Synthesis of Silole Skeletons via Metathesis Reactions

Abstract

Silole skeletons are constructed by ring-closing olefin metathesis of silicon-tethered dienes and trienes. A silicon-tethered enyne is also converted to a 2-alkenyl-1-silaindene via ruthenium-catalyzed ring-closing enyne metathesis.

Key words

metathesis - silole - ruthenium - molybdenum - ring closure

References and Notes

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• The inferior results of the reaction of 1d and 1e with Ru-II may be attributed to β-silyl elimination from a ruthenacyclobutane intermediate, which formes a nonalkylidene ruthenium complex that no longer exhibits any RCM activity. See:
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7

Preparation of Siladienes 1Dimethyl(1-phenylvinyl)(2-vinylphenyl)silane (1a)
To a solution of chlorodimethyl(2-vinylphenyl)silane (2.0 g, 10.2 mmol) in THF (10 mL) was added a solution of (1-phenylvinyl)magnesium bromide in THF, which was prepared from α-bromostyrene (5.0 g, 27.3 mmol) and Mg (0.68 g, 28 mmol) in THF (20 mL) at r.t. for 3 h, at 0 °C. After the mixture was stirred at r.t. for 10 h, the volatile materials were removed under reduced pressure. The residue was quenched by sat. NH₄Cl aq solution, and extracted with hexane. The extract was dried over MgSO₄ and concentrated. The residue was purified by column chromatography on silica gel(hexane). Further purification by gel-permeation chromatography (GPC) gave 1a (500 mg, 19%): ¹H NMR (300 MHz, CDCl₃): d = 0.45 (s, 6 H), 5.22 (dd, J = 11.0, 1.3 Hz, 1 H), 5.61 (dd, J = 17.4, 1.3 Hz, 1 H), 5.69 (d, J = 2.9 Hz, 1 H), 6.01 (d, J = 2.9, 1 H), 7.07-7.29 (m, 7 H), 7.35-7.41 (m, 1 H), 7.54-7.59 (m, 2 H). ¹³C NMR (75 MHz, CDCl₃): d = -1.0, 114.9, 125.2, 126.4, 126.8, 126.9, 128.1, 129.0, 129,6, 135.1, 136.0, 138.0, 134.9, 144.0, 151.5. HRMS (EI): m/z [M]⁺ calcd for C₁₈H₂₀Si: 264.1334; found: 264.1335.
Isopropenyldimethyl(2-vinylphenyl)silane (1c)
¹H NMR (300 MHz, CDCl₃): d = 0.40 (s, 6 H), 1.80 (t, J = 1.4 Hz, 3 H), 5.22 (dd, J = 10.8, 1.2 Hz, 1 H), 5.36 (q, J = 0.9 Hz, 1 H), 5.64 (dd, J = 17.3, 1.2 Hz, 1 H), 5.69 (sext, J = 1.7 Hz, 1 H), 7.04 (dd, J = 17.3, 10.8 Hz, 1 H), 7.25 (dt, J = 1.3, 7.3 Hz, 1 H), 7.37 (dt, J = 1.5, 7.5 Hz, 1 H), 7.50 (dd, J = 7.4, 1.4 Hz, 1 H), 7.56 (d, J = 7.5 Hz, 1 H). ¹³C NMR (75 MHz, CDCl₃): d = -2.1, 22.6, 114.7, 125.0, 126.5, 126.9, 129.5, 135.0, 135.7, 138.0, 144.1, 146.6. HRMS (EI): m/z [M]⁺ calcd for C₁₃H₁₈Si: 202.1178; found: 202.1173.
Dimethyl(1-phenylvinyl)(2-vinylphenyl)germane (1k)
¹H NMR (300 MHz, CDCl₃): d = 0.57 (s, 6 H), 5.22 (dd, J = 10.5, 1.5 Hz, 1 H), 5.55 (d, J = 2.1 Hz, 1 H), 5.63 (dd, J = 17.4, 1.2 Hz, 1 H), 6.03 (d, J = 2.1 Hz, 1 H), 6.98 (dd, J = 17.4, 11.1 Hz, 1 H), 7.15-7.28 (m, 6 H), 7.32-7.38 (m, 1 H), 7.49-7.53 (m, 1 H), 7.56-7.60 (m, 1 H). ¹³C NMR (75 MHz, CDCl₃): d = -1.1, 115.0, 125.1, 126.0, 126.6 [overlapping], 127.1, 128.2, 129.1, 134.3, 137.8, 139.0, 143.2, 143.5, 152.2. HRMS (EI): m/z [M]⁺ calcd for C₁₈H₂₀Ge: 310.0777; found: 310.0786.

9

General Procedure for Ring-Closing Metathesis1,1-Dimethyl-2-phenyl-1-silaindene (2a) ¹⁴
To Schrock catalyst (11.5 mg, 0.015 mmol) was added a solution of 1a (76.45 mg, 0.289 mmol) in toluene (5 mL), and the mixture was stirred at r.t. for 2 h. The reaction mixture was taken up with hexane and passed through a pad of Florisil^®. Removal of volatile materials afforded 2a (61.4 mg, 0.257 mmol, 89%): ¹H NMR (300 MHz, CDCl₃): δ = 0.48 (s, 6 H), 7.20-7.40 (m, 6 H), 7.49-7.56 (m, 4 H). ¹³C NMR (75 MHz, CDCl₃): d = -3.1, 124.3, 126.4, 126.6, 127.0, 128.7, 130.0, 131.7, 138.2, 139.0, 141.1, 145.3, 148.8. ²⁹Si NMR (79 MHz, CDCl₃): d = -15.9. HRMS (EI): m/z [M]⁺ calcd for C₁₆H₁₆Si: 236.1021; found: 236.1019.
2-(3-Methoxyphenyl)-1,1-dimethyl-1-silaindene (2b)
To Grubbs second-generation catalyst (8.7 mg, 0.010 mmol) was added a solution of 1b (58.62 mg, 0.199 mmol) in toluene (2 mL), and the mixture was stirred at 80 °C for 2 h. The reaction mixture was taken up with hexane and passed through a pad of Florisil^® (hexane-EtOAc = 10:1). After removal of volatile materials, the residue was subjected to preparative thin-layer chromatography to give 2b (50.66 mg, 0.190 mmol, 96%): ¹H NMR (300 MHz, CDCl₃): d = 0.49 (s, 6 H), 3.87 (s, 3 H), 6.79-6.85 (m, 1 H), 7.04-7.11 (m, 2 H), 7.19-7.39 (m, 4 H), 7.53-7.57 (m, 2 H). ¹³C NMR (75 MHz, CDCl₃): d = -3.1, 55.2, 111.9, 112.4, 119.3, 124.3, 126.7, 129.6, 130.0, 131.7, 138.3, 140.5, 141.5, 145.2, 148.7, 159.8. HRMS (EI): m/z [M]⁺ calcd for C₁₇H₁₈OSi: 266.1127; found: 266.1121.
1,1,2-Trimethyl-1-silaindene (2c)
¹H NMR (300 MHz, CDCl₃): d = 0.28 (s, 6 H), 2.02 (d, J = 1.5 Hz, 3 H), 6.86 (q, J = 1.5 Hz, 1 H), 7.10-7.15 (m, 2 H), 7.24-7.30 (m, 1 H), 7.46 (d, J = 6.9 Hz, 1 H). ¹³C NMR (75 MHz, CDCl₃): d = -4.6, 17.4, 122.8, 125.6, 129.7, 131.6, 138.1, 142.7, 144.6, 149.5. HRMS (EI): m/z [M]⁺ calcd for C₁₁H₁₄Si: 174.0865; found: 174.0864.
1,1,3-Trimethyl-1-silaindene (2d)
¹H NMR (300 MHz, CDCl₃): δ = 0.29 (s, 6 H), 2.22 (s, 3 H), 5.92 (s, 1 H), 7.21-7.27 (m, 1 H), 7.30-7.40 (m, 2 H), 7.51-7.55 (m, 1 H). ¹³C NMR (75 MHz, CDCl₃): δ = -4.0, 19.6, 121.2, 126.5, 127.8, 129.4, 131.2, 139.8, 149.9, 156.2. ²⁹Si NMR (79 MHz, CDCl₃): δ = -19.4. HRMS (EI): m/z [M]⁺ calcd for C₁₁H₁₄Si: 174.0865; found 174.0864.
1,1-Diethyl-2-phenyl-1-silaindene (2i)
¹H NMR (300 MHz, CDCl₃): d = 0.85-1.15 (m, 10 H), 7.18-7.58 (m, 10 H). ¹³C NMR (75 MHz, CDCl₃): d = 4.3, 7.5, 124.2, 126.39, 126.45, 126.9, 128.6, 129.9, 132.3, 136.3, 139.5, 142.4, 143.7, 149.7. ²⁹Si NMR (79 MHz, CDCl₃): d = -8.7. HRMS (EI): m/z [M]⁺ calcd for C₁₈H₂₀Si: 264.1334; found 264.1332.
1,1-Dimethyl-2-phenyl-1-germaindene (2k)
¹H NMR (300 MHz, CDCl₃): d = 0.67 (s, 6 H), 7.20-7.41 (m, 6 H), 7.47-7.58 (m, 4 H). ¹³C NMR (75 MHz, CDCl₃): d = -2.2, 125.0, 126.6, 126.8, 127.1, 128.7, 129.3, 131.8, 137.8, 139.3, 140.5, 147.6, 148.0. HRMS (EI): m/z [M]⁺ calcd for C₁₆H₁₆Ge: 282.0464; found: 282.0469.

11

Dimethyl(1-phenylvinyl)(2-vinylcyclopent-1-enyl)silane (3a)
A solution of (2-vinylcyclopent-1-enyl)lithium in THF, which was prepared from 1-bromo-2-vinylcyclopent-1-ene (0.69 g, 3.99 mmol) and n-BuLi in hexane (1.55 M, 2.8 mL, 4.34 mmol) in THF (10 mL) at -78 °C for 1 h, was added to a solution of chlorodimethyl(1-phenylvinyl)silane (0.697 g, 3.54 mmol) in THF (10 mL) at 0 °C. After the mixture was stirred at r.t. for 10 h, the volatile materials were removed under reduced pressure. The residue was quenched by sat. NH₄Cl aq solution, and extracted with hexane. The extract was dried over MgSO₄ and concentrated. The residue was purified by column chromatography on silica gel (hexane) to afford 3a (0.32 mg, 32%): ¹H NMR (300 MHz, CDCl₃): d = 0.29 (s, 6 H), 1.82 (quin, J = 7.5 Hz, 2 H), 2.47-2.60 (m, 4 H), 5.09 (d, J = 10.7 Hz, 1 H), 5.13 (d, J = 17.1 Hz, 1 H), 5.65 (d, J = 3.0 Hz, 1 H), 5.92 (d, J = 3.0 Hz, 1 H), 6.80 (dd, J = 17.1, 10.7 Hz, 1 H), 7.15-7.30 (m, 5 H). ¹³C NMR (75 MHz, CDCl₃): d = -1.2, 23.6, 34.6, 39.3, 115.3, 126.6, 127.0. 128.2. 128.3, 134.3, 140.9, 144.5, 151.9, 152,7. HRMS-FAB: m/z calcd for C₁₇H₂₂Si [M⁺] 254.1491; found: 254.1476.
Dimethyl(1-phenylvinyl)(2-vinyl-3,4-dihydronaph-thalen-1-yl)silane (3b)
¹H NMR (300 MHz, CDCl₃): d = 0.45 (s, 6 H), 2.31-2.38 (m, 2 H), 2.58-2.65 (m, 2 H), 5.16 (d, J = 10.8 Hz, 1 H), 5.44 (d, J = 17.1 Hz, 1 H), 5.78 (d, J = 2.7 Hz, 1 H), 5.97 (d, J = 2.7 Hz, 1 H), 6.96 (dd, J = 17.1, 11.1 Hz, 1 H), 7.09-7.26 (m, 9 H). ¹³C NMR (75 MHz, CDCl₃): d = 2.0, 24.4, 28.5, 114.3, 125.6, 125.9, 126.4, 126.7, 126.8, 127.5, 128.0, 128.1, 135.7, 136.7, 138.1, 138.7, 143.9, 150.6, 153.3. HRMS (EI): m/z [M]⁺ calcd for C₂₂H₂₄Si: 316.1647; found: 316.1650.
1,1-Dimethyl-2-phenyl-1,4,5,6-tetrahydrocyclo-penta[ b ]silole (4a)
¹H NMR (300 MHz, CDCl₃): d = 0.37 (s, 6 H), 2.14 (quin, J = 7.2 Hz, 2 H), 2.48-2.59 (m, 4 H), 7.12-7.43 (m, 6 H). ¹³C NMR (75 MHz, CDCl₃): d = -3.7, 27.0, 32.7, 32.8, 125.9, 126.4, 128.6, 134.9, 139.5, 142.9, 147.5, 161.4. HRMS-FAB: m/z [M]⁺ calcd for C₁₅H₁₈Si: 226.1178; found: 226.1187.
2-Phenyl-4,5-dihydronaphtho[1,2- b ]silole (4b)
¹H NMR (300 MHz, CDCl₃): d = 0.55 (s, 6 H), 2.59 (t, J = 8.4 Hz, 2 H), 2.92 (t, J = 8.1 Hz, 2 H), 7.08-7.50 (m, 10 H). ¹³C NMR (75 MHz, CDCl₃): d = -2.7, 26.3, 28.4, 125.7, 126.1, 126.2, 126.6, 126.8, 127.86 128.7, 134.2, 134.6, 135.9, 138.7, 140.9, 144.7, 152.2. ²⁹Si NMR (79 MHz, CDCl₃): d = -16.2. HRMS (EI): m/z [M]⁺ calcd for C₂₀H₂₀Si: 288.1334; found: 288.1330.

14

1,1-Dimethyl-2-(pent-1-en-2-yl)-1-silaindene (6) and 1,1-Dimethyl-2-methylene-3-propyl-1,2-dihydro-1-silanaphthalene (7)
The title compounds (45.63 mg, 67%, 6/7 = 50:50) were obtained from enyne RCM of 5 (67.8 mg) using Ru-II. The isomers were separated by HPLC.
Compound 6: ¹H NMR (300 MHz, CDCl₃): δ = 0.31 (s, 6 H), 0.97 (t, J = 7.5 Hz, 3 H), 1.59 (sext, J = 7.5 Hz, 2 H), 2.43 (t, J = 7.8 Hz, 2 H), 5.61 (d, J = 1.5 Hz, 1 H), 6.03 (d, J = 1.5 Hz, 1 H), 6.29 (s, 1 H), 7.10-7.20 (m, 2 H), 7.25-7.31 (m, 1 H), 7.48 (d, J = 0.6 Hz, 1 H). ¹³C NMR (75 MHz, CDCl₃): δ = -1.3, 14.1, 22.4, 35.9, 124.7, 126.0, 128.9, 129.2, 129.6, 133.3, 133.8, 140.2, 141.9, 145.0. HRMS (EI): m/z [M]⁺ calcd for C₁₅H₂₀Si: 228.1334; found: 228.1335.
Compound 7: ¹H NMR (300 MHz, CDCl₃): δ = 0.43 (s, 6 H), 1.00 (t, J = 7.5 Hz, 3 H), 1.61 (sext, J = 7.5 Hz, 2 H), 2.40 (t, J = 7.8 Hz, 2 H), 5.08 (d, J = 6.6 Hz, 2 H), 7.16-7.35 (m, 4 H), 7.52-7.54 (m, 1 H). ¹³C NMR (75 MHz, CDCl₃): δ = -2.9, 14.0, 21.6, 35.9, 115.0, 124.2, 126.5, 129.9, 131.6, 138.3, 140.5, 146.8, 147.3, 149.0. HRMS (EI): m/z [M]⁺ calcd for C₁₅H₂₀Si: 228.1334; found: 228.1333.