Dual-Mode Multiple Ion Sensing via Analyte-Specific Modulation of Keto-Enol Tautomerization of an ESIPT Active Pyrene Derivative: Experimental Findings and Computational Rationalization.

A pyrene-based e xcited - state intramolecular proton transfer (ESIPT) active probe PMHMP was synthesized, characterized, and employed for the ppb-level, dual-mode, and high-fidelity detection of Cu2+ (LOD: 7.8 ppb) and Zn2+ ions (LOD: 4.2 ppb) in acetonitrile medium. The colorless solution of PMHMP turned yellow upon the addition of Cu2+, suggesting its ratiometric, naked-eye sensing. On the contrary, Zn2+ ions displayed concentration-dependent fluorescence rise till a 0.5 mole fraction and subsequent quenching. Mechanistic investigations indicated the formation of a 1:2 exciplex (Zn2+:PMHMP) at a lower concentration of Zn2+, which eventually turned into a more stable 1:1 (Zn2+:PMHMP) complex with an additional amount of Zn2+ ions. However, in both cases, it was observed that the hydroxyl group and the nitrogen atom of the azomethine unit were involved in the metal ion coordination, which eventually altered the ESIPT emission. Furthermore, a green-fluorescent 2:1 PMHMP-Zn2+ complex was developed and additionally employed for the fluorimetric analysis of both Cu2+ and H2PO4 - ions. The Cu2+ ion, owing to its higher binding affinity for PMHMP, could replace the Zn2+ ion from the preformed complex. On the other hand, H2PO4 - formed a tertiary adduct with the Zn2+-complex, leading to a distinguishable optical signal. Furthermore, extensive and organized density functional theory calculations were performed to explore the ESIPT behavior of PMHMP and the geometrical and electronic properties of the metal complexes.

Deconjugated butenolide: a versatile building block for asymmetric catalysis.

The wide abundance of γ-lactones in natural products and bioactive targets calls for suitable building blocks for their enantioselective synthesis. ß,γ-Unsaturated γ-butenolides, commonly known as deconjugated butenolides, owing to their easy accessibility and highly reactive nature, have emerged as the synthon of choice during the past decade for the enantioselective synthesis of γ-lactones. Their compatibility under organocatalytic, metal-catalyzed as well as cooperative catalytic conditions has resulted in numerous enantioselective transformations involving deconjugated butenolides. These reactions not only led to enantioenriched γ-lactones, but also various other heterocycles and acyclic compounds through ring-opening and fragmentation of the parent butenolide ring. The purpose of this review is to provide a comprehensive treatise on the catalytic asymmetric reactions of deconjugated butenolides reported so far. This aspect is presented alongside the preparation and reactivity comparison of deconjugated butenolides with other competing synthons of γ-lactones. Limitations of the existing protocols and the possible scope for future development are also discussed.

Enantioselective dearomatization of isoquinolines by anion-binding catalysis en route to cyclic α-aminophosphonates.

An enantioselective dearomatization of isoquinolines has been developed using chiral anion-binding catalysis. This transformation, catalyzed by a simple and easy to prepare tert-leucine-based thiourea derivative, makes use of silyl phosphite as a nucleophile and generates cyclic α-aminophosphonates. This is the first time asymmetric anion-binding catalysis has been applied to the synthesis of α-aminophosphonates.