Current Organic Chemistry - Volume 23, Issue 4, 2019

The primary aim of this article is to update many important synthetic pathways, properties and applications of the polyurethanes and its composites. Polyurethanes (PUs) are a special group of versatile materials with a great potential for different use in the development of modern, healthy and clean society, including its multifaceted use in the fields of construction and building related work, transportation, furniture and bedding, appliances, packaging, textiles, fibres, apparel, machinery and foundry, electronics, footwear, medical and so forth. Over the last 8-9 decades, several synthetic strategies of the diverse polyurethanes (PUs) are maturely designed and actively executed using various sustainable and non-sustainable methods for miscellaneous applications in different areas. The major advantages of the modern PUs are to impose desired properties in the materials pertinent to the field of work during their preparation by changing a different kind of monomers and additives. Briefly, this review summarizes the overall accounts, importance, synthetic approaches, properties, and miscellaneous applications in the desired scenario in details.

The present review article surveys an outline on the most recent efforts and exciting developments (between 2010-2018 years) in the application of chitosan and modified chitosan derivatives as bio support for metal immobilization in the cross coupling reactions. The procedures incorporated in this review comprise metal nanoparticles (Pd, Ni, Cu, Au, Co) or metal ions immobilization on non-modified chitosan, porous chitosan microspheres, chitosan hybrid with other organic and inorganic polymers and functionalized chitosan with different ligands such as amine, amide, thiourea, amino acid, carbene and Schiff base derivatives. Also, in each case, the catalytic efficiency was described in various cross coupling reactions.

The nucleosides modified in the 2’- and/or 3’-position have been known for years and include important, bioactive compounds such as zidovudine, cytarabine, didanosine, puromycin, and fludarabine. This group consists of analogs with altered configuration, 2’,3’-dideoxy and 2’,3’-dideoxy-didehydro nucleosides, as well as derivatives with additional substituents. These compounds are often targeted against viruses and tumors. The sugar-base anhydro nucleosides have been known since the middle of the 20th century. However, their application has not yet been fully explored and described. The number of 2’,3’-dimodified derivatives, obtainable through sugar-base anhydrocyclic synthons, could be vast, especially taking into consideration various combinations of S-alkyl, S-aryl, O-alkyl, O-aryl, halogen, triazole, amine and azide substituents in both pyrimidine and purine nucleosides. Furthermore, application of anhydrocyclic structures can be an efficient method of introducing isotope labeled groups. The aim of this article is to provide an overview of the known methods of functionalization of the 2’- and/or 3’-position of nucleosides, using anhydrocyclic structures, and also to present a future outlook for this subject.

The PVP and its derivatives have been broadly applied in polymers, organic syntheses, and catalysis processes. The crosslinked PVP is a well-known polymer support for numerous reagents and catalysts. Cross-linked PVPs are commercially available polymers and have attracted much attention over the past due to their interesting properties such as the facile functionalization, high accessibility of functional groups, being nonhygroscopic, easy to prepare, easy filtration, and swelling in many organic solvents. A brief explanation of the reported applications of PVPs in different fields followed by the discussion on the implementation of methodologies for catalytic efficiency of PVP-based reagents in the organic synthesis is included. The aim is to summarize the literature under a few catalytic categories and to present each as a short scheme involving reaction conditions. In the text, discussions on the synthesis and the structural determination of some typical polymeric reagents are presented, and the mechanisms of some organic reactions are given. Where appropriate, advantages of reagents in comparison with the previous reports are presented. This review does not include patent literature.

Stable nitroxide free radicals have traditionally been associated with 2,2,6,6- tetramethylpiperidine-1-oxyl (TEMPO) or its 4-substituted derivatives as relatively inexpensive and readily accessible compounds with limited possibilities for further chemical modification. Over the past two decades, there has been a resurgence of interest in stable free radicals with proper functionalization tuned for various applications. The objective of this review is to present recent results with synthetic methodologies to achieve stable nitroxide free radicals fused with aromatic carbocycles and heterocycles. There are two main approaches for accessing stable nitroxide free radicals fused with arenes, e.g., isoindoline- like nitroxides: further functionalization and oxidation of phthalimide or inventive functionalization of pyrroline nitroxide key compounds. The latter also offers the constructions of versatile heterocyclic scaffolds (furan, pyrrole, thiophene, 1,2-thiazole, selenophene, pyrazole, pyrimidine, pyridine, pyridazine, 1,5-benzothiazepine) that are fused with pyrroline or tetrahydropyridine nitroxide rings. The possible applications of these new stable nitroxide free radicals, such as covalent spin labels and noncovalent spin probes of proteins and nucleic acids, profluorescent probes, building blocks for construction of dual active drugs and electroactive materials, and substances for controlled free radical polymerization, are discussed.