Facile synthesis of iodopyridines from N-propargylic β-enaminones via iodine-mediated electrophilic cyclization

A facile, efficient and general synthetic method for iodopyridines is described. When treated with molecular iodine in the presence of sodium bicarbonate, N-propargylic β-enaminones have underwent electrophilic cyclization to afford iodo-substituted pyridines in good to high yields. Iodocyclization has been found to be general for a broad range of N-propargylic β-enaminones and tolerated the presence of aliphatic, aromatic and heteroaromatic groups with electron-withdrawing and electron-donating substituents. The starting N-propargylic β-enaminones have been prepared by conjugate addition of propargylamine to α,β-alkynic ketones, followed by Sonogashira coupling with aryl iodides.