Current Organic Chemistry - Volume 25, Issue 22, 2021

The 1,3-dipolar Cycloadditions (DCs) of Nitrile Oxides (NOs) have been used as a powerful tool in synthetic organic chemistry. The cycloadducts arising from Cycloadditions (CAs) of NOs to alkenes and alkynes (2-isoxazolines and isoxazoles respectively) are valuable synthetic intermediates because, among others, their capacity to mask other functionalities including α, β -unsaturated ketones, β -hydroxy carbonyl compounds and 1,3- aminoalcohols. In particular, the β-hydroxy ketone functionality is an illustrative example, making the NOs alkenes CAs reactions a synthetically equivalent methodology of aldol reactions. The vast majority of these reactions are carried out in organic solvents. Nevertheless, the use of water as an alternative solvent has evident advantages on the “Green Chemistry” concept. The critical discussion on the use of water instead of “conventional” solvents in the 1,3-DCs reactions of NOs is the objective of the present review.

Radical chemistry is known for two centuries. Due to the fascinating nature of the radical-mediated processes, these reactions have attracted the attention of organic chemists to prepare new compounds with diverse stereochemistry. Radical-induced methods mostly follow atom economical principles. Tin-based radical annulation method is the most common and widely used procedure for the synthesis of a wide range of organic compounds with medicinal significance. In this review, we report recent stereoselective tin-mediated radical cyclization reactions. The versatility of tinbased reagents in the cyclization process as reported herein will encourage chemists to construct many other molecules of interest following the principles involved in these reactions.

2,7-Naphthyridine is one of the six structural isomers of pyridopyridine. Biological investigations have shown that these compounds have a broad spectrum of activity. They have been found to have antitumor, antimicrobial, analgesic and anticonvulsant effects. The broad spectrum of biological activity of 2,7-naphthyridine derivatives is the main reason for the preparation of new compounds containing this scaffold. This review aims to present various methods of obtaining 2,7-naphthyridine analogs. Compounds containing a 2,7-naphthyridine moiety can be synthesized from a variety of substrates and may be classified into four main categories: those derived from acyclic compounds, from quinoline derivatives, from pyridine derivatives, and from other compounds. Most of them were obtained by the cyclocondensation or intramolecular cyclization of pyridine derivatives. Cyclocondensations of non-cyclic substrates also produced 2,7-naphthyridine derivatives. Tricyclic benzo[2,7]naphthyridines were prepared from quinolines. The 2,7-naphthyridine scaffold has also been synthesized by the rearrangement of pyrrolo[3,4-c]pyridines, pyrano[3,4-c]pyridines or thiopyrano[3,4-c]pyridines.

Various diketones such as 1,2-diketones, 1,3-diketones, 1,4-diketones, β - diketones and dicarbonyl compounds are used in the synthesis of core heterocyclic compounds such as pyrazoles, isoxazoles, triazoles and quinolones. They play an important role in synthetic organic chemistry. The diketones and dicarbonyl compounds also act as chelating ligands for the lanthanides and a large number of transition metals in material chemistry. 50% of drugs contain nitrogen heterocyclic compounds, so organic chemists have made efforts for the synthesis of nitrogen-containing heterocyclic compounds. This review article has compiled different methodologies for the synthesis of five- and six-membered nitrogencontaining heterocyclic compounds.

Synthesis of cycloolefin-based polymers via metathesis-accompanied cyclopolymerization and tandem Ring-Opening/Ring-Closing Metathesis (RO/RCM) polymerization are undergoing exciting developments and emerging as an area of great interest in the field of polymer synthesis. Among the conventional polymerization techniques, both cyclopolymerization and tandem polymerization give access to highly functional cycloolefin ring-based polymers. This review provides an overview of the synthesis of such cycloolefin-based conjugated and non-conjugated polymers following cyclopolymerization and tandem RO/RCM polymerization methodologies.