A Simple Preparation of Alkylzinc Reagents Compatible with Carbonyl Functions

Herein, we report a direct method to prepare alkylzinc compounds from functionalized alkyl bromides using cobalt catalysis under mild conditions. This procedure only requires a simple catalytic system composed of CoBr₂ and bipyridine as ligand in a mixture of acetonitrile/pyridine. This reaction is stable under air and moisture conditions opening the way to an accessible procedure. A wide range of functional groups such as esters, cyano and halogens on primary and secondary alkyl bromides was well tolerated and gave high yields of the corresponding alkylzinc compounds. Additionally, we managed to form alkylzinc reagents bearing sensitive functional groups such as ketones and aldehydes with good yields. The direct application of these alkylzinc derivatives in palladium-catalyzed Negishi cross-coupling with various functionalized aryl bromides proved the efficiency and robustness of this methodology.