1,3,4-Trisubstituted Pyrazoles: Synthesis, Antimicrobial Evaluation, and Time Resolved Studies

Abstract

In this article, an efficient and practicable synthesis of 1,3,4-trisubstituted pyrazoles with an acyl functionality attached on the 4-position of the pyrazole scaffolds is reported. The precursor 4-cyanopyrazoles used for the fabrication of target compounds were synthesized from 4-formylpyrazoles via oxime formation followed by reaction with Vilsmeier–Haack reagent. The reaction of 4-cyanopyrazoles with various Grignard reagents afforded the corresponding 1,3,4-trisubstituted pyrazoles in 71–88% yield. The operational simplicity, economical starting materials, and high efficiency compared to reported methods are the advantages of this approach. All the pyrazole derivatives have been screened for antimicrobial activity and some of the derivatives exhibit significant activity against bacterial and fungal isolates. Further, time resolved photoluminescence studies for 5d, 5h, & 5o were carried out using pulsed nitrogen laser as the source with a pulse width of few nanoseconds and wavelength of 337 nm. The spectrum was observed in microsecond time domain in all the cases, however, fluorescent lifetime is found to higher in 5d & 5h.