One-Pot Palladium(II)-Catalyzed Synthesis of Fluorenones via Decarboxylative Cyclization

Abstract

A one-pot palladium-catalyzed synthesis of fluoronones via decarboxylative cyclization is reported. This protocol offers good yields and tolerates a broad range of functional groups. Based on the extensive experimental data, we propose a plausible decarboxylative insertion mechanism.

Key words

palladium-catalyzed - decarboxylative insertion - C–C cleavage - control experiment - mechanism

• References and Notes

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• 16 A mixture of 1 (0.5 mmol), DMSO (50% aq, 3 mL), Pd(OTf)₂ (5 mol%), and Ag₂CO₃ (2 equiv) was stirred at 140 °C under air atmosphere for 24 h. The reaction mixture was washed H₂O, and the aqueous phase was extracted with EtOAc (3×). The combined organic layer was washed with brine, dried over Na₂SO₄, and evaporated under reduced pressure. The crude product was purified by silica gel column chromatography to give the corresponding products (3a–i,¹⁷ 3k–m,¹⁷ 3o–p ¹⁷ according to the literature). 3-Bromo-9H-fluoren-9-one (3j) Yield: 59%. ¹H NMR (500 MHz, CDCl₃): δ = 7.66 (d, J = 8.2 Hz, 1 H), 7.57 (d, J = 8.2 Hz, 1 H), 7.52–7.47 (m, 3 H), 7.35–7.31 (m, 1 H), 7.25 (t, J = 6.4 Hz, 1 H). ¹³C NMR (125 MHz, CDCl₃): δ = 192.3, 146.1, 143.1, 140.9, 134.8, 134.3, 132.3, 129.8, 128.9, 125.3, 124.5, 120.9, 120.5. HRMS: m/z calcd for C₁₃H₇BrO: 259.0981; found: 259.0980 3-Fluoro-6-methoxy-9H-fluoren-9-one (3n) Yield: 62%. ¹H NMR (500 MHz, CDCl₃): δ = 7.53–7.49 (m, 1 H), 7.42 (d, J = 8.2 Hz, 1 H), 7.16 (s, 1 H), 7.02 (m, 2 H), 6.83 (m, 1 H), 3.76 (s, 3 H). ¹³C NMR (125 MHz, CDCl₃): δ = 191.7, 167.2 (d, J = 254 Hz), 147.3 (d, J = 10.2 Hz), 145.8, 143.2 (d, J = 2.4 Hz), 132.3, 130.3, 126.2 (d, J = 10.2 Hz), 124.2, 121.4, 115.3 (d, J = 22.8 Hz), 108.2 (d, J = 24.4 Hz), 56.5. HRMS: m/z calcd for C₁₄H₉FO₂: 228.2185; found: 228.2189.
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