Palladium-Catalyzed Cascade Sonogashira Cyclization for Synthesis of Fluorescent Benzofuran Amino Acids.

In this work, we developed an efficient methodology for the synthesis of benzofurans using Sonogashira-type reactions between iodotyrosine and alkyne derivatives (aromatic, heteroaromatic, and alkyl), catalyzed by palladium salts. The methodology enabled the formation of the desired products under mild conditions, with yields ranging from 35% to 92%. The reaction exhibited broad tolerance toward different substituent groups on the aromatic rings, demonstrating its synthetic versatility. Fluorescence quantum yields of selected derivatives ranged from 11% to 35%, with specific aryl substituents affording markedly enhanced emission efficiencies.