Mini-Reviews in Organic Chemistry - Volume 18, Issue 2, 2021

The chemistry of hypervalent iodine reagents has emerged as an astonishing field in synthetic organic chemistry owing to its easy availability and benign environmental features. Hypervalent iodine reagents are mostly employed as alternatives in various metal-catalyzed reactions since they show similar reactivity to the transition metals, are less toxic, and less expensive. These reagents are often used as oxidants as well as electrophilic reagents in a number of organic transformations, such as oxidative functionalization, alpha C-H bond functionalization of carbonyl compounds, rearrangements, and cyclization reactions. Furthermore, the application of iodine(III) and iodine(V) reagents in various oxidative rearrangement processes generating a diverse array of molecules have been well explored. In this mini-review, the recent developments in the area of oxidative rearrangements, using hypervalent iodine reagents, have been covered.

Iodine(III)-based reagents have been broadly used in oxidative reactions for structural functionalization with several functional groups. Among the more relevant and useful synthetic transformations using these hypervalent λ³-reagents, the fluorination, chlorination, bromination, as well as the iodination protocols, can be found. Herein, we present some of the most representative oxidative halogenation procedures of arenes, olefins and alkynes dating from the oldest to the more recent advances in the area, highlighting the discovery and application of new iodine(III)-based halogenating species.

[¹⁸F]-labeled drugs and radioligands are most frequently used in positron-emission tomography (PET) radiopharmaceuticals for both clinical and preclinical research. Various methods for the introduction of [¹⁸F]fluorine into complex molecules through fluorination reactions have been reported. Herein, recent advances in [¹⁸F]-fluorination utilizing aryliodonium(III) compounds are highlighted.

The importance of selenium in biology, in organic catalysis, and green chemistry is well established. Selenoproteins, among which are ubiquitous Glutathione Peroxidases (GPx), play a key role in mitigating oxidative stress by reducing H2O2 and hydroperoxides using glutathione as a cofactor. Organoselenides, particularly diphenyl diselenide, in the presence of H2O2, are efficient and often green oxygen transfer agents in important organic reactions, such as Baeyer-Villiger oxidations of ketones/aldehydes, the conversion of alkenes into epoxides, and the oxidations of alcohols and nitrogen- containing compounds. NMR spectroscopy can facilitate the investigation of the properties of this element in a biological environment and the characterization of the peculiar species of its chemistry. In this short review, a brief overview of the experimental and computational ⁷⁷Se NMR-based techniques is outlined, with a particular focus on their applications to the study of biologically relevant organoselenium compounds and bio-mimetic systems. Experimental protocols, together with computational methods used in different contexts, are presented and their potential as efficient investigation tools is critically discussed. It emerges that while the ⁷⁷Se NMR measurement is a consolidated technique, no standard computational protocol is available to compute the shielding constant of the chalcogen nucleus with accuracy and the optimal approach combines molecular dynamics in solution and quantum chemistry calculations to take into account the conformational freedom.

The arylaluminum reagents are good nucleophiles for organic reactions because of their high reactivity, high chemoselective, low toxicity, and ease of preparation. Therefore, arylaluminum reagents are widely applied in many organic reactions. This review summarizes the recent advancement of the arylaluminum reagents applied in cross-coupling reactions, involving various reaction systems and properties of reaction.

This review reports various synthetic routes of pyrazolone/ pyrazolinone derivatives via the addition of cycloaddition, condensation, cyclocondensation, modification, alkylation, as well as formylation, regioselective, and ring-opening reactions under reflux, microwave irradiation, and/ or ultrasonication conditions. It also presents critical chemical behaviors towards nucleophilic and electrophilic reagents. The chemical reactivities of pyrazolone/ pyrazolinone derivatives involve alkylation, acylation, condensation, catalyzed diazo coupling, oxidation, heteroarylation, phosphorylation, stereoselective alkenylation, enantioselective alkylation, addition, and complexation reactions. The review also summarizes the significant biological activity of pyrazolone/ pyrazolinone derivatives as antibacterial, antifungal, anti-inflammatory, anticancer, antitumor, anthelmintic, analgesic, as well as antioxidant, anthelmintic, antibiofilm, and anti-HIV. Moreover, some pyrazolone/ pyrazolinone derivatives used to remove various metal or soft metal ions from the wastewater. Besides, they exhibited stable complexes with some metals, for example, Ag (I), Cu (I), Cu (II), Hg (II), Pb (II), Sn (II), and Sb (V) as new materials, catalysis, and precursors for CVD in the microelectronic industry and as potential antitumoral.

Several easy, efficient and convenient procedures to access indoles fused heterocyclic systems are described in this review. These heterocyclic systems were synthesized from several cyclic or acyclic molecules via a variety of reactions such as Diels-Alder reaction, Michael addition, Morita- Baylis-Hillmann reaction and many other domino/Cascade approaches with high selectivity. Most of the given protocols in this review proceed through organocatalytic pathways; however, some underwent different catalytic and non-catalytic reactions.

The removal of volatile compounds with unfavorable fishy odor from fish has attracted considerable research attention especially in surimi production industry. The binding of these volatile compounds by fish proteins are reported to affect the deodorization of fishy odor. To remove the protein- bound fishy substances effectively, the mechanisms underlying the interaction between proteins and flavor substances and methods that can extract and analyze the aromatic substances have been extensively studied. This paper briefly reviews the typical fishy compounds and the combination modes and mechanisms of fish proteins with these compounds. Moreover, factors affecting the interactions including protein conformation and solution conditions are discussed in detail.