Base- and Phosphine-Free Palladium-Catalyzed Homocoupling of ­Arylboronic Acid Derivatives under Air

Abstract

In the presence of a catalytic amount of Pd(OAc)₂, ­various arylboronic acids underwent homocoupling in MeOH at ambient temperature under air to give rise to symmetrical biaryls. The homocoupling of arylboronic acids was also carried out using polyurea-encapsulated Pd(OAc)₂ as a recyclable catalyst.

biaryls - boron - catalysis - coupling - palladium

References and Notes

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11

Typical Procedure for the Synthesis of 2a.
Method i: To a solution of p-tolylboronic acid (1a, 115.7 mg, 0.85 mmol) in MeOH (17 mL) was added Pd(OAc)₂ (5.7 mg, 0.026 mmol), and the reaction mixture was stirred for 5 h at r.t. under air. The reaction mixture was concentrated in vacuo and the residue was diluted with EtOAc (15 mL). After filtration of insoluble materials, the filtrate was concentrated in vacuo and the residue was purified by silica gel column flush chromatography (eluent: hexane) to afford 2a (72.6 mg, 94%) as colorless solids.
Method ii: To a solution of p-tolylboronic acid (1a, 68.0 mg, 0.50 mmol) in MeOH (10 mL) was added PdEnCat 30 (ca. 0.4 mmol/g, 37.5 mg, 0.015 mmol), and the reaction mixture was stirred for 24 h at r.t. under air. After filtration of the catalyst, the filtrate was concentrated in vacuo and the residue was purified by silica gel column flush chromato-graphy (eluent: hexane) to afford 2a (29.2 mg, 64%) as colorless solids. All starting materials and products are known compounds.

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