Synthesis and Derivatization of Julolidine: A Powerful Heterocyclic Structure

Julolidines constitute a class of N-heterocycle compounds which have in common the 2,3,6,7-tetrahydro-1H,5H-benzo[1,2]quinolizine ring. Due mainly to its fluorescence properties, such structures have shown potential application in a range of scientific and technological areas and have attracted attention of a great variety of research groups. For example, julolidines have been used for detection of ions and volatile compounds in environmental and biological samples, to the construction of dye-sensitized solar cells, photoconductive materials and as fluorescent sensors for bioimaging. This review summarizes the strategies reported to the synthesis of the julolidine ring and the principal modifications for obtaining more complex julolidine derivatives with improved fluorescence properties of these compounds. In this context, aldol condensation, olefination, imine synthesis, and cross-coupling reactions have been extensively explored and discussed. Examples of applications, which illustrate the great potential of such structures, will also be briefly presented.