Abstract
An efficient Suzuki coupling protocol that affords reaction products in high purity without the need for chromatography or aqueous work-up is reported. The reaction, which utilises a combination of polymer-supported reagents, can be performed under thermal or microwave heating conditions and is particularly suited to parallel synthesis.
Key words
polymer-supported reagents - encapsulated palladium catalyst - microwave heating - Suzuki cross-coupling - parallel synthesis
References and Notes
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6 Standard solution-phase conditions employed for Suzuki coupling reaction: To a solution of 4-iodoanisole (1 mmol) and 4-tolylboronic acid (2 mmol) in DMF (10 mL) was added Na2 CO3 (0.4 mmol), H2 O (2 mL) and Pd(OAc)2 EnCat™ (5 mol%, based on palladium content). The reaction mixture was stirred at 85 °C for 18 h.
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11f Microwave reactions were performed using an Emrys® synthesiser available from Biotage AB
12 Microwave temperatures were measured externally to the reactor vial using the IR sensor fitted to the Emrys® synthesiser. It is extremely unlikely that these values accurately reflect the significantly higher localised temperatures attained at the catalyst metal surface under microwave irradiation
13 Palladium residue levels were determined using inductively coupled plasma optical emission spectroscopy performed on 4′-methoxy-4-methylbiphenyl(3 ) for both thermal and microwave reactions and indicated residual palladium levels in 3 corresponding to Pd leaching from Pd(OAc)2 EnCat™ to be 2.1% and 1.7%, respectively
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