Improved Synthesis of Unsymmetrical, Heteroaromatic 1,2-Diketones and the Synthesis of Carbazole Ring Substituted Tetraaryl Cyclopentadieneones

Full text of DOI:10.1021/jo9904213

6102
J . Org. Chem. 1999, 64, 6102-6105
and light-emitting applications9 due to their superior
Im p r oved Syn th esis of Un sym m etr ica l,
charge-transport properties. In this paper, we report an
improved and convenient preparation of unsymmetrical
1,2-diketones needed to prepare heteroaromatic ring
substituted tetracyclones, such as 1, and the use of 1 as
a diene in a Diels-Alder cycloaddition reaction.
Heter oa r om a tic 1,2-Dik eton es a n d th e
Syn th esis of Ca r ba zole Rin g Su bstitu ted
Tetr a a r yl Cyclop en ta d ien eon es
Christopher J . Walsh† and Braja K. Mandal*
Tetracyclones are usually prepared by condensation of
a 1,2-diketone with a 1,3-diaryl acetone derivative. As
seen in Scheme 1, a convenient synthesis of 1 relies on
an efficient preparation of the unsymmetrical 1,2-dike-
tone 5. Unsymmetrical 1,2-diketones have been prepared
in high yield by the controlled oxidation of alkynes by a
variety of reagents.10 While permanganate oxidation11
was most attractive, due to the availabilty of the starting
materials and ease of workup, it had not been used on
alkynes substituted with heterocyclic moieties such as
pyridine or thiophene.12 We were pleased to find that
when alkyne 4, prepared by Pd-catalyzed coupling13 of
9-hexyl-3-iodocarbazole14 with phenylacetylene, was
treated with permanganate in neutral, buffered aqueous
acetone, a 96% yield of the new diketone 1-[3-(9-hexyl)-
carbazoyl]-2-phenylethane-1,2-dione, 5, was obtained.
The success of the permanganate oxidation prompted
us to study the suitability of the reaction with alkynes
substituted by other heteroaromatic moieties, including
pyridine and thiophene. A variety of known heteroaro-
matic ring-substituted unsymmetrical alkynes were pre-
pared in high yields from readily available brominated
heteroaromatics using conditions similar to those for
alkyne 4 (Table 1).13 The alkynes then reacted smoothly
with permanganate in neutral aqueous acetone to give
the 1,2-diketones in good to excellent yields. The electron-
rich carbazole and thiophenes worked well (Table 1,
entries 1-3) and gave high yields of both coupled and
oxidized products. The pyridine derivatives gave slightly
lower yields in the oxidation reaction. When the phenyl
ring was replaced with a strong electron-withdrawing
phthalonitrile ring, no 1,2-diketone was observed (Table
1, entry 6). Therefore, this method appears unsuitable
for strong electron-withdrawing aromatic or heteroaro-
matic substituted alkynes. We believe that this two-step
(alkyne coupling and controlled oxidation) methodology
to prepare heteroaromatic ring-substituted unsymmetri-
cal 1,2-diketones offers distinct advantages over other
methods previously reported, such as the mixed “benzoin-
type” condensation followed by oxidation,6a,d the SeO2
oxidation of benzylic ketones or internal alkynes,15 reac-
tion of organometallic reagents with 1,4-dialkylpipera-
zine-2,3-diones,16 and the reaction of acyl anion equiva-
Department of Biological, Chemical, and Physical Sciences,
Illinois Institute of Technology, 3255 South Dearborn,
Chicago, Illinois 60616
Received March 9, 1999
Substituted cyclopentadieneones have received much
interest lately, functioning as important building blocks
in several new syntheses of polyaromatic materials.1 For
instance, tetraarylcyclopentadieneones (tetracyclones)
have been employed extensively in the preparation of
large graphite disks.2 Diarylcyclopentadieneones have
been used to prepare soluble, blue light-emitting PPV-
type polymers3 and in the synthesis of corranulene,4 a
C60 buckyball fragment. In our laboratory, alkoxy deriva-
tives of tetracyclone have been utilized to make soluble
polyphenylated phthalocyanines for nonlinear optical
(NLO) applications.5 Since these polyaromatic materials
exhibit useful properties, we wished to extend our studies
to tetracyclone systems incorporating heteroaromatic ring
moieties, especially those containing a carbazole ring,
such as tetracyclone 1.6 Materials containing carbazole
moieties are attractive for xerographic,7 photorefractive,8
† Kilpatrick Pre-Doctoral Fellow, IIT, 1998-1999.
(1) See, for example: (a) Morgenroth, F.; Berresheim, A. J .; Wagner
M.; Mu¨llen, K. J . Chem. Soc., Chem. Commun. 1998, 1139. (b) Ku¨bel,
C.; Chen, S. L.; Mu¨llen, K. Macromolecules 1998, 31, 6014. (c) Haag,
R.; Ohlhorst, B.; Noltenmeyer, M.; Fleischer, R.; Stalke, D.; Schuster,
A.; Kuck, D.; de Meijere, A. J . Am. Chem. Soc. 1995, 117, 10474. (d)
Kumar, U.; Neenan, T. X. Macromolecules 1995, 28, 124.
(2) (a) Iyer, V. S.; Yoshimura, K.; Enkelmann, V.; Epsch, R.; Rabe,
J . P.; Mu¨llen, K. Angew. Chem., Int. Ed. Engl. 1998, 37, 2696 and
references therein.
(3) Hsieh, B. R.; Yu, Y.; Forsythe, E. W.; Scaaf, G. M.; Feld, W. A.
J . Am. Chem. Soc. 1998, 120, 231.
(4) 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.
(5) Mandal, B. K.; Walsh, C. J .; Li, X.; McCarron, H.; Sen, R.; Begum,
N.; Behroozi, S. J .; Castro, C. In Macromolecules New Frontiers;
Srinivasan, K. S. V., Ed.; Allied Publishers: New Delhi, 1998; Vol. 1,
p 289.
(6) Heteroaromatic derivatives of tetracyclone have been reported.
For pyridine derivatives, see: (a) Newkome, G. R.; Islam, N. B.;
Robinson, J . M. J . Org. Chem. 1975, 40, 3514. For thiophene, furan,
and pyrrole derivatives, see: (b) Kawase, T.; Ohsawa, T.; Enomoto,
T.; Oda, M. Chem. Lett. 1994, 1333. (c) Yamashita, Y.; Masumura, M.
Heterocycles 1980, 14, 29. (d) Bergmann, P.; Paul, H. Chem. Ber. 1967,
100, 828.
(9) (a) Romero, D. B.; Nuesch, F.; Benazzi, T.; Ades, D.; Siove, A.;
Zuppirol, L. Adv. Mater. 1997, 9, 1158. (b) Shim, H. K.; Kim, H. J .;
Ahn, T.; Kang, I. N.; Zyung, T. Y. Synth. Met. 1997, 91, 289.
(10) For a general review, see: Haines, A. H. In Methods for the
Oxidation of Organic Compounds; Academic Press: London, 1985; p
153.
(11) Srinivasan, N. S.; Lee, D. G. J . Org. Chem. 1979, 44, 1574.
(12) For an example with furan, see: Holland, S.; Epsztein, R. Bull.
Chim. Soc. Fr. 1971, 1694.
(13) Alami, M.; Ferri, F.; Linstrumelle, G. Tetrahedron Lett. 1993,
34, 6403.
(14) Beginn, C.; Grazulevicius, J . V.; Strohriegl, P.; Simmerer, J .;
Haarer, D. Makromol. Chem. Phys. 1994, 195, 2353.
(15) (a) Pfu¨ller, O. C.; Sauer, J . Tetrahedron Lett. 1998, 39, 8821.
(b) Rabjohn, N. Org. React. 1976, 24, 261.
(7) Yang, M. J .; Xu, J . L.; Hu, Q. M. J . Photochem. Photobiol. A 1995,
85, 147.
(8) (a) Marder, S. R.; Kippelen, B.; J en, A. K.-Y.; Peyghambarian,
N. Nature 1997, 388, 845. (b) Zhang, Y. D.; Wada, T.; Wang, L. N.;
Aoyama, T.; Sasabe, H. J . Chem. Soc., Chem. Commun. 1996, 2325.
(16) Mueller-Westerhoff, V. T.; Zhou, M. J . Org. Chem. 1994, 59,
4988.
10.1021/jo9904213 CCC: $18.00 © 1999 American Chemical Society
Published on Web 07/14/1999

Notes
J . Org. Chem., Vol. 64, No. 16, 1999 6103
Sch em e 1
F igu r e 1. Cyclic voltammogram of 1: 5 × 10-3 M in
acetonitrile containing 0.1 M tetrabutylammonium tetrafluo-
roborate; room temperature; scan rate 100 mV/s; glassy carbon
working electrode; platinum wire counter electrode.
Ta ble 1. Yield s for th e Syn th esis of Cou p led Alk yn es
a n d 1,2-Dik eton es
a
Yield of coupling between bromo-aromatic and phenylacety-
lene. 3-Iodo-9-hexylcarbazole was used. c Yield of coupling be-
tween 4-iodophthalonitrile and 2-ethynylpyridine. No 1,2-dike-
b
F igu r e 2. Electronic absorption spectra of 1 (solid line) and
d
tetracyclone (dashed line) in CH2Cl2.
tone was observed.
potentials of 1 occur at -1.25 and -1.80 V, compared
with -1.15 and -1.75 V for unsubstituted tetracylone.
The onset of several irreversible oxidations of 1 occurs
at 0.80 V compared with 1.2 V for unsubstituted tetra-
cylone under identical conditions (given in the caption
of Figure 1). The electronic absorption spectra of 1 and
unsubstituted tetracyclone are shown in Figure 2. Tet-
racyclone exhibits two characteristic absorptions at 508
and 336 nm with substitution in the 2,5 positions
affecting the 508 nm absorbance and substitution in the
3,4 positions affecting the 336 nm absorbance.19 Com-
lents with acyl chlorides.17 All of these methods have
limitations when applied to pyridine or thiophene, such
as low yields, the use of harsh conditions,15 or sym-
metrical byproducts.16 The 1,2-diketone 5 was then
condensed with 1,3-diphenylacetone in triethylene glycol
using benzyltrimethylammonium hydroxide as catalyst
to produce the heteroaromatic ring substituted tetracy-
clone 1 (Scheme 1) in 73% yield.
Cyclic voltammetry and electronic absorption spectros-
copy have been used to study substitutent effects in
cyclopentadieneones.6b,18 The cyclic voltammogram of 1
is shown in Figure 1. Two pseudoreversible reduction
(18) Fox, M. A.; Campbell, K.; Maier, G.; Franz, L. J . Org. Chem.
1983, 48, 1762.
(17) (a) Olah, G. A.; Wu, A. J . Org. Chem. 1991, 56, 902. (b) van
Leusen, D.; van Leusen, A. M. Tetrahedron Lett. 1977, 48, 4233.
(19) Ogliaruso, M. A.; Romanelli, M. G.; Becker, E. I. Chem. Rev.
1965, 65, 261.

6104 J . Org. Chem., Vol. 64, No. 16, 1999
Notes
hexane afforded 18.5 g (90%) of 3 as an off-white solid, mp 58-
60 °C (lit.13 mp 38 °C).
Sch em e 2
1-[3-(9-Hexyl)ca r ba zoyl]-2-p h en yleth yn e (4). In an oven-
dried, 100 mL flask held under argon pressure was placed 3.000
g (7.95 mmol) of 3, 25 mL of dry diisopropylamine, 15 mL of dry
toluene, and 0.2758 g (3 mol %) of Pd(PPh3)4. The reaction
mixture was heated to 60 °C, and 0.8118 g (7.95 mmol) of
phenylacetylene and 0.0303 g (2 mol %) of CuI were added. The
reaction was stirred under argon at 60 °C for 12 h. The flask
was allowed to cool to room temperature, and 25 mL of diethyl
ether was added. The mixture was washed with 10% HCl, water,
and saturated aqueous NaCl and dried over Na2SO4. The solvent
was evaporated, and the residue was chromatographed over
silica gel using 20% ethyl acetate in hexane. The combined pure
fractions yielded upon removal of the solvent 2.73 g (98%) of a
yellow solid that was recrystallized from hexane and gave 4 as
yellow needles: mp 82-83 °C; 1H NMR (CDCl3, 300 MHz) δ 8.33
(s, 1H), 8.12 (d, J ) 7.5 Hz, 1H), 7.68-7.25 (m, 10H), 4.32 (t, J
) 6.3 Hz, 2H), 1.95-1.82 (m, 2H), 1.48-1.25 (m, 6H), 0.89 (t, J
) 5.2 Hz, 3H); 13C NMR (CDCl3, 300 MHz) δ 140.7, 140.0, 131.4,
129.2, 128.3, 127.7, 126.0, 123.9, 122.8, 122.4, 120.5, 119.3, 113.0,
108.9, 108.7, 90.9, 87.5, 43.1, 31.5, 28.9, 26.9, 22.5, 14.0; FTIR
(neat, cm-1) 2212; HRMS (EI, m/e) calcd for C26H25N 351.1987
(M+), found 351.1998. Anal. Calcd for C26H25N: C, 88.85; H, 7.17;
N, 3.98. Found: C, 89.11; H, 7.15; N, 3.84.
1-[3-(9-H exyl)ca r b a zoyl]-2-p h en ylet h a n e-1,2-d ion e (5).
The method of Srinivasan11 was followed. The crude solid was
chromatographed over silica with 10% ethyl acetate in hexane
as eluent. The combined pure fractions yielded upon removal of
the solvent 2.11 g (96%) of a yellow solid that was recrystal-
lized from a 3:1 ether-hexane solution and gave 5 as yellow
needles: mp 93-94 °C; 1H NMR (CDCl3, 300 MHz) δ 8.73 (s,
1H), 8.18-8.04 (m, 3H), 7.70-7.64 (m, 1H), 7.58-7.44 (m, 5H),
7.35-7.26 (m, 2H), 4.35 (t, J ) 8.2 Hz, 2H), 1.98-1.82 (m, 2H),
1.49-1.2 (m, 6H), 0.88 (m, 3H); 13C NMR (CDCl3, 300 MHz) δ
195.5, 194.2, 144.2, 141.3, 134.6, 133.5, 130.0, 128.9, 127.5, 126.8,
123.9, 122.9, 120.9, 120.5, 109.4, 108.9, 43.4, 31.5, 28.8, 26.8,
22.5, 13.9; FTIR (neat, cm-1) 1675, 1656; HRMS (EI, m/e) calcd
for C26H25NO2 (M+) 383.1885, found 383.1898. Anal. Calcd for
pound 1 shows a bathochromic shift with respect to
tetracyclone (336 nm to 411 nm), similar to the N,N-
dimethylaminobenzene-substituted tetracyclones.19 These
findings suggest there is extensive electronic interaction
between the electron-rich carbazole ring and the cyclo-
pentadieneone ring and that 1 is an activated diene for
Diels-Alder-type cycloaddition reactions.
To test this conclusion, 1 was reacted with diphenyl-
acetylene in a sealed tube at 215 °C for 8 h to give 1-[3-
(9-hexyl)carbazoyl]-2,3,4,5,6-pentaphenylbenzene, 6, in
70% yield (Scheme 2).
In conclusion, an improved two-step synthesis of
unsymmetrical, heteroaromatic 1,2-diketones is reported.
This procedure was used to synthesize a new class of
carbazole-substituted tetracyclones that can act as dienes
to produce polyaromatic compounds containing the car-
bazole moiety. Future work will include the synthesis of
tetracyclones multisubstituted with carbazole and their
use as dienes to produce polyaromatic macromolecules
of interest in NLO and light-emitting applications.
C
26H25NO2: C, 81.43; H, 6.57; N, 3.65. Found: C, 81.49; H, 6.29;
N, 3.52.
3-[3-(9-Hexyl)ca r ba zoyl]-2,4,5-tr ip h en ylcyclop en ta -2,5-
d ien -1-on e (1). In a 5 mL reaction vessel were placed 0.3546 g
(0.926 mmol) of 5, 0.1948 g (0.926 mmol) of 1,3-diphenylacetone,
and 1.5 mL of triethylene glycol. The mixture was heated to 100
°C, and 0.142 mL of a 40 wt % solution in MeOH of benzyltri-
methylammonium hydroxide was carefully added in one portion
under the surface of the reaction. The dark brown mixture was
stirred at 100 °C for 10 min and poured into ice-water. The
mixture was extracted with methylene chloride. The combined
extracts were washed with saturated aqueous NaCl and dried
over Na2SO4. Removal of the solvent gave a brown oil that was
chromatographed over silica gel with 1:1 methylene chloride-
hexane as eluent. The pure fractions yielded 0.3760 g (73%) of
a brown solid that was recrystallized from acetonitrile and gave
1 as brown needles: mp 176-177 °C; 1H NMR (CDCl3, 300 MHz)
δ 7.73 (d, J ) 6.9 Hz, 1H), 7.55 (s, 1H), 7.47-6.96 (m, 20H),
4.23 (t, J ) 8.0 Hz, 2H), 1.93-1.78 (m, 2H) 1.45-1.22 (m, 6H),
0.88 (t, J ) 5.5 Hz, 3H); 13C NMR (CDCl3, 300 MHz) δ 200.5,
155.7, 154.4, 140.5, 133.5, 131.4, 130.9, 130.2, 129.5, 128.3, 127.9,
127.6, 127.3, 127.0, 125.9, 124.0, 123.1, 122.7, 122.0, 120.2, 119.2,
Exp er im en ta l Section
Gen er a l Meth od s. All melting points recorded are uncor-
rected. Carbazole, brominated pyridines and thiophenes, phen-
ylacetylene, CuI, 1,3-diphenylacetone, benzyltrimethylammo-
nium hydroxide, and potassium permanganate were purchased
20
from Aldrich Chemical Co. and used as received. Pd(PPh3)4
and 3-iodocarbazole14 were synthesized according to published
procedures. Toluene, dimethyl sulfoxide, diisopropylamine, and
acetonitrile were distilled from CaH2, under an argon atmo-
sphere, prior to use and stored over 4 Å molecular sieves.
Reagent-grade acetone was used as received from Fisher Chemi-
cal Co.
Electrochemical experiments were performed in a standard,
single compartment three-electrode assembly using Ag/AgNO3
in acetonitrile (0.1 M) as reference couple.
9-Hexyl-3-iod oca r ba zole (3). This procedure is a modifica-
tion of the procedure given by Turner.21 In a 500 mL flask
immersed in a water bath and fitted with mechanical stirrer
was added 100 mL of dimethyl sulfoxide followed by 18 g (0.302
mol) of finely powdered potassium hydroxide. To the rapidly
stirred suspension was added dropwise a solution of 16 g (0.0546
mol) of 3-iodocarbazole in 25 mL of dimethyl sulfoxide. The color
of the solution became dark brown during addition. The mixture
was stirred at room temperature for 30 min, and 9.915 g (0.060
mol) of 1-bromohexane was added dropwise. The reaction was
stirred for an additional 1 h and poured over ice-water. The
solid precipitate was collected by filtration and washed thor-
oughly with water. Occasionally, the precipitate would not form,
and the liquids were removed in vacuo. Recrystallization from
108.8, 108.1, 43.2, 31.5, 28.9, 26.9, 22.5, 13.9. FTIR (neat, cm-1
)
1703; HRMS (EI, m/e) calcd for C41H35NO (M+) 557.2719, found
557.2741. Anal. Calcd for C41H35NO: C, 88.30; H, 6.32; N, 2.51.
Found: C, 87.94; H, 6.22; N, 2.41.
1-[3-(9-Hexyl)ca r b a zoyl]-2,3,4,5,6-p en t a p h en ylb en zen e
(6). To a 10 mL glass ampule was added 0.1000 g (0.179 mmol)
of 1, 0.0319 g (0.179 mmol) of diphenylacetylene, and 3 drops of
cyclohexylbenzene. The glass ampule was deoxygenated by three
freeze-pump-thaw cycles and evacuated to 0.01 mmHg. The
ampule was sealed under vacuum by way of a torch and heated
to 215 °C for 8 h. The ampule was allowed to cool to room
temperature and carefully opened (caution: contents may be
under pressure), and the solids were dissolved in CHCl3 and
chromatographed over silica gel using 30% CHCl3 in hexane as
eluent. The pure fractions yielded upon removal of the solvent
0.0887 g (70%) of an off-white solid that was recrystallized from
(20) Coulson, D. Inorg. Synth. 1972, 13, 121.
(21) Turner, S. R.; Pai, D. M. Macromolecules 1979, 12, 1.

Notes
J . Org. Chem., Vol. 64, No. 16, 1999 6105
methylcyclohexane and gave 6 as a white powder: mp 245-
707.3551. Anal. Calcd for C54H45N: C, 91.61; H, 6.41; N, 1.98.
Found: C, 91.47; H, 6.29; N, 1.88.
1
246 °C; H NMR (CDCl3, 300 MHz) δ 7.78 (d, J ) 7.5 Hz, 1H),
7.57-7.53 (m, 1H), 7.39-7.29 (m, 1H), 7.12-7.06 (m, 1H), 7.05-
6.65 (m, 28H), 4.10 (t, J ) 7.0 Hz, 2H), 1.81-1.65 (m, 2H), 1.35-
1.17 (m, 6H), 0.9-0.78 (m, 3H); 13C NMR (CDCl3, 300 MHz) δ
140.8, 140.2, 138.4, 131.4, 129.4, 126.5, 125.0, 123.5, 123.0, 121.4,
119.9, 118.2, 108.4, 106.7, 42.8, 31.5, 28.7, 26.7, 22.5, 13.9;
HRMS (FAB, m/z) calcd for C54H45N (M+) 707.3552, found
Ack n ow led gm en t. This work is supported in part
by the U.S. Army Research Office under Grant No.
DAAH04-96-I-0130 and by the IIT-ERIF grant.
J O9904213