Y. Maegawa et al. / Tetrahedron Letters 47 (2006) 6957–6960
6959
R
N
R
N
CH3(CH2)16CH2N+Me3Cl-
[Rh(cod)(CH3CN)2]BF4, HSi(OEt)3
Et3N, DMF
NaOH aq
Si(OEt)3
3.6 nm
I
I
(EtO)3Si
5a
2a : R =H
2b : R = Me
2c : R = octyl
4a : R =H, 89% yield
4b : R = Me, 75% yield
4c : R = octyl, 70% yield
carbazole-silica
mesoporous material
Scheme 2.
M. P.; Yang, Q.; Inagaki, S. J. Am. Chem. Soc. 2002, 124,
15176–15177; (d) Kapoor, M. P.; Yang, Q.; Inagaki, S.
Chem. Mater. 2004, 16, 1209–1213; (e) Kapoor, M. P.;
Inagaki, S.; Ikeda, S.; Kakiuchi, K.; Suda, M.; Shimada,
T. J. Am. Chem. Soc. 2005, 127, 8174–8178.
N-methylcarbazole at 25 °C for 40 h gave the corre-
sponding iodinated compound 2b in 93% yield, but the
reaction was not completed within 20 h (Table 2, entries
1 and 2). The reaction of N-octylcarbazole gave an
inseparable mixture of di- and monoiodinated com-
pounds, and was not completed even with prolonged
reaction times (Table 2, entry 3). While seeking the opti-
mal reaction conditions, we found that the use of 2 equiv
of trifluoromethanesulfonic acid at 25 °C for 60 h gave
the desired product 2c in excellent yield (95%; Table 2,
entry 7). Furthermore, N-phenylcarbazole was success-
fully diiodinated to give N-phenyl-3,6-diiodocarbazole
exclusively in an isolated yield of 93% (Table 2, entry 9).
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The resulting diiodocarbazoles 2a–c were subjected to
rhodium-catalyzed disilylation with triethoxysilane,
which proceeded smoothly to give the corresponding
bis(triethoxysilyl)carbazoles 4a–c in 89%, 75% and
70% yields,15 respectively, although the use of 3,6-dibromo-
carbazole as a starting material under similar reaction
conditions resulted in no reaction. In addition, we devel-
oped a purification method, using charcoal, for the
resulting crude products 4a–c, which allowed separation
of the reduction product 1a.16 The purified 4a was poly-
merized in 6 M sodium hydroxide in the presence of
octadecyltrimethylammonium chloride to give carba-
zole–silica mesoporous material 5a with a diameter of
3.6 nm (Scheme 2).17 This novel preparation method
for arylene-bridged organosilanes should allow the
development of numerous promising precursors for
sol–gel polymerization.
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In summary, we have developed a useful method
for diiodination of N-unsubstituted, N-methyl and
N-octylcarbazoles with bis(pyridine)iodonium tetrafluo-
roborate followed by subsequent rhodium-catalyzed
silylation with triethoxysilane at the 3,6-position to give
the corresponding 3,6-bis(triethoxysilyl)carbazole deriv-
atives in good yield.
References and notes
1. (a) Wight, A. P.; Davis, M. E. Chem. Rev. 2002, 102,
3589–3614, and references cited therein; (b) Loy, D. A.;
Shea, K. J. Chem. Rev. 1995, 95, 1431–1442, and
references cited therein; (c) Cerveau, G.; Chappellet, S.;
Corriu, R. J. P.; Dabiens, B. J. Organomet. Chem. 2001,
626, 92–99.
2. (a) Inagaki, S.; Guan, S.; Ohsuna, T.; Terasaki, O. Nature
2002, 416, 304–307; (b) Yang, Q.; Kapoor, M. P.; Inagaki,
S. J. Am. Chem. Soc. 2002, 124, 9694–9695; (c) Kapoor,
13. Shimada, T.; Suda, M.; Nagano, T.; Kakiuchi, K. J. Org.
Chem. 2005, 70, 10178–10181.
14. General procedure for the diiodination of carbazole (1a)
with bis(pyridine)iodonium tetrafluoroborate. To a solution
of bis(pyridine)iodonium tetrafluoroborate (278 mg,
0.75 mmol) and carbazole (1a) (50.0 mg, 0.30 mmol) in