Microwave-Assisted Synthesis of Fluorescent Pyrido[2,3-b]indolizines from Alkylpyridinium Salts and Enaminones

Abstract

Pyridinium ylides are well recognized as dipoles for cycloaddition reactions. In its turn, the microwave-assisted interaction of N-(cyanomethyl)-2-alkylpyridinium salts with enaminones unexpectedly proceeds as a domino sequence of cycloisomerization and cyclocondensation reactions, instead of a 1,3-dipolar cycloaddition. The reaction takes place in the presence of sodium acetate as base and employs benign solvents. The optical properties of the resulting pyrido[2,3-b]indolizines were studied, showing green light emission with high fluorescence quantum yields.

Recent Advances in Reactions Using Enaminone in Water or Aqueous Medium

“…Van der Eycken and co‐workers [25] reported the reactions of alkylpyridinium salts 32 and enaminones 1 in aqueous i ‐PrOH for the synthesis of pyridine‐fused heterocyclic products 33 . The reactions were conducted with microwave irradiation at 150 °C.…”

Color-Tunable Indolizine-Based Fluorophores and Fluorescent pH Sensor

“…Due to a high demand for the development of novel fluorescent core skeletons, considerable progress has been made over the past few decades, which has resulted in the synthesis of various new fluorophores characterized by specific photophysical properties allowing the development of novel fluorescent probes [ 9 , 10 , 11 , 12 , 13 ]. As an example, indolizine-based organic molecules were successfully exploited in new fluorophores and fluorescent probes [ 14 , 15 , 16 , 17 , 18 , 19 , 20 ]. Synthetic methods for various types of indolizine scaffolds have led to the development of well-defined fluorophore scaffolds with an in-depth studied structure-fluorescence relationship.…”