Facile synthesis of aryl-substituted pyridines via Suzuki-Miyaura approach

A facile and efficient synthetic route to arylpyridines is reported. When heated with boronic acids in the presence of 5 mol % PdCl2(PPh3)(2) and KHCO3 in 4:1 DMF/H2O solution at 110 degrees C, 5-iodopyridines have undergone Suzuki-Miyaura coupling reactions to afford 5-aryl-substituted pyridines in good to excellent yields. The coupling reaction has been found to be general for a broad range of iodopyridines and boronic acids, and demonstrated good tolerance to a variety of aliphatic, aromatic, heteroaromatic and ferrocenyl groups with electron-withdrawing and electron-donating substituents. This coupling approach could accommodate various functional groups and provide rapid access to a library of functionalized arylpyridines of pharmacological interest. The starting 5-iodopyridines have been prepared from alpha,beta-alkynic ketones, involving conjugate addition of propargylamine to alkynones, followed by metal-catalyzed cross-coupling of the resulting N-propargylic beta-enaminones with aryl iodides and electrophilic cyclization with molecular iodine