Novel CuBr·SMe₂ Catalyzed Conjugate Addition of 3-Trimethylsilyl-1-propenylzirconocene to Divinylketones. Stereoselective Synthesis of Poly­substituted Cyclohexanones

Abstract

Conjugate addition of (E)-3-trimethylsilyl-1-propenylziroconocene to (E,E)-divinylketones in the presence of catalytic amount of CuBr·SMe₂ affords (E)-allylsilanes containing (E)-α,β-unsaturated carbonyl moiety under mild conditions with good yield. They undergo highly stereocontrolled silicon-assisted intramole­cular cylization when treated with TiCl₄ leading to polysubstituted cyclohexanones.

Key words

alkenylzirconocene - conjugate addition - intramolecular cylization - allylsilane - cyclohexanone

References

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General Procedure, Preparation of 3. A suspension of Cp₂ZrHCl (1.50 mmol) in THF (8 mL) was treated with propargyltrimethyl siliane (1.50 mmol). The mixture was stirred at r.t. for 30 min. To the resulting clear 1 light yellow solution was added CuBr·SMe₂ (0.025 mmol) and divinylketone 2 (1 mmol) and stirred at r.t., monitored by TLC, quenched with wet Et₂O (20 mL) and extracted with sat. NaHCO₃ aq solution (2 × 10 mL). The organic layer was dried (MgSO₄), filtered through silica gel, and concentrated. The residue was purified by flash chromatography (silica/hexanes-EtOAc 10:1) to afford 3.Preparation of 4. To a solution of 3 (1 mmol) in CH₂Cl₂ (8 mL) TiCl₄ (1.2 mmol, 0.13 mL) was added slowly at -78 °C. After stirring for 3 h at this temperature, 2 mL of MeOH were added at once and the mixture was allowed to warm up to r.t. The reaction mixture was washed with a sat. solution of NaHCO₃, extracted with Et₂O, dried over MgSO₄ and rotoevaporated. Purification of the resulting oil by flash-chromatography (EtOAc-hexanes, 1:10) gave 4.

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Selected Data of Compounds 3b and 4b: (a) Spectral and analytical data for 3b: IR (neat): 1690, 1662, 1611, 1592, 1566, 1490, 853 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 7.45 (d, J = 16 Hz, 1 H), 7.43 (d, J = 8.4 Hz, 2 H), 7.36 (d, J = 8.4 Hz, 2 H,), 7.26 (d, J = 8.4 Hz, 2 H), 7.16 (d, J = 8.4 Hz, 2 H,), 6.65 (d, J = 16 Hz, 1 H), 5.42-5.50 (dt, J = 16, 7.6 Hz, 1 H,), 5.36-5.41 (dd, J = 7.4, 16 Hz, 1 H), 3.97 (m, 1 H,), 2.94-3.07 (m, 4 H), 1.42 (d, J = 7.6 Hz, 2 H), -0.05 (s, 9 H). ¹³C NMR (100 MHz.CDCl₃): δ = 197.9, 141.2, 136.4, 132.9, 131.9, 130.1, 129.4, 129.2, 128.8, 128.6, 127.8, 126.6, 47.3, 43.6, 22.8. MS (EI): m/z (%) = 417 (0.55) [M⁺], 401 (0.53), 73(100). Anal. Calcd for C₂₃H₂₆Cl₂OSi: C, 66.13; H, 6.23. Found: C, 66.24; H, 6.35.
(b) Spectral and analytical data for 4b: IR (neat): 1713, 1640, 1660, 1489, 1407, 823 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 6.97-7.30 (m, 8 H,), 5.39-5.48 (ddd, J = 17.6, 10.0, 8.4 Hz, 1 H), 4.98-5.03 (dd, J = 17.6, 10.0 Hz, 2 H), 3.41-3.45 (dt, J = 6.0, 4.4 Hz, 1 H), 3.23-3.29 (dt, J = 5.6, 8.0 Hz, 1 H), 2.93-2.98 (m, 1 H) 2.68-2.84 (m, 4 H). ¹³C NMR (100 MHz, CDCl₃): δ = 210.1, 142.0, 140.0, 137.0, 131.8, 131.3, 130.2, 129.3, 120.8, 120.6, 118.0, 50.6, 45.4, 44.2, 43.7, 43.2. MS (EI): m/z (%) = 345 (0.91) [M⁺], 205 (2.77), 164 (43.5), 121 (100). Anal. Calcd for C₂₀H₁₈Cl₂O: C, 69.57; H, 5.25. Found: C, 69.71; H, 5.34.