3-Halochromones Through Oxidative α-Halogenation of Enaminones and its Photophysical Investigation: Another Case of Photo-induced Partially Aromatised Intramolecular Charge Transfer?

A versatile synthesis strategy for fluorescent 3-halo-4H-chromen-4-one derivatives is reported. The method involves the oxidative α-halogenation of enaminones performed by an efficient and sustainable oxidation system. The use of Oxone® in combination with KCl, KBr, or KI enables the preparation of 3-chloro-, 3-bromo-, or 3-iodo-4H-chromen-4-one in good to excellent yields, with great functional group tolerance where the protocol is amenable to gram-scale synthesis. The analysis of the photophysical properties of the presented 4H-chromen-4-one showed absorption in the UV region and fluorescence emission in the violet-to-cyan region with a relatively large Stokes shift. In solution, all compounds present a dual fluorescence emission, regardless of the solvent, assigned to a partially aromatised intramolecular charge transfer mechanism, considering the presence of a pseudo-aromatic ring in the chromone scaffold and the absence of the influence of substituent electronic features in optical behaviour.

Versatile Electrochemical Synthesis of Selenylbenzo[b]Furan Derivatives Through the Cyclization of 2-Alkynylphenols.

We report an electrochemical oxidative intramolecular cyclization reaction between 2-alkynylphenol derivatives and different diselenides species to generate a wide variety of substituted-benzo[b]furans. Driven by the galvanostatic electrolysis assembled in an undivided cell, it provided efficient transformation into oxidant-, base-, and metal-free conditions in an open system at room temperature. With satisfactory functional group compatibility, the products were obtained in good to excellent yields.