Convenient synthesis of alkenyl-, alkynyl-, and allenyl-substituted imidazo[1,2-a]pyridines via palladium-catalyzed cross-coupling reactions

A systematic study on the Stille and Sonogashira cross-coupling of iodinated imidazo[1,2-a]pyridines was performed, permitting the preparation of various vinyl-, ethynyl-, and allenyl-substituted derivatives. These methods are particularly valuable, given their experimental simplicity and high degree of flexibility with regard to functional groups that can be introduced in positions 3, 6, or 8 of the imidazo[1,2-a]pyridine core. Effects concerning different substitution positions and the nature of the 2-substituent under various reaction conditions are reported in detail for the above types of unsaturated groups introduced.