Polycyclic aromatic hydrocarbons by ring-closing metathesis

Article abstract of DOI:10.1021/jo051418o

A strategy for the synthesis of polycyclic aromatic hydrocarbons (PAHs) by the ring-closing olefin metathesis (RCM) of pendant olefins on a phenylene backbone has been developed. RCM of 2,4′,6′,2″-tetravinyl-[1, 1′;3′,1″]terphenyl and 2,2′,5′,2″- tetravinyl-[1,1′;4′,1′]terphenyl affords in high yield the isomeric [a,j] and [a,h] dibenzanthracenes, respectively. In contrast with other intramolecular annulation methods, such as Friedel-Crafts acylations, this reaction is completely regioselective. Since RCM is reversible and PAHs are often thermodynamic sinks, this strategy is an effective and general method for the preparation of PAHs. Density functional theory calculations support these results. Carbon disulfide is a suitable solvent for these reactions.

Full text of DOI:10.1021/jo051418o

Polycyclic Aromatic Hydrocarbons by Ring-Closing Metathesis
Margel C. Bonifacio, Charles R. Robertson, Jun-Young Jung, and Benjamin T. King*
Department of Chemistry, University of Nevada, Reno, Reno, Nevada, 89557
king@chem.unr.edu
Received July 8, 2005
A strategy for the synthesis of polycyclic aromatic hydrocarbons (PAHs) by the ring-closing olefin
metathesis (RCM) of pendant olefins on a phenylene backbone has been developed. RCM of 2,4′,6′,2′′-
tetravinyl-[1,1′;3′,1′′]terphenyl and 2,2′,5′,2′′-tetravinyl-[1,1′;4′,1′]terphenyl affords in high yield the
isomeric [a,j] and [a,h] dibenzanthracenes, respectively. In contrast with other intramolecular
annulation methods, such as Friedel-Crafts acylations, this reaction is completely regioselective.
Since RCM is reversible and PAHs are often thermodynamic sinks, this strategy is an effective
and general method for the preparation of PAHs. Density functional theory calculations support
these results. Carbon disulfide is a suitable solvent for these reactions.
Introduction
tion,15,16 Scholl cyclodehydrogenation,17 Wittig olefina-
tion,15,18 and diaryl coupling.19,20
Interest in the preparation of polycyclic aromatic
hydrocarbons (PAHs) has been stimulated by the desire
to understand their mechanisms of carcinogenesis and
by the discovery of fullerenes and nanotubes. Numerous
synthetic procedures for the construction of polycyclic
aromatic systems have been described in the literature.
This area has been recently reviewed1 and described in
a monograph.2 Classic methods include the Pschorr
synthesis,3 the Elbs reaction,4 alkylation of activated
carbonyl compounds,5 dimerization or trimerization of
acetylenes and arynes,6,7 Diels-Alder cycloaddition,8
Wagner-Meerwein rearrangements,9 annulation of o-
quinones,10 cyclodehydrohalogenation,11 cyclodehydration
methods,12 flash vacuum pyrolysis,13,14 photocycliza-
(8) (a) LeHoullier, C. S.; Gribble, G. W. J. Org. Chem. 1983, 48,
1682-1685. (b) Crump, S. L.; Netka, J.; Rickborn, B. J. Org. Chem.
1985, 50, 2746-2750. (c) Gribble, G. W.; Perni, R. B.; Onan, K. D. J.
Org. Chem. 1985, 50, 2934-2939. (d) Pascal, R. A., Jr.; McMillan, W.
D.; Van Engen, D.; Eason, R. G. J. Am. Chem. Soc. 1987, 109, 4660-
4665. (e) Carren˜o, M. C.; Mahugo, J.; Urbano, A. Tetrahedron Lett.
1997, 38, 3047-3050. (f) Chan, S.-H.; Yick, C.-Y.; Wong, H. N. C.
Tetrahedron 2002, 58, 9413-9422.
(9) (a) Floyd, A. J.; Dyke, S. F.; Ward, S. E. Chem. Rev. 1976, 76,
509-562. (b) Harvey, R. G.; Abu-Shaqara, E.; Yang, C. J. Org. Chem.
1993, 58, 5866.
(10) Sukumaran, K. B.; Harvey, R. G. J. Org. Chem. 1981, 46, 2740-
2745.
(11) (a) Amin, S.; Huie, K.; Hussain, N.; Balanikas, G.; Hecht, S. S.
J. Org. Chem. 1985, 50, 1948-1954. (b) Sardella, D. J.; Ghoshal, P.
K.; Boger, E. J. Fluorine Chem. 1982, 20, 459-473. (c) Wang, L.;
Shevlin, P. B. Org. Lett. 2000, 2, 3703-3705. (d) Reisch, H. A.;
Bratcher, M. S.; Scott, L. T. Org. Lett. 2000, 2, 1427-1430.
(12) (a) Platt, K. L.; Oesch, F. J. Org. Chem. 1981, 46, 2601-
2603. (b) Di Raddo, P.; Harvey, R. G. Tetrahedron Lett. 1988, 29,
3885-3886. (c) Bushman, D. R.; Grossman, S. J.; Jerina, D. M.; Lehr,
R. E. J. Org. Chem. 1989, 54, 3533-3544. (d) Harvey, R. G.; Pataki,
J.; Cortez, C.; Di Raddo, P.; Yang, C. J. Org. Chem. 1991, 56, 1210-
1217.
(1) Harvey, R. G. Curr. Org. Chem. 2004, 8, 303-323.
(2) Harvey, R. G. Polycyclic Aromatic Hydrocarbons; Wiley-VCH:
New York, 1997.
(3) (a) Duclos, R. I.; Tung, J. S.; Rapoport, H. J. J. Org. Chem. 1984,
49, 5243-5246. (b) Leardini, R.; Nanni, D.; Tundo, A.; Zanardi, G.
Synthesis 1988, 333-335.
(4) Newman, M. S.; Khanna, V. K. J. Org. Chem. 1980, 45, 4507-
4508.
(5) Cho, B. P.; Harvey, R. G. J. Org. Chem. 1987, 52, 5668-5678.
(6) (a) Blanco, L.; Helson, H. E.; Hirthammer, M.; Mestdagh, H.;
Spyroudis, S.; Vollhardt, K. P. C. Angew. Chem., Int. Ed. Engl. 1987,
26, 1276-1277. (b) Pen˜a, D.; Pe´rez, D.; Guitia´n, E.; Castedo, L. Org.
Lett. 1999, 1, 1555-1557.
(7) Lu, J.; Zhang, J.; Shen, X.; Ho, D. M.; Pascal, R. A., Jr. J. Am.
Chem. Soc. 2002, 124, 8035-8041.
(13) (a) Scott, L. T.; Hashemi, M. M.; Meyer, D. T.; Warren, H. B.
J. Am. Chem. Soc. 1991, 113, 7082-7084. (b) Plater, M. J. Tetrahedron
Lett. 1994, 35, 6147-6150. (c) Rabideau, P. W.; Sygula, A. Acc. Chem.
Res. 1996, 29, 235-242. (d) Yamamoto, K.; Sonobe, H.; Matsubara,
H.; Sato, M.; Okamoto, S.; Kitaura, K. Angew. Chem., Int. Ed. Engl.
1996, 35, 69-70. (e) Scott, L. T.; Cheng, P.-C.; Hashemi, M. M.;
Bratcher, M. S.; Meyer, D. T.; Warren, H. B. J. Am. Chem. Soc. 1997,
119, 10963-10968. (f) Mehta, G.; Rao, H. S. P. Tetrahedron 1998, 54,
13325-13370.
10.1021/jo051418o CCC: $30.25 © 2005 American Chemical Society
Published on Web 09/14/2005
8522
J. Org. Chem. 2005, 70, 8522-8526

Polycyclic Aromatic Hydrocarbons by RCM
SCHEME 1. Cyclization versus Dimerization
FIGURE 1. RCM catalysts.
Strategies involving transition metal catalysis are
attractive because of the mild reaction conditions. For
example, palladium-catalyzed cross-coupling is popular
for the formation of aryl-aryl σ-bonds.19 Ring-closing
olefin metathesis (RCM) has emerged as a powerful tool
for the preparation of double bonds in cyclic organic
compounds21 but has only recently been applied to
PAHs.22 The popularity of RCM is enhanced by the
commercial availability of metal alkylidene catalysts such
as those developed by Schrock23 (1-Mo) and Grubbs24
(2-Ru, 3-Ru) (Figure 1).
In Katz’s seminal paper on the mechanism of olefin
metathesis, 2,2′-divinylbiphenyl (1) was converted to
phenanthrene.25 This reaction was run as a mechanistic
probe and only allowed to proceed to ∼1% conversion.
The yield of phenanthrene was not reported. A recent
report by Iuliano and co-workers22 demonstrates the
preparative utility of RCM to generate functionalized
phenanthrenes from 2,2′-divinylbiphenyl derivatives.
We hypothesized that RCM could be a useful method
for the preparation of larger polycyclic aromatic hydro-
carbons since it is reversible26 and aromatic rings are
often thermodynamic sinks. The potential to form mul-
tiple aromatic rings in a single step was especially
intriguing. The formation of multiple cyclopentenyl rings
from 1,2-polydienes by RCM was reported by Coates and
Grubbs.27 We report herein computational and experi-
mental results for the RCM of 1 to afford phenanthrene
and for the double RCM of 2,4′,6′,2′′-tetravinyl-[1,1′;3′,1′′]-
terphenyl (2) and 2,2′,5′,2′′-tetravinyl-[1,1′;4′,1′]terphenyl
(3) to afford dibenz[a,j]anthracene (4) and dibenz[a,h]-
anthracene (5), respectively.
We also sought to develop reaction conditions that
would circumvent the poor solubility of many PAHs.
Carbon disulfide is an unusually effective solvent for
28
many PAHs (for example, it is the best solvent for C60
)
but has received little attention as a medium for transi-
tion metal catalyzed reactions due to its perceived
tendency to poison metal catalysts. We report effective
olefin metathesis using Schrock’s catalyst 1-Mo in CS2.
Results and Discussions
Two thermodynamic criteria should be satisfied for this
RCM approach to be useful for the synthesis of large
PAHs. First, the desired product should be a thermody-
namic sink. Second, if multiple rings are to be formed in
a single reaction, the energies of their formation should
be additive. Quantitative knowledge of reaction energies
is useful for the designed synthesis of high-energy PAHs,
such as fullerenes14 or Pascal’s crowded PAHs.7
(14) Scott, L. T.; Boorum, M. M.; McMahon, B. J.; Hagen, S.; Mack,
J.; Blank, J.; Wegner, H.; de Meijere, A. Science 2002, 295, 1500-
1503.
(15) (a) Sudhakar, A.; Katz, T. J. Tetrahedron Lett. 1986, 27, 2231-
2234. (b) Mallory, F. B.; Butler, K. E.; Evans, A. C.; Brondyke, E. J.;
Mallory, C. W.; Yang, C.; Ellenstein, A. J. Am. Chem. Soc. 1997, 119,
2119-2124. (c) Mallory, F. B.; Butler, K. E.; Be´rube´, A.; Luzik, E. D.,
Jr.; Mallory, C. W.; Brondyke, E. J.; Hiremath, R.; Ngo, P.; Carroll, P.
J. Tetrahedron 2001, 57, 3715-3724.
(16) (a) Mallory, F. B.; Mallory, C. W. Org. React. 1984, 30, 1-456.
(b) Prinsen, W. J. C.; Hajee, C. A. J.; Laarhoven, W. H. Polycyclic
Aromat. Compd. 1990, 1, 21-31. (c) Liu, L.; Yang, B.; Katz, T. J.;
Poindexter, M. K. J. Org. Chem. 1991, 56, 3769-3775. (d) Zhang, F.-
J.; Harvey, R. G. J. Org. Chem. 1998, 63, 1168-1171. (e) Harvey, R.
G.; Dai, W.; Zhang, J.-T.; Cortez, C. J. Org. Chem. 1998, 63, 8118-
8124.
(17) (a) Simpson, C. D.; Mattersteig, G.; Martin, K.; Gherghel, L.;
Bauer, R. E.; Ra¨der, H. J.; Mu¨llen, K. J. Am. Chem. Soc. 2004, 126,
3139-3147. (b) Rempala, P.; Kroul´ık, J.; King, B. T. J. Am. Chem.
Soc. 2004, 126, 15002-15003.
(18) Yang, C.; Yang, D. T. C.; Harvey, R. G. Synlett 1992, 799-800.
(19) Hassan, J.; Se´vignon, M.; Gozzi, C.; Schulz, E.; Lemaire, M.
Chem. Rev. 2002, 102, 1359-1470.
(20) (a) Wegner, H. A.; Scott, L. T.; de Meijere, A. J. Org. Chem.
2003, 68, 883-887. (b) Sharma, A. K.; Kumar, S.; Amin, S. J. Org.
Chem. 2004, 69, 3979-3982.
We used density functional theory (B3LYP/6-31G*,
∆G298) calculations to quantitatively evaluate these cri-
teria. To examine the first condition, the intramolec-
ular reaction of 1 to afford phenanthrene and ethylene
was compared to its dimerization (Scheme 1). The cy-
clization is calculated to be exergonic by -28 kcal/mol.
In the dimerization, trans/trans (two conformations),
cis/cis, and cis/trans isomers were considered. The
trans/trans twisted conformation is lowest in energy, but
its formation was exergonic by only -0.7 kcal/mol. All
other isomers were less stable by at least 3 kcal/mol.
Cyclization to the aromatic ring is therefore favored over
dimerization or other processes, such as acyclic diene
metathesis (ADMET) by ∼27 kcal/mol.
(21) (a) Grubbs, R. H.; Chang, S. Tetrahedron 1998, 54, 4113-4450.
(b) Fu¨rstner, A. Angew. Chem., Int. Ed. 2000, 39, 3012-3043. (c) Trnka,
T. M.; Grubbs, R. H. Acc. Chem. Res. 2001, 34, 18-29.
(22) Iuliano, A.; Piccioli, P.; Fabbri, D. Org. Lett. 2004, 6, 3711-
3714.
Next, we examined the RCM of the isomeric tetravinyl
terphenyls 2 or 3 to give isomeric dibenzanthracenes 4
or 5 (Scheme 2). These reactions are calculated to be
(23) Schrock, R. R.; Murdzek, J. S.; Bazan, G. C.; Robbins, J.;
DiMare, M.; O’Regan, M. J. Am. Chem. Soc. 1990, 112, 3875-3886.
(24) (a) Schwab, P.; France, M. B.; Ziller, J. W.; Grubbs, R. H. Angew.
Chem., Int. Ed. Engl. 1995, 34, 2039-2041. (b) Scholl, M.; Ding, S.;
Lee, C. W.; Grubbs, R. H. Org. Lett. 1999, 1, 953-956.
(25) Katz, T. J.; Rothchild, R. J. Am. Chem. Soc. 1976, 98, 2519-
2526.
(27) Coates, G. W.; Grubbs, R. H. J. Am. Chem. Soc. 1996, 118, 229-
230.
(28) Sivaraman, N.; Dhamodaran, R.; Kaliappan, I.; Srinivasan, T.
G.; Vasudeva Rao, P. R.; Mathews, C. K. J. Org. Chem. 1992, 57, 6077-
6079.
(26) Ivin, K. J.; Mol, J. C. Olefin Metathesis and Metathesis
Polymerization, 2nd ed.; Academic Press: New York, 1997.
J. Org. Chem, Vol. 70, No. 21, 2005 8523

Bonifacio et al.
SCHEME 2. Double RCM
SCHEME 3. Preparation of Isomeric
Tetravinylterphenylsa
exergonic by -57 and -60 kcal/mol, respectively, releas-
ing almost exactly twice as much energy as the RCM of
biphenyl 1. The energy released from multiple RCM
reactions in the same molecule is additive, suggesting
the feasibility of multiple cyclizations.
These computational results motivated us to prepare
substrates to test this methodology. First, we reinvesti-
gated Katz’s initial work with 1. Treating this compound
with Grubbs’ catalyst 2-Ru gave phenanthrene in quan-
titative yield, in agreement with the recent work of
Iuliano.22
To demonstrate the efficiency of this reaction for one-
step multiple cyclizations, we sought to prepare 4 and
5
29,30 from the RCM of 2 and 3, respectively, as illustrated
a [a] Br2, I2, dark, 0 °C, 16 h, 58% (6) and 67% (10); [b] NBS,
CCl4, hν, reflux 9 h, 88%; [c] AgNO3, H2O, EtOH, reflux 0.5 h,
96%; [d] (Ph)3PCH3Br, KOtBu, THF, 25 °C, 16 h, 61%; [e]
Pd(PPh3)4, o-styrenyl boronic acid, aq. Na2CO3, DME, EtOH, reflux
16 h, 93% (2) and 94% (3); [f] NBS, benzene, initiator, reflux 8 h,
44%; [g] PPh3, paraformaldehyde, KOtBu, DMF, THF, 90%.
in Scheme 2.
The preparation of the tetravinylterphenyls 2 and 3 is
outlined in Scheme 3. Initial electrophilic bromination
using the method of Schlu¨ter31 of m-xylene smoothly
afforded the dibromoxylene32 6 on 0.5 mol scale. Subse-
quent polybromination of 6 under forcing conditions gave
bis(benzalbromide) 7 in good yield. We were unable to
cleanly monobrominate the two benzylic positions of 6
(i.e., prepare 1,5-dibromo-2,4-bis-bromomethylbenzene)
using any of a wide range of conditions. Dialdehyde 833
was obtained by silver nitrate-promoted hydrolysis of 7
in excellent yield. Double Wittig olefination with meth-
ylenetriphenyl phosphorane gave 1,5-dibromo-2,4-divi-
nylbenzene 9.
TABLE 1. Comparison of Tetravinylterphenyl RCM
with Different Catalystsa
catalyst
substrate
time (h)
yield (%)b
1-Mo
2
3
2
3
2
3
2.5
1.5
87
95
88
88
92
92
2-Ru
3-Ru
8.5
18.5
2.5
3.5
a Reactions were performed at 25 °C at 5 mol % loading in C6D6
and for 1-Mo and in CD2Cl2 for 2-Ru and 3-Ru. b Based on 1H
NMR using an internal standard.
Likewise, electrophilic bromination of p-xylene afforded
the dibromoxylene 10.31 In contrast to 6, 10 could be
cleanly converted to the bis(benzylbromide)34 11. Double
Wittig olefination with para-formaldehyde gave 1,4-
dibromo-2,5-divinylbenzene 12.
tetravinylterphenyl with Grubbs’ catalyst 2-Ru in dry
dichloromethane at 35 °C furnished the dibenzan-
thracenes 4 and 5 in 98% and 83% isolated yield, respec-
tively, with no detectable side products. The yield of 5 is
likely to be higher, but we did not obtain a second crop
of crystals to minimize the handling of this highly
carcinogenic compound.
The RCM of 2 and 3 to form 4 and 5, respectively, was
also investigated with 1-Mo or 3-Ru. The reaction using
1-Mo and 3-Ru was faster than using 2-Ru (Table 1),
but all three catalysts were effective.
The low solubility of many PAHs must be addressed
to extend this methodology to larger systems. Although
carbon disulfide is a good solvent for many large PAHs,
sulfur-containing compounds are often considered to be
incompatible with transition metal catalysts. Heck, Mi-
oskowski, and co-workers37 have, however, shown that
metathesis of thiols and thioethers is possible using 3-Ru.
After optimization, Suzuki coupling35 of 9 or 12 with
o-styrenylboronic36 acid provided the isomeric tetravi-
nylterphenyls 2 or 3 in high yield. Not surprisingly,
terphenyls 2 and 3 both exhibited atropisomerism, with
rotational barriers of 17 kcal/mol, measured by variable-
1
temperature H NMR (see Supporting Information).
With substrates 2 and 3 in hand, we focused our
attention on the RCM. Simply treating the corresponding
(29) (a) Pollart, D. J.; Rickborn, B. J. Org. Chem. 1986, 51, 3155-
3161. (b) Elmalak, O.; Rabinovitz, M.; Blum, J. J. Heterocycl. Chem.
1993, 30, 291-292. (c) Platt, K. L.; Setiabudi, F. J. Chem. Soc., Perkin
Trans. 1 1992, 2005-2009.
(30) Harvey, R. G.; Cortez, C.; Jacobs, S. A. J. Org. Chem. 1982,
47, 2120-2125.
(31) Rehahn, M.; Schlu¨ter, A.-D.; Feast, W. J. Synthesis 1988, 5,
386-388.
(32) Auwers, K.; Traun, F. A. Chem. Ber. 1899, 32, 3309.
(33) Jakobs, A.; Christiaens, L.; Renson, M. Bull. Soc. Chim. Belg.
1991, 100, 1-4.
(34) Blum, J.; Zimmerman, M. Tetrahedron 1972, 28, 275-280.
(35) Schmid, G. A.; Borschberg, H.-J. Helv. Chim. Acta 2001, 84,
388-400.
(37) Spagnol, G.; Heck, M. P.; Nolan, S. P.; Mioskowski, C. Org. Lett.
2002, 4, 1767-1770.
(36) Dale, W. J.; Rush, J. E. J. Org. Chem. 1962, 27, 2598-2603.
8524 J. Org. Chem., Vol. 70, No. 21, 2005

Polycyclic Aromatic Hydrocarbons by RCM
TABLE 2. Results of RCM in CS2 with 1-Mo, 2-Ru, and
3-Rua
2,2′-Divinylbiphenyl (1). A solution of 2-bromostyrene
(0.109 mL, 1.00 mmol) and tetrakis(triphenylphosphine)-
palladium(0) (0.035 g, 0.03 mmol) in dimethoxyethane (DME,
4.35 mL) was stirred for 10 min at 25 °C. To this solution, a
solution of o-vinylbenzeneboronic acid (0.163 g, 1.10 mmol) in
1 mL of ethanol and a solution of Na2CO3 (0.212 g, 2.00 mmols)
in 1 mL of water were added. The mixture was heated at reflux
for 16 h. After cooling, DME was removed in vacuo and the
residue was extracted with water and hexane. Silica gel
column chromatography with hexane mobile phase and crys-
tallization from hexane afforded colorless crystals (181 mg,
88%). EI-MS: m/z 206.0. The product was spectrally identical
to previously reported samples.21
cat. load
(mol %)
yield
(%)b
catalyst
substrate
product
1-Mo
2
3
1
2
1
10
20
10
10
10
4
68
79
0
5
2-Ru
-
-
0
3-Ru
phenanthrene
71
a Reactions were performed at 25 °C for 1 h and monitored by
GC/MS. b Isolated yields.
Phenanthrene from 1 in CDCl2 Using 2-Ru. The inter-
nal standard 1,3,5-trimethoxybenzene (14 mg, 0.083 mmol),
substrate 1 (15 mg, 0.073 mmol), and 0.80 mL of degassed and
dry CD2Cl2 were combined. After recording an initial NMR
spectrum, we added Cl2(PCy3)2RudCHPh (6 mg, 0.007 mmol).
After 8 h at 25 °C, the 1H NMR spectrum was recorded.
Integration versus the internal standard provided the yield
(87%).
Because of its promise to dissolve large PAHs, we
attempted the RCM of 1 using 1-Mo, 2-Ru, and 3-Ru in
CS2. The 2-Ru catalyst was readily quenched, generating
an inactive and uncharacterized purple precipitate.
Schrock’s catalyst worked better: in less than 15 min at
25 °C, 1-Mo cleanly converted 1 to phenanthrene. The
catalyst 3-Ru proved also to be useful in CS2. Within 1
h, 3-Ru cleanly catalyzed the conversion of 1 to phenan-
threne. However, within 3 h in CS2 at 25 °C, 3-Ru
decomposed to an inactive mixture. We then investigated
the use of 1-Mo for the preparative scale multiple RCM
of 2 to 4 and 3 to 5 in CS2. The desired products were
formed within 20 min at 25 °C in good yield (Table 2).
The stability of 1-Mo and 3-Ru in CS2 was monitored
by 13C and 1H NMR spectroscopy in CS2 (see Supporting
Information). For 1-Mo, resonances at 284.8 (13C) and
12.29 ppm (1H) match literature values38 for the molyb-
denum alkylidene carbon bearing hydrogen. The 1-Mo
spectra were unchanged after 36 h at 25 °C. For 3-Ru,
resonances at 221.8, 221.2 (13C), and 19.43 ppm (1H)
match the literature values39 for the imidazolinylidene
ruthenium and alkylidene carbon atoms and for the
alkylidene protons. After 36 h at 25 °C, the 3-Ru spectra
revealed decomposition to several products, with the
alkylidene resonance vanishing and a new, unassigned
resonance appearing at 10.4 ppm.
Phenanthrene from 1 in CS2 Using 1-Mo. A Schlenk
flask was charged with 1 (58.5 mg, 0.284 mmol) and 1-Mo (24
mg, 10 mol %). Carbon disulfide (11.7 mL) was transferred
into the flask by bulb-to-bulb distillation. The solution was
stirred at room temperature for 1 h and then quenched by
pouring onto 5 g of silica gel. The product was eluted with
toluene. Removal of solvent by rotary evaporation gave white
crystals (36.2 mg, 71%). EI-MS: m/z 178.0. The product was
spectrally identical to an authentic standard (Aldrich).
2,4′,6′,2′′-Tetravinyl-[1,1′; 3′,1′′]terphenyl (2). A mixture
of 9 (0.720 g, 2.50 mmol) and tetrakis(triphenylphosphine)-
palladium(0) (0.173 g, 0.150 mmol) was dissolved in 22.0 mL
of 1,2-dimethoxyethane and stirred at 25 °C for 10 min. To
this was added a solution of o-vinylbenzene boronic acid (0.814
g, 5.50 mmol) in 7 mL of ethanol and a solution of sodium
carbonate (1.06 g, 10.0 mmol) in 5 mL of water. The yellow
solution was heated at reflux for 16 h. After cooling, the
mixture was diluted with diethyl ether and water was added.
The ether layer was collected, and the aqueous layer was
washed with ether (2 × 30 mL). The organic layers were
combined, dried over magnesium sulfate, and concentrated to
5 mL. The solution was diluted with hexane (20 mL). Flash
chromatogaphy (hexane/silica) afforded colorless viscous oil
(0.780 g, 93%). 1H NMR at 110 °C (DMSO-d6): δ 7.95 (s, 1H),
7.68 (d, J ) 8.0 Hz, 2H), 7.41-7.33 (m, 4H), 7.17 (d, J ) 7.5
Hz, 2H), 6.84 (s, 1H), 6.49-6.39 (m, 4H), 5.77 (d, J ) 17.5 Hz,
2H), 5.64 (d, J ) 17.5 Hz, 2H), 5.19 (d, J ) 11.0 Hz, 2H), 5.16
(d, J ) 11.0 Hz, 2H). 13C NMR (CDCl3): δ 139.3, 139.2, 139.1,
139.0, 136.6, 136.5, 135.8, 135.4, 135.2, 133.3, 132.8, 130.7,
127.9, 127.6, 127.5, 125.3, 125.1, 121.8, 121.6, 115.1, 115.0,
114.9. UV (hexane, nm): λmax 252 (ꢀ 50 200). EI-MS: m/z 334.0.
Exact Mass Calcd for C26H22: 334.1721. Found: 334.1715.
2,2′,5′,2′′-Tetravinyl-[1,1′; 4′,1′′]terphenyl (3). This was
prepared by the reaction of 12 (0.144 g, 0.500 mmol) with
o-vinylbenzene boronic acid (0.163 g, 1.10 mmol) in the same
manner as described for 2. After chromatography, colorless
crystals were obtained from hexane (0.157 g, 94%). mp 124-
126 °C. 1H NMR at 110 °C (DMSO-d6): δ 7.31 (d, J ) 7.5 Hz,
2H), 7.03-6.96 (m, 6H), 6.82 (d, J ) 7.0 Hz, 2H), 6.05 (dd, J
) 11.5, 17.5 Hz, 2H), 5.95 (dd, J ) 11.0, 17.5 Hz, 2H), 5.27 (d,
J ) 17.5 Hz, 2H), 5.18 (d, J ) 17.5 Hz, 2H), 4.76 (d, J ) 11.5
Hz, 2H), 4.69 (d, J ) 11.0 Hz, 2H). 13C NMR (300 MHz,
CDCl3): δ 139.7, 139.2, 136.6, 136.6, 135.5, 134.9, 130.9, 128.0,
127.77, 127.2, 125.1, 115.0. UV (methylene chloride, nm): λmax
229; EI-MS: (m/z) 334.0. Anal. Calcd for C26H22: C, 93.37; H,
6.63. Found: C, 93.23; H, 6.75.
Conclusions
Calculations show that the RCM of divinyl substituents
to give phenanthrene units is exergonic by 28 kcal/mol.
The phenanthrene units are thermodynamic sinks, ∼27
kcal/mol more stable than competing products. RCM is
a synthetically useful method to generate multiple new
benzenoid rings in a single step. Three commercially
available catalysts, 1-Mo, 2-Ru, and 3-Ru, are effective,
although 2-Ru is less reactive. RCM with catalyst 1-Mo
is effective in carbon disulfide.
Experimental Section
Caution: Benzylic bromides are lachrymators. Dibenzan-
thracenes are carcinogenic and should be handled with care
in accordance with NIH Guidelines for the Laboratory Use of
Chemical Carcinogens.40 Carbon disulfide is highly flammable
and possesses an extremely low autoignition temperature of
90 °C.
Dibenz[a,j]anthracene (4) by Reaction in CH2Cl2.
Compound 2 (0.133 g, 0.40 mmol), Cl2(PCy3)2RudCHPh (6.6
(38) Fox, H. H.; Lee, J.-K.; Park, L. Y.; Schrock, R. R. Organome-
tallics 1993, 12, 759-768.
(39) (a) C¸ etinkaya, B.; Demir, S.; O¨ zdemir, I.; Toupet, L.; Se´meril,
D.; Bruneau, C.; Dixneuf, P. H. Chem.-Eur. J. 2003, 9, 2323-2330.
(b) Huang, J.; Stevens, E. D.; Nolan, S. P.; Petersen, J. L. J. Am. Chem.
Soc. 1999, 121, 2674-2678.
(40) NIH Guidelines for the Laboratory Use of Chemical Carcino-
gens; NIH Publication No. 81-2385; National Institutes of Health:
Washington, DC, 1981.
J. Org. Chem, Vol. 70, No. 21, 2005 8525

Bonifacio et al.
mg, 0.008 mmol), and dry dichloromethane (3.4 mL) were
mixed and heated to 35 °C for 23 h. The solution was
concentrated to 1 mL and purified by silica gel chromatography
with 4% ethyl acetate in hexane to give 4 (109.1 mg, 98%).
removed, and purification by column chromatography using
hexane provided 9 (2.10 g, 61%) as white crystals. mp 84-86
1
°C. H NMR (CDCl3): δ 7.76 (s, 1H), 7.68 (s, 1H), 6.96 (dd, J
) 10.8, 17.4 Hz, 2H), 5.75 (d, J ) 17.1 Hz, 2H), 5.41 (d, J )
11.1 Hz, 2H). 13C NMR (CDCl3): δ 137.2, 136.3, 135.2, 124.7,
123.0, 117.5. UV (hexane, nm): λmax 245 (ꢀ 27,600). EI-MS: m/z
288.0. Anal. Calcd for C10H8Br2: C, 41.71; H, 2.80. Found: C,
42.02; H, 2.86.
1
mp 197-198 °C (lit.30 mp 195-197 °C). H NMR (CDCl3): δ
10.08 (s, 1H), 9.05 (m, 2H), 8.38 (s, 1H), 7.46-8.10 (m, 10 H),
in agreement with reported values.29
Dibenz[a,j]anthracene (4) by Reaction in CS2. Com-
pound 2 (28.9 mg, 0.086 mmols) and 1-Mo (6 mg, 10 mol %)
were added to a Schlenk flask. Freshly distilled CS2 (6 mL)
was added, and the solution was stirred for 1 h under nitrogen.
The solution was then poured onto silica gel and eluted with
hexane. The solvent was removed to give white crystals (16.4
mg, 68%) that were spectrally identical to previous reports.29
Dibenz[a,h]anthracene (5) by Reaction in CH2Cl2. This
was prepared from 3 (0.100 g, 0.30 mmol) and Cl2(PCy3)2Rud
CHPh (0.040 g, 0.049 mmol) in dichloromethane (6.0 mL) in
the same manner as 4. Recrystallization gave pure 4 (0.069 g,
1,4-Dibromo-2,5-dimethylbenzene (10). This was pre-
pared from p-xylene (23.1 mL, 0.19 mol), iodine (0.30 g, 1.18
mmol), and bromine (19.8 mL, 0.385 mol) in the same manner
as described for 6, yielding 10 (33.3 g, 67%) as white crystals.
1
mp 72-74 °C; H NMR (CDCl3): δ 7.39 (s, 2H), 2.33 (s, 6H).
1,4-Dibromo-2,5-bis(bromomethyl)benzene (11). A mix-
ture of 10 (20.4 g, 77.1 mmol), N-bromosuccinimide (28.3 g,
0.159 mol), and 1,1′-azobis(cyclohexanecarbonitrile) (0.010 g,
0.041 mmol) in benzene (380 mL) was heated at reflux for 8
h. The solvent was removed in vacuo, and recrystallization
with absolute ethanol afforded 11 (14.4 g, 44%) as white
crystals. mp 156-158 °C. 1H NMR (CDCl3): δ 7.66 (s, 2H),
4.51 (s, 4H).
1
83%) as colorless crystals. H NMR (CDCl3): δ 9.16 (s, 2H),
8.88 (d, 2H), 7.63-7.99 (m, 10 H). The product was spectrally
identical to an authentic standard (Aldrich).
Dibenz[a,h]anthracene (5) by Reaction in CS2. A solu-
tion of 3 (52.4 mg, 0.157 mmol) and 1-Mo (24 mg, 20 mol %)
in CS2 (9.3 mL) was stirred in a Schlenk flask for 1 h. The
solution was poured over silica gel and eluted with toluene.
Removal of the solvent afforded 5 (34 mg, 79%). The product
was spectrally identical to an authentic standard (Aldrich).
1,5-Dibromo-2,4-dimethylbenzene (6). To an ice-cooled
solution of iodine (0.20 g, 0.79 mmol) in neat m-xylene (19.7
mL, 0.16 mol) was added bromine (54.6 g, 0.34 mol) dropwise
over 1 h in the absence of light. After 16 h at room tempera-
ture, 20% aqueous KOH (100 mL) was added. The mixture
was shaken under slight warming until the disappearance of
the yellow color and was then allowed to cool. The aqueous
layer was decanted, and the remaining solids were washed
with water (4 × 50 mL). Recrystallization from absolute
ethanol gave 6 (24.4 g, 58%) as white crystals. mp 71-72 °C.
1H NMR (CDCl3): δ 7.68 (s, 1H), 7.10 (s, 1H), 2.31 (s, 6H).
1,5-Dibromo-2,4-bis(dibromomethyl)benzene (7). N-
Bromosuccinimide was added in three equal portions (3 × 3.82
g, 0.063 mol) over 9 h to a solution of 6 (2.64 g, 0.010 mol) in
refluxing CCl4 (60 mL) under incandescent irradiation (100
W). The mixture was cooled to room temperature and filtered
through a sintered glass frit, and the residue was washed twice
with hexane. The filtrate was evaporated in vacuo. Recrystal-
lization from hexane afforded 7 (5.09 g, 88%) as tan crystals.
mp 115-118 °C. 1H NMR (CDCl3): δ 8.66 (s, 1H), 7.71 (s, 1H),
6.97 (s, 2H). 13C NMR (CDCl3): δ 141.5, 136.0, 133.7, 121.3,
37.8. UV (MeOH, nm): λmax 229 (ꢀ 41 000). EI-MS: m/z 499.0.
Anal. Calcd for C8H4Br6: C, 16.58; H, 0.70. Found: C, 16.82;
H, 0.88.
1,4-Dibromo-2,5-divinylbenzene (12). A mixture of 11
(4.40 g, 10.4 mmol) and triphenylphosphine (6.83 g, 26.0 mmol)
in dimethylformamide (50 mL) was heated at reflux for 18 h.
The solvent was removed, and tetrahydrofuran (80 mL) and
paraformaldehyde (7.04 g) were added. Potassium tert-butox-
ide (3.51 g, 31.3 mmol) in tetrahydrofuran (15 mL) was then
transferred in the reaction vessel, turning the mixture cloudy
and light yellow. The solvent was evaporated, and the residue
was separated using a silica column with hexane. Removal of
solvent and recrystallization from absolute ethanol afforded
12 (2.70 g, 90%) as white crystals. mp 81-83 °C. 1H NMR
(CDCl3): δ 7.71 (s, 2H), 6.95 (dd, J ) 12, 18 Hz, 2H), 5.71 (d,
J ) 15 Hz, 2H), 5.40 (d, J ) 12 Hz, 2H). 13C NMR (CDCl3): δ
138.4, 134.7, 130.8, 122.7, 117.9. UV (methylene chloride,
nm): λmax 276 (ꢀ 24 000); EI-MS (m/z): 288.0; Anal. Calcd for
C10H8Br2: C, 41.71; H, 2.80. Found: C, 42.01; H, 2.72.
Phenanthrene from 1 in CS2 (NMR Scale). The vinyl
compound (1, 10 mg) was placed into either a J-Young tube
or a thick-walled NMR tube. A sealed capillary containing dry,
degassed CDCl3 or C6D6 was inserted into the tube. In a
glovebox, 10 mol % of catalyst (∼3 mg of 1-Mo or 4 mg of
2,3-Ru) was added. To the tube, 200 µL of CS2 was distilled
via bulb-to-bulb distillation using a vacuum line and liquid
nitrogen. The tube was then sealed under vacuum and allowed
1
to warm to room temperature. The H NMR was taken after
15 min.
General Procedure for Preparative CS2 Reactions.
The pendant vinyl compound (30-50 mg of 1, 2, or 3) was
placed into a Schlenk flask, evacuated, and back-filled with
nitrogen. In a glovebox, 10 mol % of catalyst was then added
to the flask. The carbon disulfide (∼8 mL) was added by bulb-
to-bulb distillation under vacuum. The final concentration of
the solution was ∼6 mg of substrate per 1 mL of CS2. The
reaction was stirred at room temperature for 1 h. The solution
was poured onto silica gel in a filter and washed with hexane
or toluene. The solvent was then removed by rotary evapora-
4,6-Dibromobenzene-1,3-dicarbaldehyde (8). To a solu-
tion of 7 (15.6 g, 0.027 mol) in 95% ethanol (625 mL) was added
a solution of AgNO3 (19.2 g, 0.113 mol) in water (125 mL),
and the mixture was stirred at reflux for 30 min. The solution
was allowed to cool, AgBr was filtered off, and the cake was
washed with 95% ethanol (3 × 20 mL). The filtrate was
evaporated to dryness under reduced pressure. The residue
was washed with water until neutral and dried in vacuo to
yield 8 (7.53 g, 96%) as a white solid. mp 192-193 °C (lit.33
1
tion. Products were analyzed by GC/MS and H NMR.
Acknowledgment. Acknowledgment is made to the
Donors of the Petroleum Research Fund, administered
by the American Chemical Society, for partial support
of this research. This research was also supported by
awards from the Research Corporation and the Office
of Naval Research.
1
mp 192 °C). H NMR (CDCl3): δ 10.32 (s, 2H), 8.39 (s, 1H),
8.04 (s, 1H); the observed chemical shifts were not in agree-
ment with reported values.33 13C NMR (DMSO-d6): δ 189.9,
138.4, 133.0, 130.8, 130.5. EI-MS: m/z 291.0.
1,5-Dibromo-2,4-divinylbenzene (9). Potassium tert-bu-
toxide (2.83 g, 0.025 mol) was added to methyltriphenylphos-
phonium bromide (9.77 g, 0.027 mol) dissolved in 180 mL of
tetrahydrofuran. The yellow solution was stirred for 5 min and
placed in an ice bath, and 8 (3.50 g, 0.012 mol) was slowly
added. The reaction mixture was stirred overnight at 25 °C.
The solvent was evaporated in vacuo, and the residue was
filtered through silica gel using hexane. The solvent was
Supporting Information Available: Computational meth-
ods, geometries, energies, experimental procedures, and 1H
and 13C NMR spectra. This material is available free of charge
via the Internet at http://pubs.acs.org.
JO051418O
8526 J. Org. Chem., Vol. 70, No. 21, 2005