Elsevier

Tetrahedron Letters

Volume 46, Issue 13, 28 March 2005, Pages 2267-2271
Tetrahedron Letters

High-intensity ultrasound and microwave, alone or combined, promote Pd/C-catalyzed aryl–aryl couplings

https://doi.org/10.1016/j.tetlet.2005.02.015Get rights and content

Abstract

Pd-catalyzed homo- and cross-couplings of boronic acids and aryl halides were successfully carried out both in aqueous media under high-intensity ultrasound (US) and in DME under microwave (MW). Heterogeneous catalysis with Pd/C was employed, avoiding phosphine ligands and phase-transfer catalysts. In a trial series involving 15 different iodo- and bromoaryls and 7 boronic acids, both energy sources drastically reduced reaction times affording biaryls in acceptable to good yields. With palladium(II) acetate as catalyst, electron-deficient aryl chlorides also reacted, affording a few biaryls in acceptable yields. Ullmann-type zinc-mediated homocoupling of iodo- and bromoaryls in the presence of Pd/C under CO2 atmosphere was achieved in aqueous media under US, though not under MW. Suzuki homo- and cross-couplings were also carried out in a new reactor developed in our laboratory, featuring combined US and MW irradiation, further improving a green synthetic method.

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Acknowledgements

COST Action D32 is gratefully acknowledged. The present work was supported by MIUR (COFIN—project: ‘Sviluppo di processi sintetici eco-compatibili nella sintesi organica’). The combined US/MW reactor has been developed in collaboration with NTS srl Arcugnano (Vicenza, Italy).

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