LETTER
Synthesis of Indolo[3,2-b]carbazoles
327
Table 1 Synthesis of Indolo[3,2-b]carbazoles 2 from the 3,3¢-
Bis(indolyl)methanes 1 Catalyzed by Iodine
In summary, we have reported a very simple, mild, and
highly efficient method for the synthesis of indolo[3,2-
b]carbazoles from 3,3¢-bis(indolyl)methanes of aromatic
aldehydes in the presence of molecular iodine as catalyst.
This very simple, mild, and cost-effective procedure for
the synthesis of various indolo[3,2-b]carbazoles is a valu-
able addition to the chemistry of indolocarbazoles.
Producta
R
Time
(
Yield Mp
min) (%)b
(°C)
2
2
2
2
a
b
c
20
80
80
84
55
350
20
20
35
>400
384
Me
MeO
Cl
Acknowledgment
The authors thank Dr. P. G. Rao, the Director, NEIST, Jorhat for
providing the facilities to perform the work. M.L.D. thanks CSIR
(India) for the award of a Senior Research Fellowship.
d
365
References and Notes
(
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2
2
2
e
f
35
22
20
50
75
75
340
>400
358
1
(
Cl
R.; Bergman, J. Chem. Biol. 1995, 2, 841.
(3) Wei, Y.; Helleberg, H.; Rannug, U.; Rannug, A. Chem. Biol.
Interact. 1998, 110, 39.
HO
(
(
(
4) Gonzalez, F. J.; Fernandez-Salguero, P.; Ward, J. M.
J. Toxicol. Sci. 1996, 21, 273.
g
5) Wu, Y. L.; Li, Y.; Gardner, S.; Ong, B. S. J. Am. Chem. Soc.
2
005, 127, 614.
6) Grotta, H. M.; Riggle, C. J.; Bearse, A. E. J. Org. Chem.
961, 26, 1509.
OH
1
HO
2
2
2
h
i
20
20
35
75
85
68
392
>400
373
(
(
(
7) Robinson, B. J. Chem. Soc. 1963, 3097.
8) Bergman, J. Tetrahedron 1970, 26, 3353.
9) Katritzky, A. R.; Li, J. Q.; Stevens, C. V. J. Org. Chem.
MeO
MeO
1995, 60, 3401.
(
10) Wille, G.; Mayser, P.; Thoma, W.; Monsees, T.; Baumgart,
A.; Schmitz, H.-J.; Schrenk, D.; Polborn, K.; Steglich, W.
Bioorg. Med. Chem. 2001, 9, 955.
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12) Pindur, U.; Muller, J. Arch. Pharm. (Weinheim, Ger.) 1987,
20, 280.
13) Wahlstrom, N.; Stensland, B.; Bergman, J. Synthesis 2004,
187.
MeO
MeO
(
(
O
O
j
3
(
1
a
(14) (a) Bandgar, B. P.; Shaikh, K. A. Tetrahedron Lett. 2003, 44,
1959. (b) Wu, J.; Xia Guang, H.; Gao, K. Org. Biomol.
Chem. 2006, 4, 126. (c) Sun, J.; Dong, Y.; Cao, L.; Wang,
X.; Wang, S.; Hu, Y. J. Org. Chem. 2004, 69, 8932.
All reactions were performed at 1 mmol scale using 2 mol% of I2.
Isolated yields.
b
of 3,3¢-bis(indolyl)methane. As we expected that decom-
position of [A] would lead to formation of [B] avoiding
the presence of indole [C] we performed the reaction of 3-
alkylated indoles [A] under thermal conditions using a
catalytic amount of iodine in an attempt to form indo-
lo[3,2-b]carbazoles. Unfortunately, we did not obtain the
desired product. Hence it was concluded that the interme-
diate [B] does not form in the absence of indole under
these reaction conditions. However, these observations
further support our proposed mechanism shown in
Scheme 2.
(15) Gu, R.; Hameurlaine, A.; Dehaen, W. Synlett 2006, 1535.
(16) (a) Bhuyan, P. J.; Boruah, R. C.; Sandhu, J. S. Tetrahedron
Lett. 1989, 30, 1421. (b) Deb, M. L.; Bhuyan, P. J.
Tetrahedron Lett. 2006, 47, 1441. (c) Devi, I.; Bhuyan, P. J.
Synlett 2004, 283. (d) Devi, I.; Borah, H. N.; Bhuyan, P. J.
Tetrahedron Lett. 2004, 45, 2405. (e) Devi, I.; Bhuyan, P. J.
Tetrahedron Lett. 2004, 45, 8625. (f) Devi, I.; Baruah, B.;
Bhuyan, P. J. Synlett 2006, 2593. (g) Deb, M. L.; Bhuyan,
P. J. Tetrahedron Lett. 2007, 48, 2159. (h) Kalita, P.;
Baruah, B.; Bhuyan, P. J. Tetrahedron Lett. 2006, 47, 7779.
(
17) Experimental Procedure: 3,3¢-Bis(indolyl)phenylmethane
(
1a, 1 mmol, 322 mg) was taken up in a round-bottom flask
containing MeCN (5 mL). I (2 mol%) was added and the
2
We then studied the reaction using different Lewis acid
catalysts such as InCl , CAN, ZnCl , but only InCl gave
the desired product (15%) after refluxing for two hours.
Hence iodine is the optimal catalyst for the purpose of the
reaction. Further study of the reaction is in progress.
mixture refluxed for 20 min. The obtained solid was filtered,
dried, and recrystallized from a mixture of DMF–CHCl .
3
2
3
3
The structure of the compound obtained was identified from
spectroscopic data and elemental analysis.
6,12-Diphenyl-5,11-dihydroindolo[3,2-b]carbazole (2a)
White solid, mp 350 °C. Yield 80% (326 mg). R = 0.84
f
[
EtOAc (7%)–PE]. IR (KBr): 3394 (NH stretch), 3062 (w),
Synlett 2008, No. 3, 325–328 © Thieme Stuttgart · New York