Ring expansion of 11H-benzo[b]fluorene-11-methanols and related compounds leading to 17,18-diphenyldibenzo[a,o]pentaphene and related polycyclic aromatic hydrocarbons with extended conjugation and novel architectures

Article abstract of DOI:10.1016/j.tet.2006.02.066

Condensation between 7-(1,1-dimethylethyl)-13-phenyl-8H-indeno[2,1-b]phenanthrene and paraformaldehyde produced the corresponding 9-fluorenylmethanol derivative, which on treatment with P₂O₅ to promote a Wagner-Meerwein rearrangement

Full text of DOI:10.1016/j.tet.2006.02.066

Tetrahedron 62 (2006) 4364–4371
Ring expansion of 11H-benzo[b]fluorene-11-methanols
and related compounds leading to
17,18-diphenyldibenzo[a,o]pentaphene and related polycyclic
aromatic hydrocarbons with extended conjugation
and novel architectures
†
Yonghong Yang, Weixiang Dai, Yanzhong Zhang, Jeffrey L. Petersen and Kung K. Wang
*
C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, WV 26506-6045 USA
Received 26 December 2005; revised 22 February 2006; accepted 22 February 2006
Abstract—Condensation between 7-(1,1-dimethylethyl)-13-phenyl-8H-indeno[2,1-b]phenanthrene and paraformaldehyde produced the
corresponding 9-fluorenylmethanol derivative, which on treatment with P2O5 to promote a Wagner–Meerwein rearrangement for ring
expansion furnished 14-phenyldibenzo[a,j]anthracene in 88% yield. Similarly, 17,18-diphenyldibenzo[a,o]pentaphene possessing a helical
twist and bearing two phenyl substituents at the most sterically congested C17 and C18 positions and other related compounds were likewise
synthesized. Subsequent intramolecular arylation reactions involving the phenyl substituents produced polycyclic aromatic hydrocarbons
with novel architectures.
q 2006 Elsevier Ltd. All rights reserved.
1. Introduction
to occur, producing polycyclic aromatic hydrocarbons with
novel architectures.
The Wagner–Meerwein rearrangement of 9-fluorenyl-
methanols and related fluorene derivatives provides an
efficient pathway for ring expansion to form phenan-
threnes.1 Specifically, the phosphorous pentoxide-induced
rearrangement of the parent 9-fluorenylmethanol occurs in
refluxing xylene to produce phenanthrene in excellent yield
(Eq. 1).2 We recently reported the synthesis of a variety of
11H-benzo[b]fluorenes and related derivatives via the
benzannulated enediynyl propargylic alcohols.3–10 We
now report the use of these benzofluorenyl derivatives to
prepare 11H-benzo[b]fluorene-11-methanols for the sub-
sequent Wagner–Meerwein rearrangement leading to
phenanthrenes having extended conjugation and bearing
one or two aryl substituents at the sterically most hindered
positions. The presence of these aryl substituents also allows
intramolecular electrophilic aromatic substitution reactions
(1)
2. Results and discussion
Indenophenanthrene 8 was prepared by a synthetic sequence
reported previously3 involving condensation between tert-
butyl 2-naphthyl ketone (1) and the benzannulated
enediynyl lithium acetylide 2 to form the benzannulated
enediynyl propargylic alcohol 3 followed by reduction with
triethylsilane in the presence of trifluoroacetic acid to give 4
(Scheme 1). Treatment of 4 with potassium tert-butoxide in
refluxing toluene for 3 h then provided 7-(1,1-dimethyl-
ethyl)-13-phenyl-8H-indeno[2,1-b]phenanthrene (8) in 89%
yield. Presumably, a cascade sequence of reactions occurred
as reported previously3 involving an initial 1,3-prototropic
rearrangement to form the benzannulated enyne-allene 5
followed by a Schmittel cyclization reaction11–15 to
generate biradical 6 for the subsequent intramolecular
radical–radical coupling to furnish 7 and, after a second
prototropic rearrangement, indenophenanthrene 8. It is
Keywords: 9-Fluorenylmethanols; Wagner–Meerwein rearrangement; Ring
expansion; 17,18-Diphenyldibenzo[a,o]pentaphene; Polycyclic aromatic
hydrocarbons.
*
Corresponding author. Tel.: C1 304 293 3068x6441; fax: C1 304 293
4904; e-mail: kung.wang@mail.wvu.edu
† To whom correspondence concerning the X-ray structures should be
addressed. Tel.: C1 304 293 3435x6423; fax: C1 304 293 4904; e-mail:
jeffrey.petersen@mail.wvu.edu
0040–4020/$ - see front matter q 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.02.066

Y. Yang et al. / Tetrahedron 62 (2006) 4364–4371
4365
Scheme 1.
worth noting that the intramolecular radical–radical coup-
ling reaction of biradical 6 involved only the a-position of
the naphthyl ring to produce 7 preferentially. Attaching the
b-position to form an indeno-fused anthracene derivative
did not appear to occur. The higher reactivity of the
a-position than the b-position of naphthalene in homolytic
addition may be responsible for the regioselectivity.16–17
Conversion of 8 to the 9-fluorenylmethanol derivative 9
was readily accomplished by treatment of 8 with lithium
diisopropylamide (LDA) followed by paraformaldehyde.18
Unlike the parent 9H-fluorene, the presence of a sterically
demanding tert-butyl group in 9 appeared to prevent it from
condensation with a second molecule of formaldehyde even
in the presence of excess LDA and paraformaldehyde.
On exposure to P2O5, 9 was transformed smoothly via the
Wagner–Meerwein rearrangement to form 10 in situ
followed by the loss of the tert-butyl group to give
14-phenyldibenzo[a,j]anthracene (11) in 88% yield. The
tert-butyl group is removed from 10 by protonation of the C7
carbon followed by dealkylation as observed previously
in other aromatic systems.19–22 It is also possible that the tert-
butyl group was first removed from 9 followed by a Wagner–
Meerwein rearrangement to furnish 11.
Similarly, the benzannulated enediynyl propargylic alcohol
16 was synthesized by condensation between 2,2-dimethyl-
propiophenone (15) and the benzannulated enediyne 14,
which was readily prepared by the Sonogashira reaction
between phenylacetylene and 12 to form 13 followed by
treatment of 13 with dimethyl (1-diazo-2-oxopropyl)-
phosphonate23 (Scheme 2). Reduction of 16 followed by
treatment of the resulting 17 with potassium tert-butoxide in
refluxing toluene then afforded 8-(1,1-dimethylethyl)-13-
phenyl-7H-dibenzo[b,g]fluorene (18) in 80% yield along
with two minor adducts 19 and 20. Presumably, a 1,3-
prototropic rearrangement of 17 gave the benzannulated
enyne-allene 23, which could undergo either a Schmittel
cyclization reaction to give biradical 24 leading to 18 or a
Scheme 2.

4366
Y. Yang et al. / Tetrahedron 62 (2006) 4364–4371
spectrometer, corresponding to rotational barriers of
14.4 and 14.5 kcal/mol at these two temperatures, which
are slightly higher than those of 1-phenylbenzo[a]phenan-
threnes (DG‡rotZca. 13 kcal/mol) reported earlier.28
The diindeno-fused phenanthrene 27 was synthesized
previously from diketone 26 and 2 equiv of 2 in three
steps in 38% overall yield (Scheme 4).6 The X-ray structure
of 27 showed that the presence of the two phenyl
substituents at the congested C4 and C5 positions of the
phenanthrene moiety caused a severe helical twist of the
diindeno-fused phenanthrene system. Treatment of 27 with
2 equiv of LDA followed by paraformaldehyde produced
28a–c as a mixture of three diastereomers in a 63 (28a or
28b): 34 (28c): 3 (28a or 28b) ratio in 76% combined yield.
The major isomer (28a or 28b) having a C2 symmetry and
28c without a C2 symmetry were separated by silica gel
chromatography to allow structural elucidation. The use of a
mixture of 28a–c containing all three diastereomers for two
consecutive Wagner–Meerwein rearrangements, promoted
by P2O5 in p-xylene at 110 8C for 15 min, was also
successful, giving rise to 17,18-diphenyldibenzo[a,o]penta-
phene (29) with the two phenyl substituents at the most
sterically congested C17 and C18 positions.
Scheme 3.
Myers–Saito cyclization reaction24–27 to form biradical 25
leading to 19 and 20 (Scheme 3). Treatment of 18 with LDA
followed by paraformaldehyde then produced 21 for the
subsequent Wagner–Meerwein rearrangement to furnish
14-phenylnaphth[1,2-a]anthracene (22) with the phenyl
substituent at one of the most sterically hindered positions
in 74% yield. Because of steric hindrance, the rotation of the
carbon–carbon bond attaching the phenyl substituent to the
naphth[1,2-a]anthracene system is restricted. As a result,
the 1H NMR signals (600 MHz) of the ortho and meta
hydrogens of the phenyl substituent appeared as broad
humps at d 8.2, 7.5, 6.7, and 6.1 at 25 8C. However, at
K20 8C two doublets at d 8.24/6.14 for the ortho hydrogens
and two triplets at d 7.49/6.67 for the meta hydrogens
could be clearly discerned. The coalescence temperatures
were determined to be at 50 8C for the ortho hydrogens
and at 40 8C for the meta hydrogens on a 270 MHz
Interestingly, when a mixture of 28a–c was exposed to P2O5
at a higher temperature (138 8C) in refluxing p-xylene for
1.5 h, compound 30was produced in 77% yield. Treatment of
29 with P2O5 under the same condition (refluxing p-xylene,
1.5 h) also produced 30. Apparently under this reaction
condition, the transformation from 28a–c to 30 proceeds via
an initial formation of 29 in situ followed by protonation of
the C7 carbon of 29 to furnish 32 (Scheme 5). A subsequent
intramolecular electrophilic aromatic substitution reaction
involving the phenyl substituent at the C17 position to form
Scheme 4.

Y. Yang et al. / Tetrahedron 62 (2006) 4364–4371
4367
138 8C, 12 h), 39 was likewise produced. Compared to 31,
which belongs to the group C2v, the structure of 39 retains
the C2 symmetry but no longer has the two planes of
symmetry and thus belongs to the group C2. The chirality of
the helical structure is lost in the transformation from 27 to
31, whereas the chirality of 36 is retained in 39. As a result,
the 1H NMR signals of the diastereotopic methylene
hydrogens of 39, recorded on a 600 MHz NMR
spectrometer, were observed as an AB quartet at d 4.46
(JZ21.6 Hz) and d 4.43 (JZ21.0 Hz).
Scheme 5.
33 followed by deprotonation then gave 30. The reaction
sequence of protonation followed by an intramolecular
electrophilic aromatic substitution reaction is reminiscent of
what was reported previously in the transformation of
1-phenylbenzo[a]anthracene to dibenzo[a,l]pyrene.29
It was also possible to promote a second intramolecular
electrophilic aromatic substitution reaction involving the
phenyl substituent of 30 by protonation of the C10 carbon.
Treatment of either 28a–c or 30 with P2O5 in refluxing
p-xylene over a longer period of time (12 h) furnished 31
having a C2 symmetry and two vertical planes of symmetry
and thus belonging to the group C2v. It is interesting to note
that 31 can be regarded as the Diels–Alder adduct of the
cycloaddition reaction between the central benzene ring of
the central anthracene unit of 34 and benzyne to produce the
triptycene moiety in 31 (Eq. 2).30–32
(2)
Scheme 6.
The benzo[b]fluorene derivative 409 was also successfully
employed to produce 41 (Scheme 7). However, attempts to
promote the Wagner–Meerwein rearrangement to give 42
Compare to 30 in which an AB quartet of 1H NMR signals at
d 4.83 (JZ22.8 Hz) and d 4.77 (JZ23.0 Hz) were observed
for the two methylene hydrogens because of the lack of
symmetry, a singlet 1H NMR signal at d 4.42 was observed
for the four methylene hydrogens of 31. Oxidation of 31
with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)
produced 35 (Eq. 3), which has its structure established by
X-ray structure analysis.
(3)
Similarly, treatment of 366 with 2 equiv of LDA and
paraformaldehyde gave 37 as a mixture of two diastereo-
mers (isomer ratioZ55:45), which on exposure to P2O5 in
refluxing benzene at 80 8C for 15 min underwent two
Wagner–Meerwein rearrangements to give 38 (Scheme 6).
Under a harsher reaction condition (P2O5, p-xylene at
Scheme 7.

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Y. Yang et al. / Tetrahedron 62 (2006) 4364–4371
resulted in the formation of 43 even under mild reaction
conditions (P2O5, 25 8C, 5 min). The structure of 43 was
established by X-ray structure analysis. Apparently,
protonation of the initially formed 42 and the subsequent
intramolecular electrophilic aromatic substitution reaction
are very facile under the reaction condition, preventing 42
from being isolated. However, the resulting 43 is resistant to
further transformation to 44 on heating in refluxing p-xylene
at 138 8C for 12 h. Apparently, it is difficult to protonate the
naphthalene moiety of 43 for the subsequent intramolecular
electrophilic aromatic substitution reaction.
After an additional 15 min, 5 mL of a saturated sodium
bicarbonate solution was introduced, and the reaction
mixture was extracted with diethyl ether. The combined
organic extracts were washed with brine and water, dried
over magnesium sulfate, and concentrated. The residue was
purified by flash column chromatography (silica gel/20%
diethyl ether in hexanes) to afford 0.311 g of 9 (0.727 mmol,
91%) as a white solid: mp 207–209 8C; IR 3401 (br), 832,
750, 697 cmK1; 1H d 8.50 (1H, d, JZ9.6 Hz), 7.79 (1H, dd,
JZ7.9, 1.5 Hz), 7.69–7.52 (7H, m), 7.41–7.31 (2H, m), 7.21
(1H, td, JZ7.4, 1.0 Hz), 7.04–6.93 (2H, m), 5.94 (1H, d, JZ
7.9 Hz), 5.02 (1H, dd, JZ7.5, 3.8 Hz), 4.43 (1H, m), 3.53
(1H, m), 1.91 (9H, s), 1.50 (1H, OH); 13C d 146.3, 143.3,
142.9, 140.8, 139.9, 139.4, 134.2, 132.8, 132.5, 131.4,
130.2, 130.0, 129.9, 128.7, 127.9, 127.6, 126.9, 126.8,
126.2, 125.6, 124.5, 124.28, 124.25, 123.6, 67.8, 51.4, 38.5,
34.6; MS m/z 429 (MHC), 415, 355.
3. Conclusion
The Wagner–Meerwein rearrangement was successfully
applied to a variety of 11H-benzo[b]fluorene-11-methanols
and related fluorene derivatives leading to highly con-
jugated aromatic systems bearing one or two aryl
substituents at the most sterically hindered positions.
These sterically congested aromatic systems are prone to
protonation for subsequent intramolecular electrophilic
aromatic substitution reactions, leading to polycyclic
aromatic hydrocarbons with novel architectures not easily
attainable by other synthetic methods. The synthetic
sequence is simple and straightforward, making it easily
adoptable for the synthesis of other polycyclic aromatic
compounds.
4.1.2. 14-Phenyldibenzo[a,j]anthracene (11). To a flask
containing 0.069 g (0.161 mmol) of 9 were added 0.256 g
(1.80 mmol) of phosphorus pentoxide and 10 mL of
p-xylene. The reaction mixture was heated under reflux
for 2 h. After the reaction mixture was allowed to cool to
room temperature, 10 mL of a saturated sodium bicarbonate
solution was introduced, and the organic layer was
separated. The aqueous layer was back extracted with
diethyl ether. The combined organic extracts were washed
with water, dried over magnesium sulfate, and concentrated.
The residue was purified by flash column chromatography
(silica gel/10% methylene chloride in hexanes) to provide
0.050 g of 11 (0.141 mmol, 88%) as a white solid: mp 259–
261 8C; IR 1443, 878, 790, 743, 696 cmK1; 1H d 8.35 (1H,
s), 7.82 (2H, d, JZ8.9 Hz), 7.79 (2H, dd, JZ8.2, 1.5 Hz),
7.69 (2H, d, JZ8.7 Hz), 7.66–7.58 (3H, m), 7.52–7.48 (2H,
m), 7.39 (2H, ddd, JZ7.9, 6.9, 1.0 Hz), 7.21 (2H, d, JZ
8.7 Hz), 6.99 (2H, ddd, JZ8.7, 6.9, 1.7 Hz); 13C d 145.4,
138.8, 134.2, 131.5, 131.3, 131.2, 130.6, 129.0, 128.4,
128.2, 128.13, 128.10, 127.8, 126.9, 125.9, 124.5; MS m/z
354 (MC), 337, 313; HRMS calcd for C28H18 354.1409,
found 354.1402.
4. Experimental
4.1. General
All reactions were conducted in oven-dried (120 8C)
glassware under a nitrogen atmosphere. Diethyl ether and
tetrahydrofuran (THF) were distilled from benzophenone
ketyl prior to use. n-Butyllithium (2.5 M) in hexanes, tert-
butyllithium (1.7 M) in pentane, lithium diisopropylamide
(LDA, 2.0 M) in heptane/THF/ethylbenzene, triethylsilane,
trifluoroacetic acid, potassium tert-butoxide (1.0 M) in
THF, 2-naphthoyl chloride, 1-bromo-2-naphthalenecarbox-
aldehyde (12), phenylacetylene, Pd(PPh3)2Cl2, copper(I)
iodide, CuBr$SMe2, triethylamine, 2,2-dimethylpropiophe-
none (15), paraformaldehyde, and phosphorus pentoxide
were purchased from chemical suppliers and were used as
received. 1,2-Bis[(2-ethynylphenyl)ethynyl]benzene was
prepared as reported previously.6 Melting points were
uncorrected. 1H (270 MHz) and 13C (67.9 MHz) NMR
spectra were recorded in CDCl3 using CHCl3 (1H d 7.26)
and CDCl3 (13C d 77.0) as internal standards unless
otherwise indicated for those recorded on a 600-MHz
NMR spectrometer.
4.1.3. Diols 28a–c. To a solution of 0.344 g (0.557 mmol) of
27 in 60 mL of benzene and 50 mL of THF under a nitrogen
atmosphere at 0 8C was added 1.80 mL of a 2.0 M solution
of LDA (3.60 mmol) in heptane/tetrahydrofuran/ethylben-
zene. After 20 min at 0 8C, 0.220 g (7.33 mmol) of
paraformaldehyde was transferred into the reaction mixture
via a 1208 angle glass tubing fitted with ground joints at both
ends. The reaction mixture was then allowed to warm to
room temperature. After an additional 30 min, 10 mL of a
saturated sodium bicarbonate solution was introduced, and
the reaction mixture was extracted with diethyl ether. The
combined organic extracts were washed with brine and
water, dried over magnesium sulfate, and concentrated. The
residue was purified by flash column chromatography (silica
gel/50% diethyl ether in hexanes) to afford 0.287 g of 28a–c
(0.423 mmol, 76%, a mixture of three isomers, isomer
ratioZ63:34:3) as a pale yellow solid. The 1H NMR
spectrum suggested that all three diastereomers, 28a and
28b having a C2 symmetry (63 and 3% not necessarily
respectively) and 28c without a C2 symmetry (34%), were
produced. The major isomer (28a or 28b) and 28c were
further separated by column chromatography on a silica gel
4.1.1. 7-(1,1-Dimethylethyl)-13-phenyl-8H-indeno[2,1-
b]phenanthrene-8-methanol (9). To a solution of 0.317 g
(0.796 mmol) of 8 in 8 mL of THF under a nitrogen
atmosphere at 0 8C was added 0.53 mL of a 2.0 M solution
of LDA (1.06 mmol) in heptane/tetrahydrofuran/ethyl-
benzene. After 10 min at 0 8C, 0.030 g (1.00 mmol) of
paraformaldehyde was introduced via a 1208 angle glass
tubing fitted with ground joints at both ends. The reaction
mixture was then allowed to warm to room temperature.

Y. Yang et al. / Tetrahedron 62 (2006) 4364–4371
4369
column. 28a–c: mp 221–225 8C; IR 3412 (br), 1052,
(1H, s), 7.90–7.70 (6H, m), 7.64–7.58 (3H, m), 7.45 (1H, d,
JZ8.4 Hz), 7.36 (1H, td, JZ7.1, 1.0 Hz), 7.31–7.22 (3H,
m), 7.06–6.92 (3H, m), 6.61 (3H, br s), 4.83 (1H, d, JZ
22.8 Hz), 4.77 (1H, d, JZ23.0 Hz); 13C d 149.1, 139.5,
136.1, 133.7, 133.3, 133.0, 132.4, 131.9, 131.8, 130.5,
130.4, 130.1, 129.3, 129.2, 128.72, 128.65, 128.4, 128.2,
127.9, 127.63, 127.58, 127.0, 126.9, 126.3, 126.2, 125.7,
125.6, 125.2, 125.1, 124.6, 53.4, 35.8; MS m/z 530 (MC),
453, 435, 424; HRMS calcd for C42H26 530.2035, found
530.2030.
1
704 cmK1; H (28a or 28b) d 7.81 (2H, s), 7.49 (2H, d,
JZ7.5 Hz), 7.13 (2H, tm, JZ7.5, 1 Hz), 7.10 (2H, tm, JZ
7.5, 1 Hz), 6.99 (4H, t, JZ7.5 Hz), 6.78 (2H, t, JZ7.2 Hz),
6.46 (4H, d, JZ6.9 Hz), 6.22 (2H, d, JZ7.9 Hz), 4.70 (2H,
dd, JZ5.9, 3.0 Hz), 4.47 (2H, m), 3.82 (2H, m), 1.82 (18H,
s), 1.13 (2H, OH); 13C (28a or 28b) d 146.6, 140.7, 140.6,
138.7, 137.4, 135.1, 134.9, 132.1, 131.2, 128.2, 126.56,
126.51, 126.0, 123.8, 122.9, 121.9, 67.0, 50.7, 37.7, 34.3; 1H
(28c) d 7.97 (1H, d, JZ9.7 Hz), 7.88 (1H, d, JZ9.3 Hz),
7.50 (1H, d, JZ7.5 Hz), 7.45 (1H, d, JZ7.1 Hz), 7.19–6.91
(8H, m), 6.83–6.74 (2H, m), 6.47 (4H, t, JZ8.1 Hz), 6.32
(2H, t, JZ6.9 Hz), 4.85 (1H, dd, JZ7.7, 3.8 Hz), 4.73 (1H,
dd, JZ6.1, 3.2 Hz), 4.47 (1H, m), 4.36 (1H, m), 3.74 (1H,
m), 3.47 (1H, t, JZ8 Hz), 1.86 (9H, s), 1.85 (9H, s), 1.64
(1H, OH), 1.17 (1H, OH); 13C (28c) d 146.7, 146.6, 140.8,
140.5, 140.4, 139.0, 138.9, 138.5, 138.4, 137.3, 135.9,
134.9, 134.6, 133.3, 133.0, 132.5, 132.2, 127.7, 126.9,
126.6, 126.1, 123.8, 123.5, 123.3, 123.0, 122.8, 122.1, 69.6,
67.2, 52.2, 50.7, 38.3, 37.8, 34.5, 34.2; The 1H NMR signals
attributable to the minor isomer having a C2 symmetry (28a
or 28b) were observed at d 8.05 (2H, s) and 1.90 (18H, s);
MS m/z 678 (MC), 664, 647, 605; HRMS calcd for
C50H46O2 678.3492, found 678.3496.
4.1.6. Hydrocarbon 31. To a flask containing 0.048 g
(0.071 mmol) of a mixture of 28a–c were added 0.496 g
(3.49 mmol) of phosphorus pentoxide and 20 mL of
p-xylene. The reaction mixture was heated under reflux
for 12 h before it was allowed to cool to room temperature.
A saturated sodium bicarbonate solution (10 mL) was
introduced, and the organic layer was separated. The
aqueous layer was back extracted with diethyl ether. The
combined organic extracts were washed with water, dried
over magnesium sulfate, and concentrated. The residue was
allowed to precipitate out from hexanes to provide 0.033 g
of 31 (0.062 mmol, 88%) as a light brown solid: mp O
380 8C; IR 1455, 797, 779, 744 cmK1; 1H d 8.02 (2H, d, JZ
8.2 Hz), 7.99 (2H, d, JZ8.7 Hz), 7.75 (2H, d, JZ8.4 Hz),
7.60 (2H, d, JZ8.4 Hz), 7.49 (2H, td, JZ7.7, 0.9 Hz), 7.27
(2H, td, JZ8, 1 Hz), 6.85 (2H, s), 6.79–6.71 (8H, m), 4.42
(4H, s); 13C d 146.0, 134.8, 133.4, 132.5, 130.5, 128.8,
128.6, 128.2, 126.7, 125.6, 124.9, 124.7, 124.1, 123.7, 54.1,
33.8; MS m/z 530, 453; HRMS calcd for C42H26 530.2035,
found 530.2025.
4.1.4. 17,18-Diphenyldibenzo[a,o]pentaphene (29). To a
flask containing 0.0134 g (0.0198 mmol) of a mixture of
28a–c were added 0.100 g (0.704 mmol) of phosphorus
pentoxide and 10 mL of p-xylene. The reaction mixture was
heated at 110 8C for 15 min. After the reaction mixture was
allowed to cool to room temperature, 10 mL of a saturated
sodium bicarbonate solution was introduced. The organic
layer was separated, and the aqueous layer was back
extracted with diethyl ether. The combined organic extracts
were washed with water, dried over magnesium sulfate, and
concentrated. The residue was purified by flash column
chromatography (silica gel/10% methylene chloride in
hexanes) to provide 0.0076 g of 29 (0.014 mmol, 73%) as
a light yellow solid: mp 272–275 8C; IR 1437, 879, 797,
744, 697 cmK1; 1H d 8.03 (2H, s), 7.71 (2H, d, JZ8.9 Hz),
7.65 (2H, d, JZ7.7 Hz), 7.61 (2H, d, JZ8.9 Hz), 7.44 (2H,
s), 7.19 (2H, td, JZ7.9, 1.0 Hz), 7.00 (2H, tt, JZ7.4,
1.0 Hz), 6.81 (4H, t, JZ7.7 Hz), 6.62 (2H, td, JZ7.8,
1.5 Hz), 6.51 (2H, d, JZ8.7 Hz), 6.40 (4H, d, JZ8.0 Hz);
13C d 141.2, 139.3, 133.9, 132.52, 132.45, 132.3, 130.9,
128.90, 128.84, 128.2, 127.7, 127.2, 127.0, 126.37, 126.35,
126.0, 125.5, 123.6, 122.8; MS m/z 530 (MC), 453, 437,
424; HRMS calcd for C42H26 530.2035, found 530.2035.
4.1.7. Diketone 35. To a flask containing 0.021 g
(0.040 mmol) of 31 were added 0.101 g (0.445 mmol) of
DDQ and 25 mL of benzene. The reaction mixture was
heated under reflux for 72 h before it was allowed to cool to
room temperature. The reaction mixture and then diethyl
ether solvent were allowed to flow through an aluminum
oxide column. The effluent was concentrated, and the
residue was purified by flash column chromatography (silica
gel/10% diethyl ether in hexanes) to provide 0.017 g of 35
(0.030 mmol, 77%) as a light yellow solid: mp O370 8C; IR
1654, 758 cmK1; 1H d 8.82 (2H, d, JZ8.7 Hz), 8.31 (2H, d,
JZ8.9 Hz), 8.17 (2H, d, JZ8.2 Hz), 8.12 (2H, s), 7.88 (2H,
d, JZ8.7 Hz), 7.74 (2H, ddd, JZ8.0, 6.8, 1.2 Hz), 7.45 (2H,
ddd, JZ8.4, 6.9, 1.2 Hz), 6.84 (4H, dd, JZ5.7, 3.2 Hz),
6.72 (4H, dd, JZ5.7, 3.2 Hz); 13C d 182.6, 150.8, 143.6,
136.7, 136.5, 132.5, 131.7, 131.4, 130.3, 129.9, 129.2,
128.5, 125.79, 125.75, 125.70, 124.5, 122.9, 53.3; MS m/z
558 (MC), 529, 498, 479, 464; HRMS calcd for C42H22O2
558.1620, found 558.1603. Recrystallization of 35 from
CH2Cl2/2-propanol produced a single crystal suitable for
X-ray structure analysis.
4.1.5. Hydrocarbon 30. To a flask containing 0.083 g
(0.12 mmol) of a mixture of 28a–c were added 0.310 g
(2.2 mmol) of phosphorus pentoxide and 15 mL of
p-xylene. The reaction mixture was heated under reflux
for 1.5 h. After the reaction mixture was allowed to cool to
room temperature, 10 mL of a saturated sodium bicarbonate
solution was introduced. The organic layer was separated,
and the aqueous layer was back extracted with diethyl ether.
The combined organic extracts were washed with water,
dried over magnesium sulfate, and concentrated. The
residue was allowed to precipitate out from hexanes to
provide 0.050 g of 30 (0.094 mmol, 77%) as a bright yellow
solid: mp 260–262 8C; IR 1443, 873, 738, 703 cmK1; 1H d
9.50 (1H, dd, JZ6.4, 3.5 Hz), 8.31 (2H, d, JZ8.2 Hz), 8.12
4.1.8. Diol 37. The same procedure was repeated as
described for 28 except that 0.094 g (0.122 mmol) of 36
in a mixture of 30 mL of benzene and 20 mL of THF was
treated with 0.50 mL of a 2.0 M solution of LDA
(1.0 mmol) in heptane/tetrahydrofuran/ethylbenzene
followed by 0.050 g (1.67 mmol) of paraformaldehyde to
afford 0.078 g of 37 (0.094 mmol, 77%, a mixture of two
isomers, isomer ratioZ55:45) as a bright yellow solid. The
major isomer does not possess a C2 symmetry, whereas

4370
Y. Yang et al. / Tetrahedron 62 (2006) 4364–4371
the minor isomer has a C2 symmetry. Compound 37: mp
support sabbatical leave in the Department of Chemistry at
the National Taiwan University. J.L.P. acknowledges the
support (CHE-9120098) provided by the National Science
Foundation for the acquisition of a Siemens P4 X-ray
diffractometer. The financial support of the NSF-EPSCoR
(1002165R) for the purchase of a 600 MHz NMR
spectrometer is also gratefully acknowledged.
1
235–238 8C; IR 3416 (br), 768, 728, 696 cmK1; H d 8.00
(major isomer, 0.55H, d, JZ9.4 Hz), 7.90 (major isomer,
0.55H, d, JZ9.4 Hz), 7.85 (minor isomer, 0.9H, s), 7.68–
7.62 (4H, m), 7.51–7.25 (12H, m), 7.13–7.05 (2H, m), 6.80–
6.73 (2H, m), 6.62–6.58 (4H, m), 6.47–6.34 (2H, m), 4.88–
4.71 (2H, m), 4.54–4.38 (2H, m), 3.92–3.73 and 3.54–3.46
(2H, m), 1.88 (major isomer, s, t-Bu), 1.87 (major isomer, s,
t-Bu), 1.84 (minor isomer, s, t-Bu), 1.10 (br, OH); 13C d
(two isomers) 146.8, 146.6, 141.1, 141.00, 140.8, 140.73,
140.67, 140.6, 140.5, 140.4, 139.3, 139.15, 139.08, 138.91,
138.87, 137.9, 137.7, 137.56, 137.53, 137.4, 136.1, 134.9,
134.6, 134.5, 134.3, 133.0, 132.6, 132.2, 132.0, 131.2,
131.0, 128.85, 128.76, 127.2, 126.8, 126.7, 126.6, 126.4,
126.2, 126.1, 126.0, 123.9, 123.6, 123.3, 123.0, 122.9,
122.8, 122.3, 122.0, 69.6, 67.1, 66.9, 52.3, 50.7, 38.3, 37.8,
37.7, 34.5, 34.3, 34.2; MS m/z 830 (MC), 799, 681, 656;
HRMS calcd for C62H54O2 830.4118, found 830.4073.
Supplementary data
Supplementary data associated with this article can be found,
in the online version, at doi:10.1016/j.tet.2006.02.066.
Experimental procedures and spectroscopic data for 1, 3, 4,
1
8, 13, 14, 16–22, 41, and 43; H and 13C NMR spectra of
compounds 1, 3, 4, 8, 9, 11, 13, 14, 16–22, 28a or 28b, 28c,
29–31, 35, 37–39, 41, and 43; ORTEP drawings of the crystal
structures of 18, 35, 41, and 43. Crystallographic data for the
structures in this paper have been deposited with the
Cambridge Crystallographic Data Centre. The CCDC nos.
292502, 292503, 292504, and 292505 have been assigned for
the compounds 18, 41, 43, and 35, respectively. Copies of the
data can be obtained, free of charge, on application to CCDC,
12 Union Road, Cambridge CB2 1EZ, UK [fax: C44 1223
336033 or e-mail: deposit@ccdc.cam.ac.uk].
4.1.9. Hydrocarbon 38. The same procedure was repeated
as described for 29 except that 0.0085 g (0.0102 mmol) of
37, 0.100 g (0.704 mmol) of phosphorus pentoxide, and
10 mL of benzene were used. The reaction mixture was
heated under refluxing benzene at 80 8C for 15 min to afford
0.0062 g of 38 (0.0091 mmol, 89%) as a yellow solid: mp
1
264–267 8C; IR 1449, 732, 697 cmK1; H d 8.06 (2H, s),
7.73 (2H, d, JZ8.7 Hz), 7.65–7.54 (8H, m), 7.47 (2H, s),
7.40 (4H, t, JZ7.3 Hz), 7.33–7.26 (2H, m), 7.17 (2H, tt, JZ
7.9, 1.3 Hz), 7.12 (4H, d, JZ8.4 Hz), 6.68–6.59 (4H, m),
6.54 (4H, d, JZ8.2 Hz); 13C d 140.7, 140.5, 138.8, 138.6,
134.0, 132.7, 132.5, 132.4, 130.9, 129.0, 128.7, 128.1,
127.9, 127.5, 127.3, 127.2, 126.7, 126.5, 125.9, 125.6,
123.9, 122.9; MS m/z 682 (MC), 528, 448, 425; HRMS
calcd for C54H34 682.2661, found 682.2687.
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