A convenient approach for the synthesis of substituted pyrroles by using phosphoric acid as a catalyst and their photophysical properties

Twenty-three new pyrrole compounds aside from six knowns, including the synthetically challenging tetra- and penta-substituted pyrroles from the corresponding 1,4-dicarbonyl through Paal-Knorr synthesis in the presence of 5% phosphoric acid as the catalyst. Our method is noteworthy for cheap catalyst, uncomplicated experimental setup under air atmosphere, scalability, and excellent yields. The fluorescence of some selected pyrroles was investigated in dilute solution, and we found that all novel pyrroles emit strong blue fluorescences with considerable Stokes shifts. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

A total of 23 new pyrrole compounds were successfully synthesized in this study, including tetra- and penta-substituted pyrroles which are known to be synthetically challenging. The method utilized a cheap catalyst, simple experimental setup, scalability, and achieved excellent yields. Some selected pyrroles exhibited strong blue fluorescence with considerable Stokes shifts.