Current Organic Chemistry - Volume 21, Issue 25, 2017

Background and Objective: It may seem that the reaction first performed over 120 years ago is an out of date subject on which everything has been said and there is nothing left to be discovered-but first impressions can be deceiving. Even of lately, the Dimroth rearrangement pops up here and there, sometimes chosen deliberately as a method of synthesis, but sometimes it is brought back to life in order to explain unexpected results of experiments. Substrates for the rearrangement are heterocycles, and products are isomeric molecules in which certain heteroatoms (typically N, O, S, rarely Se) change places. Methodology: The reaction may appear separately as a method of synthesis, or it can constitute a stage of the mechanism of a particular reaction. It is a useful tool for obtaining the desired compounds and introducing isotopes (e.g. 15N) into the heterocyclic skeleton of certain molecules (e.g. nucleoside chemistry). Conclusion: The aim of this review is to present a general outlook on the Dimroth rearrangement along with the situations in which it may occur, and to briefly describe its potential applications.

The recent explosion in mRNA cap analogs underscores the importance of mRNA as a powerful tool in the study of RNA metabolism and highlights the potential of targeting mRNA for the treatment of cancer, gene therapy, antiviral therapy and improvement of the localization of nuclease-targeting drugs. The chemically modified mRNA cap analogs consist of a unique cap structure, m7G[5']ppp[5']N (where N = G, A, C or U), present at the 5'-end of many eukaryotic cellular and viral RNAs and several non-coding RNAs. The presence of sugar substitution on m7G moiety of cap analog has had a great impact on the nature of the orientation, translational efficiency, binding affinity and nuclear stability. It is noteworthy that these modified cap analogs are classified as anti-reverse cap analog (ARCA) that incorporates into mRNA exclusively in the forward orientation. This review focuses on the recent development in the synthesis of various cap analogs with modifications on 7- methylguanosine (m7G) sugar substitution such as 3'-propargyl, 2',3'-isopropylidene, 2',3'-diacetyl and 2'-amino, triphosphate bridging such as imidodiphosphate and methylenebis(phosphonate), triphosphate non-bridging such as BH3, Se and S, and nucleobase substitution such as 6-thioguanosine and triazole. In addition, the biological applications of these novel cap analogs are discussed.

This review article is an attempt to highlight the most important contributions toward the synthesis of functionalized 2-quinolone derivatives from cyclization of N-arylpropiolamides with the emphasis on the mechanistic aspects of the reactions.

The development of spinels as catalysts for various organic transformations has gained a considerable importance over the last decade. In this article, an overview is given about the use of spinels and functionalized spinels in heterogeneous catalysis. In particular, these can be either normal or inverse spinels and they can trigger catalytic reactions without modification, with modification, as core material and also decorated on carbon materials. Catalytic application of these ferrite spinels in the nano size range including diamagnetic, paramagnetic, ferromagnetic magnetic materials is used in C-C coupling, dehydration reactions, oxidations, reductions, reforming reactions. These nano spinels can be easily recovered and recycled with a help of external magnet after the reactions. In most of the cases, all these spinels are characterized with the help of X-ray Powder Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) and X-ray Photo electron Spectroscopy (XPS).

Background: The design of a highly active catalyst is a key point in olefins epoxidation. Recently, polyoxometalates have received an increasing interest in selective oxidation of organic compounds. Their scope as nanoparticle carriers is of immense importance as the high anionic charge associated with them prevents sintering of the nanoparticles which is a major issue related to nanoparticle based catalysts thus increasing the stability of the catalyst. Objective: We have immobilized Na9PMo11O39 (PMo11) and gold nanoparticles on chloropropyltriethoxysilane functionalized SBA-15 mesoporous material. We investigated the molecular oxygen activation ability and stability of this heterogeneous hybrid catalytic system for green epoxidation of cyclohexene under mild reaction conditions. Method: PMo11 was prepared according to the literature, while PMo11/CPTES-SBA-15, Au/CPTES-SBA-15 and Au/PMo11/CPTES-SBA-15 were prepared by wet deposition method. The catalytic performance was evaluated in a PTFE lined autoclave and analysis was done by gas chromatography. Results: Cyclohexene epoxidation was carried out on different heterogeneous catalytic systems which included polyoxometalate and CPTES-SBA-15 support, nano gold and CPTES-SBA-15 support and the hybrid material Au/PMo11/CPTES-SBA-15 with varying amounts of doped nanogold. All the samples showed good conversion of cyclohexene and significant selectivity for oxidized products with molecular oxygen as an oxidant under mild conditions. 1 % Au/PMo11/CPTES-SBA-15 delivered 48.1 % conversion and 35.9 % selectivity to epoxide. Conclusion: The CPTES-SBA-15 supported Au/PMo11 hybrid catalytic system demonstrated relatively high catalytic activity and selectivity for the green epoxidation of cyclohexene with molecular oxygen as an oxidant under mild reaction conditions. The hybrid catalyst was regenerated and reused for three cycles without compromising the catalytic performance.

Branched amino functional polyoctahedral silsesquioxanes (POSS) were prepared by using different stoichiometric ratios of two olefins: allylamine and vinyltrimethoxysilane. Amino-rich CPG particles were produced by direct silanisation with amino-POSS silanes. The parameters of surface morphology (total volume and size of pores) of the obtained supports were determined by Brunauer-Emmett-Teller method. Results from Scanning Electron Microscopy show that there is no alteration in surface chemistry and only modest changes in mechanical properties are detected. The POSS-modified CPG supports were demonstrated as effective scaffolds for the chemical synthesis of nucleic acids.