol), and p-toluenesulfonic acid mono-
hydrate (1.8 g, 9.5 mmol) were heated to 111 °C in toluene (60
mL) with a Dean-Stark trap for 4 days. The crude reaction mixture
was washed with saturated NaHCO3 (aq) (2 × 50 mL), water (1 ×
50 mL), and brine (2 × 75 mL). The organic layer was dried (CaCl2)
and concentrated at reduced pressure. The crude product was
recrystallized from HOAc/Ac2O to yield 7 (0.21 g, 36%).
Experimental Section
3a,4,7,7a-Tetrahydro-4,7-diphenylphthalic Anhydride (1). 1,4-
Diphenyl-2,3-butadiene (39.4 g, 0.191 mol) and maleic anhydride
(20.5 g, 0.209 mol) were heated at 137-144 °C in xylenes (500
mL) for 15 h. The solution was chilled, and white crystalline
precipitate was filtered off to afford 1 (46.6 g, 80%). mp ) 205-
209 °C (lit. 207 °C38). 1H NMR (500 MHz, CDCl3) δ (ppm): 3.74
(dd, 2H, J ) 4.88, 2.44 Hz), 3.84 (d, 2H, J ) 4.88 Hz), 6.55 (s,
2H), 7.34-7.39 (m, 6H), 7.41-7.45 (m, 4H). 13C NMR (100 MHz,
CDCl3) δ (ppm): 41.4, 47.7, 127.9, 128.8, 128.9, 132.3, 138.1,
169.9.
4,7-Diphenylphthalic Anhydride (2). Adduct 1 (46.4 g, 0.152
mol) and DDQ (80.2 g, 0.353 mol) were combined in toluene (500
mL), and the red solution was heated at 111 °C for 18 h. The solvent
was removed at reduced pressure, and crude product was rinsed
with copious amounts of 95% ethanol to yield 2 (39.6 g, 87%).
From 6a and 6b. The adducts 6a and 6b (2.38 g, 6.45 mmol)
were combined with freshly recrystallized (CHCl3) p-toluenesulfonic
acid (3.65 g, 21.2 mmol) in toluene (90 mL) and heated to 111 °C
with a Dean-Stark trap for 4 days. The toluene was removed at
reduced pressure, dichloromethane (50 mL) added, and the organic
layer washed with saturated NaHCO3 (aq) (2 × 85 mL), water (2
× 100 mL), and brine (2 × 75 mL). The organic layer was dried
(CaCl2) and concentrated at reduced pressure. The residue was taken
up in a solution of HOAc (30 mL) and Ac2O (5 mL), and the
mixture was heated to 118 °C for 2 h. The resulting solution was
chilled overnight, and the ensuing precipitate was filtered off and
rinsed with HOAc (15 mL) and water (40 mL) to yield yellow-
green crystals of 7 (1.58 g, 70%). mp ) 240-242 °C (lit. 235-
1
mp ) 223-225 °C (lit. 220, 224 °C18,19). H NMR (500 MHz,
CDCl3) δ (ppm): 7.50-7.54 (m, 6H), 7.57-7.60 (m, 4H), 7.85 (s,
2H). 13C NMR (100 MHz, CDCl3) δ (ppm): 128.0, 128.7, 129.5,
135.2, 137.9, 142.2, 162.1 (coincidental overlap of two signals at
137.9 ppm).
4,7-Diphenylphthalide (3). Compound 2 (39.0 g, 0.130 mol)
and zinc dust (85 g, 1.3 mol) were heated to 100 °C in glacial
acetic acid (500 mL) for 17 h with mechanical stirring. The solution
was filtered hot, and residual solids were rinsed with hot acetic
acid and hot chloroform. The combined filtrate was concentrated
at reduced pressure. The crude product was rinsed with methanol
(25 mL) to yield 3 (33.3 g, 89%). mp ) 170-172 °C (lit. 170-
171, 173-175 °C21,39). 1H NMR (400 MHz, CDCl3) δ (ppm): 5.38
(s, 2H), 7.43-7.59 (m, 11H), 7.72 (d, 1H, J ) 7.80 Hz). 13C NMR
(100 MHz, CDCl3) δ (ppm): 68.7, 122.5, 128.1, 128.3, 128.64,
128.67, 129.4, 129.9, 131.8, 133.9, 136.0, 136.5, 137.7, 141.9,
145.7, 170.1.
1
236 °C28). H NMR (500 MHz, CDCl3) δ (ppm): 7.48-7.61 (m,
10H), 7.78 (s, 2H), 8.64 (s, 2H). 13C NMR (100 MHz, CDCl3) δ
(ppm): 125.8, 127.1, 128.7, 129.2, 130.2, 131.0, 135.3, 139.0,
142.9, 163.4. HRMS (FAB) m/z ) 351.1023 (M + H+), calcd m/z
) 351.10212 (M + H+).
3-Benzoyl-5,8-diphenylnaphthalene-2-carboxylic Acid (8).
Compound 7 (86 mg, 0.244 mmol) was dissolved in benzene (7
mL). To the stirring solution was added aluminum chloride (0.179
g, 1.34 mmol) in small portions at room temperature. The red
solution was heated to 80 °C with a drying tube in place. After 20
(38) Diels, O.; Alder, K. Chem. Ber. 1929, 62, 2081.
(39) Smith, J. G.; Wikman, R. T. Tetrahedron 1974, 30, 2603.
3028 J. Org. Chem., Vol. 72, No. 8, 2007

4,7-Diphenylisobenzofuran
h, the solution was cooled to room temperature, and a slurry of
concentrated sulfuric acid (5 drops) in crushed ice was added slowly.
The organic layer was allowed to evaporate, the remaining aqueous
solution filtered, and product rinsed with water (20 mL) to yield
pink solids. The solids were dried in an oven (75 °C) for 2 h yielding
8 (94 mg, 91%). mp ) 226-228 °C. 1H NMR (400 MHz, CDCl3)
δ (ppm): 7.3-7.7 (m, 17H), 8.0 (s, 1H), 8.75 (s, 1H). 13C NMR
(100 MHz, CDCl3) δ (ppm): 125.8, 127.0, 128.1, 128.3, 128.6,
128.9, 129.0, 129.7, 130.2, 130.3, 131.5, 131.7, 133.2, 133.5, 137.6,
137.9, 139.6, 140.7, 141.7, 171.4, 197.1 (coincidental overlap of
signals in the congested aromatic region). HRMS (FAB) m/z )
428.1433, calcd m/z ) 428.14124.
2H), 7.32-7.34 (endo 12a, m, 4H), 7.43-7.66 (endo 12a and exo
12a, m, 28H), 7.76 (exo adduct 12b, m, 2H), 8.16 (exo adduct
12b, m, 2H). 13C NMR (125 MHz, CDCl3) δ (ppm): 49.5, 51.7,
82.8, 85.2, 126.2, 127.4, 127.97, 127.99, 128.4, 128.7, 129.0, 129.2,
133.3, 133.9, 134.1, 134.6, 134.8, 135.6, 138.6, 138.7, 139.9, 143.1,
193.1, 195.4 (coincidental overlap of signals in the congested
aromatic region). HRMS (FAB) m/z ) 429.1489 (M + H+), calcd
m/z ) 429.14907 (M + H+).
1,4-Diphenyltetracene-6,11-quinone (13). Compound (()-4
(1.45 g, 5.02 mmol) and 1,4-naphthoquinone (0.871 g, 5.50 mmol)
were heated to 70 °C in acetic acid (12 mL) for 2 h. Five drops of
concentrated sulfuric acid were added, and the solution was
heated for an additional hour at 70 °C. The solution was chilled in
an ice bath, and the precipitate was filtered off and rinsed with
methanol (7 mL) to yield 13 as orange solids (1.00 g, 49%). mp )
3,5,8-Triphenyl-3H-naphtho[2,3-c]furan-1-one ((()-9). Com-
pound 8 (0.566 g, 1.32 mmol) was added to a solution of sodium
hydroxide (5.5 g) in 95% ethanol (100 mL) and water (20 mL).
Sodium borohydride was added (0.303 g, 8.20 mmol), and the
solution was stirred for 3 days. The solution was then brought to
pH 9 by addition of concentrated HCl. Sodium borohydride (0.127
g, 3.42 mmol) was again added, and the solution was stirred for an
addition 3 days. The solution was acidified with concentrated HCl
and filtered. The filtrate was concentrated under reduced pressure.
Chloroform was added (50 mL), and the organic layer was washed
with saturated NaHCO3 (aq) (2 × 50 mL), water (50 mL), and
brine (50 mL). The organic layer was dried (CaCl2) and concen-
trated under reduced pressure to yield the crude product, which
was recrystallized from ethanol to yield (()-9 (0.316 g, 58%). mp
1
282-285 °C. H NMR (500 MHz, CDCl3) δ (ppm): 7.52-7.59
(m, 10H), 7.70 (s, 2H), 7.79 (m, 2H), 8.33 (m, 2H), 9.01 (s, 2H).
13C NMR (125 MHz, CDCl3) δ (ppm): 127.6, 128.3, 128.7, 129.0,
129.7, 130.2, 130.4, 134.2, 134.4, 134.8, 139.6, 142.5, 183.2. HRMS
(FAB) m/z ) 411.1386 (M + H+), calcd m/z ) 411.13850 (M +
H+).
1,4-Diphenyl-6,11-dihydrotetracene (14a) and 1,4-Diphenyl-
5,12-dihydrotetracene (14b). Compound 13 (0.288 g, 0.702 mmol)
was heated to 118 °C in a mixture of HI (20 mL, 47%) and acetic
acid (100 mL) under nitrogen in the dark for 4 days. The reaction
was quenched with saturated NaHSO3 (aq) (15 mL), water added
(50 mL), and the aqueous mixture extracted with dichloromethane
(4 × 25 mL). The combined organic extracts were washed with
saturated NaHSO3 (aq) (20 mL), saturated NaHCO3 (aq) (2 × 75
mL), water (50 mL), and brine (50 mL). The organic layer was
dried (CaCl2) and concentrated at reduced pressure. The crude
product was purified via silica column chromatography (benzene,
eluent) to yield a mixture of the isomers 14a and 14b (Rf ) 0.8,
64 mg, 24% combined). mp ) 110-135 °C. 1H NMR (500 MHz,
CDCl3) δ (ppm): 3.96 (s, 4H), 4.10 (s, 4H), 7.14 (m, 2H), 7.23
(m, 4H), 7.33 (m, 2H), 7.38 (s, 2H), 7.57 (s, 2H), 7.42-7.54 (m,
20H), 7.66 (m, 2H), 7.86 (s, 2H). 13C NMR (125 MHz, CDCl3) δ
(ppm): 34.9, 37.0, 123.9, 125.0, 125.4, 126.1, 126.4, 127.2, 127.4,
127.6, 128.5, 129.8, 130.3, 131.0, 132.5, 135.5, 136.0, 136.4, 137.1,
139.4, 139.9, 141.3, 141.6 (coincidental overlap of signals in the
congested aromatic region). HRMS (FAB) m/z ) 382.1722, calcd
m/z ) 382.17215.
1,4-Diphenyltetracene (15). A mixture of 14a and 14b (60 mg,
0.157 mmol) and 10% Pd/C (65 mg) was heated to 180 °C in 1,2-
dichlorobenzene (50 mL) under nitrogen in the dark for 3 days.
The resulting solution was cooled, filtered to remove Pd/C, and
the solid Pd/C rinsed with dichloromethane (15 mL). The combined
organic filtrate was concentrated at reduced pressure under low-
light conditions. The resulting orange-brown solids were dried on
a vacuum pump to yield 15 (55 mg, 93%). mp ) 214-217 °C. 1H
NMR (500 MHz, CDCl3) δ (ppm): 7.36 (m, 2H), 7.39 (s, 2H),
7.54 (m, 2H), 7.59 (m, 4H), 7.68 (m, 4H), 7.93 (m, 2H), 8.56 (s,
2H), 8.75 (s, 2H). 13C NMR (100 MHz, CDCl3) δ (ppm): 125.4,
125.8, 125.9, 126.9, 127.8, 128.5, 128.7, 130.1, 130.5, 130.9, 131.9,
140.1, 141.2. HRMS (FAB) m/z ) 380.1548, calcd m/z )
380.15650.
1
) 169-172 °C. H NMR (400 MHz, CDCl3) δ (ppm): 6.52 (s,
1H), 7.24-7.27 (m, 3H), 7.32-7.36 (m, 3H), 7.42-7.63 (m, 11H),
7.9 (s, 1H), 8.66 (s, 1H). 13C NMR (100 MHz, CDCl3) δ (ppm):
83.1, 120.8, 123.6, 126.3, 127.4, 127.7, 128.0, 128.2, 128.8, 129.0,
129.1, 129.5, 129.9, 130.2, 130.3, 132.6, 135.4, 137.3, 139.9, 140.1,
140.4, 142.3, 143.4, 170.7. HRMS (FAB) m/z ) 413.1546 (M +
H+), calcd m/z ) 413.15415 (M + H+).
4,6,9,11-Tetraphenylanthra[2,3-c]furan-1,3-dione (11). (()-9
(127 mg, 0.307 mmol) was dissolved in dry THF (10 mL). The
solution was placed in an ice bath, and a drying tube was attached
to the vessel. Phenylmagnesium bromide (0.2 mL, 3 M in Et2O)
was added dropwise over 3 min. After 1 h, the reaction was
quenched with NH4Cl (aq) (3 mL). Diethyl ether (35 mL) was
added, and the solution was washed with NaHCO3 (aq) (50 mL),
water (50 mL), and brine (50 mL). The organic layer was dried
(CaCl2) and concentrated at reduced pressure at room temperature.
The viscous liquid was triturated with hexanes, and the resulting
powder was rinsed with hexanes (10 mL). The lactol (see Scheme
3) was air-dried to yield an off-white powder (101 mg, 67%). A
benzene solution of this powder (36 mg, 0.07 mmol), maleic
anhydride (29 mg, 0.30 mmol), and p-toluenesulfonic acid mono-
hydrate (0.172 g, 0.903 mmol) was heated to 80 °C with a Dean-
Stark trap for 24 h. The organic layer was washed with saturated
NaHCO3 (aq) (20 mL), water (25 mL), and brine (25 mL). The
organic layer was dried (CaCl2) and concentrated at reduced
pressure. The crude solids were rinsed with acetone (15 mL), and
the remaining solid was air-dried to yield 11 (8 mg, 20%). mp )
1
336 °C (dec). H NMR (500 MHz, CDCl3) δ (ppm): 7.36-7.49
(m, 20H), 7.63 (s, 2H), 8.66 (s, 2H). 13C NMR (100 MHz, CDCl3)
δ (ppm): 120.5, 127.7, 128.2, 128.4, 128.9, 129.8, 129.9, 132.1,
132.5, 133.4, 139.1, 140.4, 144.2, 162.1 (coincidental overlap of
signals in the congested aromatic region). HRMS (FAB) m/z )
553.1805 (M + H+), calcd m/z ) 553.18037 (M + H+).
1,4,8,11-Tetraphenyl-5,7,12,14-diendoxo-5a,6a,12a,13a-tet-
rahydropentacene-6,13-quinone (16b). Lactol (()-4 (1.75 g, 6.07
mmol) and freshly sublimed p-benzoquinone (0.315 g, 2.91 mmol)
were heated to 118 °C in glacial acetic acid (35 mL) for 8 h. The
white precipitate was filtered, rinsed with HOAc (5 mL) and water
(20 mL), and air-dried to yield 16b (1.70 g, 90%). mp ) 293 °C
(dec). 1H NMR (500 MHz, CDCl3) δ (ppm): 3.37 (s, 4H), 6.03 (s,
4H), 7.42-7.49 (m, 16H), 7.53-7.56 (m, 8H). 13C NMR (125 MHz,
CDCl3) δ (ppm): 55.1, 81.3, 127.9, 128.2, 129.1, 133.4, 138.7,
142.2, 205.2 (coincidental overlap of two aromatic signals). Anal.
Calcd for C46H32O4: C, 85.16; H, 4.97. Found: C, 84.99; H, 4.86.
Diols 18a and 18b. Compound 16b (38 mg, 0.059 mmol) and
sodium borohydride (11 mg, 0.29 mmol) were heated to 66 °C in
Adducts of 4,7-Diphenylisobenzofuran and 1,4-Naphtho-
quinone, 12a and 12b. Compound (()-4 (1.03 g, 3.56 mmol) and
1,4-naphthoquinone (0.568 g, 3.77 mmol) were heated to 60 °C in
acetic acid (20 mL) for 2 h. The solution was chilled in an ice
bath, precipitate filtered, and solids rinsed with cold acetic acid (5
mL). The resulting white powder is a mixture of endo 12a and exo
12b cycloaddition adducts (1.30 g, 85% combined). mp ) 222-
1
223 °C. H NMR (400 MHz, CDCl3) δ (ppm): 3.50 (exo adduct
12b, s, 2H), 3.64 (endo adduct 12a, m, 2H), 5.94 (exo adduct 12b,
s, 2H), 6.25 (endo adduct 12a, m, 2H), 7.24 (endo adduct 12a, s,
J. Org. Chem, Vol. 72, No. 8, 2007 3029

Rainbolt and Miller
dry THF (50 mL) for 2.5 h. The reaction was quenched with 4 M
HCl and concentrated at reduced pressure. The crude product was
taken up in dichloromethane (40 mL), and the organic layer was
washed with saturated NaHCO3 (aq) (50 mL), water (50 mL), and
brine (50 mL). The organic layer was dried (CaCl2) and concen-
trated at reduced pressure. The crude was purified via silica
preparative plate chromatography (10% EtOAc in CHCl3 as eluent).
Reduced products 18a (Rf ) 0.27, 11 mg, 28%) and 18b (Rf )
0.42, 10 mg, 26%) were isolated.
bubbling ceased. The orange precipitate was then filtered and
washed with saturated NaHCO3 (aq) and water. The orange powder
was taken up in boiling benzene (15 mL) and filtered, and the
persistent precipitate was washed with boiling benzene (2 × 10
mL). The combined benzene filtrate was concentrated, and the crude
product was purified via silica preparative plate chromatography
(45% hexanes in CHCl3 as eluent) to yield 20 (Rf ) 0.7, 2 mg,
1.6%). mp ) 348 °C (dec). 1H NMR (500 MHz, CDCl3) δ (ppm):
4.05 (s, 4H), 7.39 (s, 4H), 7.50-7.52 (m, 20H), 7.83 (s, 4H). 13C
NMR (125 MHz, CDCl3) δ (ppm): 37.04, 123.6, 126.0, 127.2,
128.3, 130.1, 130.9, 135.8, 139.3, 141.1. HRMS (FAB) m/z )
584.2509, calcd m/z ) 548.25040.
C2W Symmetric [60]Fullerene Monoadduct of 1,4,8,11-Tet-
raphenylpentacene (22) and C2W Symmetric cis-Bis[60]fullerene
Bisadduct of 1,4,8,11-Tetraphenylpentacene (23). Compound 20
(15 mg, 0.026 mmol), DDQ (55 mg, 0.243 mmol), and [60]fullerene
(135 mg, 0.187 mmol) were dissolved in 150 mL of benzene. The
solution was heated to 80 °C under nitrogen in the dark for 18 h.
The solvent was removed at reduced pressure, and the crude product
mixture was purified via silica column chromatography (CS2 as
eluent) to yield 22 and 23 (Rf ) 0.5, 4.3 mg). 1H NMR (400 MHz,
CDCl3:CS2, 1:1) δ (ppm): 5.73 (monoadduct 22, s, 2H), 6.17
(bisadduct 23, s, 4H), 7.39-7.55 (monoadduct 22 and bisadduct
23, m, 48H), 8.06 (bisadduct 23, s, 2H), 8.24 (monoadduct 22, s,
4H). 13C NMR (100 MHz, CDCl3:CS2, 1:1) δ (ppm): 54.7, 58.0,
71.7, 72.3, 122.8, 123.2, 127.0, 127.3, 127.5, 128.1, 128.4, 128.5,
129.4, 130.2, 131.4, 136.3, 136.8, 137.1, 138.7, 138.9, 139.3,
139.65, 139.71, 139.8, 139.9, 140.0, 140.6, 141.2, 141.35, 141.43,
141.8 (3), 141.9, 142.1, 142.2, 142.3 (2), 142.7, 142.9 (2), 144.4,
144.5, 144.97, 145.00, 145.1, 145.2 (2), 145.27, 145.3, 146.0 (2),
146.2, 146.3, 147.3 (2), 154.8, 155.2 (2) (numbers in parentheses
indicate multiple numbers of discernible signals including shoulders
at the indicated chemical shift). MALDI and LDI-MS m/z ) 582,
720.
18a. mp ) 318 °C (dec). 1H NMR (500 MHz, CDCl3) δ (ppm):
1.96 (OH, d, 2H, J ) 4.64 Hz, disappears with D2O), 2.49 (m,
2H), 2.72 (m, 2H), 4.24 (bs, 2H), 5.42 (d, 2H, J ) 0.98 Hz), 5.87
(s, 2H), 7.36-7.59 (m, 24H). 13C NMR (125 MHz, CD2Cl2) δ
(ppm): 46.0, 46.3, 69.1, 77.8, 81.0, 127.0, 127.1, 127.3, 127.4,
128.3, 128.4, 128.7, 128.8, 132.65, 132.70, 139.3, 143.5, 145.0.
HRMS (FAB) m/z ) 651.2524 (M - H), calcd m/z ) 651.25353
(M - H).
18b. mp ) 290 °C (dec). 1H NMR (500 MHz, CDCl3) δ (ppm):
2.09 (OH, d, 1H, J ) 4.64 Hz, disappears with D2O), 2.48 (dd,
1H, J ) 10.98, 8.54 Hz), 2.63-2.69 (m, 2H), 2.78 (dd, 1H, J )
8.17, 2.56 Hz), 3.67 (OH, d, 1H, J ) 3.66 Hz, disappears with
D2O), 4.59 (m, 1H, with D2O converges to dd, J ) 10.98, 5.61
Hz), 4.65 (m, 1H), 5.24 (s, 1H), 5.51 (s, 1H), 5.59 (s, 1H), 5.88 (s,
1H), 7.34-7.59 (m, 24H). 13C NMR (125 MHz, CD2Cl2) δ (ppm):
42.5, 44.2, 45.3, 47.9, 69.7, 69.9, 78.2, 80.8, 81.0, 81.1, 127.02,
127.1, 127.3, 127.37, 127.43, 127.45, 127.47, 127.49, 128.28,
128.30, 128.33, 128.5, 128.8, 128.87, 128.9, 132.7, 132.8, 133.1,
139.1, 139.27, 139.30, 139.5, 142.2, 144.1, 144.8, 144.9.
HRMS (FAB) m/z ) 651.2553 (M - H), calcd m/z ) 651.25353
(M - H).
1,4,8,11-Tetraphenylpentacene-6,13-quinone (19). Compound
16b (0.26 g, 0.4 mmol) and p-toluenesulfonic acid (0.28 g, 1.61
mmol) were heated to 80 °C in benzene (25 mL) under nitrogen
with a Dean-Stark trap for 24 h. The benzene was removed at
room temperature, and crude black product was washed with
copious amounts of acetone to yield 19 (42 mg, 17%). mp )
458 °C (subl.). 1H NMR (500 MHz, CDCl3) δ (ppm): 7.48-7.58
(m, 20H), 7.00 (s, 4H), 9.02 (s, 4H). 13C NMR: Lack of solubility
prohibits 13C NMR spectroscopy. HRMS failed to produce a
molecular ion, and elemental analysis failed due to incomplete
combustion of C.
Acknowledgment. We thank the National Science Founda-
tion for support of this work (Nanoscale Exploratory Research,
NSF-0403954; Nanoscale Science and Engineering Center for
High-Rate Nanomanufacturing, NSF-0425826) and Professor
Gary Weisman for discussions concerning variable-temperature
NMR studies.
1,4,8,11-Tetraphenyl-6,13-dihydropentacene (20). Compound
19 (119 mg, 0.194 mmol) was suspended in a mixture of HI (10
mL, 47%), glacial acetic acid (70 mL), and chloroform (70 mL).
The solution was heated to 85 °C under nitrogen in the dark for 5
days. The solvent was concentrated to approximately 10 mL at
reduced pressure, and saturated NaHCO3 (aq) was added until
1
Supporting Information Available: Select H, 13C, and vari-
able-temperature NMR data for compounds 1-23. This material
is available free of charge via the Internet at http://pubs.acs.org.
JO062675B
3030 J. Org. Chem., Vol. 72, No. 8, 2007