Current Organic Chemistry - Volume 26, Issue 4, 2022

Substituted thiazoles are widely known as natural products, approved drugs, and a number of synthetic compounds as bioactive agents. Due to the worth of this heterocycle nucleus, a large number of synthetic methodologies have been reported over the years to synthesize its derivatives. In this perspective, recent advances in the synthesis of thiazole compounds by using domino/cascade and multicomponent approaches have been summarized.

Photoredox catalysis as a powerful strategy for the activation of small molecules requires the use of reactants which are suitable to undergo single-electron transfer with the formation of radicals. In this perspective, we highlight the unique ability of organoboronic acid derivatives to form radicals under photoredox catalysis conditions with particular emphasis placed on the methods of activation of B-C bonds. Key to facilitate the activation relies on use of easily oxidizable organoboronate complexes: organotrifluoroborates, alkoxyorganoboronates or nitrogen-containing Lewis base adducts. The low reduction potentials of these compounds allows facile single-electron oxidation to generate non-stabilized alkyl radicals, including primary radicals, under mild conditions. The use of molecular oxygen is also a common way to activate boronic acids in photocatalytic reactions. The role of the oxygen relies on addition of the oxygen anion-radical formed in the photocatalytic cycle to the boron center affording the easily oxidizable boronate adduct. Amongst the variety of activation methods, the protocols avoiding the use of external Lewis base are especially valuable. This has been demonstrated in visible-light-mediated alkenylation of alkylboronic acids using alkenylsulfones as coupling partners. The radical species resulting from alkylboronic acid derivatives could be utilized in the formation of C–X or C–C bonds including enantioselective photoreactions. The application of boronic acids in the visible light-driven installation of side chains at dehydroalanine residues in proteins shows the increasing role of these compounds in future syntheses of complex natural products.

Gelsemine is a remarkable indole alkaloid isolated from the medicinal plant Gelsemium elegans (Carolina or yellow jasmine) and demonstrates effectiveness in alleviating cognitive impairment, suggesting it could treat Alzheimer's disease. Gelsemine comprises seven adjoining chiral carbon centres and hexacyclic cage structures, making it an oddly difficult synthetic target. The unique structure and potential bio-pharmacological properties of gelsemine have led to the publication of nine interesting total syntheses of gelsemine (including three asymmetric syntheses) in the near past three decades by eight distinguished research groups. Several strategies are brimming with modern concepts of synthesis, such as highly enantioselective organocatalytic Diels–Alder reaction and the biomimetic enol–oxonium cyclization reaction. To better explore the therapeutic effects of gelsemine, this review summarizes the progress in the total synthesis tactics and strategies of the fascinating natural product gelsemine.

Sulfinic acids, sodium sulfinates, and sulfonyl hydrazides are stable, inexpensive, and readily available building blocks, which have been recently utilized as synthons to access various heterocyclic motifs via radical sulfonylation and cyclization. This review systematically summarizes the radical cyclization cascades and discusses their mechanisms. Moreover, it also discusses multi-component reactions, rearrangements, cycloadditions, coupling, green chemistry, etc. We hope that this review will promote future research in this area.

Organic azides are placed in the interphase between chemistry, biology, medicine, and materials science. Their uses in peptide chemistry, combinatorial chemistry, and the synthesis of heterocycles are extensively explored. In this review, the focus is placed on the azidoreductive cyclization of azides and detailed its significant insights. The wide-ranging literature for synthesizing various heterocycles, employing chemoselective and straightforward protocols for azido-reduction with concomitant intramolecular cyclization, has been elaborated. In due course, the azido-reductive cyclization strategy witnessed the synthesis of essential heterocycles, such as benzodiazepine, quinazolinone, piperidine, pyrrole and their derivatives. In addition, the review includes application of azido-reductive cyclization strategies towards the synthesis of various iminosugars, drugs/APIs, and natural products embedding such heterocycles.

The last decade has witnessed a remarkable progress in the field of nanoscience and nanotechnology. Nanoparticles have been extensively used in diverse areas, including medicine, sensor, and catalysis. The easy accessibility of nanoparticles (NPs) with different shapes, sizes and compositions has inspired researchers to investigate their applications in catalysis. Recently, magnetic nanoparticles, such as iron-based nanoparticles, have attracted much consideration due to their unique properties, such as superparamagnetism, greater surface area, surface-to-volume ratio, and easy separation methodology. They increase the competence of organic reactions in terms of activity, selectivity, yield, simplicity, and sustainability. In this review, we focus on the developments of iron/iron oxide-based nanoparticles-catalyzed organic reactions and some examples of magnetic iron oxide nanoparticles as carriers/support for the main catalyst in organic reactions. Owing to magnetic properties, these nanocatalysts can be easily recovered from the reaction mixture by an external magnet and reused for several runs without loss of catalytic activity. Iron-based nanoparticles are used in a wide range of catalytic processes and applications. Notable focus has been on the hydrogenation of alkenes and alkynes, and also the hydrogenation of nitroarenes to aniline. Other catalyzed organic reactions, such as hydroboration of aldehydes and ketones, oxidative dehydrogenation of N-heterocycles, azide-alkyne cycloaddition reactions, synthesis of various heterocyclic compounds, multicomponent reactions, and crosscoupling reactions for C–C and C–heteroatom bond formation have been covered.

Background: Phosphine-free Pd-catalytic platforms, i) combination with chitosan- Schiff base (CS-Py/Pd), ii) immobilized on chitosan-Schiff base (CS-Py@Pd), and iii) anchored to modified carbon nanotube support (CNT@CS-Py@Pd), Methods: They were evaluated regarding a novel pathway for the cross-coupling reaction of arylboronic acids with acid chlorides. Results: The CS-Py@Pd platform had the highest catalytic efficiency of the three platforms, yielding moderate to excellent yields of diaryl ketones. Conclusion: The catalytic activity of the Pd-catalyst was highly dependent upon the manufacturing process and type of support.