Ruthenium(II) Complex Catalyzed O-Borylation of Alcohols with Vinylboronates

Abstract

A new, highly effective method for the selective synthesis of boryl ethers via O-borylation of alcohols with vinylboronates catalyzed by the Ru-H complexes [Ru(CO)ClH(PPh₃)₃] and [Ru(CO)ClH(PCy₃)₂] is described. The mechanism of catalysis of this new de-ethenative borylation is supported by equimolar reaction of Ru-B complex with alcohol.

homogeneous catalysis - vinylboronates - ruthenium - coupling reactions - boryl ethers

References and Notes

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O-Borylation of alcohols by vinylboronates; general procedure: The ruthenium catalyst [Ru(CO)ClH(PPh₃)₃] (II) (2 mol%) was dissolved in toluene and placed in a glass ampoule. The reagents and dodecane as internal standard (5% by volume all components), alcohol (0.5 mmol) and
2-vinyl-1,3,2-dioxaborinane (1-2.5 mmol) were added and the ampoule was heated at 60-80 ˚C for 24 h. Alcohol conversion was determined by GC and GC-MS. After the reaction, the solvent and excess borane were removed under vacuum, and the crude product was purified by column chromatography (silica gel modified with HMDS; hexane-EtOAc).
2-Butoxy-1,3-dioxaborinane: ^¹H NMR (300 MHz, CDCl₃): δ = 1.10 (t, J = 7.2 Hz, 3H, CH ₃), 1.78 (q, J = 7.0 Hz, 2H, CH ₂CH₃), 1.92 (quin, J = 5.5 Hz, 2H, BOCH₂CH ₂CH₂O), 2.16 (brH ₂CH₂CH₃), 3.85 [t, J = 4.6 Hz, 2H, CH ₂ (CH₂)₂CH₃], 4.03 (t, J = 5.5 Hz, 4H, BOCH ₂CH₂CH ₂O). ^¹³C NMR (75 MHz, CDCl₃): δ = 15.8 (CH₃), 20.3 (CH₂CH₃), 27.2 (BOCH₂ CH₂CH₂O), 33.2 (CH₂CH₂CH₃), 62.7 (BOCH₂CH₂ CH₂O), 64.7 [BOCH_{2 (}CH₂)₂CH₃]. ^¹¹B NMR (96 MHz, CDCl₃): δ = 28.7. MS (EI): m/z (%) = 143 (1)
[M⁺ - 15], 129 (2), 115 (100), 103 (29), 85 (22), 71 (11), 56 (14). Anal. Calcd for C₇H₁₅BO₃: C, 53.21; H, 9.57. Found: C, 53.01; H, 9.44.
3-(1′,3′,2′-Dioxaborinan-2′-yloxy)propanonitrile: ^¹H NMR (300 MHz, CDCl₃): δ = 1.99 (quin, J = 5.5 Hz, 2H, BOCH₂CH ₂CH₂O), 2.60 (t, J = 6.0 Hz, 2H, CH ₂C≡N), 3.89 (t, J = 6.0 Hz, 2H, CH ₂CH₂C≡N), 4.03 (t, J = 5.5 Hz, 4H, BOCH ₂CH₂CH ₂O). ^¹³C NMR (75 MHz, CDCl₃): δ =
26.3 (CH₂C≡N), 27.1 (BOCH₂ CH₂CH₂O), 57.9 (BOCH₂CH₂C≡N), 62.8 (BOCH₂CH₂ CH₂O), 117.6 (C≡N). ^¹¹B NMR (96 MHz, CDCl₃): δ = 28.7. MS (EI): m/z (%) = 156 (6) [M⁺ + 1], 140 (7), 125 (10), 115 (100), 98 (25), 85 (23), 71 (10), 54 (28). Anal. Calcd for C₆H₁₀BNO₃: C, 58.74; H, 9.31; N, 9.04. Found: C, 58.88; H, 9.23; N, 9.18.

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Experimental procedure for the stoichiometric experiment: In an NMR tube, [Ru(BO₂C₆H₄)(CO)Cl(PCy₃)₂] (III) (10 mg, 0.012 mmol) and cyclohexan-1-ol (1.6 mg, 0.016 mmol) and toluene-d ₈ (0.6 mL) were placed under argon. The reaction was carried out at 80 ˚C and monitored by ^¹H NMR.

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