3-methoxybenzo[c]phenanthrene 11b (0.053 g, 93%) was ob-
tained as a yellow solid: m.p. 75–76 ◦C; IR mmax (solid)/cm−1
1612, 1503, 1463, 1428, 1358, 1258, 1298, 1265, 1228, 1029, 923,
867, 832, 797 and 750; 1H NMR (300 MHz; CDCl3; Me4Si) 4.01
(3H, s, OCH3), 7.31–7.38 (2H, m, ArH), 7.59–7.69 (2H, m, 2 ×
ArH), 7.78–7.86 (4H, m, 4 × ArH), 8.00 (1H, d, J 7.6, ArH) and
9.03–9.08 (2H, m, 2 × ArH); 13C NMR (75 MHz; CDCl3) 55.4
(OCH3), 108.0 (CH), 117.1 (CH), 125.1 (C), 125.8 (CH), 126.0
(CH), 126.5 (CH), 126.8 (CH), 126.9 (CH), 127.5 (CH), 127.9
(CH), 128.5 (CH), 129.5 (CH), 129.8 (C), 130.1 (C), 133.6 (C),
135.1 (C) and 157.5 (C); MS m/z 259 (27%), 258 (M+, 100), 216
(12), 215 (57), 213 (17) and 189 (13); HRMS calcd for C19H14O:
258.1044, found: 258.1043.
(CH), 125.8 (C), 126.1 (CH), 126.6 (C), 126.7 (CH), 126.9 (CH),
127.2 (CH), 127.3 (C), 128.5 (CH), 128.7 (CH), 128. 9 (CH),
129.2 (C), 131.4 (C), 132.4 (C), 136.3 (C), 142.0 (C), 150.4 (C),
150.7 (C) and 192.5 (CHO); MS m/z 356 (M+, 100%), 340 (41),
326 (79), 311 (46), 281 (44), 307 (54), 297 (40), 276 (66), 269
(37), 252 (36), 239 (38) and 150 (34); HRMS calcd for C24H20O3:
356.1412, found: 356.1416.
KOBut (0.213 g, 1.90 mmol) was added to 10d (0.085 g,
0.24 mmol) dissolved in dry DMF (20 cm3) and after subjecting
the reaction mixture to the normal reaction conditions but with-
out exposure to the light source followed by chromatography (5–
20% EtOAc–hexane), led to the isolation of only one product
9,14-dimethoxynaphtho[1,2-a]anthracene 11e (0.063 g, 79%).
Single crystals of compound 11e suitable for X-ray diffraction
were selected directly from the analytical samples.
Pentahelicene 11c and 5,6-Dihydropentahelicene 11d. (a) KOBut
(0.114 g, 1.02 mmol) was added to 10c (0.076 g, 0.25 mmol)
dissolved in dry DMF (9 cm3) and after subjecting the reac-
tion mixture to the normal reaction conditions and column
chromatography (5–20% EtOAc–hexane), two compounds were
isolated. The major◦product was pentahelicene 11c (0.049 g,
70%): m.p. 135–137 C (not recrystallised); (lit. m.p. 145 ◦C26);
1H NMR (300 MHz; CDCl3; Me4Si) 7.30–7.33 (2H, m, 2 ×
ArH), 7.54–7.58 (2H, m, 2 × ArH), 7.91–8.03 (8H, m, 8 × ArH)
and 8.56 (1H, d, J 8.5, ArH);27 13C NMR (75 MHz; CDCl3) 124.3
(CH), 126.2 (CH), 126.3 (CH), 127.0 (C), 127.2 (CH), 127.5
(CH), 127.8 (CH), 129.0 (CH), 130.8 (C), 132.3 (C) and 132.6
(C); MS m/z 278 (74%), 277 (M+, 100), 276 (95), 274 (19) and
238 (13); HRMS calcd for C22H14: 278.1095 Found 278.1088. 5,6-
Dihydropentahelicene 11d was obtained as the minor product
(0.010 g, 14%): 1H NMR (300 MHz; CDCl3; Me4Si) 2.72–3.13
(4H, m, 4 × ArH), 6.98–7.05 (1H, m, ArH), 7.10–7.22 (2H, m,
ArH), 7.33–7.48 (3H, m, 3 × ArH), 7.50–7.56 (1H, m, ArH),
7.65–7.73 (3H, m, 3 × ArH), 7.80 (1H, d, J 8.5, ArH) and 8.45
(1H, d, J 8.5, ArH); HRMS calcd for C22H14: 280.1255, found:
279.1183.
Crystal structure determination of compound 11e: crystal data.
C24H18O2, M = 338.38, orthorhombic, a =7.7959(9), b =
3
˚
˚
20.639(3), c = 11.0953(14) A, U = 1785.2(4) A , T = 293(2) K,
space group Pca21 (No. 29), Z = 4, l(Mo-Ka) = 0.079 mm−1,
10163 reflections measured, 1858 unique (Rint = 0.044) which
were used in all calculations. Final R indices [I > 2r(I)], R1 =
0.0464, wR(F2) = 0.1268. CCDC reference number 248479. See
http://www.rsc.org/suppdata/ob/b4/b412932f/ for crystallo-
graphic data in .cif or other electronic format.
2-Bromo-1,4-dimethoxy-3-methylnaphthalene
A solution of SnCl2·2H2O (39.5 g, 0.175 mol) in concentrated
HCl (33 cm3) was added to a warm solution of 2-bromo-
3-methylnaphthoquinone (13.24 g, 0.05273 mol) in EtOH
(96%, 160 cm3). H2O was then added and the precipitate
was filtered and recrystallized (H2O) to afford the desired
intermediate, 2-bromo-3-methyl naphthohydroquinone as◦white
needles (13.08 g, 98%); m.p. 253–254◦C (water) (lit. >250 C24);
1H NMR (400 MHz; CDCl3; Me4Si) 2.52 (3H, s, ArCH3), 5.31
(2H, brs, 2 × ArOH), 7.42–7.52 (2H, m, 2 × ArH) and 8.12–8.16
(2H, m, 2 × ArH); 13C NMR (100 MHz; CDCl3) 15.8 (ArCH3),
108.0 (C), 117.3 (CH), 121.1 (CH), 121.5 (C), 123.0 (C), 124.5
(C), 126.1 (CH), 126.3 (CH), 142.1 (C) and 142.5 (C).
(b) Repeating the reaction but using 8 equivalents of KOBut
(0.241 g, 2.15 mmol) and 10c (0.080 g, 0.27 mmol) led to the
isolation of pentahelicene 11c in good yield (0.062 g, 82%).
9,14-Dimethoxynaphtho[1,2-a]anthracene 11e and 1-(3-methyl-
1,4-dimethoxy-2-naphthyl)-2-naphthaldehyde 11f. KOBut
(0.075 g, 0.67 mmol) was added to 10d (0.060 g, 0.17 mmol)
dissolved in dry DMF (9 cm3) and after subjecting the reaction
mixture to the normal reaction conditions and column chro-
matography (5–20% EtOAc–hexane), two compounds were iso-
lated, 9,14-dimethoxynaphtho[1,2-a]anthracene 11e and 1-(3-
methyl-1,4-dimethoxy-2-naphthyl)-2-naphthaldehyde 11f. The
minor product was 11e (0.010 g, 18%): IR mmax (film)/cm−1 3050,
3005, 2932, 2837, 1731, 1617, 1591, 1559, 1504, 1473, 1451,
1412, 1363, 1289, 1113, 1096, 1060, 977, 834 and 752; 1H NMR
(300 MHz; CDCl3; Me4Si) 3.00, 4.20 (each 3H, s, OMe), 7.55–
7.69 (5H, m, 5 × ArH), 7.83 (1H, d, J 8.4, ArH), 7.95–7.97 (1H,
m, ArH), 8.01 (1H, d, J 8.4, ArH), 8.26 (1H, d, J 8.9, ArH),
8.32–8.41 (2H, m, 2 × ArH) and 8.56–8.59 (1H, m, ArH); 13C
NMR (75 MHz; CDCl3) 60.2 (OCH3), 63.6 (OCH3), 118.5 (C),
121.8 (CH), 122.2 (CH), 123.4 (CH), 124.6 (CH), 125.0 (C),
125.5 (C), 125.6 (CH), 125.6 (CH) 125.9 (C), 125.9 (CH), 126.0
(CH), 126.7 (CH), 126.8 (C), 127.0 (CH), 128.5 (CH), 129.4 (C),
130.3 (CH), 131.3 (C), 132.7 (C), 147.8 (C) and 150.2 (C); MS
m/z 338 (M+, 100%), 323 (92), 292 (32), 279 (25), 250 (13), 219
(36), 167 (38), 154 (31), 149 (97), 139 (30), 125 (16), 83 (22) and 71
(24); HRMS calcd for C24H18O2: 338.1307, found: 338.1321. The
second product was 1-(3-methyl-1,4-dimethoxy-2-naphthyl)-2-
naphthaldehyde 11f (0.042 g, 70%): IR mmax (film)/cm−1 2955,
2927, 2854, 1727, 1590, 1454, 1352, 1283, 1095, 1061, 836, 797,
An aqueous solution of KOH (50%, 22 cm3) was added to
the intermediate naphthohydroquinone (0.502 g, 1.98 mmol)
and dimethyl sulfate (6.85 cm3). After heating at reflux for 1 h
the reaction mixture was extracted with CH2Cl2 (2 × 30 cm3),
washed with aqueous 25% NH3 (3 × 20 cm3), dried (MgSO4)
and evaporated. Recrystallisation (MeOH) gave the desired
2-bromo-1,4-dimethoxy-3-methylnaphthalene as white plates
◦
(0.491 g, 88%): m.p. 84–85 ◦C (MeOH) (lit. 84–85 C24,28,29);
1H NMR (400 MHz; CDCl3; Me4Si) 2.55 (3H, s, ArCH3), 3.88,
3.97 (each 3H, s, ArOCH3), 7.41–7.56 (2H, m, 2 × ArH) and
8.01–8.08 (2H, m, 2 × ArH).
2-(1,4-Dimethoxy-3-methyl-2-naphthyl)benzaldehyde 15
A
solution of ortho-bromobenzaldehyde 14 (0.169 g,
0.913 mmol) in DME (8.0 cm3) was deoxygenated by passing N2
through the mixture for 10 min. The deoxygenated mixture was
added to Pd(PPh3)4 (12 mol%, 0.122 g, 0.106 mmol) and stirred
under N2 for 10 min. A deoxygenated solution of arylboronic
acid 9d (synthesized in the same manner as indicated earlier,
0.400 g, 1.63 mmol) in DME (3 cm3) was added to the mixture.
After 10 min a deoxygenated aqueous Na2CO3 solution (2 M,
4.5 cm3) was added to the reaction mixture that was stirred
at rt for 10 min before being heated under reflux for 42 h. The
cooled solution was quenched with H2O (40 cm3), extracted with
CH2Cl2 (4 × 30 cm3), dried (MgSO4) and concentrated in vacuo.
The residue was purified by column chromatography on silica gel
to afford the biaryl compound 15 as an orange oil (0.230 g, 82%)
and recovered 1,4-dimethoxy-2-methylnaphthalene (0.028 g): IR
mmax (film)/cm−1 3483, 3379, 3070[el], 3014, 2933, 2841, 2746, 1717,
1
772 and 750; H NMR (300 MHz; CDCl3; Me4Si) 1.96 (3H, s,
ArCH3), 3.37, 3.96 (each 3H, s, OMe), 7.42–7.45 (1H, m, ArH),
7.49–7.66 (4H, m, 4 × ArH), 7.96 (1H, brd, J 8.2, 1H), 8.01 (1H,
brd, J 8.7, 1H), 8.11–8.16 (2H, m, 2 × ArH), 8.21–8.24 (1H, m,
ArH) and 9.90 (1H, d, J 0.8, CHO); 13C NMR (75 MHz; CDCl3)
13.6 (ArCH3), 61.6 (2×OCH3), 122.3 (CH), 122.4 (CH), 122.9
1
1625, 1596, 1570, 1482, 1455, 1348, 1252 and 1266; H NMR
3 5 0 8
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 3 5 0 4 – 3 5 0 9