Organoselenium compounds beyond antioxidants

Organoselenium chemistry has become a significant field due to its role in synthesizing numerous biologically active and therapeutic compounds. In early phase, researchers focused on designing organoselenium compounds with antioxidant properties and were quite successful. In last two decades, synthetic chemists shifted their focus toward synthesis of organoselenium compounds with biological properties, moving beyond their traditional antioxidant properties. The review includes synthesis and study of organo-selenium compounds as anticancer, antimicrobial, antiviral, antidiabetic, antithyroid, anti-inflammatory therapies, contributing to disease treatment. This review covers the synthesis and medicinal applications of synthetic organoselenium compounds over the past 10 years, thus making it a valuable resource for researchers in the field of medicinal chemistry.

Palladium-Catalyzed Direct Selanylation of Chalcogenophenes and Arenes Assisted by 2-(Methylthio)amide

The direct and selective conversion of a C-H bond into a C-Se bond remains a significant challenge, which is even more intricate with substrates having an innate regioselectivity under several reaction conditions, such as chalcogenophenes. We overrode their selectivity toward selanylation using palladium, copper, and the 2-(methylthio)amide directing group. This chelation-assisted direct selanylation was also suitable for mono and double ortho functionalization of arenes. The mechanistic studies indicate high-valent Pd(IV) species in the catalytic cycle, a reversible C-H activation step, and Cu(II) as a sequestering agent for organoselenide byproducts.

Selective Synthesis of Bis-Heterocycles via Mono- and Di-Selenylation of Pyrazoles and Other Heteroarenes

The insertion of selenium was achieved in the form of mono-selenides and di-selenides for the preparation of novel bis-heterocyclic compounds. This method is more general and provides scaffold diversity with high yields of products. The concentration-dependent mono- and di-selenylation reaction selectivity was achieved using SeO₂ as an efficient selenylating reagent.

Regio- and stereoselective synthesis of new ensembles of diversely functionalized 1,3-thiaselenol-2-ylmethyl selenides by a double rearrangement reaction

The reaction of 2-(bromomethyl)-1,3-thiaselenole with potassium selenocyanate proceeded via a rearrangement with ring expansion, leading to a six-membered 2,3-dihydro-1,4-thiaselenin-2-yl selenocyanate (kinetic product) which in turn underwent rearrangement with ring contraction to a 1,3-thiaselenol-2-ylmethyl selenocyanate (thermodynamic product). These rearrangements occurred by a nucleophilic attack of the selenocyanate anion at two different carbon atoms of the seleniranium intermediate. The efficient regioselective synthesis of alkyl, allyl, 2-propynyl, benzyl, 4-fluorobenzyl, and 2-pyridinylmethyl 1,3-thiaselenol-2-ylmethyl selenides was developed based on the generation of sodium 1,3-thiaselenol-2-ylmethylselenolate from 1,3-thiaselenol-2-ylmethyl selenocyanate or bis(1,3-thiaselenol-2-ylmethyl) diselenide followed by nucleophilic substitution reactions. Sodium 1,3-thiaselenol-2-ylmethylselenolate underwent nucleophilic addition to alkyl propiolates in a regio- and stereoselective manner affording 1,3-thiaselenol-2-ylmethyl vinyl selenides in high yields predominantly with Z-configuration. Not a single representative of the 1,3-thiaselenol-2-ylmethyl selenide scaffold has been previously described in the literature.

Chelation-assisted transition metal-catalysed C–H chalcogenylations

This review summarizes recent advances in C–S and C–Se formationsviatransition metal-catalyzed C–H functionalization utilizing directing groups to control the site-selectivity.