Ultrasound Assisted Synthesis of 1,5-Diaryl and 1,3,5-Triaryl-2-pyrazolines by Using KOH/EtOH System with Cu(I) Catalyst

Abstract

INTRODUCTION Recently, in organic synthesis, ultrasound technique is widely used. The chemical reaction is enhanced by the ultrasonic irradiation with the help of the process of the acoustic cavitation. The reaction time is shortened by the use of ultrasonic irradiation. In the field of organic chemistry, additional convenience is offered through simple procedure of experiments, increased yields, selectivity and clean reactions of many organic transformations [1-4]. Loomis and Richards [5] first time introduced the chemical effects, which were resulted from ultrasonic irradiation in aqueous medium. There has been report of zinc-Cu(I) ultrasound-mediated conjugate addition reactions developed by Luche & co-workers which involves reactions carried out under aqueous conditions [6,7]. This methodology has been utilized in synthesis of vitamin D analogues. According to a recent trend of synthetic organic chemistry, ultrasound has been emerged as a significant tool to be used for high yield and shorter reaction time in the chemical reactions [8]. In the synthesis of natural products nitrogenous heterocycles and their derivatives are broadly applied [9]. For carbon-nitrogen bond formation, aza-Michael addition of nucleophiles to α,β-unsaturated ketones, esters and nitriles is proved as an effective tool. These reactions are used in synthesis of kinase inhibitor [10], alkaloids [11], β-lactams [12], amino acids [13]. The most popular method for the preparation of 2-pyrazolines refluxing with α,β-unsaturated aldehydes and ketones using phenyl hydrazine in acetic acid [14]. The substituted pyrazolines have biological activities such as antibacterial [15], analgesic