PAPER
Short Synthesis of N-(2-Ethylhexyl)-2,7-diiodocarbazole
1475
er hand, the base NaH in DMSO gave similar yields, but
the use of base K CO was connected with lower yield.
3
1
H NMR (300.1 MHz, CDCl –DMSO-d , 3:1, v/v): d = 8.29 (d,
J = 9.0 Hz, 2 H ), 7.92 (d, J = 9.0 Hz, 2 H ), 7.87 (d, J = 10.8
Hz, 2 Harom), 7.55 (d, J = 8.7 Hz, 2 Harom).
3
6
2
3
arom
arom
In conclusion, overall yields for the published five-step
3
5
procedure (Lit. 14%, Lit. 17%) and for our three-step
procedure (18%) are fully comparable. The advantage of
the shorter procedure is of course the fast performance of
the reported synthesis. Sometimes, the price of initial 4,4¢-
diiodobiphenyl can be also important, which is ca. 40%
less than that of 4,4¢-dinitro-2-biphenylamine (Aldrich).
1
3
C NMR (75 MHz, CDCl –DMSO-d = 3:1, v/v): d = 95.80 (1 C),
24.11 (2 C), 127.70 (2 C), 129.28 (2 C), 137.44 (1 C), 137.99 (2
3
6
1
C), 145.66 (1 C), 146.91 (1 C) (all aromatic).
Anal. Calcd for C H INO (325.1): C, 44.33; H, 2.48; N, 4.31; I,
3
1
2
8
2
9.04. Found: C, 44.18; H, 2.57; N, 4.25; I, 39.06.
From this point of view our reported synthesis is more 2,7-Diiodocarbazole (5)
,4¢-Diiodo-2-nitrobiphenyl (2; 6.21 g, 0.0138 mol) and Ph P (21 g,
4
than two times cheaper in comparison with the published
3
1
5,16
0.080 mol) in o-DCB (90 mL) were heated at 180 °C under argon
for 16 h. The excess of o-DCB was distilled off (70 °C/2 mbar) and
the residue was extracted with toluene–heptane (1:1, v/v, 2 × 200
mL) at 100 °C. The combined organic layers were reduced in vol-
ume and chromatographed on silica gel using the same solvent sys-
procedures. An aromatic Finkelstein reaction
ble N-arylation of primary amines
or dou-
1
7,18
could represent
another possibility for the syntheses of 2,7-dihalocarba-
zoles, but according to the best of our knowledge, these
synthetic methods were not applied to 2,7-diiodo deriva- tem as eluent. The process was controlled by TLC and the fractions
tives yet.
containing 2,7-diiodocarbazole (5) were combined and dried; yield:
1
9
3
.75 g (65%); mp 284–285 °C (Lit. mp 265–266 °C).
FT IR (ATR): 3389 (N–H stretch), 3067 (C–H stretch), 1980, 1888,
714 (overtone bands), 1590, 1471, 1453, 1416 (ring stretch), 1135
C–N stretch), 1237, 1043, 993 and 942 (C–H in-plane), 858, 819
and 800 (C–H out-of-plane), 727 (N–H wag), 523 (C–I stretch), 499
The starting 4,4¢-diiodobiphenyl and the other chemicals were pur-
chased from Aldrich and used directly without purification. Silica
gel 60 (0.063–0.200 mm, Merck) was used for column chromatog-
raphy (columns ø 3–4 × 60 cm). The TLC was performed with silica
1
(
–
1
1
13
cm (C–N–C bend).
gel 60 F2 aluminum sheets (Merck). H NMR and C NMR spec-
54
1
tra were measured in CDCl or DMSO-d with an upgraded Bruker
H NMR (300.1 MHz, CDCl –DMSO-d , 3:1, v/v): d = 10.97 (s, 1
3
6
3
6
Avance DPX-300 spectrometer at 300.13 and 75.45 MHz, respec-
tively, with hexamethyldisiloxane as internal standard. FT-IR spec-
tra were measured on a Perkin-Elmer Paragon 1000 PC Fourier
transform infrared spectrometer by means of diamond ATR. GC-
MS measurements were performed with a Perkin-Elmer Auto Sys-
tem XL gas chromatograph equipped with a Turbo Mass mass spec-
trometer.
H, NH), 7.80 (d, J = 1.2 Hz, 2 Harom), 7.78 (s, 1 Harom), 7.75 (s, 1
Harom), 7.45 (d, J = 1.5 Hz, 1 Harom), 7.42 (d, J = 1.5 Hz, 1 Harom).
13
C NMR (75 MHz, CDCl –DMSO-d , 3:1, v/v): d = 90.51 (2 C),
3
6
1
19.95 (2 C), 121.77 (4 C), 127.71 (2 C), 140.97 (2 C) (all aromat-
ic).
Anal. Calcd for C H I N (419.0): C, 34.40; H, 1.68; N, 3.34; I,
12 7 2
6
0.57. Found: C, 34.66; H, 1.57; N, 3.32; I, 60.26.
4
,4¢-Diiodo-2-nitrobiphenyl (2)
N-(2-Ethylhexyl)-2,7-diiodocarbazole (7)
To a suspension of 4,4¢-diiodobiphenyl (1; 20.30 g, 0.050 mol) in
AcOH (250 mL) at 70 °C (partial dissolution of 1) was slowly add-
ed fuming (100%) HNO (100 mL) (ca. 5 min) under stirring. The
2
2
,7-Diiodocarbazole (5; 6.50 g, 0.0155 mol), Bu NBr (0.50 g) and
-ethylhexyl bromide (25.0 g, 0.13 mol) were dissolved in toluene–
4
3
DMSO (80:35 mL) under argon. Aq 50% NaOH (120 mL) was add-
ed and the reaction mixture was heated at 80 °C for 3 h under vig-
orous stirring. The toluene–DMSO layer was separated and the aq
NaOH layer was extracted with toluene (2 × 70 mL). The combined
organic layers were washed with brine (2 × 100 mL) and dried
temperature was increased to 80 °C and kept for 30 min (complete
dissolution was noted) and the mixture was left to cool to r.t. H O
2
(900 mL) was added and the yellow precipitate was collected by fil-
tration (S2), washed with H O (150 mL), and dried to give material
2
A; yield: 19.82 g. This material was crystallized from EtOH to get
material B; yield: 12.53 g (35% of 2 calculated per starting 1, see
Table 1). The EtOH insoluble material (6.52 g) was recrystallized
from CHCl3 to obtain yellow crystals as part C (i.e., 3);
(
MgSO ). The solvents were evaporated under vacuum (95 °C) and
4
the yellow crystalline material obtained was dissolved in hot tolu-
ene (20 mL) and chromatographed on silica gel using toluene–
heptane (1:1, v/v) as eluent. The nicely separated fractions of the
product 7 were combined, evaporated, and crystallized from EtOH;
yield: 6.55 g (80%); mp 110–111 °C.
1
1
yield: 3.82 g; mp 214–215 °C (Lit. mp 212–214 °C). Column
chromatography of material B (mainly 2 + 3, see Table 2) on silica
gel using toluene–heptane (1:1, v/v) as eluent gave the pure material
1
0
2
; yield: 6.05 g; mp 154–155 °C (Lit. mp 156 °C).
FT IR (ATR): 3063 (aromatic C–H stretch), 2956, 2922, 2854 (ali-
phatic C–H stretch), 1855, 1716, 1682 (overtone bands), 1578,
2
1
483, 1446, 1421 (ring stretch), 1134 (C–N stretch), 1249, 1046,
1
H NMR (300.1 MHz, CDCl –DMSO-d , 3:1, v/v): d = 8.29 (d,
J = 8.1 Hz, 1 H ), 8.08 (d, J = 8.1 Hz, 1 H ), 7.80 (d, J = 7.8
3
6
994, and 942 (C–H in-plane), 867, 846, 820, 792 (C–H out-of-
–1
arom
arom
plane), 586 (C–I stretch), 501 cm (C–N–C bend).
Hz, 2 Harom), 7.29 (d, J = 8.1 Hz, 1 Harom), 7.11 (d, J = 8.1 Hz, 2
Harom).
1
H NMR (300.1 MHz, CDCl ): d = 7.74 (d, J = 8.1 Hz, 2 Harom),
3
7
.67 (s, 2 Harom), 7.49 (d, J = 6.9 Hz, 2 Harom), 4.02 (m, 2 H, NCH2),
1
3
C NMR (75 MHz, CDCl –DMSO-d , 3:1, v/v): d = 93.83 (1 C),
3
6
1.98 (m, 1 H, =CH), 1.31 (m, 8 H, 4 × CH ), 0.89 (t, J = 14.7 Hz, 6
2
9
1
5.11 (1 C), 129.74 (2 C), 132.17 (1 C), 133.20 (1 C), 133.57 (1 C),
35.77 (1 C), 137.59 (2 C), 144.23 (1 C), 148.95 (1 C) (all aromat-
H, 2 × CH ).
3
1
3
C NMR (75 MHz, CDCl ): d = 10.93, 14.10, 23.08, 24.33, 28.51,
3
ic).
3
0.74, 39.15, 47.55 (8 C, aliphatic) and 90.81 (2 C), 118.27 (2 C),
Anal. Calcd for C H I NO (451.0): C, 31.96; H, 1.56; N, 3.11; I,
12
7
2
2
121.77 (4 C), 128.18 (2 C), 141.72 (2 C) (all aromatic).
5
6.28. Found: C, 32.25; H, 1.53; N, 3.20; I, 55.91.
Anal. Calcd for C H I N (531.2): C, 45.22; H, 4.36; N, 2.64; I,
2
0
23 2
4
7.78. Found: C, 45.32; H, 4.16; N, 2.55; I, 47.95.
Synthesis 2011, No. 9, 1472–1476 © Thieme Stuttgart · New York