Synthesis of Pentacyclic Pyran Fused Pyrazolo Benzo[h]quinolines by Multicomponent Reaction and Their Photophysical Studies

Herein we report for the first time a one-pot method for the synthesis of pentacyclic pyran fused pyrazolo benzo[h]quinolines in acetic acid medium from the three-component reaction of 2-hydroxy-1,4-naphthoquinone, alpha, beta-unsaturated aldehydes and 5-aminopyrazoles under the reflux conditions. In this reaction, four new bonds (2 C-C, 1 C-N and 1 C-O) and two new rings (pyridine and pyran) were formed in one-pot. The novel products contain four bioactive moieties such as pyran, pyridine, pyrazole and alpha-naphthol. The salient features of this method are: one-pot process, short reaction time, easier purification, no need of column chromatography and good yields of the products. All the products were characterized by IR, NMR and HRMS. Most of our synthesized compounds were found highly fluorescent. Therefore, we further studied their photophysical properties by UV-Visible and Fluorescence spectroscopy. We have calculated their quantum yields which were found in the range 0.243-0.424 in CHCl3 solution (c=10(-5) M). Compound 4 e showed the highest quantum yield of 0.424.

Automated summary

A new method for the synthesis of pentacyclic pyran fused pyrazolo benzo[h]quinolines was reported in this study, which involved a one-pot reaction in acetic acid medium. The method allowed the formation of new bonds and rings, resulting in the synthesis of bioactive compounds. The method has the advantages of one-pot process, short reaction time, easier purification, and good product yields.