8080
Y. Tobe et al. / Tetrahedron 57 2001) 8075±8083
5 h and then ®ltered. The ®ltrate was concentrated and
subjected to column chromatography on silica gel :eluent:
hexane) to afford 1-bromo-3-t-butyl-5-[:trimethylsilyl)-
129.56 :d), 123.72 :s), 121.64 :s), 106.40 :s), 91.05 :s),
81.35 :s), 73.82 :s), 34.67 :s), 31.04 :q), 18.69 :d), 11.36
21
:q);IR :KBr) 2950, 2850, 2150, 1580, 875, 680, cm
;
1
ethynyl]benzene as a yellow oil :58.4 g, 98%): H NMR
HRMS :EI) m/z calcd for C46H66Si2 674.4703, found
674.4708. Anal. calcd for C46H66Si2: C, 81.83;H, 9.85;Si,
8.32. Found: C, 81.93;H, 10.04.
:270 MHz, CDCl3) d 7.45 :t, J1.9 Hz, 1H), 7.43 :t,
J1.9 Hz, 1H), 7.39 :t, J1.9 Hz, 1H), 1.28 :s, 9H), 0.25
:s, 9H); 13C NMR :67.5 MHz, CDCl3) d 153.31 :s), 131.81
:d), 129.06 :d), 127.73 :d), 124.54 :s), 121.93 :s), 103.95 :s),
94.97 :s), 34.83 :s), 31.04 :s), 20.09 :q);IR :neat) 2950,
2880, 2150, 1548, 1240, 928, 850, 752, 682 cm21;HRMS
:EI) m/z calcd for C15H21BrSi 308.0596, found 308.0590.
1.1.8. Dimer 5b. To a solution of 5a :3.34 g, 5.09 mmol) in
50 mL of THF was added dropwise a solution of TBAF in
THF :1.0 M, 12.7 mL, 12.7 mmol) and the mixture was
stirred at room temperature for 2.5 h. The mixture was
diluted with water and extracted with hexane. The extract
was washed with brine and dried over MgSO4. After
removal of the solvent, ¯ash chromatography :eluent:
hexane) afforded 5b as a pale yellow solid :1.78 g, 96%):
1.1.5. 1-t-Butyl-3-[,triisopropylsilyl)ethynyl]-5-[,trimethyl-
silyl)ethynyl]benzene ,6a). Compound 6a was prepared
according to the same procedure as described above using
1-bromo-3-t-butyl-5-[:trimethylsilyl)ethynyl]benzene :20.1 g,
65.0 mmol), :triisopropylsilyl)acetylene :17.4 mL, 78.0
mmol), Pd:PPh3)4 :2.25 g, 1.95 mmol), CuI :742 mg,
3.9 mmol), and Et3N :54.4 mL, 390 mmol) in 100 mL of
benzene. Puri®cation by column chromatography :eluent:
1
m p 97±988C; H NMR :270 MHz, CDCl3) d 7.53 :t, J
1.7 Hz, 2H), 7.51 :t, J1.7 Hz, 2H), 7.46 :t, J1.7 Hz, 2H),
3.06 :s, 2H), 1.29 :s, 18H); 13C NMR :67.5 MHz, CDCl3) d
151.74 :s), 132.97 :d), 130.19 :d), 130.05 :d), 122.30 :s),
121.70 :s), 82.98 :d), 81.20 :s), 77.53 :s), 73.92 :s), 34.63
:s), 30.95 :q);IR :KBr) 3280, 2950, 2860, 2170, 2100, 1570,
872, 685 cm21;MS :EI) m/z 362 :M1). Anal. Calcd for
C28H26: C, 92.77;H, 7.23. Found: C, 92.58;H, 7.27.
1
hexane) afforded 6a as a pale yellow oil :22.8 g, 85%): H
NMR :270 MHz, CDCl3) d 7.41±7.43 :m, 3H), 1.29 :s, 9H),
1.13 :s, 21H), 0.25 :s, 9H); 13C NMR :67.5 MHz, CDCl3) d
151.26 :s), 132.81 :d), 129.08 :d), 129.04 :d), 123.46 :s),
123.08 :s), 106.82 :s), 104.86 :s), 93.94 :s), 90.32 :s), 34.59
:s), 31.11 :q), 18.73 :d), 11.46 :q), 0.01 :q);IR :neat) 2940,
1.1.9. Mono-brominated monomer 6c. To a solution of
411 mg :1.00 mmol) of 6a in 7 mL of acetone was added
successively 178 mg :1.00 mmol) of NBS and 10 mg
:0.06 mmol) of AgNO3. The mixture was stirred at room
temperature for 2 h, and after dilution with water, the
mixture was extracted with hexane. The extract was washed
with brine and dried over MgSO4. Removal of the solvent
followed by ¯ash chromatography :eluent: hexane) afforded
6c as a light yellow oil :399 mg, 96%): 1H NMR :270 MHz,
CDCl3) d 7.43 :t, J1.6 Hz, 1H), 7.41 :t, J1.6 Hz, 1H),
7.40 :t, J1.6 Hz, 1H), 1.29 :s, 9H), 1.13 :s, 21H); 13C NMR
:67.5 MHz, CDCl3) d 151.53 :s), 132.77 :d), 129.25 :d),
129.14 :d), 123.51 :s), 122.47 :s), 106.51 :s), 90.80 :s),
79.81 :s), 49.68 :s), 34.65 :s), 31.05 :q), 18.67 :d), 11.33
2850, 2140, 1570, 1242, 968, 847, 835, 752, 683 cm21
;
HRMS :EI) m/z calcd for C26H42Si2 410.2825, found
410.2805.
1.1.6. 1-t-Butyl-3-ethynyl-5-[,triisopropylsilyl)ethynyl]-
benzene ,6b). To a solution of 6a :5.0 g, 12 mmol) in
THF :20 mL) and MeOH :20 mL), 1 M aqueous K2CO3
:0.5 mL) was added under nitrogen and the mixture
was stirred at room temperature for 2 h. The reaction was
quenched by dilution with water, and the mixture was
extracted with hexane. The extract was washed with brine
and dried over MgSO4. The solvent was removed in vacuo,
and the residue puri®ed with ¯ash chromatography to give
6b as a pale yellow oil :4.03 g, 98%): 1H NMR :270 MHz,
CDCl3) d 7.40±7.44 :m, 3H), 3.00 :s, 1H), 1.27 :s, 9H), 1.11
:s, 21H); 13C NMR :67.5 MHz, CDCl3) d 151.44 :s), 132.92
:d), 129.31 :d), 129.25 :d), 123.54 :s), 122.01 :s), 106.64 :s),
90.65 :s), 83.37 :d), 77.07 :s), 34.58 :s), 31.05 :q), 18.69 :d),
11.36 :q);IR :neat) 2950, 2860, 2150, 1580, 1460, 958, 878,
680 cm21;HRMS :EI) m/z calcd for C23H34Si 338.2430,
found 338.2395.
:q);IR :neat) 2940, 2860, 2200, 2150, 1580, 875, 690 cm 21
;
HRMS :EI) m/z calcd for C23H33SiBr 416.1535, found
416.1525.
1.1.10. TIPS-protected linear tetramer 8a. A ¯ask was
charged with dimer 5b :1.09 g, 3.01 mmol), bromide 6c
:3.77 g, 9.03 mmol), Pd2:dba)3´CHCl3 :187 mg, 0.181
mmol), CuI :28.7 mg, 0.151 mmol), LiI :161 mg, 1.20
mmol), HMPA :0.21 mL, 1.2 mmol), and benzene :20
mL) under nitrogen. After stirring at room temperature for
5 min, 1,2,2,6,6-pentamethylpiperidine :3.05 mL, 16.8
mmol) was added dropwise. After stirring at room tempera-
ture for 7 h, the reaction mixture was poured into 1N
aqueous HCl and the mixture was extracted with CHCl3.
The extract was washed with water and dried over
MgSO4. Evaporation of the solvent followed by ¯ash
chromatography gave 8a as a yellow solid :942 mg, 30%).
At the same time, 228 mg of 5a, the dimer of 6c was also
isolated. 8a: mp 133±1348C; 1H NMR :270 MHz, CDCl3) d
7.55±7.56 :m, 4H), 7.46±7.51 :m, 8H), 1.36 :s, 36H), 1.14
:s, 42H); 13C NMR :67.5 MHz, CDCl3) d 152.02 :s), 151.70
:s), 133.25 :d), 133.19 :d), 130.65 :d), 130.60 :d), 129.90
:d), 129.62 :d), 123.71 :s), 122.03 :s), 121.90 :s), 121.48 :s),
106.35 :s), 91.13 :s), 81.63 :s), 81.18 :s), 80.91 :s), 74.14
:s), 74.03 :s), 73.67 :s), 34.79 :s), 34.70 :s), 31.04 :t), 30.99
1.1.7. Doubly TIPS-protected dimer 5a. To a solution of
Cu:OAc)2 :5.40 g, 29.7 mmol) in pyridine :40 mL) and
MeOH :40 mL), a solution of 4.03 g :11.8 mmol) of 6b in
20 mL of the same solvent was added under a nitrogen
atmosphere. The mixture was stirred at room temperature
for 7.5 h. Evaporation of the solvent gave a residue, which
was acidi®ed with 1N aqueous HCl and extracted with ether.
The extract was washed successively with 2N aqueous
NaOH, water, and brine and dried over MgSO4. The solvent
was evaporated in vacuo, and subsequent puri®cation with
¯ash chromatography :eluent: hexane) gave 5a as a color-
less solid :3.44 g, 86%): mp 157±1588C; 1H NMR
:270 MHz, CDCl3) d 7.49 :t, J1.7 Hz, 2H), 7.47 :d, J
1.7 Hz, 4H), 1.31 :s, 18H), 1.14 :s, 42H); 13C NMR
:67.5 MHz, CDCl3) d 151.64 :s), 133.23 :d), 129.78 :d),