January 2012
Silole-Core Phenylacetylene Dendrimers and Their Application in Detecting Picric Acid
69
recorded using an LCQ Advantage mass spectrometer. Absorp-
tion spectra were measured with a CARY 100 Conc UV–vis
spectrophotometer. Fluorescence spectra were recorded with a
CARY Eclipse fluorescence spectrophotometer in a 1-cm
quartz cell. All reagents were purchased from commercial
sources and distilled or dried when necessary using the stand-
ard procedures. All solvents and reagents were of reagent
quality, purchased from commercial sources and used without
further purification unless mentioned below. Triethylamine
was distilled from calcium hydride. Reactions were carried out
under an inert atmosphere (dry argon) when necessary.
Synthesis. The synthetic route is shown in Schemes 1 and 2.
4,40-(5-Bromo-1,3-phenylene)bis(ethyne-2,1-diyl)bis(tert-
butylbenzene) (3a). A flask with 30-mL degassed Et3N was
charged with compound 2 (1.5 g, 4.8 mmol, 1 eq.), CuI
(18 mg, 0.095 mmol, 0.02 eq.) and Pd(PPh3)4 (110 mg,
0.095 mmol, 0.02 eq.) under a stream of Ar. Compound 1
(1.65 g, 10.5 mmol, 2.2 eq.) dissolved in 10-mL degassed Et3N
was dropwised more than 1 h at 80ꢁC. After that, the solution
was stirred for 4 h. Then, the mixture was diluted with dichloro-
methane, washed with water, dried by MgSO4, and filtered. The
concentrated product was purified by flash chromatography, elut-
ing with petroleum ether to give 3a as white powder (1.452 g,
64.4%). 1H NMR (CDCl3, 500 MHz) d: 1.35 (s, 18 H), 7.39
(d, J ¼ 8.3 Hz, 4 H), 7.46 (d, J ¼ 8.3 Hz, 4 H), 7.61 (s, 3H).
MS(EI): m/z 468.1 [M]þ (calcd for C30H29Br 468.1).
4-(3,5-Bis((3,5-bis((4-tert-butylphenyl)ethynyl)phenyl)ethynyl)-
phenyl)-2-methylbut-3-yn-2-ol (4b). Compound 4b was synthe-
sized analogous to compound 3b except that toluene was
added as co-solvent. The product was purified by flash chro-
matography, eluting with 50% CH2Cl2/petroleum ether to give
4b as white powder (106 mg, 54%). 1H NMR (CDCl3, 500
MHz) d: 1.36 (s, 36 H), 1.64 (s, 6H), 7.40 (d, J ¼ 8.4 Hz, 8
H), 7.47 (d, J ¼ 8.4 Hz, 8 H), 7.56–7.58 (m, 2 H), 7.62–7.64
(m, 5 H), 7.66–7.68 (m, 2 H). MS(ESI): m/z 985.5 [MþH]þ
(calcd for C75H68OþH 985.5).
4,40,400,4000-(5,50-(5-Ethynyl-1,3-phenylene)bis(ethyne-2,1-diyl)-
bis(benzene-5,3,1-triyl))tetrakis(ethyne-2,1-diyl)tetrakis(tert-
butylbenzene) (4c). Compound 4c was synthesized analogous
to compound 3c. The concentrated product was purified by
flash chromatography, eluting with 10% CH2Cl2/petroleum
ether to give 4c as white powder (76 mg, 82%). 1H NMR
(CDCl3, 500 MHz) d: 1.34 (s, 36 H), 3.15 (s, 1 H), 7.39 (d,
J ¼ 8.4 Hz, 8 H), 7.48 (d, J ¼ 8.4 Hz, 8 H), 7.62–7.65 (m, 6
H), 7.66–7.68 (m, 3 H). MS(ESI): m/z 927.5 [MþH]þ (calcd
for C72H62þH 927.5).
2,5-Dibromo-1,1-dimethyl-3,4-diphenylsilole (5a). Compound
5a was synthesized according to the literature þ[13]. yield:
64.0%. m.p. 162–163ꢁC. MS(EI): m/z 419.9 [M] (calcd for
C18H16Br2Si 420.2).
2,5-Bis((4-tert-butylphenyl)ethynyl)-1,1-dimethyl-3,4-diphe-
nylsilole (6). A flask was charged with 5a (200 mg, 0.478
mmol, 1 eq.), compound 1 (107 mg, 1.05 mmol, 2.2 eq.),
ZnCl2 (40.8 g, 0.3 mmol), Pd(PPh3)4 (12 mg, 0.01 mmol),
5-mL Et3N and 20-mL THF, then degassed by Ar. The result-
ing mixture was placed in a 65ꢁC oil bath for 7 h. Upon com-
pletion, the mixture was diluted with petroleum ether and fil-
tered through a thin pad of silica (50% CH2Cl2/petroleum
ether). The concentrated product was purified by flash chroma-
tography, eluting with 10% CH2Cl2/petroleum ether to give 6
as yellow powder (186 mg, 67.5%).1H NMR (CDCl3, 400
MHz) d: 0.55 (s, 6 H), 1.30 (s, 18 H), 7.20 (s, 10 H), 7.24 (d,
J ¼ 8.8 Hz, 4 H), 7.29 (d, J ¼ 8.8 Hz, 4 H). MS(EI): m/z
574.3 [M]þ (calcd for C42H42Si 574.3).
4-(3,5-Bis((4-tert-butylphenyl)ethynyl)phenyl)-2-methylbut-3-
yn-2-ol (3b). A flask with 20-mL degassed Et3N was charged
with compound 3a (357 mg, 0.76 mmol, 1 eq.), 2-methylbut-
3-yn-2-ol (128 mg, 1.52 mmol, 2 eq.), CuI (3 mg, 0.015
mmol, 0.02 eq.), and Pd(PPh3)4 (18 mg, 0.015 mmol, 0.02 eq.)
under a stream of Ar. The solution was stirred about 5 h at
80ꢁC. Then the mixture was diluted with dichloromethane,
washed with water, dried by MgSO4, and filtered. The concen-
trated product was purified by flash chromatography, eluting
with 15% EtOAc/petroleum ether to give 3b as white powder
1
(274 mg, 76.3%). H NMR (CDCl3, 500 MHz) d: 1.36 (s, 18
H), 1.64 (s, 6H), 7.39 (d, J ¼ 8.4 Hz, 4 H), 7.46 (d, J ¼ 8.4
Hz, 4 H), 7.53 (s, 2H), 7.64 (s, 1 H). MS(EI): m/z 472.3 [M]þ
(calcd for C35H36O 472.3).
2,5-Bis((3,5-bis((4-tert-butylphenyl)ethynyl)phenyl)ethynyl)-
1,1-dimethyl-3,4-diphenylsilole (7). Compound 7 was synthe-
sized analogous to compound 6. The concentrated product was
purified by flash chromatography, eluting with 15% CH2Cl2/
petroleum ether to give 7 as yellow powder (84 mg, 53.2%).
1H NMR (CDCl3, 400 MHz) d: 0.52 (s, 6 H), 1.26 (s, 36 H),
7.11–7.18 (m, 10 H), 7.31 (d, J ¼ 8.8 Hz, 12 H), 7.39 (d, J ¼
8.4 Hz, 8 H), 7.49 (t, J ¼ 1.6 Hz, 2H). MS(ESI): m/z 1125.6
[MþK]þ (calcd for C82H74SiþK 1125.6).
4,40-(5-Ethynyl-1,3-phenylene)bis(ethyne-2,1-diyl)bis(tert-
butylbenzene) (3c). Compound 3b (274 mg, 0.58 mmol), KOH
(0.1 g, 1.8 mmol), and 15-mL toluene were added into a flask and
protected by Ar. The solution was stirred about 3 h at reflux. Then,
the mixture was diluted with dichloromethane, washed with water,
dried by MgSO4, and filtered. The concentrated product was puri-
fied by flash chromatography, eluting with petroleum ether to give
1
3c as colorless oil (225 mg, 93.6%). H NMR (CDCl3, 500 MHz)
2,5-Bis((3,5-bis((3,5-bis((4-tert-butylphenyl)ethynyl)phenyl)-
ethynyl)phenyl)ethynyl)-1,1-dimethyl-3,4-diphenylsilole (8).
Compound 5b was synthesized analogous to compound 5a
except using I2 instead of NBS. After concentration, the mix-
ture was used in the next step directly without purification.
Compound 4c (260 mg, 0.28 mmol), mixture with 5b, ZnCl2
(10 mg, 0.07 mmol), Pd(PPh3)4 (24 mg, 0.02 mmol), 40-mL
THF and 8-mL Et3N were charged in a flask, then degassed by
Ar. The resulting mixture was placed in a 40ꢁC oil bath for 12
h. However, when checked by TLC, there were lots of
unreacted 4c and no products and temperature was raised to
65ꢁC. After 12 h, the mixture was diluted with petroleum ether
and filtered through a thin pad of silica (50% CH2Cl2/petro-
leum ether). The concentrated product was purified by flash
d: 1.36 (s, 18 H), 3.10 (s, 1 H), 7.38 (d, J ¼ 8.2 Hz, 4 H), 7.46 (d,
J ¼ 8.2 Hz, 4 H), 7.58 (s, 2 H), 7.66 (s, 1 H). MS(EI): m/z 414.2
[M]þ (calcd for C32H30 414.2).
4,40,400,4000-(5,50-(5-Bromo-1,3-phenylene)bis(ethyne-2,1-diyl)-
bis(benzene-5,3,1-triyl))tetrakis(ethyne-2,1-diyl)tetrakis(tert-
butylbenzene) (4a). Compound 4a was synthesized analogous
to compound 3a except that toluene was added as cosolvent.
The product was purified by flash chromatography, eluting
with 10% CH2Cl2/petroleum ether to give 4a as white powder
1
(256 mg, 40.8%). H NMR (CDCl3, 500 MHz) d: 1.35 (s, 36
H), 7.39 (d, J ¼ 8.3 Hz, 8 H), 7.47 (d, J ¼ 8.3 Hz, 8 H),
7.62–7.68 (m, 9 H). MS(ESI): m/z 981.4 [MþH]þ (calcd for
C70H61Br þ H 981.4).
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet