Synthesis and Photochemical Characterization of Indolizine Fluorophores Obtained by a Multicomponent Palladium Iodide−Catalyzed Oxidative Aminocarbonylation Approach

Abstract

A catalytic carbonylative method for the direct, multicomponent synthesis of indolizine fluorophores has been developed. The process is based on the PdI2/KI‐catalyzed oxidative aminocarbonylation of 2‐(pyridin‐2‐yl)pent‐4‐yn‐1‐carbonyl compounds leading to the corresponding 2‐ynamide intermediates, followed in situ by 5‐exo‐dig cyclization (by amine‐promoted conjugate addition of the pyridine ring nitrogen) and aromatization, to give the finally isolated N,N‐disubstituted 2‐(indolizin‐3‐yl)acetamides. Reactions are carried out under relatively mild conditions (100 °C under 20 atm of a 4:1 mixture CO‒air for 6‐15 h) in MeCN as the solvent and with a low catalyst loading (0.33 mol% PdI2), in the presence of 0.5 equiv of KI and 3 equiv of a secondary amine. The optical properties of representative 2‐(indolizin‐3‐yl)acetamide products have also been investigated.