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

Pyridinium ylides are well recognized as dipoles for cycloaddition reactions. In its turn, the microwave-assisted interaction of -(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- ]indolizines were studied, showing green light emission with high fluorescence quantum yields.