A Modular Synthesis of Functionalized Pyridines through Lewis-Acid-Mediated and Microwave-Assisted Cycloadditions between Azapyrylium Intermediates and Alkynes
conditions to furnish the expected pyridine derivatives 3k and 3l in respectable yields. The 3-bromo-substituted pyridines 11 were further functionalized through palladium-catalyzed couplings such as Suzuki or Sonogashira reactions, which led smoothly to tri- or tetrasubstituted pyridine derivatives such as 19–21 and 23. Reductive debromination of 11e afforded the pyridine 17 in excellent yield, whereas