Palladium-catalyzed carbonylative coupling of pyridine halides with aryl boronic acids

The carbonylative Suzuki cross-coupling of a variety of mono-iodopyridines and bromopyridines (, , ) catalyzed by palladium-phosphane systems has been studied to prepare benzoylpyridine derivatives (, , ). The selectivity and the rate of the reaction are highly dependent on the reaction conditions, i.e. nature of the palladium catalyst precursor, solvent, temperature and CO pressure. The main side-products arise from direct, non-carbonylative cross-coupling. Under optimized conditions, benzoylpyridines are recovered in high yields (80–95%). The order of reactivity decreases from iodo- to bromopyridines and from 2-, 4- to 3-substituted halopyridines. The reactivity of dihalopyridines has been investigated; 2,6-dibromopyridine () and 3,5-dibromopyridine () are selectively transformed into either the corresponding benzoyl-phenylpyridine (, ) or the corresponding dibenzoylpyridine (, ). Dissymmetric 2,5-dihalopyridines () are transformed into 2-benzoyl-5-bromopyridine () or 2,5-dibenzoylpyridine () in high yields.