Highly Effective Recyclable Palladium-Catalyzed Ligand-Free Heck Reactions under Aerobic Conditions

Abstract

An effective protocol was developed for the Heck coupling reactions between various aryl halides and olefins. In the presence of 2 mol% of Pd(OAc)₂, the desired products could be obtained in good yields under ligand-free and aerobic conditions. The catalytic system could be easily recycled for five times with high efficiency.

Key words

coupling reactions - Heck reaction - aryl halides - olefins - ligand-free

References and Notes

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9

General Procedure for the Ligand-Free Palladium-Catalyzed Heck-Type Coupling Reactions of Aryl Halide and Terminal Olefin
A mixture of aryl halide (0.5 mmol), olefin (3.0 mmol), Pd(OAc)₂ (2 mol%), K₂CO₃ (2 equiv), and TBAF (2 g) in a sealed tube was stirred under air atmosphere at 70 ˚C for the desired time until complete consumption of starting material as monitored by TLC. After the mixture was poured into Et₂O, then the mixture was washed with H₂O, extracted with EtOAc, dried over anhyd Na₂SO₄, filtered and evaporated under vacuum, and the residue was purified by flash column chromatography (PE or PE-EtOAc) to afford the corresponding coupling products.
( E )-Methyl Cinnamate
^¹H NMR (400 MHz, CDCl₃): δ = 3.82 (s, 3 H), 6.45 (d, J = 16.0 Hz, 1 H), 7.39 (t, J = 3.2 Hz, 3 H), 7.52-7.55 (m, 2 H), 7.71 (d, J = 16.0 Hz, 1 H) ppm. ^¹³C NMR (100 MHz, CDCl₃): δ = 52.1, 118.0, 128.4, 129.2, 130.6, 134.6, 145.2, 167.8 ppm. HRMS (ESI⁺): m/z calcd for [C₁₀H₁₀O₂]⁺: 162.0681; found: 162.0679.