Synthesis of β-Boryl-α,β-unsaturated Carbonyl Compounds via Palladium-Catalyzed Cross-Coupling Reaction of Bis(pinacolato)diboron with Vinyl Triflates

Abstract

Cross-coupling reaction of bis(pinacolato)diboron with β-(trifluoromethanesulfonyloxy)-α,β-unsaturated carbonyl compounds was carried out in the presence of PdCl₂(PPh₃)₂-2PPh₃ (3 mol%) and KOPh in toluene or K₂CO₃ in dioxane for the synthesis of cyclic and acyclic β-boryl-α,β-unsaturated esters, amides, and ketones in high yields.

diboron - vinyl triflate - palladium - cross-coupling - catalysis

References

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A representative procedure for 3: A flask placed with PdCl₂(PPh₃)₂ (0.03 mmol), PPh₃ (0.06 mmol), pin₂B₂ 1 (1.1 mmol), and KOPh or K₂CO₃ (1.5 mmol) was flushed with nitrogen. Toluene or dioxane (6 mL) and ethyl 2-(trifluoromethanesulfonyloxy)-1-cyclohexenecarboxylate (1.0 mmol) were then added. The resulting mixture was stirred at 50 °C or 80 °C for the period shown in Table [2] . The product was isolated by chromatography over silica gel followed by Kugelrohr distillation to give an analytically pure sample: ¹H NMR (400 MHz, CDCl₃, TMS) δ 1.27 (t, 3 H, J = 7.2 Hz), 1.33 (s, 12 H), 1.55-1.65 (m, 4 H), 2.20-2.25 (m, 4 H), 4.21 (q, 2 H, J = 7.2 Hz); ¹³C NMR (100 MHz, CDCl₃, TMS) δ 14.25, 21.42, 21.85, 24.12, 24.77, 27.93, 60.70, 83.34, 134.24, 169.19; HRMS, Found: m/z, 280.1846. Calcd for C₁₅H₂₅BO₄: M⁺, 280.1846.

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The 1,3-dienes 7 shown in Table [3] could be purified by column chromatography over silica gel to give analytically pure samples.