H. Maekawa et al.
Bull. Chem. Soc. Jpn. Vol. 86, No. 10 (2013) 1187
1-Isopropyldimethylsiloxy-7-isopropyldimethylsilylcyclo-
hepta-1,3,5-triene (2c). 1H NMR (400 MHz, CDCl3): ¤ 0.04
(3H, s), 0.07 (3H, s), 0.17 (3H, s), 0.18 (3H, s), 0.97-1.03
(14H, m), 1.90 (1H, d, J = 8.6 Hz), 5.11 (1H, t, J = 8.6 Hz),
5.36 (1H, d, J = 7.2 Hz), 5.96-6.00 (3H, m). 13C NMR (100
MHz, CDCl3): ¤ ¹5.24, ¹3.98, ¹3.71, 13.08, 14.41, 16.67
(©2), 17.72, 17.78, 36.51, 104.68, 121.41, 125.31, 126.78,
127.98, 148.31. IR (neat): 3012, 2955, 2865, 1254, 1183, 1140,
884, 832, 780 cm¹1. MS: m/z 308 (M+). HRMS: Calcd for
C17H32OSi2: 308.1992. Found: 308.1953.
reagent in dry DMF (25 mL) were placed in a 100-mL four-
necked flask at room temperature under nitrogen atmosphere
and then chlorotrimethylsilane (7.67 mL, 60.0 mmol) was added
in one portion. After activation of the magnesium for 1 h, the
mixture was cooled in an ice bath and 7,7-dimethoxycyclo-
hepta-1,3,5-triene (0.76 g, 5.0 mmol) in dry DMF (5 mL) was
added dropwise. Stirring was continued at 2-3 °C for 2 h. Then
the reaction mixture was poured into a saturated sodium
hydrogen carbonate solution and was extracted with ether. The
combined organic layers were washed with brine, dried over
anhydrous magnesium sulfate, and the solvent was evaporated
under reduced pressure. The residue was purified by column
chromatography to give 5a.
1-Methoxy-7-trimethylsilylcyclohepta-1,3,5-triene (5a).
1H NMR (400 MHz, CDCl3): ¤ 0.07 (9H, s), 1.95 (1H, dd,
J = 8.1 Hz, 0.7 Hz), 3.57 (3H, s), 5.16 (1H, dt, J = 8.1 Hz,
2.1 Hz), 5.22 (1H, d, J = 6.6 Hz), 5.97-6.03 (2H, m), 6.08-6.14
(1H, m). 13C NMR (100 MHz, CDCl3): ¤ ¹1.92, 37.06, 55.66,
95.81, 121.58, 124.57, 126.94, 128.04, 154.63. IR (neat): 3012,
2954, 2898, 2831, 1613, 1572, 1247, 1200, 1167, 1138, 1034,
1013, 841, 715 cm¹1. MS: m/z 194 (M+). HRMS: Calcd for
C11H18OSi: 194.1127. Found: 194.1117.
7-Ethyldimethylsilyl-1-methoxycyclohepta-1,3,5-triene
(5b). 1H NMR (400 MHz, CDCl3): ¤ 0.05 (6H, s), 0.59 (2H, q,
J = 7.9 Hz), 0.93 (3H, t, J = 7.9 Hz), 2.01 (1H, dd, J = 8.9 Hz,
1.0 Hz), 3.57 (3H, s), 5.16 (1H, t, J = 8.9 Hz), 5.21 (1H, d, J =
6.9 Hz), 5.96-6.02 (2H, m), 6.07-6.15 (1H, m). 13C NMR (100
MHz, CDCl3): ¤ ¹4.02, ¹3.91, 6.56, 7.38, 36.08, 55.74, 95.93,
121.74, 124.71, 126.99, 128.20, 154.68. IR (neat): 3012, 2953,
2909, 2874, 2832, 1613, 1247, 1200, 1167, 1139, 1013, 836,
819, 714, 699 cm¹1. MS: m/z 208 (M+). HRMS: Calcd for
C12H20OSi: 208.1284. Found: 208.1267.
7-Isopropyldimethylsilyl-1-methoxycyclohepta-1,3,5-tri-
ene (5c). 1H NMR (400 MHz, CDCl3): ¤ 0.03 (3H, s), 0.04
(3H, s), 0.82-1.00 (7H, m), 2.06 (1H, d, J = 9.0 Hz), 3.57 (3H,
s), 5.22 (1H, d, J = 6.6 Hz), 5.71 (1H, t, J = 9.0 Hz), 5.96-6.04
(2H, m), 6.10-6.17 (1H, m). 13C NMR (100 MHz, CDCl3):
¤ ¹5.46, ¹5.23, 13.14, 17.69, 17.77, 34.79, 55.72, 96.01,
121.79, 124.75, 126.91, 128.26, 154.42. IR (neat): 3012, 2954,
2864, 2833, 1613, 1464, 1247, 1200, 1167, 1140, 1013, 1001,
883, 808, 715, 690 cm¹1. MS: m/z 222 (M+). HRMS: Calcd for
C13H22OSi: 222.1440. Found: 222.1483.
Typical Procedure for DDQ Oxidation of 2 and 5. To a
solution of 2a (3.0 mmol) in dry benzene (30 mL) was added
2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) (0.83 g, 3.6
mmol) at room temperature under nitrogen atmosphere, and
the reaction mixture was stirred for 1 h. Then a 5% sodium
hydroxide solution (100 mL) was added to the reaction mixture
and the products were extracted with ether. The combined
organic layers were washed with sodium hydrogen carbonate
and brine, dried over anhydrous magnesium sulfate, and the
solvent was evaporated under reduced pressure. The residue
was purified by column chromatography to give 3a.
2-Trimethylsilylcyclohepta-2,4,6-trien-1-one
(3a).5
1H NMR (400 MHz, CDCl3): ¤ 0.15 (9H, s), 6.73-6.94 (4H,
m), 7.24 (1H, d, J = 7.8 Hz). 13C NMR (100 MHz, CDCl3):
¤ ¹0.08, 135.09, 135.73, 135.94, 140.83, 142.81, 158.58,
¹1
193.00. IR (neat): 3026, 2953, 1627, 1577, 1246, 841 cm
MS: m/z 178 (M+).
.
2-Ethyldimethylsilylcyclohepta-2,4,6-trien-1-one (3b).
1H NMR (400 MHz, CDCl3): ¤ 0.22 (6H, s), 0.78 (2H, q,
J = 7.7 Hz), 0.93 (3H, t, J = 7.7 Hz), 6.82 (1H, d, J = 11.6 Hz),
6.85-6.92 (1H, m), 6.93-6.99 (1H, m), 6.97-7.03 (1H, m), 7.30
(1H, dd, J = 7.8 Hz, 1.2 Hz). 13C NMR (100 MHz, CDCl3): ¤
¹3.35, 6.82, 7.52, 134.00, 134.62, 134.70, 139.80, 141.96,
156.81, 192.11. IR (neat): 3026, 2952, 2907, 2873, 1627, 1580,
1513, 1458, 1410, 1383, 1273, 1245, 1210, 1010, 981, 837,
813, 785, 697, 646, 617 cm¹1. MS: m/z 192 (M+). HRMS:
Calcd for C11H16OSi: 192.0971. Found: 192.0992.
2-Isopropyldimethylsilylcyclohepta-2,4,6-trien-1-one
(3c). 1H NMR (400 MHz, CDCl3): ¤ 0.19 (6H, s), 0.94 (6H, d,
J = 7.5 Hz), 1.28 (1H, sept, J = 7.5 Hz), 6.82 (1H, d, J =
11.9 Hz), 6.85-9.92 (1H, m), 6.93-6.99 (1H, m), 6.97-7.03
(1H, m), 7.29 (1H, dd, J = 7.8 Hz, 1.2 Hz). 13C NMR (100
MHz, CDCl3): ¤ ¹5.11, 12.63, 17.72, 133.95, 134.54, 134.63,
139.64, 142.18, 156.40, 192.12. IR (neat): 3027, 2952, 2890,
2862, 1628, 1579, 1513, 1459, 1273, 1245, 1210, 1005, 976,
882, 834, 809, 784, 768, 686, 648 cm¹1. MS: m/z 206 (M+).
HRMS: Calcd for C12H18OSi: 206.1127. Found: 206.1121.
2-Dimethylphenylsilylcyclohepta-2,4,6-trien-1-one (3e).
1H NMR (400 MHz, CDCl3): ¤ 0.57 (6H, s), 6.82-6.91 (3H,
m), 6.97-7.04 (1H, m), 7.15-7.20 (1H, m), 7.35-7.41 (3H, m),
7.59-7.63 (2H, m). 13C NMR (100 MHz, CDCl3): ¤ ¹2.74,
127.79, 129.13, 134.32, 134.39, 134.66, 134.96, 137.71,
140.30, 143.18, 156.32, 191.86. IR (neat): 3068, 3047, 3024,
2955, 2899, 1626, 1574, 1514, 1459, 1427, 1275, 1246, 1212,
1113, 977, 814, 787, 739, 702, 658 cm¹1. MS: m/z 240 (M+).
HRMS: Calcd for C15H16OSi: 240.0971. Found: 240.0986.
Typical Procedure for Coupling of 7,7-Dimethoxycyclo-
1-Methoxy-7-dimethylphenylsilylcyclohepta-1,3,5-triene
(5e). 1H NMR (400 MHz, CDCl3): ¤ 0.38 (3H, s), 0.42 (3H,
s), 2.21 (1H, d, J = 8.9 Hz), 3.53 (3H, s), 5.16 (1H, dt, J =
8.9 Hz, 1.6 Hz), 5.27 (1H, d, J = 6.6 Hz), 6.01-6.06 (2H, m),
6.13-6.19 (1H, m), 7.32-7.39 (3H, m), 7.54-7.59 (2H, m).
13C NMR (100 MHz, CDCl3): ¤ ¹3.11, ¹3.07, 36.31, 55.70,
96.39, 121.02, 124.77, 127.39, 127.50, 128.24, 128.85, 133.93,
138.37, 153.97. IR (neat): 3068, 3048, 3011, 2956, 2903, 2832,
1613, 1427, 1248, 1200, 1168, 1140, 1113, 1034, 1013, 813,
701 cm¹1. MS: m/z 256 (M+). HRMS: Calcd for C16H20OSi:
256.1284. Found: 256.1312.
Anodic Oxidation of 5a.
Into a 50-mL beaker-type
undivided cell equipped with platinum plates (4 cm2) as the
cathode and the anode, were introduced 30 mL of freshly dis-
tilled methanol as a solvent, tetraethylammonium p-toluene-
sulfonate (2 g, 6.6 mmol) and sodium methoxide (2 g, 37 mmol)
as supporting electrolytes, and 5a (0.58 g, 3 mmol) as the
hepta-1,3,5-triene (4) with Chlorotrialkylsilane.
Non-
pretreated magnesium turnings (0.97 g, 40.0 mmol) for Grignard