G. Kaupp, M. R. Naimi-Jamal
FULL PAPER
(CDCl3): δ ϭ 3.83 (s, 6 H), 6.87 (pseudo-d, 4 H), 7.50 (pseudo-d,
125.2, 126.0, 127.8, 129.1, 130.8, 131.1, 131.4, 132.8, 132.9, 136.3,
4 H), 7.72 (pseudo-d, 2 H), 8.13 (pseudo-d, 2 H). 13C NMR 137.6, 140.7, 144.0, 168.7.
(CDCl3): δ ϭ 55.3 (2 C), 113.8 (4 C), 129.0 (2 C), 129.5 (2 C), 131.3
(4 C), 131.8 (2 C), 141.1 (2 C), 153.0 (2 C), 160.2 (2 C).
b) Reaction in the Melt: Compounds 1a (216 mg, 2.00 mmol) and
4 (348 mg, 2.00 mmol) were heated to 110 °C for 30 min in an
evacuated 5-mL flask. Pure 5 (492 mg, 100%) was obtained after
drying in a vacuum at 80 °C.
b) Reaction in the Melt: Compounds 1a (108 mg, 1.00 mmol) and
2Ј (270 mg, 1.00 mmol) were heated to 130 °C for 30 min in an
evacuated 5-mL flask. Pure 3aЈ (342 mg, 100%) was obtained after
drying in a vacuum at 80 °C.
3-(3-Oxo-3,4-dihydroquinoxalin-2-yl)propionic Acid (7): 2-Oxoglut-
aric acid (6, 292 mg, 2.00 mmol) and 1a (216 mg, 2.00 mmol) were
coground in a mortar and heated to 120Ϫ125 °C for 30 min in a
vacuum. Pure 7 (472 mg, 100%) was obtained, m.p. 252Ϫ254 °C
2,3-Diphenyl-6-methylquinoxaline (3b): 4-Methyl-o-phenylenediam-
ine (1b, 122 mg, 1.00 mmol) and 2 (210 mg, 1.00 mmol) were co-
ground in a mortar and heated to 100 °C for 15 min under vacuum.
Pure 3b (296 mg, 100%) was obtained, m.p. 109Ϫ110 °C (111 °C[7]).
1H NMR (CDCl3): δ ϭ 2.60 (s, 3 H), 7.32 (m, 6 H), 7.50 (m, 4 H),
7.60 (m, 1 H), 8.00 (m, 1 H), 8.10 (m, 1 H). 13C NMR (CDCl3):
δ ϭ 21.8, 128.0, 128.2 (4 C), 128.6 (2 C), 129.8 (4 C), 132.3, 134.8,
139.2 (2 C), 139.7, 140.4, 141.2, 152.5, 153.3.
1
(255Ϫ257 °C[21]). H NMR ([D6]DMSO): δ ϭ 2.70 (t, J ϭ 7.0 Hz,
2 H), 3.00 (t, J ϭ 7 Hz, 2 H), 7.22Ϫ7.28 (m, 2 H), 7.45 (m, 1 H),
7.67 (m, 1 H), 12.26 (br. peak, 2 NH). 13C NMR ([D6]DMSO):
δ ϭ 27.6, 29.6, 115.2, 123.0, 128.0, 129.4, 131.4, 131.6, 154.5,
160.2, 173.8.
1,4-Dihydroquinoxaline-2,3-dione (9): Compound 1a (108 mg,
1.00 mmol) and oxalic acid dihydrate (8, 126 mg, 1.00 mmol) were
coground in a mortar and heated to 150 °C for 8 h, or to 180 °C
for 30 min, or to 210Ϫ220 °C for 10 min under vacuum. Pure 9
(162 mg, 100%) was obtained in all cases, m.p. Ͼ 300 °C (365Ϫ367
2,3-Bis(4-methoxyphenyl)-6-methylquinoxaline (3bЈ)
a) In the Solid State: 4-Methyl-o-phenylenediamine (1b, 122 mg,
1.00 mmol) and 4,4Ј-dimethoxybenzil (2Ј, 270 mg, 1.00 mmol) were
ball-milled at 80 °C for 1 h and then dried at 80 °C in a vacuum
for 1 h. Pure 3bЈ (356 mg, 100%) was obtained, m.p. 123Ϫ125 °C.
1H NMR (CDCl3): δ ϭ 2.59 (s, 3 H), 3.82 (s, 6 H), 6.86 (AAЈBBЈ,
4 H), 7.47 (BBЈAAЈ, 4 H), 7.54 (m, 1 H), 7.89 (m, 1 H), 8.00 (m,
1 H). 13C NMR (CDCl3): δ ϭ 21.8, 55.2 (2 C), 113.7 (4 C), 127.8,
128.5, 131.2 (4 C), 131.8, 131.9, 139.5, 139.9 (2 C), 141.1, 152.1,
152.8, 160.0 (2 C). HRMS (EI) calcd. for C23H20N2O2 356.1525;
found 356.1509.
1
°C[22]). H NMR ([D6]DMSO): δ ϭ 6.85 (m, 2 H), 6.70 (m, 2 H).
13C NMR ([D6]DMSO): δ ϭ 117.0 (2 C), 119.6 (2 C), 132.6 (2 C),
162.7 (2 C).
1H,1ЈH-[2,2Ј]Bis(benzimidazolyl) (10) and 5,12-Dihydroquinoxal-
ino[2,3-b]quinoxaline (11)
a) From 1a and 9: Compounds 1a (54 mg, 0.50 mmol) and 9 (81 mg,
0.50 mmol) were heated to 240 °C for 12 h under vacuum. The
conversion was quantitative and 10 and 11 (117 mg, 100%) were
b) Reaction in the Melt: Compounds 1b (122 mg, 1.00 mmol) and
2Ј (270 mg, 1.00 mmol) were heated to 130 °C for 30 min in an
evacuated 5-mL flask. Pure 3c (356 mg, 100%) was obtained after
drying in a vacuum at 80 °C.
1
obtained in a ratio of 94:6 according to H NMR analysis.
b) From 1a·2HCl and 9: Compounds 1a·2HCl (45 mg, 0.25 mmol)
and 9 (40 mg, 0.25 mmol) were sealed under vacuum in a glass tube
and heated to 140 °C for 6 h. After treatment of the solid with 1
NaOH and four washings with water, a quantitative yield of an
80:20 mixture of 10 and 11 was obtained.
2,3-Bis(4-methoxyphenyl)-5-methylquinoxaline (3cЈ): 3-Methyl-o-
phenylenediamine (1c, 122 mg, 1.00 mmol) and 4,4Ј-dimethoxyben-
zil (2Ј, 270 mg, 1.00 mmol) were ball-milled for 30 min at 75 °C
and dried in a vacuum at 80 °C for 1 h. Pure 3cЈ (356 mg, 100%)
was obtained, m.p. 156Ϫ158 °C. 1H NMR (CDCl3): δ ϭ 2.83 (s, 3
H), 3.82 (s, 6 H), 6.80Ϫ6.90 (m, 4 H), 7.45Ϫ7.65 (m, 6 H), 7.94
(m, 1 H). 13C NMR (CDCl3): δ ϭ 17.0, 55.3 (2 C), 113.6 (2 C),
113.8 (2 C), 126.7, 129.2, 129.4, 131.1 (2 C), 131.4 (2 C), 132.0,
137.3 (2 C), 140.2, 140.9, 151.3, 152.3, 160.1 (2 C). HRMS (CI)
calcd. for C23H20N2O2 ϩ H 357.1603; found 357.1602.
c) From 1a and 12: Compounds 1a (108 mg, 1.00 mmol) and 2,3-
dichloroquinoxaline (12, 199 mg, 1.00 mmol) were heated to 150
°C in a vacuum for 30 min. The crude mixture contained 1a·2HCl
(39%), 10 (7%), and 11 (53%) according to 1H NMR analysis. It
was treated with 1 NaOH, filtered, and washed with water and
cold ethanol (20 mL). The residue contained 11 and 10 in a 93:7
ratio. Pure 11 was obtained by heating the mixture with 5 mL of
ethanol, hot filtration, and washing of the crystals three times with
3 mL of hot ethanol.
6-Nitro-2,3-diphenylquinoxaline (3d): 4-Nitro-o-phenylenediamine
(1d, 153 mg, 1.00 mmol) and 2 (210 mg, 1.00 mmol) were coground
in a mortar and heated to 160 °C under vacuum for 15 min. Pure
3d (327 mg, 100%) was obtained, m.p. 186.5Ϫ187.5 °C
(187.5Ϫ187.9 °C[5]). 1H NMR (CDCl3): δ ϭ 7.40 (m, 6 H), 7.56
(m, 4 H), 8.29 (m, 1 H), 8.52 (m, 1 H), 9.07 (m, 1 H). 13C NMR
(CDCl3): δ ϭ 123.3 (2 C), 125.6 (2 C), 128.4 (2 C), 129.6 (2 C),
129.8 (2 C), 129.9 (2 C), 130.7 (2 C), 138.1, 140.0, 143.6, 147.9,
155.7, 156.3.
Compound 10: M.p.
Ͼ
300 °C (470 °C[23]). 1H NMR
([D6]DMSO):[24] δ ϭ 7.40 (pseudo-d, 4 H), 7.72 (pseudo-d, 2 H),
7.85 (pseudo-d, 2 H), 13.70 (br. s, 2 NH). 13C NMR ([D6]DMSO):
δ ϭ 112.1 (2 C), 119.2 (2 C), 122.2 (2 C), 123.6 (2 C), 134.8 (2 C),
143.6 (2 C), 143.8 (2 C).
Compound 11: M.p. Ͼ 300 °C (Ͼ 360 °C[14]). 1H NMR (CDCl3/
CF3COOH): δ ϭ 7.38 (m, 4 H), 7.48 (m, 4 H). 13C NMR (CDCl3/
CF3COOH): δ ϭ 118.9 (4 C), 125.9 (4 C), 130.4 (4 C), 142.8 (2 C).
Benzo[a]phenazin-5-ol (5)
N-[(3-Oxo-3,4-dihydroquinoxalin-2-yl)carbonyl]urea (15)
a) In the Solid State: o-Phenylenediamine (1a, 108 mg, 1.00 mmol)
and 2-hydroxy-1,4-naphthoquinone (4, 174 mg, 1.00 mmol) were a) Solid-Solid Reaction: Compound 1a (108 mg, 1.00 mmol) and
ball-milled for 15 min at 70 °C. Pure 5 (246 mg, 100%) was ob- alloxane hydrate (14, 160 mg, 1.00 mmol) were ball-milled for 1 h
tained, m.p. Ͼ 300 °C (Ͼ 300 °C[9]). 1H NMR (CDCl3/CF3COOH): at room temperature. Pure 15 (232 mg, 100%) was obtained, m.p.
δ ϭ 7.35 (s, 1 H), 7.85Ϫ8.18 (m, 5 H), 8.43 (m, 1 H), 8.50 (m, 1
254Ϫ256 °C (250 °C[12]; 238Ϫ239 °C[17]). 1H NMR (CDCl3/
H), 9.26 (m, 1 H). 13C NMR (CDCl3/CF3COOH): δ ϭ 96.0, 118.6, CF3COOH): δ ϭ 7.30 (br. s, 1 NH), 7.50 (pseudo-d, 1 H), 7.68 (m,
1372
Eur. J. Org. Chem. 2002, 1368Ϫ1373