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Ligand-Controlled Palladium-Catalyzed Regiodivergent Suzuki- Miyaura Cross-Coupling of Allylboronates and Aryl Halides-

Reaction Scheme


Pd-PEPPSI-IPent has proven to be an excellent catalyst for the Negishi cross-coupling reaction of secondary alkylzinc reagents with a wide variety of aryl/heteroaryl halides. Importantly, b-hydride elimination/migratory insertion of the organometallic leading to the production of isomeric coupling products has been significantly reduced using the highly-hindered IPent ligand.



An oven-dried vial (3 mL screw-cap threaded) equipped with a stir bar was charged with PdPEPPSI-IPr (3.4 mg, 1 mol %) or Pd-PEPPSI-IPent (Table 1: 4 mg, 1 mol %, Table 2: 8 mg, 2 mol %,). The vial was sealed with a Teflon-lined screw cap and purged with argon (3X). If liquid, the aryl bromide (0.5 mmol) was added via syringe along with enough toluene to bring the total reaction volume to 2 mL. Alternatively, if the aryl bromide was a solid at room temperature, it was introduced into the reaction vial prior to purging with argon. The solution was cooled to 0 �C in an ice bath and a THF solution of alkyl zinc halide (0.6 mmol) was added slowly via syringe over 2 min. The ice bath was removed after the addition and the reaction was stirred at rt for 3h. The reaction mixture was then quenched by addition of hydrochloric acid (1N), extracted with ethyl acetate (3X), and the organic phase washed with brine (1X). The combined organic layer was dried over anhydrous Na2SO4, filtered, and concentrated in vacuo. The resulting residue was purified by flash chromatography using the Biotage Isolera Flash Purification System with 10g pre-packed silica cartridges to afford the product mixture. The ratio of the branched to the linear cross coupled product was determined readily by 1 H NMR spectroscopic analysis



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