Preparation of Condensed Aromatics by Superacidic Dehydrative Cyclization of Arvl Pinacols and Eooxides

Article abstract of DOI:10.1021/jo970293n

Aryl pinacols and epoxides, respectively, are cleanly and in high yield converted via superacidic dehydrative cyclization to the corresponding condensed aromatics. Dehydrative cyclization of benzopinacol (1a), triphenylacetophenone (2), and tetraphenylethylene oxide (9) give 9,10-diphenylphenanthrene (3a) as the major product in acidic media stronger than H_o = -11. Aryl pinacol 12a forms the condensed aromatic 13a as the major product in acidic media stronger than H_o = -13.5. It is proposed that the dehydrative cyclizations to provide aromatics 3a and 13a occurs through dicationic intermediates. Substituted benzopinacols 1f, 1g, and 1j are prepared and give the corresponding phenanthrenes (3f, 3g, and 3j) in high yields. The regiochemistry of the cyclization of substituted benzopinacols is controlled by deactivating substituents on the aryl rings. Aryl pinacols (12a-d) derived from acenaphthenequinone and pinacol 15 also give condensed aromatics (13a-d and 16, repectively) with superacidic triflic acid.

Full text of DOI:10.1021/jo970293n

6666
J . Org. Chem. 1997, 62, 6666-6671
P r ep a r a tion of Con d en sed Ar om a tics by Su p er a cid ic Deh yd r a tive
Cycliza tion of Ar yl P in a cols a n d Ep oxid es1a
Douglas A. Klumpp,*,# Donald N. Baek,1b,† G. K. Surya Prakash,† and George A. Olah*,†
Department of Chemistry, California State Polytechnic University, Pomona, California, 91768, and
Loker Hydrocarbon Research Institute, University of Southern California, University Park,
Los Angeles, California 90089-1661
Received February 14, 1997 (Revised Manuscript Received J uly 18, 1997X)
Aryl pinacols and epoxides, respectively, are cleanly and in high yield converted via superacidic
dehydrative cyclization to the corresponding condensed aromatics. Dehydrative cyclization of
benzopinacol (1a ), triphenylacetophenone (2), and tetraphenylethylene oxide (9) give 9,10-
diphenylphenanthrene (3a ) as the major product in acidic media stronger than Ho ) -11. Aryl
pinacol 12a forms the condensed aromatic 13a as the major product in acidic media stronger than
Ho ) -13.5. It is proposed that the dehydrative cyclizations to provide aromatics 3a and 13a occurs
through dicationic intermediates. Substituted benzopinacols 1f, 1g, and 1j are prepared and give
the corresponding phenanthrenes (3f, 3g, and 3j) in high yields. The regiochemistry of the
cyclization of substituted benzopinacols is controlled by deactivating substituents on the aryl rings.
Aryl pinacols (12a -d ) derived from acenaphthenequinone and pinacol 15 also give condensed
aromatics (13a -d and 16, repectively) with superacidic triflic acid.
In tr od u ction
When pinacols are reacted with acids, dehydration and
rearrangement products arise.2 This well-known reaction
is generally refered to as the pinacol rearrangement. The
pinacol rearrangement can be promoted by both Bronsted
and Lewis acids, and the reaction is general to many
types pinacols or 1,2-diols.3a When benzopinacol (1a ) is
reacted with acids of moderate strength, the pinacol
rearrangement leads to 2,2,2-triphenylacetophenone (2)
in high yield.3b It is also well-known that appropriate
epoxides with acids undergo similar ring-opening rear-
rangement to products such as 2.3c,d,f Recently, we found
that benzopinacol (1a ) and substituted benzopinacols
(1b,c,d ,h ,i) react in triflic acid (TfOH) to yield 9,10-
diphenylphenanthrene (3a ) and substituted 9,10-dia-
rylphenanthrenes in excellent yield.4,5 We now report
studies on the general dehydrative condensation of aryl
pinacols and related epoxides to condensed aromatics in
superacids and their mechanism which involves super-
electrophilic, dicationic intermediates.
or two molecules of water, respectively. With superacidic
TfOH (Ho ) -14.1),6b 2 itself gives 3a . Since weaker acid
systems convert 1a to 2, the question arises as to the
level of acidity that is required for the conversion of 2 to
3a . A series of reactions was carried out using the TfOH/
CF3CO2H system6a of increasing acidity in order to
establish the threshold level of acid strength needed for
conversion of 2 to 3a . These results are presented in
Table 1. In the different acid systems, only 3a was
formed from 2 when the acid strength exceeded about
Ho ) -11.6b Benzopinacol (1a ) was also reacted in the
TfOH/CF3CO2H acid systems to verify that the results
for 2 were similar to those of 1a . As shown in Table 1,
product 3a is formed exclusively in acid systems with
strengths greater than Ho ) -12 (i.e., with superacids).
Shudo and co-workers recently reported that a phenyl
ketone similar to 2 is fully protonated in acidic medium
stronger than Ho ) -9.7a In more strongly acidic media,
there is the possibility for further protonation of the
Resu lts a n d Discu ssion
Depending on the strength of the acid catalyst, ben-
zopinacol (1a ) gives either 2 or 3a by elimination of one
#
California State Polytechnic University.
† University of Southern California.
X Abstract published in Advance ACS Abstracts, September 1, 1997.
(1) (a) Chemistry in Superacids. 23. For part 22, see: Olah, G. A.;
Rasul, G. J . Am. Chem. Soc. 1996, 118, 8503. (b) Undergraduate
research participant.
(2) (a) Rickborn, B. In Comprehensive Organic Synthesis; Trost, B.
M., Ed.; Pergamon: Oxford, 1991; Vol. 3, p 721. (b) March, J . Advanced
Organic Chemistry, 4th ed.; Wiley: New York, 1992; p 1072. (c) Collins,
C. J . Q. Rev. 1960, 14, 357.
(3) (a) Bartok, M.; Molnar, A. In The Chemistry of Functional
Groups; Patai, S., Ed.; Wiley: New York, 1980; Suppl. E; p 721. (b)
Bachmann, W. E. Organic Syntheses; Blatt, A. H., Ed.; Wiley: New
York, 1943; Collect. Vol. 2, p 73. (c) Pocker, Y.; Ronald, B. P. J . Org.
Chem. 1970, 35, 3362. (d) Gebhart, H. J ., J r.; Adams, K. H. J . Am.
Chem Soc. 1954, 76 , 3925. (e) Hill, G. A.; Flosdorf, E. W. Organic
Syntheses, Gilman, H., Ed.; Wiley: New York, 1941; Collect. Vol. 1,
2nd ed.; p 462. (f) Pocket, Y.; Ronald, B. P. J . Am. Chem Soc. 1970,
92, 3385.
(4) Olah, G. A.; Klumpp, D. A.; Neyer, G.; Wang, Q. Synthesis 1996,
321. For a review of triflic acid chemistry, see: Stang, P. J .; White, M.
R. Aldrichimica Acta 1983, 16, 15.
(5) Olah, G. A.; Klumpp, D. A. Abstract of Papers, 211st National
Meeting of the American Chemical Society, Chicago, IL, August 1995;
American Chemical Society: Washington, DC, 1995; Abstract ORGN
17.
(6) (a) Saito, S.; Saito, S.-i.; Ohwada, T.; Shudo, K. Chem. Pharm.
Bull. 1991, 39, 2718. (b) For a general discussion of superacids, see:
Olah, G. A.; Prakash, G. K. S.; Sommer, J . Superacids; Wiley: New
York, 1985.
(7) (a) Saito, S.; Sato, Y.; Ohwada, T.; Shudo, K. J . Am. Chem. Soc.
1994, 116, 2312. (b) Shudo, K.; Ohwada, T. In Stable Carbocation
Chemistry; Prakash, G. K. S., Schleyer, P. v. R., Eds.; Wiley: New York,
1997; pp 540-541.
(8) (a) Olah, G. A. Angew. Chem., Int. Ed. Engl. 1993, 32, 767. (b)
Ohwada, T.; Yagamata, N.; Shudo, K. J . Am. Chem. Soc. 1991, 113,
1364. (c) Yamazaki, T.; Saito, S.-i.; Ohwada, T.; Shudo, K. Tetrahedron
Lett. 1995, 36, 5749. (d) Olah, G. A.; Ramaiah, P.; Wang, Q.; Prakash,
G. K. S. J . Org. Chem. 1993, 58, 6900. (e) Hartz, N.; Rasul, G.; Olah,
G. A. J . Am. Chem. Soc. 1993, 155, 1277. (f) Olah, G. A.; Rasul, G.;
Aniszfeld, R.; Prakash, G. K. S. J . Am Chem. Soc. 1992, 114, 5608. (g)
Berkessel, A.; Thauer, R. K. Angew. Chem., Int. Ed. Engl. 1995, 34,
2247.
S0022-3263(97)00293-4 CCC: $14.00 © 1997 American Chemical Society

Preparation of Condensed Aromatics
J . Org. Chem., Vol. 62, No. 19, 1997 6667
Ta ble 1. Resu lts of th e CF 3SO3H:CF 3CO2H-Ca ta lyzed
Rea ction of 1a , 2, a n d 9a
a cation, donor-acceptor complex (8) which however itself
possesses significant dicationic nature.
starting
material
TfOH/CF3CO2H %
w/w
products
2:3a
6
Ho
2
2
2
2
-14.1
-12.5
-11.5
-10.6
-2.7
-14.1
-12.5
-11.5
-10.6
-2.7
-14.1
-12.5
-11.5
-10.6
-2.7
100% TfOH
72.8
43.5
0:100
0:100
30:70
100:0
100:0
0:100
0:100
29:71
40:60
100:0
0:100
8:91
22.1
2
100% CF3CO2H
100% TfOH
72.8
43.5
22.1
100% CF3CO2H
100% TfOH
72.8
43.5
22.1
1a
1a
1a
1a
1a
9
9
9
9
9
Like benzopinacol, tetraphenylethylene oxide (9) also
gives 3a in good yield when reacted with TfOH. The
conversion of 9 to form 3a can be rationalized by the
protonation of the epoxide oxygen, followed by ring
opening, and subsequent protonation of the oxygen to
give the dicationic intermediate 5. When 9 was reacted
in the TfOH/CF3CO2H acid systems of varying strength
(Table 1), product 3a was formed exclusively only in
superacidic media of Ho < -12.5. In less acidic media,
the ketone 2 was formed in greater amounts. These
observations are consistant with the formation of a
dicationic intermediate, such as 5, and are in accord with
the results of reactions from 1a and 2.
42:58
95:5
100:0
100% CF3CO2H
a
Product ratio determined by 1H NMR integration; Reaction
conditions: 50 mg starting material, 0.5 mL C6H6 and 0.5 mL acid
(24 h at 25 °C).
Sch em e 1. P r op osed Mech a n ism for th e
F or m a tion of 3a fr om 1a
The results from 9, 1a , and 2 indicate that highly acidic
media are necessary to form 3a as the exclusive product.
Since lower levels of acidity involve the intermediacy of
monocations, the results indicate that the highly acidic
media allow the formation of dicationic intermediates
which results in the dehydrative cyclization giving 3a .
While superelectrophilic activation is recognized for
intermolecular reactions, few examples have been re-
ported of intramolecular conversions involving dicationic,
superelectrophiles. Shudo and co-workers described the
cyclodehydration of 1,3-diaryl-1-propanones in superacid
to provide substituted indenes.7a In these studies, the
yields of indene products and cyclization rates increased
dramatically in acid systems stronger than Ho ) -10,
suggesting dicationic intermediates. In another study,
Shudo found evidence for superelectrophilic activation in
the intramolecular reaction of a nitrile with a phenyl
group.7b The earlier work by Shudo and the present
results indicate that superelectrophilic activation may be
synthetically useful for intramolecular cyclizations lead-
ing to condensed products.
Wishing to explore the synthetic scope of the pinacol
conversion in superacids, we prepared a series of aryl
pinacols from substituted benzophenones and reacted
them in TfOH. The results from these studies are
presented in Table 2. In most cases, the aryl pinacols
gave the condensed arenes in excellent yield. The
substituted benzopinacols 1b to 1d yielded the corre-
sponding phenanthrenes 3b to 3d sometimes in quanti-
tative yield when reacted in TfOH. When the aryl
pinacols are substituted on just two of the aryl rings,
carbonyl group. Protosolvolytic activation of onium ions
has been studied extensively by Olah, Shudo, and others.8
Protosolvated intermediates may behave as highly reac-
tive electrophiles, or superelectrophiles. Since 1a and 2
give 3 only in strongly acidic media (Ho < -11) and
phenyl ketones are known to be fully protonated in less
acidic media, this indicates a protosolvated reactive
intermediate to be involved in the transformation of 1a
to give 3a .
The proposed mechanism for this conversion is shown
in Scheme 1. We suggest that the dication 5 is the
reactive intermediate which leads to cyclization giving 6
followed by dehydration to yield 3a . It also could be that
the dicationic intermediate 4 induces a retropinacol
rearrangement to give 5. There is reported evidence for
epoxide intermediates in pinacol rearrangements,3d,f and
these intermediates may also participate in the formation
of 3a . Alternatively, 5 may dehydrate to provide tet-
raphenylethylene dication (7), which is known to form
3a .9 It was reported that 1,2-dichlorotetraphenylethane
gives 3a when reacted with an excess of AlCl3.10 This
conversion may proceed through dication 7, or through
nism may also explain the observed regioselectivity in the formation
of products 3f-j. A dication such as 7 would tend to delocalize positive
charge into the more electron rich rings, which would then cyclize and
lead to products 3f-j.
(10) (a) Schmidlin, J .; Escher, R. Chem. Ber. 1910, 43, 1153. (b)
Schoepfle, C. S.; Ryan, J . D. J . Am. Chem. Soc. 1932, 54, 3687.
(9) (a) Olah, G. A.; Grant, J . L.; Spear, R. J .; Bollinger, J . M.; Serianz,
A.; Sipor, G. J . Am. Chem. Soc. 1976, 98 , 2501. (b) As suggested by a
referee, the cyclization of 7 may be thought of as an electrocyclization
reaction followed by the loss of two protons. This cyclization mecha-

6668 J . Org. Chem., Vol. 62, No. 19, 1997
Klumpp et al.
groups are deactivated relative to the alkylphenyl groups
in 1j, and thus the regiocontrol is maintained in the
reaction.
there is the possibility of several regioisomers being
formed. Pinacol 1e gives a mixture of isomeric phenan-
threnes, and the overall yield of products is high. NMR
evidence suggests the formation of at least three isomers.
This indicates cyclization to form the phenanthrenes
proceeding through both the phenyl and fluorophenyl
rings. However, when the two aryl rings are substituted
by a pair of fluorine atoms (1f) phenanthrene 3f is formed
regioselectively (Table 2). Similarly when the aryl rings
are substituted by more strongly deactivating groups,
such as chloro and bromo substituents in pinacols 1h and
1i, phenanthrenes 3h and 3i are formed regioselectively
and in high yields. These data suggest that the cycliza-
tion to the phenanthrenes is occurring more rapidly
through the unsubstituted phenyl rings than through the
substituted deactivated ones. This is consistant with the
fact that chloro and bromo substituents are stronger
deactivating groups than a fluoro substituent and that
deactivating groups retard the rate of electrophilic reac-
tions with aryl rings.11 In the case of 1e and 1f, one
fluorine (1e) does not allow for regioselective product
formation, but two fluorines (1f) deactivate the substi-
tuted rings sufficiently to provide good regioselectivity.
Some pinacols have also been prepared by the reaction
of aryl Grignard and lithium reagents with acenaph-
thenequinone and these derivatives (12a -d ) gave con-
densed aromatic products 13a -d (Table 3). Pinacol 15
could be prepared in good yield from 2-methylnaphtha-
lene,25 and 15 provides aromatic 16 with TfOH. Like
benzopinacol (1a ), 12a undergoes dehydrative cyclization
leading to a condensed aromatic product. When 12a was
reacted in acid systems of varying strength, 13a was only
formed in superacidic media, Ho < -12 (Table 4). If an
analogy is made with the related studies with 1a , the
data with 12a suggest a dicationic intermediate such as
17 leading to a cyclization to eventually form product
13a . Aryl pinacols 12a -d and 15 provided the expected
aromatic products 13a -d and 16, respectively; however,
the yields of these product were somewhat lower than
those from benzopinacols 1a -i. Products 13a -d and 16
were sometimes accompanied by the formation of varying
amounts of insoluble polymer and other byproducts.
Nevertheless, the results in Table 3 demonstrate that the
dehydrative cyclization of aryl pinacols in superacid is a
useful route to structurally diverse aromatic products.
It was also found that epoxide 10 gave 3h in quantita-
tive yield. Consequently epoxides with deactivating
substituent groups may also allow regioselective product
formation of substituted phenanthrenes.
As a further demonstration of regiocontrol in the
pinacol cyclization, pinacol 1j was found to give the nonyl-
substituted phenanthrene 3j as a single regioisomer in
high yield (Table 2). Pinacol 1j was prepared by the
acylation of 1-phenylnonane, followed by the photolysis
of the aryl ketone. 1j was produced as the meso-dl
diastereomeric pair, and the mixture of stereoisomers
gave the single product 3j with TfOH. The bromophenyl
When pinacol 18 was reacted with TfOH, the expected
dehydrative cyclization product was not formed and 19
and 20 were obtained. 19 is the product from the pinacol
rearrangement, and it is produced in greater than 80%
yield with reaction times of 2 h or less. However, with
longer reaction times, 20 is the major product and is
(11) (a) Gore, P. H. In Freidel-Crafts and Related Reactions; Olah.
G. A., Ed.; Interscience: New York, 1964; Vol. 3, Chapter 31. (b) Taylor,
R. Electrophilic Aromatic Substitution; Wiley: New York, 1990;
Chapter 2.

Preparation of Condensed Aromatics
J . Org. Chem., Vol. 62, No. 19, 1997 6669
Ta ble 2. Tr iflic Acid Ca ta lyzed Rea ction of Ar yl P in a cols 1a -j
obtained in greater than 90% yield. If 19 is isolated and
reacted with TfOH, 20 is formed. The identity of 20 was
unambigously verified by its X-ray crystal structure12 as
Con clu sion s
1
well as its H, 13C, and HETCOR NMR spectra. Although
It was shown that aryl pinacols 1a -d and 1f-j yield
in superacidic TfOH substituted phenanthrenes 3a -d
and 3f-j, repectively, in excellent yield. Aryl epoxides
9 and 10 also give substituted phenanthrenes (3a and
3h ) under similar conditions. The regiochemistry of
products obtained can be controlled by deactivating
groups on the aryl rings. The results suggest that
dicationic intermediates are involved, inducing a cycliza-
tion leading to products. Experiments showed that the
reaction medium must be of acid strength greater than
Ho ) -12, i.e., superacidic, for effective conversion to the
phenanthrene 3a from 1a , 2, or 9. Aryl pinacols 12a -d
and 15 also gave condensed aromatics 13a -d and 16,
respectively, in fair to good yields. The acid system must
be again more acidic than Ho ) -12 for the conversion
12a to 13a , suggesting the necessity of dicationic inter-
mediates leading to 13a . The described reactions of aryl
pinacols in superacidic TfOH are an effective synthetic
method to condensed aromatics.
it is not exactly clear how 20 arises, the ring system is
likely generated by ring expansion involving the proto-
nated carbonyl group of 19. The formation of 20 is
similar to the formation of aromatic 22 from 21 in
anhydrous HF.13 In this work, it was suggested that 22
may be formed via a dicationic intermediate followed by
electron transfer reactions to give the final product.
(12) Crystallographic data: colorless prism; crystal size (mm) 0.25
× 0.4 × 0.75; monoclinic; space group P21/n; unit cell dimensions (Å),
a ) 12.172 (2), b ) 7.628, c ) 17.691(2); â ) 97.40 (2)°; volume 1628.9
(5) Å 3; R ) 0.07.
(13) Mitchell, R. H.; Fyles, T.; Ralph, L. M. Can. J . Chem. 1977, 55,
1480.

6670 J . Org. Chem., Vol. 62, No. 19, 1997
Klumpp et al.
Ta ble 3. Tr iflic Acid Ca ta lyzed Rea ction of Ar yl
Ta ble 4. CF 3SO3H:CF 3CO2H-Ca ta lyzed Rea ction of 12a a
P in a cols 12a -d a n d 15
tolysis (typically less than 6 h reaction time), the product was
isolated either by filtration of precipitated product, or by
concentration in vacuo.
1,2-Bis(3,4-d iflu or op h en yl)-1,2-d ip h en yl-1,2-et h a n e-
d iol (1f). Using the general photolysis procedure, 3,4-difluo-
robenzophenone (0.40 g, 1.8 mmol) gave 1f (0.79 g, 100%) as
a viscous oil (mixture of diastereomers).
1,2-Bis(4-b r om op h e n yl)-1,2-b is(4-n on ylp h e n yl)-1,2-
eth a n ed iol (1j). Using the general photolysis procedure, 11
(0.72 g, 1.9 mmol) gave 1j (0.74 g, 100%), which was purifed
by column chromatography (19:1 hexane:Et2O) to give the
mixture of diastereomers as a viscous oil.
Exp er im en ta l Section
9,10-Dip h en ylp h en a n th r en e (3a ). Epoxide 9 (0.325 g,
0.76 mmol) was prepared according to a published procedure17
and was added to 5 mL of TfOH. The mixture was stirred for
8 h at 25 °C, poured over ca. 10 g of ice, and extracted twice
with C6H6. The organic phase was washed with water and
then brine and dried over MgSO4. Concentration in vacuo and
recrystallization from CH2Cl2 gave 3a 18 (0.208 g, 83%).
9,10-Bis(4-ch lor op h en yl)p h en a n th r en e (3h ). Epoxide
10 (0.202 g, 0.49 mmol) was prepared according to a published
procedure19 and dissolved in 2 mL of C6H6. The solution of
10 was added to 5 mL of TfOH. The mixture was stirred for
8 h at 25 °C, poured over ca. 10 g of ice, and extracted twice
with C6H6. The organic phase was washed with water and
then brine and dried over MgSO4. Concentration in vacuo
gave 3h 18 (0.20 g, 100%).
9,10-Bis(3,4-d iflu or op h en yl)p h en a n th r en e (3f).20 To 5
mL of TfOH, 1f (0.35 g, 0.8 mmol) was added. The mixture
was stirred for 8 h at 25 °C, poured over ca. 10 g of ice, and
extracted twice with C6H6. The organic phase was washed
with water and then brine and dried over MgSO4. Concentra-
tion in vacuo and purification by preparative thin layer
chromatography (9:1 hexane:Et2O) gave 3f (0.23 g, 70%) as
pale yellow crystals.
Melting points are uncorrected. Unless otherwise noted, 1H
NMR spectra were recorded at 300 MHz and 13C NMR spectra
were recorded at 75 MHz. High-resolution mass spectra were
recorded at the Southern California Mass Spectrometry Facil-
ity, University of California, Riverside. Elemental analyses
were performed at Galbraith Laboratories, Knoxville, TN.
Solvents were dried according to standard procedures.14
Column chromatography was done with Merck silica gel (grade
9385) according to standard procedures.15 Triflic acid was
obtained from 3M and distilled prior to use. Benzopinacol (1a ),
aryl ketones, acenaphthenequinone, phenylmagnesium bro-
mide, p-tolylmagnesium bromide, and (4-fluorophenyl)mag-
nesiumbromide were obtained from Aldrich and used as
received; 3,4-difluorobenzophenone was purchased from Lan-
caster; and pinacols 1b-j were prepared by photolysis of the
appropriate aryl ketones. Photochemical preparations were
accomplished with a 450 W medium pressure Hg vapor lamp
(Pyrex filter).
Gen er a l P h otolysis P r oced u r e16 for th e P r ep a r a tion
of Ar yl P in a cols 1b-j. The aryl ketone was dissolved (0.1
M) in degassed 2-propanol and the solution placed a Pyrex tube
under an argon or nitrogen atmosphere. Photolysis was done
at room temperature, and product formation was monitored
by thin layer chromatography. Upon completion of the pho-
(17) Zeigler, H. E.; Wo, S. J . Org. Chem. 1995, 60, 5925.
(18) Analytical data found in ref 4.
(19) Sato, R.; Nagaoka, T.; Saito, M. Tetrahedron Lett. 1990, 31,
5749.
(20) Products 3f and 3g exhibited complex NMR spectra at ambient
temperature, suggesting that the aryl rings in the 9,10 positions of
the phenanthrenes possess restricted rotation.
(14) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals, 3rd ed.; Pergamon: New York, 1988.
(15) Still, W. C.; Kahn, M.; Mitra, A. J . Org. Chem. 1978, 43, 2923.
(16) (a) Schonburg, A.; Mustafa, A. Chem. Rev. 1947, 40, 181. (b)
Gilbert, A.; Baggott, J . Essentials of Molecular Photochemistry; CRC
Press: Boca Raton, FL, 1991; p 302.

Preparation of Condensed Aromatics
J . Org. Chem., Vol. 62, No. 19, 1997 6671
9,10-Bis(2-ch lor op h en yl)p h en a n th r en e (3g).20 Using a
similar procedure to that of 3f, 1g21 (0.15 g, 0.34 mmol) gave
3g (0.14 g, 100%) as a white solid.
After standard workup, and column chromatography with
hexanes:ether(19:1), 13a 23 (0.162 g, 72%) was isolated as a
bright yellow crystalline solid.
Acen a p h th ylen o[1,2-i]p icen e (13d ). With stirring under
nitrogen at 25 °C, pinacol 12d 22b (0.31 g, 0.71 mmol) was added
to TfOH (10 mL) and the mixture was stirred for 24 h. After
standard workup, and column chromatography with hexane,
13d (0.110 g, 39%) was isolated as an orange crystalline
solid: 306-310 °C; 1H NMR (CDCl3) δ 9.47 (2H, d, J ) 7.5
Hz), 8.66 (2H, d, J ) 7.2 Hz), 8.57 (2H, d, J ) 8.4 Hz), 7.96
(2H, d, J ) 7.5 Hz), 7.91 (2H, d, J ) 8.7 Hz), 7.78 (2H, d, J )
8.1 Hz), 7.62 (4H, m), 7.46 (2H, m); 13C NMR (CDCl3)24 δ 138.3,
133.7, 133.0, 131.5, 129.9, 129.6, 129.4, 129.0, 127.8, 127.7,
127.6, 127.2, 127.1, 127.0, 124.7, 124.2, 121.3; HRMS calcd
for C32H18 402.1408, found 402.1407.
9,10-Bis(4-br om oph en yl)-3,6-din on ylph en an th r en e (3j).
To a mixture of 1j (0.27 g, 0.35 mmol) in 5 mL of C6H6 was
added TfOH (10 mL), and the solution was stirred for 12 h at
25 °C. After workup similar to that of for 3f, and column
chromatography with hexanes, 3j (0.24 g, 86%) was isolated
as a waxy, white solid.
4-Br om o-4′-n on ylben zop h en on e (11). To a mixture of
1-phenylnonane (1.53 mL, 6.4 mmol) and anhydrous AlCl3 (0.9
g, 6.8 mmol) in CH2Cl2 (10 mL) at 0 °C was added a solution
of 4-bromobenzoyl chloride (1.4 g, 6.4 mmol) in CH2Cl2 (10 mL).
The resulting mixture was stirred at 25 °C for 8 h, then poured
over ca. 20 g of ice, extracted into CH2Cl2, and washed with
dilute HCl, H2O, and then brine. After drying over MgSO4
and concentrating in vacuo, the crude product mixture was
purified by column chromatography (19:1 hexane:Et2O). 11
Diben zo[d ,h ]cr ysen e (20). To a solution of 1826 (0.23 g,
0.64 mmol) in C6H6 was added 5 mL of TfOH, and the mixture
was stirred at 25 °C for 15 h. The solution was then poured
over ice and then extracted into C6H6. The organic solution
was then washed with 1 M NaOH, brine, and dried with
MgSO4. After column chromatography with hexanes:ether (4:
1), 2027 (0.20 g, 96%) was isolated as a white solid.27
1
was isolated (1.1 g, 44%) as a white solid: mp 48-51 °C; H
NMR (CDCl3) δ 0.82-0.92 (m, 3H), 1.16-1.38 (m, 14H), 2.70
(t, J ) 8.1 Hz, 2H), 7.28 (d, J ) 8.1 Hz, 2H), 7.58 (d, J ) 8.7
Hz, 2H), 7.65 (d, J ) 8.7 Hz, 2H), 7.70 (d, J ) 8.1 Hz, 2H); 13
C
Ack n ow led gm en t. Support of our work by the
National Science Foundation is gratefully acknowl-
edged. We thank Professor Robert Bau at the Univer-
sity of Southern California for his assistance in obtain-
ing the X-ray crystal structure of compound 20.
NMR (CDCl3) δ 14.0, 22.6, 29.2, 29.4, 29.5, 31.1, 31.5, 31.8,
36.0, 127.1, 128.3, 130.1, 131.3, 131.4, 134.5, 136.6, 148.4,
195.1; HRMS calcd for C22H27OBr 386.1245, found 386.1239
1,2-Dih yd r oxy-1,2-b is(4-flu or op h en yl)a cen a p h t h en e
(12b). To a solution of (4-fluorophenyl)magnesium bromide
(11 mmol) in 25 mL of THF at 0 °C was added acenaphthene-
quinone (0.50 g, 2.7 mmol). The mixture was stirred at 25 °C
for 12 h and then poured into a dilute solution of H2SO4. The
resulting mixture was extracted into ether, and the organic
extracts were washed with NaHCO3, brine, and dried with
MgSO4. After column chromatography with hexanes:ether (4:
1), 12b (0.43 g, 42%) was isolated as a white solid: mp 184-
185 °C; 1H NMR (CDCl3) δ 2.10 (s, 2H), 7.03 (m, 4H), 7.21 (m,
4H), 7.34 (d, J ) 6.9 Hz, 2H), 7.65 (m, 2H), 7.34 (d, J ) 8.1
Hz, 2H); 13C NMR (CDCl3) δ 89.3, 114.7 (d, J C-F ) 21 Hz),
121.7, 125.6, 129.0, 129.7 (d, J C-F ) 8.0 Hz), 131.2, 136.1 (d,
J C-F ) 4.0 Hz), 137.0, 145.2, 162.5 (d, J C-F ) 245 Hz). Anal.
Calcd for C25H16F2O2: C, 76.99; H, 4.31. Found: C, 76.39; H,
4.31.
Su p p or tin g In for m a tion Ava ila ble: Analytical data for
compounds 1f, 1j, 3f, 3g, 3j, 13a , 13b, 13c, 15, and 20. 1H
NMR spectra for all products. Synthetic procedures for 13b,
13c, and 15 (16 pages). This material is contained in libraries
on microfiche, immediately follows this article in the microfilm
version of the journal, and can be ordered from the ACS; see
any current masthead page for ordering information.
J O970293N
(22) (a) Acree, S. F. J . Am. Chem. Soc. 1912, 34, 3687. (b) Moriconi,
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T. J . Am. Chem. Soc. 1959, 81, 6472.
(23) Buchta, E.; Maar, H. Chem. Ber. 1962, 95, 1826.
(24) Due to low solubility of 13d , quarternary 13C signals could not
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(25) (a) Trost, B. M. J . Am. Chem. Soc. 1966, 88, 853. (b) Tatsugi,
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236.
Diben zo[e,g]flu or a n th en e (13a ). With stirring under
nitrogen at 25 °C, pinacol 12a 22a (0.250 g, 0.74 mmol) was
added to TfOH (10 mL) and the mixture was stirred for 12 h.
(27) Dias, J . R. Handbook of Polycyclic Hydrocarbons; Elsevier: New
York, 1987.
(21) Hatt, H. H. J . Chem. Soc. 1929, 1623.