A new Suzuki-Heck-type coupling cascade: Indeno[1,2,3]-annelation of polycyclic aromatic hydrocarbons

Article abstract of DOI:10.1021/jo020367h

Under palladium catalysis, o-bromobenzeneboronic acid can be coupled with 1-bromonaphthalene (6) and with oligocyclic bromoarenes to furnish indeno-annelated polycyclic aromatic hydrocarbons 1-4 and 25 in a single operation in moderate to good yields (27-87%). Alternatively, o-dibromoarenes and 1,2-dibromocycloalkenes can be cross-coupled with 1-naphthaleneboronic acid under the same conditions to yield analogous products (6-87%), and indenocorannulene (19) can be prepared likewise in a single step from pinacol corannuleneboronate (18) (40%).

Full text of DOI:10.1021/jo020367h

A New Su zu k i-Heck -Typ e Cou p lin g Ca sca d e:
In d en o[1,2,3]-An n ela tion of P olycyclic Ar om a tic Hyd r oca r bon s
Hermann A. Wegner,† Lawrence T. Scott,‡ and Armin de Meijere*,†
Institut fu¨r Organische Chemie der Georg-August-Universita¨t Go¨ttingen, Tammannstrasse 2,
D-37077 Go¨ttingen, Germany, and Department of Chemistry, Merkert Chemistry Center,
Boston College, Chestnut Hill, Massachusetts 02467-3860
armin.demeijere@chemie.uni-goettingen.de
Received J une 3, 2002
Under palladium catalysis, o-bromobenzeneboronic acid can be coupled with 1-bromonaphthalene
(6) and with oligocyclic bromoarenes to furnish indeno-annelated polycyclic aromatic hydrocar-
bons 1-4 and 25 in a single operation in moderate to good yields (27-87%). Alternatively,
o-dibromoarenes and 1,2-dibromocycloalkenes can be cross-coupled with 1-naphthaleneboronic acid
under the same conditions to yield analogous products (6-87%), and indenocorannulene (19) can
be prepared likewise in a single step from pinacol corannuleneboronate (18) (40%).
In tr od u ction
Significant effort has been directed recently toward the
synthesis of polycylic aromatic hydrocarbons (PAHs)
containing fully unsaturated five-membered rings that
are externally fused to six-membered ring perimeters
(CP-PAHs) and indeno-annelated polycyclic aromatic
hydrocarbons (indeno-PAHs).1,2 The latter class includes
such compounds as fluoranthene (1), indeno[1,2,3-cd]-
fluoranthene (2), rubicene (3), and isorubicene (4). Special
interest in these nonalternant hydrocarbons stems from
their resemblance to partial structures of C60-fullerene
(5) and its higher analogues, their unusual (photo)-
physical properties, e.g., anomalous fluorescence and high
electron affinities,3,4 and the carcinogenicity exhibited by
several representatives of this family of hydrocarbons.5,6
Recently Dang et al. published a one-step palladium-
catalyzed cyclopentannelation of 9-bromoanthracene with
terminal acetylenes.7 In this paper we present a new one-
step synthesis of a variety of indeno[1,2,3]-annelated
* To whom correspondence should be addressed: Fax: + 49-551/
399475.
PAHs. Our strategy relies on the Suzuki coupling reac-
tion to join two ring systems together initially and then
on an intramolecular Heck-type arylation to close the
five-membered ring. Since both steps are catalyzed by
palladium, our goal was to find conditions under which
the entire indeno-annelation sequence could be effected
in a single operation. The early work of Rice and Cai,2
who used aryl triflates, showed that Heck-type arylations
are able to close the five-membered ring of the fluoran-
thene ring system.
† Georg-August-Universita¨t Go¨ttingen.
‡ Boston College.
(1) (a) Scott, L. T. Pure Appl. Chem. 1996, 68, 291-300. (b) Necula,
A.; Scott, L. T. J . Anal. Appl. Pyrolysis 2000, 54, 65-87. (c) Scott, L.
T.; Bronstein, H. E.; Preda, D. V.; Ansems, R. B. M.; Bratcher, M. S.;
Hagen, S. Pure Appl. Chem. 1999, 71, 209-219. (d) Rabideau, P. W.;
Sygula, A. Acc. Chem. Res. 1996, 29, 225-242.
(2) Rice, J . E.; Cai, Z. W. J . Org. Chem. 1993, 58, 1415-1424.
(3) Gooijer, C.; Kozin, I.; Velthorst, N. H.; Sarobe, M.; J enneskens,
L. W.; Vlietstra, E. J . Spectrochim. Acta, Part A 1998, 54, 1443-1449
and references therein.
(4) (a) Necula, A. Ph.D. Thesis, Boston College, Chestnut Hill, MA,
1996. (b) Sarobe, M. Ph.D. Thesis, Utrecht University, Utrecht, The
Netherlands, 1998.
Resu lts a n d Discu ssion
(5) Sarobe, M.; J enneskens, L. W.; Wesseling, J .; Wiersum, U. E. J .
Chem. Soc., Perkin Trans. 2 1997, 703-708 and references therein.
(6) (a) Lowe, J . P.; Silverman, B. D. Acc. Chem. Res. 1984, 17, 332-
338. (b) Ball, L. M.; Warren, S. H.; Sangaiah, R.; Nesnow, S.; Gold, A.
Mutat. Res. 1989, 224, 115-125.
(7) (a) Dang, H.; Garcia-Garibay, M. A. J . Am. Chem. Soc. 2001,
123, 355-356. (b) Dang, H.; Levitus, M.; Garcia-Garibay, M. A. J . Am.
Chem. Soc. 2002, 124, 136-143.
The first execution of this strategy began with a bro-
mo-PAH and used o-bromobenzeneboronic acid (7) as
the annelation partner (Figure 1). A variety of pallad-
ium catalysts and conditions were evaluated (Table 1).
The best results were obtained with the combination of
10.1021/jo020367h CCC: $25.00 © 2003 American Chemical Society
Published on Web 01/03/2003
J . Org. Chem. 2003, 68, 883-887
883

Wegner et al.
F IGURE 1. Suzuki-Heck-type coupling cascade of 6 and 7 to form 1. see Table 1 for conditions.
TABLE 1. Op tim iza tion of th e Con d ition s for th e Su zu k i-Heck -typ e Cou p lin g Ca sca d e Sh ow n in F igu r e 1
catalyst
(mol %)
temp
(°C)
yielda (%)
(ratio)
entry
additive
P(Cy)3
base
solvent
time (h)
products
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Pd(OAc)2, 20
Pd(OAc)2, 20
Pd(PPh3)2Cl2, 20
10, 20
Pd(MeCN)2Cl2, 20
11, 20
Pd(PPh3)4, 20
Pd2(dba)3, 20
Pd2(dba)3, 20
Pd2(dba)3, 20
Pd2(dba)3, 20
Pd2(dba)3, 20
Pd2(dba)3, 10
Pd2(dba)3, 5
Pd2(dba)3, 2
DBU
DBU
DBU
DBU
DBU
DBU
K2CO3
DBU
DBU
DBU
DBU
DBU
DBU
DBU
DBU
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
155
155
150
155
155
155
110
155
155
155
155
155
155
155
155
48
48
48
48
48
48
14
48
48
48
48
48
48
48
48
8
43
8, 9, 1
9, 1
8
8, 9
1
95 (3:1:2.6)
81 (1.2:1)
65
95 (1:18)
43
9
95b
P(Ph)3
P(p-tol)3
P(n-Bu)3
dppe
P(Cy)3
P(Cy)3
P(Cy)3
P(Cy)3
9, 1
9, 1
8, 9, 1
9, 1
1
1
9, 1
9, 1
99 (1:3)
98 (1:2.6)
94 (1:2:4.5)
22:65
97
95
81 (1:1.6)
62 (1,5:1)
a
b
If not otherwise noted, the yields were determined by NMR. Isolated yield.
Pd2(dba)3 and P(Cy)3. The amount of catalyst could be
reduced to 10 mol %, but with lower catalyst loadings
the yield dropped dramatically (Table 1, entries 13-15).
With Pd(PPh3)4 as a catalyst at 110 °C, only the Suzuki
coupling product 9 was isolated (Table 1, entry 7).
It is noteworthy that none of the catalytic systems
promoted any detectable coupling of 7 with itself. We
anticipated that the conjugate base of the boronic acid
would sterically and electronically retard oxidative ad-
dition of the ortho C-Br bond to Pd(0), and our results
are consistent with this prediction.
In view of the fact that simple areneboronic acids
are more easily prepared than o-bromoareneboronic
acids, we decided to examine a variant of this annelation
by applying the same reaction conditions to 1-naphtha-
leneboronic acid (12) and 1,2-dibromobenzene (13). In-
deed, 1 is also formed by this method and could be
isolated in 87% yield (Figure 2).
F IGURE 2. Application of the optimized conditions to 12 and
13.
increased to 19%. 1,2-Dibromocycloheptene (14c) gave
the cyclized product 16c in only 6% yield.
The same reaction conditions were also examined for
the coupling of 1,2-dibromocycloalkenes with 12. From
the reaction of 1,2-dibromocyclohexene (14b) with 12, the
ring-closed product 16b could be isolated in 58% yield.
The 2-fold Suzuki coupling product 17b, a product type
which was never observed in the reactions of o-dibro-
mobenzene (13), was obtained as a side product in 6%
yield (Figure 3). When 1,2-dibromcyclopentene (14a ) was
used, the yield of the cyclization product 16a dropped to
33%, and that of the 2-fold Suzuki coupling product 17a
Monitoring the reaction of 14b by NMR spectroscopy
revealed that the reaction is complete after 5 h. We
therefore repeated this reaction, adding the boronic acid
by syringe pump over 5 h. Unfortunately, no significant
change in the ratio of cyclized 16b to 2-fold Suzuki
product 17b was observed. The same result was obtained
for 14a . This led to the conclusion that the second Suzuki
coupling step is about as fast as the first one and
successfully competes with the Heck-type intramolecular
coupling.
884 J . Org. Chem., Vol. 68, No. 3, 2003

A New Suzuki-Heck-Type Coupling Cascade
F IGURE 3. Suzuki-Heck-type coupling cascade of dibro-
mocycloalkenes 14 with 12.
As a preliminary probe into the scope and limitations
of these cross-coupling-cyclization cascades, the reac-
tions of pinacol corannuleneboronate (18) with 1,2-
dibromobenzene (14) and of 1,4-dibromonaphthalene (20),
9,10-dibromoanthracene (21), and 1,8-dibromophenan-
threne (24) with 7 were performed under the optimized
conditions. Gratifyingly, the otherwise difficultly acces-
sible indenocorannulene (19)8 was obtained in this single-
operation procedure in 40% isolated yield (Figure 4). 2
was isolated in 51% yield from 20, along with 1 (35%).
An inseparable mixture of 3 and 4 was isolated in 28%
yield from 21 (1:1 ratio by 1H NMR analysis), along with
benzo[a]fluoranthene (22) (27%) and anthracene (23)
(19%). The reaction of 24 gave the desired 25 and the
byproduct 26 both in 27% yield. In this case, 12% starting
material 24 was also recovered (Figure 4).
As these first examples demonstrate, a new Suzuki-
Heck-type coupling cascade to build indeno[1,2,3]-PAHs
quickly in moderate to good yields has now been found.
A search for improved conditions to diminish the forma-
tion of side products is currently in progress.
F IGURE 4. Synthesis of indeno-annelated PAHs with the
new Suzuki-Heck-type coupling cascade.
the nearest 0.1 Hz. The following abbreviations are used for
the signal multiplicities: s (singlet), d (doublet), m (multiplet).
13C NMR spectra (62.9 MHz) were recorded at ambient
temperature in CDCl3, with δ(CDCl3) ) 77.0 as internal
standard. Mass spectra were recorded using electron impact
ionization at 70 eV. High-resolution mass spectroscopy (HRMS)
was performed using preselected ion peak matching at R ≈
10000 to be within (2 ppm. Elemental analyses were per-
formed at the University of Go¨ttingen, Germany. All solvents
were distilled before use. Chromatography: for standard
chromatography, silica gel of 230-400 mesh (0.063-0.200 mm)
was used, and for flash chromatography, silica gel of 70-230
mesh (0.040-0.063 mm) was used. Unless specified otherwise,
solutions of NaHCO3 were saturated aqueous solutions. An-
Exp er im en ta l Section
Gen er a l P r oced u r es. 1H NMR spectra (250 MHz) were
recorded at ambient temperature in CDCl3, using CHCl3 (δ )
7.26) or tetramethylsilane (δ ) 0.00) as internal standard.
Chemical shifts (δ) are quoted in parts per million, and
coupling constants (J ) are given in absolute values in hertz to
(8) (a) Rai, A. M. S. Thesis, Boston College, Chestnut Hill, MA, 1997.
(b) Preda, D. V. Ph.D. Thesis, Boston College, Chestnut Hill, MA, 2001.
J . Org. Chem, Vol. 68, No. 3, 2003 885

Wegner et al.
hydrous solvents were prepared according to standard labora-
tory techniques. All reactions with organometallic substances
were performed under argon. All chemicals were used as
commercially available, unless otherwise noted.
DBU (0.30 mL) in DMF (4 mL) was stirred at 155 °C for 2 d.
Column chromatography on silica gel (30 g, column 2.0 × 39
cm, pentane/CH2Cl2, 19:1) yielded 10 mg of a mixture of
1
naphthalene 8 and 16c (6%) in a ratio of 3:1 (according to H
Gen er a l P r oced u r e for th e Su zu k i-Heck -Typ e Cou p -
lin g Ca sca d e (GP 1). A 10 mL Schlenk flask was equipped
with a magnetic stirring bar, Pd2(dba)3 (10-20 mol %), P(Cy)3
(40-80 mol %), the bromoarene (0.24 mmol), the areneboronic
acid (0.29 mmol), and DBU (0.25 mL) in DMF (4 mL). The
resulting mixture was stirred at 155 °C overnight. After
dilution with 50 mL of CH2Cl2, the mixture was washed twice
with 50 mL each of HCl (10%) and once each with 50 mL of
NaHCO3 and 50 mL of H2O. Drying of the organic phase over
MgSO4 and evaporation of the solvent gave the crude product,
which was subjected to chromatography on silica gel, eluting
with pentane/CH2Cl2 mixtures.
F lu or a n th en e (1). According to GP 1, a mixture of 1-bro-
monaphthalene (6) (50 mg, 0.24 mmol), o-bromobenzenebo-
ronic acid (7) (58 mg, 0.29 mmol), Pd2(dba)3 (50 mg, 0.048
mmol), P(Cy)3 (54 mg, 0.19 mmol), and DBU (0.25 mL) in DMF
(4 mL) was stirred at 155 °C for 2 d. Column chromatography
on silica gel (30 g, column 2.0 × 39 cm, pentane/CH2Cl2, 19:1)
yielded 42 mg (87%) of 1 as colorless crystals, mp 106-108
°C. The spectroscopic data agreed with those of a commercially
available sample.
NMR). The spectroscopic data agreed with those reported in
the literature.10
P in a col Cor a n n u len ebor on a te (18). A 10 mL Schlenk
flask equipped with a magnetic stirring bar was charged
with PdCl2(dppf) (2.2 mg, 3.0 µmol), bromocorannulene (6)11
(33 mg, 0.10 mmol), triethylamine (42 µL, 0.30 mmol), pina-
colborane (22 µL, 0.15 mmol), and dioxane (0.4 mL). The
resulting mixture was stirred at 105 °C for 24 h. After dilu-
tion with 50 mL of CH2Cl2, the mixture was washed twice
with 50 mL of H2O. Drying of the organic phase over MgSO4
and evaporation of the solvent gave the crude product. Re-
crystallization from pentane/CH2Cl2 yielded 41.6 mg (95%) of
18 as yellow crystals, mp 67-70 °C. 1H NMR (250 MHz,
CDCl3): δ 1.27 (s, 12 H), 7.63-7.96 (m, 7 H), 8.46 (d, 3J )
8.8 Hz, 1 H), 8.50 (s, 1 H). 13C NMR (62.9 MHz, CDCl3): δ
25.0, 83.9, 126.77, 126.84, 126.9, 127.0, 127.1, 127.5, 128.9,
130.6, 130.8, 131.4, 134.9, 135.4, 135.7, 135.8, 136.0, 136.9,
137.4. MS (70 eV) m/z (rel intens): 376 (45) [M+], 303
(12), 276 (38), 250 (100). Correct HRMS (m/z) as calcd for
C
26H21BO2: 376.1635.
In d en ocor a n n u len e (19). According to GP 1, a mixture
1-(2′-Br om op h en yl)n a p h th a len e (9). A 10 mL Schlenk
flask was equipped with a magnetic stirring bar, Pd(PPh3)4
(0.23 g, 0.20 mmol), 6 (0.21 g, 1.0 mmol), 7 (0.24 g, 1.2 mmol),
and K2CO3 (1.4 g, 10 mmol) in DMF (5 mL). The resulting
mixture was stirred at 110 °C overnight. After dilution with
50 mL of CH2Cl2, the mixture was washed twice with 50 mL
each of HCl (10%) and once each with 50 mL of NaHCO3 and
50 mL of H2O. Drying of the organic phase over MgSO4 and
evaporation of the solvent gave the crude product. Column
chromatography on silica gel (80 g, column 3.5 × 45 cm,
pentane/CH2Cl2, 10:1) yielded 0.27 g (95%) of 9 as colorless
of 18 (0.11 g, 0.29 mmol), 1,2-dibromobenzene (13) (57 mg, 0.24
mmol), Pd2(dba)3 (50 mg, 0.048 mmol), P(Cy)3 (54 mg, 0.19
mmol), and DBU (0.25 mL) in DMF (4 mL) was stirred at 155
°C for 2 d. Column chromatography on silica gel (80 g, column
3.5 × 45 cm, pentane/CH2Cl2, 9:1) yielded 31 mg (40%) of 19
1
as yellow crystals, mp 192-194 °C (lit.8 mp 194-196 °C). H
3
NMR (400 MHz, CDCl3): δ 7.64 (d, J ) 8.4 Hz, 2H), 7.64 (s,
2H), 7.65-7.63 (m, 2H), 7.57 (d, 3J ) 8.4 Hz, 2H), 7.53 (s, 2H),
7.21-7.19 (m, 2H). The spectroscopic data agreed with those
reported previously.8
In d en o[1,2,3-cd ]flu or a n th en e (2). According to GP 1, a
mixture of 1,4-dibromonaphthalene (20) (86 mg, 0.30 mmol),
7 (0.14 g, 0.71 mmol), Pd2(dba)3 (62 mg, 0.060 mmol), P(Cy)3
(67 mg, 0.24 mmol), and DBU (0.50 mL) in DMF (4 mL) was
stirred at 155 °C for 2 d. Column chromatography on silica
gel (80 g, column 3.5 × 45 cm, pentane/CH2Cl2, 19:1) yielded
42 mg (51%) of 2 as yellow crystals, mp 255-258 °C (lit.12 mp
1
crystals, mp 82-84 °C. H NMR (250 MHz, CDCl3): δ 7.27-
3
3
7.60 (m, 8 H), 7.75 (d, J ) 8.2 Hz, 1 H), 7.92 (d, J ) 8.2 Hz,
2 H). 13C NMR (62.9 MHz, CDCl3): δ 124.35, 125.14, 125.84,
125.91, 126.11, 126.97, 127.13, 128.17, 128.23, 129.07, 131.53,
131.60, 131.97, 132.71, 133.41, 141.33. MS (70 eV) m/z (rel
intens): 285/284/283/282 (48) [M+], 204/203/202/201/199 (100),
101 (31). Correct HRMS (m/z) as calcd for C16H11Br: 282.0044.
Anal. Calcd for C16H11Br: C, 67.87; H, 3.92. Found: C, 68.17;
H, 3.75.
1
261-262 °C) and 21 mg (35%) of 1. H NMR of 2 (400 MHz,
CDCl3): δ 7.61-7.55 (m, 4H), 7.53 (s, 4H), 7.20-7.14 (m, 4H).
The spectroscopic data of 2 agreed with those reported previ-
ously.12
8,9-Tetr a h yd r o-7H-cyclop en t[a ]a cen a p h th ylen e (16a ).
According to GP 1, a mixture of 1-naphthaleneboronic acid (12)
(55 mg, 0.32 mmol), 1,2-dibromocyclopentene (14a ) (60 mg,
0.27 mmol), Pd2(dba)3 (55 mg, 0.053 mmol), P(Cy)3 (60 mg, 0.21
mmol), and DBU (0.30 mL) in DMF (4 mL) was stirred at 155
°C for 2 d. Column chromatography on silica gel (30 g, column
2.0 × 39 cm, pentane/CH2Cl2, 19:1) yielded 17 mg (33%) of
16a as yellow crystals, mp 64-67 °C (lit.9 mp 67-68 °C). The
spectroscopic data agreed with those reported in the litera-
ture.9
7,8,9,10-Tetr a h yd r oflu or a n th en e (16b). According to GP
1, a mixture of 12 (50 mg, 0.29 mmol), 1,2-dibromocyclohex-
ene (14b ) (57 mg, 0.29 mmol), Pd2(dba)3 (50 mg, 0.048
mmol), P(Cy)3 (54 mg, 0.19 mmol), and DBU (0.25 mL) in
DMF (4 mL) was stirred at 155 °C for 2 d. Column chroma-
tography on silica gel (30 g, column 2.0 × 39 cm, pentane/
CH2Cl2, 9:1) yielded 29 mg (58%) of 16b as an orange oil. The
spectroscopic data corresponded with those reported in the
literature.10
Ru bicen e (3) a n d Isor u bicen e (4). According to GP 1, a
mixture of 9,10-dibromoanthracene (21) (0.10 g, 0.30 mmol),
7 (0.14 g, 0.71 mmol), Pd2(dba)3 (62 mg, 0.060 mmol), P(Cy)3
(67 mg, 0.24 mmol), and DBU (0.50 mL) in DMF (4 mL) was
stirred at 155 °C for 2 d. Column chromatography on silica
gel (80 g, column 3.5 × 45 cm, pentane/CH2Cl2, 9:1) yielded
27 mg (28%) of an inseparable mixture of 3 and 4 as red
crystals. An 1H NMR spectrum (250 MHz, CDCl3) of the
mixture showed well-separated two-proton doublets at δ 8.57,
8.31, and 8.00 ppm for 3 and well-separated two-proton
multiplets at δ 8.43 and 6.98 ppm for 4, the integration of
which indicated a 3:4 ratio of 1:1. The spectroscopic data
agreed with those reported for materials from alternative
syntheses.13,14
Ben z[e]in d en o[1,2,3-h i]a cep h en a n t h r ylen e (25). Ac-
cording to GP 1, a mixture of 1,8-dibromophenanthrene (24)
(0.10 g, 0.30 mmol), 7 (0.14 g, 0.71 mmol), Pd2(dba)3 (62 mg,
60 µmol), P(Cy)3 (67 mg, 0.24 mmol), and DBU (0.50 mL) in
DMF (4 mL) was stirred at 155 °C for 1.5 d. Column
chromatography on silica gel (80 g, column 3.5 × 45 cm,
8,9,10,11-Te t r a h yd r o-7H -cycloh e p t [a ]a ce n a p h t h yl-
en e (16c). According to GP 1, a mixture of 12 (55 mg, 0.32
mmol), 1,2-dibromocycloheptene (14c) (68 mg, 0.27 mmol), Pd2-
(dba)3 (55 mg, 0.053 mmol), P(Cy)3 (60 mg, 0.21 mmol), and
(11) (a) Scott, L. T.; Hashemi, M. M.; Bratcher, M. S. J . Am. Chem.
Soc. 1992, 114, 1920-1921. (b) Cheng, P.-C. M. S. Thesis, University
of Nevada, Reno, NV, 1992. (c) Seiders, T. J .; Elliot, E. L.; Grube, G.
H.; Siegel, J . S. J . Am. Chem. Soc. 1999, 121, 7804-7813.
(12) Bronstein, H. E. Ph.D. Thesis, Boston College, Chestnut Hill,
MA, 2000.
(9) J ackson, D. A.; Lacy, P. H.; Smith, D. C. C. J . Chem. Soc., Perkin
Trans. 1 1989, 215-220.
(10) J ackson, D. A.; Smith, D. C. C.; Watt, C. I. F. J . Chem. Soc.,
Perkin Trans. 1 1987, 2437-2441.
886 J . Org. Chem., Vol. 68, No. 3, 2003

A New Suzuki-Heck-Type Coupling Cascade
pentane/CH2Cl2, 19:1) yielded 26 mg (27%) of 25 as yellow
crystals, mp 272-276 °C (lit.15 mp 277-278 °C) and 20 mg
(27%) of benz[e]acephenanthrylene (26). The spectroscopic data
agreed with those reported in the literature.15
Foundation. H.A.W. is indebted to the Fulbright Foun-
dation for a research fellowship, and L.T.S. is indebted
to the Alexander von Humboldt Foundation for a Senior
Scientist Fellowship. A generous gift of 1,8-dibro-
mophenanthrene from Heather St. Martin is gratefully
acknowledged.
Ack n ow led gm en t. This work was supported by the
Studienstiftung des Deutschen Volkes, the Fonds der
Chemischen Industrie, and the U.S. National Science
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectrum
of compound 18. This material is available free of charge via
the Internet at http://pubs.acs.org.
(13) Sachweh, V.; Langhals, H. Chem. Ber. 1990, 123, 1981-1987.
(14) Reisch, H.; Scott, L. T. Unpublished synthesis of isorubicene.
(15) Pogodin, S.; Biedermann, P. U.; Agranat, I. J . Org. Chem. 1997,
62, 2285-2287.
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J . Org. Chem, Vol. 68, No. 3, 2003 887