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(11.3 mmol, 50%) of crystalline 8 as well as 1.65 g (7.42 mmol, 33%)
of recovered starting material 1. This was directly used for a second
conversion so that, after two consecutive runs, the overall yield of 8
amounted to 5.23 g (15.0 mmol, 66%). Analytically pure samples were
the filtrate in vacuo, and the residual crude material was purified by
column chromatography (silica gel, hexane) to obtain 11 as a
colorless solid: yield 0.495 g (1.12 mmol, 80%). Compound 11
crystallized from a solution in MeOH/t-BuOMe (3:1) upon
evaporation in the form of thin colorless needles that were suitable
for X-ray structure analysis: 1H NMR (250.1 MHz, CDCl3) δ 0.41
(s, 18H; SiMe3), 0.42 (s, 18H; SiMe33), 7.56 (dd, 2H, 3JHH = 7.8 Hz,
4JHH = 2.0 Hz; H-5), 7.77 (dd, 2H, JHH = 7.8 Hz, 5JHH = 0.5 Hz;
H-6), 7.92 (dd, 2H, 4JHH = 2.0 Hz, 5JHH = 0.5 Hz; H-3); 13C NMR
(75.4 MHz, CDCl3) δ 2.1 (SiMe3), 2.1 (SiMe3), 126.5 (C-5), 134.4
(C-3), 135.9 (C-6), 140.4 (C-4), 145.0 (C-1), 146.8 (C-2); 29Si
INEPT NMR (59.6 MHz, CDCl3) δ −3.2, −2.9. Anal. Calcd for
C24H42Si4 [442.94]: C, 65.08; H, 9.56. Found: C, 64.78; H, 9.50.
4-Phenyl-1,2-bis(trimethylsilyl)benzene (12). Method A: via the
Suzuki-type coupling reaction of 5 and C6H5B(OH)2. This compound
was obtained according to the general procedure for Suzuki-type
coupling reactions (cf. 11). Subsequent purification by HPLC using a
RP C18 semipreparative column eluted with MeOH/t-BuOMe (3:1)
gave 12 as a colorless liquid: yield 85%. Method B: via the Suzuki-type
coupling reaction of 8 and C6H5Br. This compound was obtained
according to the general procedure for Suzuki-type coupling reactions
(cf. 11). Subsequent column chromatography (silica gel, hexane) gave
12 as a colorless liquid: yield 75%. Method C: via the Stille-type
coupling reaction of 10 and C6H5Br. 10 (0.018 g, 0.047 mmol),
C6H5Br (0.005 mL, 0.008 g, 0.05 mmol), and [Pd(PPh3)4] (0.004 g,
0.003 mmol) were dissolved in toluene (5 mL). The solution was
heated to 100 °C (oil bath temperature) under vigorous stirring for 1
day, cooled to rt, and all volatiles were removed in vacuo. The residual
crude material was purified by column chromatography (silica gel,
hexane) to obtain 12 as a colorless liquid: yield 0.011 g (0.037 mmol,
80%). Method D: via the entrainment method. Mg turnings (0.23 g,
9.5 mmol) were covered with THF (30 mL) and treated at rt with neat
Me3SiCl (0.8 mL, 0.7 g, 6 mmol) and 15 (0.21 g, 0.67 mmol). A
temperature of approximately 20 °C was maintained by means of a
water bath throughout the reaction time. A solution of 1,2-C2H4Br2
(0.060 mL, 0.13 g, 0.70 mmol) in THF (10 mL) was added dropwise
to the vigorously stirred slurry over 30 min. After further stirring for 1
day at rt, the slurry was filtered, the filtrate treated with H2O (10 mL),
and the organic phase separated with a separation funnel. The aqueous
phase was extracted with CHCl3 (3 × 10 mL), the organic phases were
combined, washed with H2O (2 × 10 mL), dried over anhydrous
MgSO4, and filtered. All volatiles were removed from the filtrate in
vacuo, and the residual crude material was purified by HPLC using a
RP C18 semipreparative column eluted with MeOH/t-BuOMe (3:1)
to obtain 12 as a colorless liquid: yield 0.120 g (0.402 mmol, 60%); 1H
NMR (400.1 MHz, CDCl3) δ 0.42 (s, 9H; SiMe3), 0.43 (s, 9H;
SiMe3), 7.37 (t, 1H, 3JHH = 7.5 Hz; C6H5), 7.46 (vt, 2H, 3JHH = 7.5 Hz;
C6H5), 7.56 (dd, 1H, 3JHH = 7.8 Hz, 4JHH = 1.8 Hz; H-5), 7.61 (d, 2H,
1
obtained by column chromatography (silica gel, hexane): H NMR
(250.1 MHz, CDCl3) δ 0.36 (s, 9H; SiMe3), 0.38 (s, 9H; SiMe3), 1.33
(s, 12H; Me), 7.67 (dd, 1H, 3JHH = 7.5 Hz, 5JHH = 0.6 Hz; H-6), 7.75
(dd, 1H, 3JHH = 7.5 Hz, 4JHH = 1.2 Hz; H-5), 8.08 (m, 1H; H-3); 13
C
NMR (75.4 MHz, CDCl3) δ 2.0 (SiMe3), 2.1 (SiMe3), 25.0 (CCH3),
83.8 (CCH3), 127.9 (C-4), 134.1 (C-5), 134.6 (C-6), 141.2 (C-3),
145.1 (C-2), 149.9 (C-1); 11B NMR (96.3 MHz, CDCl3) δ 30.7 (h1/2
= 400 Hz); 29Si INEPT NMR (59.6 MHz, CDCl3) δ −3.4, −3.2. Anal.
Calcd for C18H33BO2Si2 [348.43]: C, 62.05; H, 9.55. Found: C, 61.64;
H, 9.26.
4-Methyl-1,2-bis(trimethylsilyl)benzene (9). A solution of 5 (0.205
g, 0.681 mmol) in Et2O (10 mL) was cooled to −78 °C and t-BuLi in
pentane (1.6 M, 0.70 mL, 1.1 mmol) was added dropwise with stirring.
After 45 min, the reaction mixture was slowly warmed from −78 °C to
rt and stirred for further 1 h. To the resulting pale yellow solution was
added MeI (0.070 mL, 0.16 g, 1.1 mmol), and after stirring for 12 h at
rt, the reaction mixture was quenched by the addition of a saturated
aqueous solution of NH4Cl (5 mL). The organic phase was separated
with a separation funnel, and the aqueous phase was extracted with
hexane (3 × 10 mL). The organic phases were combined, washed with
H2O (2 × 10 mL), dried over anhydrous MgSO4, and filtered. All
volatiles were removed from the filtrate in vacuo, and the residual
crude material was purified by column chromatography (silica gel,
hexane) to give 9 as a colorless liquid: yield 0.122 g (0.516 mmol,
76%). Analytically pure samples were obtained by HPLC using a RP
1
C18 semipreparative column eluted with MeOH/t-BuOMe (3:1): H
NMR (400.1 MHz, CDCl3) δ 0.36 (s, 9H; SiMe3), 0.37 (s, 9H;
SiMe3), 2.35 (s, 3H; Me), 7.15−7.18 (m, 1H; H-5), 7.49−7.50 (m,
3
1H; H-3), 7.58 (d, 1H, JHH = 7.7 Hz; H-6); 13C NMR (75.4 MHz,
CDCl3) δ 2.1 (SiMe3), 2.1 (SiMe3), 21.6 (Me), 128.7 (C-5), 135.6
(C-6), 136.3 (C-3), 137.4 (C-4), 142.4 (C-1), 146.2 (C-2); 29Si
INEPT NMR (59.6 MHz, CDCl3) δ −3.7, −3.5.
4-Trimethylstannyl-1,2-bis(trimethylsilyl)benzene (10). A solution
of 5 (0.133 g, 0.441 mmol) in THF (20 mL) was cooled to −78 °C
and t-BuLi in pentane (1.6 M, 0.65 mL, 1.0 mmol) was added
dropwise with stirring. After 15 min, a solution of Me3SnCl (0.113 g,
0.567 mmol) in THF (5 mL) was added over a period of 5 min. The
reaction mixture was slowly warmed from −78 °C to rt, stirred for
further 60 min, and quenched by the addition of a saturated aqueous
solution of NH4Cl (5 mL). The mixture was extracted with hexane
(3 × 10 mL), and the combined organic phases were washed with
H2O (2 × 10 mL), dried over anhydrous MgSO4, and filtered. All
volatiles were removed from the filtrate in vacuo, and the residual
crude material was purified by column chromatography (silica gel,
hexane) to give 10 as a colorless liquid: yield 0.110 g (0.286 mmol,
65%); 1H NMR (300.0 MHz, CDCl3) δ 0.30 (s, 9H; SnMe3), 0.37 (s,
3
3JHH = 7.5 Hz; C6H5), 7.77 (d, 1H, JHH = 7.8 Hz, H-6), 7.91 (d, 1H,
4JHH = 1.8 Hz; H-3); 13C NMR (75.4 MHz, CDCl3) δ 2.1 (SiMe3), 2.1
(SiMe3), 126.5 (C-5), 127.4 (C6H5), 127.5 (C6H5), 128.9 (C6H5),
134.2 (C-3), 135.9 (C-6), 140.3 (C-4), 141.5 (C6H5), 144.9 (C-1),
146.8 (C-2); 29Si INEPT NMR (59.6 MHz, CDCl3) δ −3.3, −2.9.
Anal. Calcd for C18H26Si2 [298.57]: C, 72.41; H, 8.78. Found: C,
72.39; H, 8.55.
4-(4′-Methoxyphenyl)-1,2-bis(trimethylsilyl)benzene (13). This
compound was obtained according to the general procedure for
Suzuki-type coupling reactions (cf. 11). Subsequent column
chromatography (silica gel, CHCl3) gave 13 as a pale yellow solid:
yield 86%. Compound 13 crystallized from a solution in hexane upon
evaporation in the form of colorless plates that were suitable for X-ray
structure analysis: 1H NMR (300.0 MHz, CDCl3) δ 0.41 (s, 9H;
SiMe3), 0.43 (s, 9H; SiMe3), 3.87 (s, 3H; OMe), 6.98−7.04 (m, 2H;
H-3′,5′), 7.50−7.58 (m, 3H; H-5, H-2′,6′), 7.75 (dd, 1H, 3JHH = 7.8 Hz,
5JHH = 0.5 Hz; H-6), 7.88 (dd, 1H, 4JHH = 2.0 Hz, 5JHH = 0.5 Hz; H-3);
13C NMR (75.4 MHz, CDCl3) δ 2.1 (SiMe3), 2.1 (SiMe3), 55.5
(OMe), 114.4 (C-3′,5′), 126.1 (C-5), 128.4 (C-2′,6′), 133.8 (C-3),
134.0 (C-1′), 135.9 (C-6), 139.9 (C-4), 144.1 (C-1), 146.7 (C-2),
159.4 (C-4′); 29Si INEPT NMR (59.6 MHz, CDCl3) δ −3.4, −3.0.
9H; SiMe3), 0.39 (s, 9H; SiMe3), 7.49 (dd, 1H, 3JHH = 7.3 Hz, 4JHH
=
3
1.1 Hz; H-5), 7.64 (dd, 1H, JHH = 7.3 Hz, 5JHH = 0.7 Hz; H-6), 7.81
4
5
(dd, 1H, JHH = 1.1 Hz, JHH = 0.7 Hz; H-3); 13C NMR (75.4 MHz,
CDCl3) δ −9.5 (SnMe3), 2.0 (SiMe3), 2.1 (SiMe3), 134.8 (C-6), 135.7
(C-5), 142.0 (C-4), 142.7 (C-3), 145.4 (C-2), 146.0 (C-1); 29Si
INEPT NMR (59.6 MHz, CDCl3) δ −3.5, −3.3; 119Sn NMR (111.9
MHz, CDCl3) δ −28.1. Anal. Calcd for C15H30Si2Sn [385.28]: C,
46.76; H, 7.85. Found: C, 46.39; H, 7.98.
General Procedure for Suzuki-Type Coupling Reactions
(5 → 11−14). 4-(3′,4′-Bis(trimethylsilyl)phenyl)-1,2-bis-
(trimethylsilyl)benzene (11). 5 (0.4280 g, 1.420 mmol), 8
(0.4942 g, 1.418 mmol), K2CO3 (0.6889 g, 4.984 mmol), and
[Pd(PPh3)4] (0.0805 g, 0.0697 mmol) were dissolved in a degassed
toluene/EtOH/H2O mixture (10:6:3, 60 mL). The solution was
heated to 80 °C (oil bath temperature) under vigorous stirring for
1 day, cooled to rt, treated with H2O (20 mL), and the organic
phase was separated with a separation funnel. The aqueous phase
was extracted with CHCl3 (3 × 20 mL), and the organic phases
were combined, washed with H2O (2 × 20 mL), dried over
anhydrous MgSO4, and filtered. All volatiles were removed from
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dx.doi.org/10.1021/jo3002936 | J. Org. Chem. 2012, 77, 3518−3523