Phenacenes: A Family of Graphite Ribbons
J. Am. Chem. Soc., Vol. 119, No. 9, 1997 2123
residue was washed with diethyl ether, and the combined organic
solution was filtered through Celite and evaporated to give 1.93 g (67%)
of 2-bromo-4-n-pentylbenzaldehyde as a pale green liquid that was
chromatographed on silica gel with 5% ethyl acetate in hexanes as
eluent to give a pale yellow liquid: 1H NMR δ 10.31 (s, 1 H; CHO),
7.83 (d, J ) 7.9 Hz, 1 H; H-6), 7.47 (d, J ) 1.1 Hz, 1 H; H-3), 7.24
(br d, J ) 7.9 Hz, 1 H; H-5), 2.64 (t, J ) 8.1 Hz, 2 H), 1.63 (quintet,
J ) 7.5 Hz, 2 H), 1.35-1.31 (m, 4 H), 0.90 (t, J ) 6.8 Hz, 3 H); MS
m/z (relative intensity) 256 (M+, 37), 254 (M+, 37), 91 (100). Anal.
Calcd for C12H15BrO: C, 56.49; H, 5.93. Found: C, 56.69; H, 5.81.
2-Bromo-4-n-pentylbenzyl Chloride. A solution of 4.0 g (15.6
mmol) of 2-bromo-4-n-pentylbenzyl alcohol in 13 mL of benzene was
cooled in an ice bath, and 3.71 g (31.2 mmol) of thionyl chloride was
added dropwise. A drop of pyridine was added, and the reaction
mixture was maintained in the ice bath for 1 h and then heated under
reflux for 2 h before being poured onto water and extracted with diethyl
ether. Aqueous workup followed by chromatography on silica gel with
hexanes as eluent gave 4.15 g (97%) of 2-bromo-4-n-pentylbenzyl
chloride as a pale yellow liquid: 1H NMR δ 7.41 (d, J ) 1.5 Hz, 1 H;
H-3), 7.36 (d, J ) 7.8 Hz, 1 H; H-6), 7.12 (dd, J ) 7.8 Hz, 1.6 Hz, 1
H; H-5), 4.68 (s, 2 H), 2.57 (t, J ) 7.8 Hz, 2 H), 1.59 (quintet, J ) 7.5
Hz, 2 H), 1.35-1.29 (m, 4 H), 0.89 (t, J ) 6.8 Hz, 3 H); MS m/z
(relative intensity) 278 (M+, 5), 276 (M+, 25), 274 (M+, 15), 103 (100).
Anal. Calcd for C12H16BrCl: C, 52.29; H, 5.85. Found: C, 52.09; H,
5.87.
0.93 (t, J ) 6.9 Hz, 6 H); MS m/z (relative intensity) 374 (M+, 100).
Anal. Calcd for C26H30O2: C, 83.38; H, 8.07. Found: C, 83.46; H,
7.86.
2,13-Di-n-pentyl[7]phenacene (2a). The reaction of 10.0 g (52
mmol) of 4-n-pentylbenzoic acid with 2.0 g (53 mmol) of LiAlH4 in
100 mL of anhydrous THF gave 5.4 g (60%) of 4-n-pentylbenzyl
alcohol16 as a pale yellow liquid: 1H NMR δ 7.27 (d, J ) 7.9 Hz, 2 H;
H-2,6), 7.17 (d, J ) 7.7 Hz, 2 H; H-3,5), 4.64 (s, 2 H), 2.59 (t, J ) 7.7
Hz, 2 H), 1.84 (br s, 1 H; OH), 1.60 (quintet, J ) 7.1 Hz, 2 H), 1.34-
1.30 (m, 4 H), 0.88 (t, J ) 6.5 Hz, 3 H).
Treatment of 5.4 g (31 mmol) of 4-n-pentylbenzyl alcohol with 26.2
g (62 mmol) of triphenylphosphine dibromide in 60 mL of anhydrous
DMF gave 6.2 g (83%) of 4-n-pentylbenzyl bromide17 as a pale yellow
1
liquid: H NMR δ 7.30 (d, J ) 8.1 Hz, 2 H; H-2,6), 7.15 (d, J ) 8.0
Hz, 2 H; H-3,5), 4.49 (s, 2 H), 2.59 (t, J ) 7.7 Hz, 2 H), 1.60 (quintet,
J ) 7.5 Hz, 2 H), 1.37-1.29 (m, 4 H), 0.89 (t, J ) 6.9 Hz, 3 H); MS
m/z (relative intensity) 242 (M+, 2), 240 (M+, 2), 161 (100).
Treatment of 1.0 g (4.1 mmol) of 4-n-pentylbenzyl bromide with
1.1 g (4.2 mmol) of triphenylphosphine gave 1.5 g (73%) of the
phosphonium salt. The Wittig reaction of 1.0 g (2.0 mmol) of this
salt with 0.21 g (0.9 mmol) of phenanthrene-1,8-dicarboxaldehyde (6)
gave 0.29 g (62%) of (E,E)-1,8-bis(4-n-pentylstyryl)phenanthrene. The
characterization of this stilbene analogue and a description of its
photocyclization to give 2,13-di-n-pentyl[7]phenacene (2a) were re-
ported earlier.2a
(Z)-2,2′-Dibromo-4,4′-di-n-pentylstilbene. Treatment of 4.15 g (15
mmol) of 2-bromo-4-n-pentylbenzyl chloride with 5.24 g (20 mmol)
of triphenylphosphine gave 6.48 g (80%) of the phosphonium salt. The
Wittig reaction of 4.03 g (7.5 mmol) of this phosphonium salt with
1.9 g (7.5 mmol) of 2-bromo-4-n-pentylbenzaldehyde gave, after
purification by molecular distillation at reduced pressure, 3.26 g (91%)
2,13-Di-tert-butyl[7]phenacene (2b). Treatment of 2.12 g (9.3
mmol) of 4-tert-butylbenzyl bromide with 3.7 g (14 mmol) of
triphenylphosphine gave 3.77 g (83%) of the phosphonium salt. The
Wittig reaction of 2.03 g (4.15 mmol) of this salt with 0.47 g (2.0
mmol) of phenanthrene-1,8-dicarboxaldehyde (6) gave 0.45 g (45%)
of (E,E)-1,8-bis(4-tert-butylstyryl)phenanthrene. The characterization
of this stilbene analogue and a description of its photocyclization to
give 2,13-di-tert-butyl[7]phenacene (2b) were reported earlier.2a
3,6-Di-n-pentyl-1,8-distyrylphenanthrene. The Wittig reaction of
0.78 g (2.0 mmol) of benzyltriphenylphosphonium chloride with 0.25
g (0.67 mmol) of 3,6-di-n-pentylphenanthrene-1,8-dicarboxaldehyde (3)
gave 0.24 g (69%) of (E,E)-3,6-di-n-pentyl-1,8-distyrylphenanthrene
as a white solid that was recrystallized from 95% ethanol/toluene: mp
132-133 °C; 1H NMR δ 8.48 (br s, 2 H; H-4,5), 8.10 (s, 2 H; H-9,10),
7.94 (d, J ) 16.0 Hz, 2 H; H-R,R′), 7.70 (br s, 2 H; H-2,7), 7.64 (d, J
) 7.3 Hz, 4 H; H-2′,6′,2′′,6′′), 7.42 (t, J ) 7.5 Hz, 4 H; H-3′,5′,3′′,5′′),
7.31 (t, J ) 7.3 Hz, 2 H; H-4′,4′′), 7.17 (d, J ) 16.0 Hz, 2 H; H-â,â′),
2.91 (t, J ) 7.8 Hz, 4 H), 1.83 (quintet, J ) 7.5 Hz, 4 H), 1.47-1.41
(m, 8 H), 0.94 (t, J ) 7.0 Hz, 6 H). Anal. Calcd for C40H42: C, 91.90;
H, 8.10. Found: C, 91.76; H, 7.80.
15,18-Di-n-pentyl[7]phenacene (2c). A solution of 160 mg (0.31
mmol) of 3,6-di-n-pentyl-1,8-distyrylphenanthrene, 160 mg (0.62 mmol)
of I2, and 8.7 mL (124 mmol) of propylene oxide13 in 300 mL of
cyclohexane was irradiated (Rayonet) for 5 d. The solvents were
evaporated, and the orange residue was dissolved in a small amount of
toluene. Chromatography on silica gel with hexanes as eluent gave
60 mg (52%) of 15,18-di-n-pentyl[7]phenacene (2c) as a yellow solid
that was recrystallized from 95% ethanol/toluene: mp 234.5-235 °C;
1H NMR δ 8.89 (br s, 4 H; H-7,8,16,17), 8.88 (d, J ) ∼9 Hz, 4 H;
H-1,6,9,14), 8.04 (dd, J ) 7.7 Hz, 1.5 Hz, 2 H; H-4,11), 8.02 (d, J )
8.8 Hz, 2 H; H-5,10), 8.18-7.63 (m, 4 H; H-2,3,12,13), 3.73 (t, J )
7.9 Hz, 4 H), 2.10 (quintet, J ) 7.7 Hz, 4 H), 1.67-1.44 (m, 8 H),
0.99 (t, J ) 7.2 Hz, 6 H); UV (benzene, nm [relative intensity]) 358
[1.0], 342 [1.1], 324 (shoulder) [2.4], 309 [4.3]. Anal. Calcd for
C40H38: C, 92.62; H, 7.38. Found: C, 92.73; H, 7.45.
of
a pale yellow liquid consisting predominantly of (Z)-2,2′-
dibromo-4,4′-di-n-pentylstilbene: 1H NMR δ 7.39 (d, J ) 1.1 Hz, 2
H; H-3,3′), 6.91 (d, J ) 7.9 Hz, 2 H; H-6,6′); 6.81 (dd, J ) 7.9 Hz, 1.4
Hz, 2 H; H-5,5′), 6.70 (s, 2 H; H-R,R′), 2.51 (t, J ) 7.7 Hz, 4 H),
1.63-1.51 (m, 4 H), 1.37-1.22 (m, 8 H), 0.88 (t, J ) 6.7 Hz, 6 H);
MS m/z (relative intensity) 480 (M+, 50), 478 (M+, 100), 476 (M+,
50). Anal. Calcd for C24H30Br2: C, 60.27; H, 6.32. Found: C, 60.15;
H, 6.38.
1
The H NMR spectrum of the Wittig product also exhibited peaks
consistent with the presence of
a small amount of (E)-2,2′-
dibromo-4,4′-di-n-pentylstilbene: 1H NMR δ 7.62 (d, J ) 8 Hz), 7.41
(d, J ) 1.5 Hz), 7.35 (s), 7.19 (br d, J ) 8 Hz), 2.56 (t, J ) 7 Hz),
1.63-1.51 (m), 1.37-1.22 (m), 0.89 (t, J ) 7 Hz).
1,8-Dibromo-3,6-di-n-pentylphenanthrene. A solution of 3.26 g
(6.8 mmol) of predominantly (Z)-2,2′-dibromo-4,4′-di-n-pentylstilbene,
1.73 g (6.8 mmol) of I2, and 79.0 g (1.36 mol) of propylene oxide13 in
500 mL of cyclohexane was irradiated (Rayonet) for 68 h. Evaporation
of the solvent followed by chromatography on silica gel with hexanes
as eluent gave 3.03 g (94%) of 1,8-dibromo-3,6-di-n-pentylphenanthrene
as a white solid. Recrystallization from 95% ethanol/toluene gave white
1
crystals: mp 86.5-88.5 °C; H NMR δ 8.41 (br s, 2 H; H-4,5), 8.18
(s, 2 H; H-9,10), 7.77 (d, J ) 1.2 Hz, 2 H; H-2,7), 2.84 (t, J ) 7.8 Hz,
4 H), 1.76 (quintet, J ) 7.5 Hz, 4 H), 1.42-1.36 (m, 8 H), 0.92 (t, J
) 7.0 Hz, 6 H); MS m/z (relative intensity) 478 (M+, 50), 476 (M+,
100), 474 (M+, 50). Anal. Calcd for C24H28Br2: C, 60.52; H, 5.93.
Found: C, 60.39; H, 5.86.
3,6-Di-n-pentylphenanthrene-1,8-dicarboxaldehyde (3). A stirred
solution of 0.79 g (1.66 mmol) of 1,8-dibromo-3,6-di-n-pentylphenan-
threne in 25 mL of anhydrous diethyl ether was cooled in an ice bath.
A solution consisting of 2.7 mL (6.64 mmol) of 2.5 M n-BuLi in
hexanes and 5 mL of anhydrous diethyl ether was added dropwise under
N2. Stirring was continued for an additional 1 h, after which 1.0 mL
(13 mmol) of anhydrous DMF was added dropwise. The reaction
mixture was allowed to warm to room temperature and then was poured
onto 1 M H3PO4. Extraction with diethyl ether followed by aqueous
workup and chromatography on silica gel with 5% ethyl acetate in
hexanes as eluent gave 0.49 g (79%) of 3 as a yellow solid.
Recrystallization from 95% ethanol gave pale yellow crystals: mp
87.0-87.5 °C; 1H NMR δ 10.56 (s, 2 H; CHO), 9.21 (s, 2 H; H-9,10),
8.78 (br s, 2 H; H-4,5), 8.00 (d, J ) 1.4 Hz, 2 H; H-2,7), 2.98 (t, J )
7.8 Hz, 4 H), 1.83 (quintet, J ) 7.6 Hz, 4 H), 1.45-1.41 (m, 8 H),
(E)-2-Bromo-4′-n-pentylstilbene. The reaction of 4-n-pentylbenzyl
alcohol16 with thionyl chloride in benzene gave 4-n-pentylbenzyl
chloride18 as a pale yellow liquid: 1H NMR δ 7.30 (d, J ) 8.1 Hz, 2 H;
H-2,6), 7.17 (d, J ) 8.1 Hz, 2 H; H-3,5), 4.57 (s, 2 H), 2.60 (t, J ) 7.8
Hz, 2 H), 1.58 (quintet, J ) 7.5 Hz, 2 H), 1.36-1.27 (m, 4 H), 0.89 (t,
J ) 6.9 Hz, 3 H). Treatment of 8.8 g (45 mmol) of 4-n-pentylbenzyl
(16) Panetta, C. A.; Garlick, S. M.; Durst, H. D.; Longo, F. R.; Ward, J.
R. J. Org. Chem. 1990, 55, 5202-5205.
(17) Cereghetti, M.; Marbet, R.; Schleich, K. HelV. Chim. Acta 1982,
65, 1318-1330.
(18) Cox, R. J.; Clecak, N. J. Mol. Cryst. Liq. Cryst. 1976, 37, 263-
267.