Letters in Organic Chemistry - Online First

Pyranopyrazole derivatives are important heterocyclic scaffolds known for diverse pharmacological and industrial applications. However, conventional methods for their synthesis often require toxic reagents, harsh reaction conditions, and extended reaction times, creating environmental and operational concerns. Developing green, efficient, and sustainable synthetic methodologies for these derivatives remains a significant need in heterocyclic and medicinal chemistry. We developed an efficient, one-pot multicomponent reaction (MCR) protocol for synthesizing pyranopyrazole derivatives using glutamic acid as a biodegradable, non-toxic, and recyclable catalyst under solvent-free conditions at room temperature. The reaction involves the condensation of ethyl acetoacetate, aromatic or heteroaromatic aldehydes, hydrazine hydrate, and malononitrile, enabling rapid and high-yield synthesis. The methodology provided the desired pyranopyrazole derivatives in excellent yields (91–94%) within short reaction times. We systematically evaluated the effects of catalyst loading, solvent variation, and catalyst recyclability, demonstrating that glutamic acid can be reused for at least five cycles with minimal loss in activity. All synthesized compounds were characterized using NMR and FTIR spectroscopy, confirming the successful formation of target structures. A plausible reaction mechanism was proposed based on literature precedents and experimental observations. This green and efficient protocol offers operational simplicity, high atom economy, a straightforward workup, and an environmentally friendly profile, aligning with green chemistry principles. The methodology provides a practical and sustainable approach for the rapid synthesis of pyranopyrazole derivatives, expanding synthetic strategies for heterocyclic compounds with potential medicinal and material applications.

Lead ions are among the most harmful and widely studied toxins responsible for a wide range of health and environmental risks. The objective of this study was to synthesize a naphthol based optical chemosensor for the detection of lead ions. A naphthol based organic probe 1-(acetylamino(2-chlorophenyl)methyl)-2-naphthol (NCC) has been synthesized by the condensation reaction of -naphthol with o-chlorobenzaldehyde in the presence of chlorosulfonic acid and characterized using various spectroscopic techniques. The probe NCC was subjected to evaluate its potential for the recognition of different mono, di, and trivalent cations in the acetonitrilic medium using UV-Visible spectroscopy. The chemosensing behaviour of NCC was analyzed under various pH, temperature, and time and also in the presence of interfering ions. The results showed an increment in the λmax at 230 nm with a small blue shift of 2 nm after the addition of Pb²⁺ ions to the solution of NCC. Under the optimum conditions, the detection limit and association constant of NCC for Pb²⁺ ions were calculated to be 28.0 ppm and 8.110³ M^-1 using titration studies. The addition of Na2EDTA quenches the absorption intensity of the NCC-Pb²⁺ complex, indicating that NCC serves as a reversible chemosensor for Pb²⁺ ions. The changes in the UV-visible spectrum of NCC in the presence of Pb²⁺ ions suggests the interaction of NCC with Pb²⁺ ions and the formation of a complex, which was found stable for a long period of time in the tested temperature range (5-45 °C). The skeleton reported in this work showed excellent suitability for the detection and determination of Pb²⁺ with minimal interference from other common cations and anions.