layer was extracted with more dichloromethane (200 mL) and
the dichloromethane extracts were washed in turn with water
125.7, 126.7, 132.2, 135.2, 137.1, 138.4, 139.7, 140.4, 146.5,
148.9.
(
3 × 200 mL), combined and dried. The residue from the evap-
orated extracts was distilled at 80–120 ЊC/15 mmHg (heating
block) giving 4-fluorophenyl isocyanide 5 (5.60 g, 77%) as a
colourless oil that rapidly becomes green on standing at room
temperature; δ 7.05–7.12 (2H, m, 2- ϩ 6-H), 7.28–7.40 (2H, m,
3
Oligomerisation of 4-fluorophenyl isocyanide 5 at 135 ؇C
Freshly distilled 4-fluorophenyl isocyanide 5 (5.60 g, 46.2
mmol) was heated at 135 ЊC (oil bath) for 3 h. The reaction
mixture on cooling set to a viscous orange–red gum and was
extracted with portions of boiling benzene (total, 150 mL),
leaving an insoluble solid. The solid was filtered off, washed
with boiling benzene until the washings were colourless, then
with hexane, and dried. This gave 5,5Ј-difluoroindigo-3,3Ј-bis-
H
- ϩ 5-H); δ 116.5 (d, J
23.5 Hz, C-3 ϩ C-5), 122.7 (br t,
C
C-3(5),F
C-1), 128.3 (d, JC-2(6),F 8.9 Hz, C-2 ϩ C-6), 164.4 (d, J4-C,F 251.6
Hz, C-4), 164.4 (br, NC).
Preparation of the pyrazino[1,2-a:4,5-aЈ]diindoles 15–18 from
the aryl isocyanides 1–4. The following general procedure was
used. A solution of the aryl isocyanide (10 mmol) and dichloro-
benzene (0.5 mL) was heated (oil bath) at 150 ЊC for 5 h. The
cooled mixture was extracted with benzene (20 mL) and the
solution was chromatographed on silica (30 × 1.9 cm). Elution
was carried out with petroleum–benzene (2 : 1) until orange–
red eluates emerged. Elution was continued with the solvent
mixture indicated and the residual solid from the evaporated
orange–red eluates was recrystallised. Heating the isocyanides
alone gave lower yields of product.
(
4-fluorophenylimine) 9 (181 mg, 3.2%) as black crystals which
were used for the X-ray crystal structure determination.
The combined benzene filtrates and washings were concen-
trated to 100 mL and hexane (100 mL) was added. A reddish
brown sludge precipitated and the supernatant solution was
decanted onto a column of silica (55 × 2.2 cm). Elution gave the
following fractions: (i) hexane–benzene (3 : 1), pale orange,
5
00 mL, contained isocyanide 5, discarded; (ii) hexane–benzene
(
2 : 1), deep orange–red, 1000 mL; (iii) hexane–benzene (2 : 1),
orange, 300 mL; (iv) hexane–benzene (1 : 1), pale orange, 600
mL. Fraction (ii) was concentrated to ca. 10 mL and hexane
(
(
100 mL) was added. 7,14-Di(4-fluorophenylamino)-6,13-di-
4-fluorophenylimino)pyrazino[1,2-a:4,5-aЈ]diindole 19 (571
7
,14-Di(phenylamino)-6,13-di(phenylimino)pyrazino[1,2-a:4,5-
aЈ]diindole 15 from phenyl isocyanide 1. Elution solvent: petrol-
eum–benzene (2 : 1). Recrystallisation from benzene–hexane
2 : 1) gave orange crystals (125 mg, 12.1%), mp 251–254 ЊC
Found: C, 81.7; H, 5.2; N, 13.6. C H N requires C, 81.5; H,
.9; N, 13.6%); δH 6.62 (4H, unresolved doublet), 6.87 (2H,
triplet), 6.99–7.41 (22H, m), 8.11 (2H, brs, NH); δ 115.9, 116.8,
17.5, 120.6, 122.0, 122.1, 123.6, 124.0, 126.6, 127.3, 128.3,
28.8, 130.0, 134.1, 140.8, 143.0, 148.6.
mg) crystallised as small red crystals which melt at 170–175 ЊC,
resolidify and remelt at 243–245 ЊC. The filtrates from fraction
(
removed, and the residue was recrystallised from hexane to give
a further 44 mg of compound 19 (total yield, 615 mg, 11%).
NMR: δH 6.69 (br), 6.79 (dd), 6.91–7.05 (m), 7.84 (vbr, NH);
δC 107.0 (d, JC,F 24.9 Hz), 115.2 (d, JC,F 25.4 Hz), 115.7 (d,
JC,F 22.7 Hz), 116.1 (s), 116.7 (d, JC,F 22.6 Hz), 118.1 (d, JC,F 8.8
Hz), 119.9 (brs), 121.9 (d, JC,F 7.6 Hz), 124.3 (d, JC,F 9.8 Hz),
(
(
4
ii) were combined with fractions (iii) and (iv), solvent was
42
30
6
C
1
1
7
,14-Di(4-methylphenylamino)-6,13-di(4-methylphenylimino)-
pyrazino[1,2-a:4,5-aЈ]diindole 16 from 4-methylphenyl isocyanide
. Elution solvent: benzene–petroleum (1 : 1). Recrystallisation
from benzene–hexane gave orange crystals (204 mg, 17.4%), mp
58–260 ЊC (Found: C, 81.4; H, 5.8; N, 11.9. C H N requires
1
(
27.8 (vbrs), 130.4 (s), 138.1 (d, JC,F 2.5 Hz), 140.3 (s), 144.2
d, JC,F 3.0 Hz), 158.1 (d, JC,F 242.2 Hz), 158.4 (d, JC,F 241.1
2
Hz), 159.4 (d, JC,F 244.9 Hz); δ Ϫ118.4, Ϫ118.6, Ϫ121.8 (br).
Compound 19 crystallised from a small volume of DMF to give
a solvate as granular red crystals having the composition
2
F
2
48
42
6
C, 82.0; H, 6.0; N, 12.0%); δ 2.258 (6H, s, 2 × Me), 2.273 (6H,
s, 2 × Me), 2.28 (6H, s, 2 × Me), 6.54 (4H, br s, Ar–H), 6.95–
.12 (18H, m, Ar–H), 7.96 (2H, br s, ∼2 × NH); δ 20.6 (2 ×
H
DMF : 1 19; these were used for the X-ray crystal structure
determination.
7
C
Me), 20.9 (2 × Me), 21.3 (2 × Me), 115.9, 116.5, 117.5, 118.8,
Oligomerisation of 4-fluorophenyl isocyanide 5 at ambient
temperature
1
1
20.4, 121.4, 124.3, 126.9, 128.0, 129.2, 129.7, 130.4, 131.4,
32.5, 133.1, 140.9, 146.2.
Freshly distilled 4-fluorophenyl isocyanide (2.42 g, 20 mmol)
was kept at ambient temperature in a sealed tube. Black needle
crystals formed within 24 h. The mixture was kept for 63 days
and gradually formed a reddish brown gum. It was then
extracted with portions of boiling benzene (200 mL) until the
gum had dissolved. The residual insoluble black solid was fil-
tered off, washed with boiling benzene until the washings were
colourless, giving 5,5Ј-difluorophenylindigo-3,3Ј-bis(4-fluoro-
phenylimine) 9 (147 mg, 6.1%) as blue–black needles (DMF)
which do not melt but decompose gradually >270 ЊC. The com-
bined benzene extracts were evaporated, the residue was redis-
solved in benzene (15 mL) and hexane (10 mL), and the solu-
tion was chromatographed on silica (45 × 1.5 cm) to give
orange–red hexane–benzene (3 : 1) eluates followed by orange–
red hexane–benzene (2 : 1) eluates (700 mL). Recrystallisation
from hexane of the residue from the combined and evaporated
eluates gave red crystals (25 mg, 1%) which were shown to
be identical with compound 19 obtained in the preceding
experiment.
7
,14-Di(4-methoxyphenylamino)-6,13-di(4-methoxyphenyl-
imino)pyrazino[1,2-a:4,5-aЈ]diindole 17 from 4-methoxyphenyl
isocyanide 3. Elution solvent: benzene–dichloromethane (2 : 1).
Recrystallisation from benzene–hexane gave red crystals (221
mg, 16.6%), mp 261–263 ЊC (decomp.) (Found: C, 72.4; H, 5.4;
N, 9.9. C H N O requires C, 72.2; H, 5.3; N, 10.5%); δ 3.59
6H, s, 2 × OMe), 3.76 (6H, s, 2 × OMe), 3.78 (6H, s, 2 × OMe),
.51–7.23 (22H, m, Ar–H), 7.76 (vbrs, 1.8H, 2 × NH); δ 55.4
2 × OMe), 55.5 (2 × OMe), 55.6 (2 × OMe), 103.3, 114.2,
48
42
6
6
H
(
6
(
1
1
C
14.3, 115.1, 115.7, 116.0, 117.8, 120.3, 121.4, 121.9, 124.3,
25.1, 129.0, 136.3, 142.0, 154.7, 156.0.
7
,14-Di(3,5-dimethylphenylamino)-6,13-di(3,5-dimethylphenyl-
imino)pyrazino[1,2-a:4,5-aЈ]diindole 18 from 3,5-dimethylphenyl
isocyanide 4. Elution solvent: benzene–petroleum (1 : 1). Re-
crystallisation from benzene–hexane gave orange crystals (187
mg, 14.3%), mp 314–315 ЊC (Found: C, 82.5; H, 6.9; N, 10.6.
C H N requires C, 82.4; H, 6.9; N, 10.7%); δ 2.13 (12H, s,
5
4
54
6
H
4
× Me of 7- ϩ 14-NAr or 6- ϩ 13-NAr), 2.19 (6H, s, 3- ϩ 10-
Me or 1- ϩ 8-Me), 2.36 (12H, s, 4 × Me of 6- ϩ 13-NAr or 7- ϩ
4-NAr), 2.40 (6H, s, 1- ϩ 8-Me or 3- ϩ 10-Me), 5.82 (4H, s,
Crystal structure determination of compound 9†
1
Crystal data. C H F N , M = 484.45, triclinic, a = 9.6207(11),
28
16
4
4
Ar–H), 6.36 (2H, s, Ar–H), 6.73 (8H, s, Ar–H), 6.84 (2H, s,
Ar–H), 8.27 (∼2H, br, NH); δC 18.8, 21.38, 21.42, 22.0 (1- ϩ
†
CCDC reference numbers 205332 and 205333. See http://
8
-Me, 3- ϩ 10-Me, 3- ϩ 5-Me of 7- ϩ 14-NAr, 3- ϩ 5-Me of 6-
www.rsc.org/suppdata/ob/b3/b302340k/ for crystallographic data in .cif
or other electronic format.
ϩ 13-NAr), 112.3, 114.0, 117.3, 118.4, 120.5, 123.8, 125.4,
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 2 1 6 8 – 2 1 7 2
2171