Mini-Reviews in Organic Chemistry - Volume 12, Issue 2, 2015

Nowadays, scientists need to work with non-contaminating technologies. Some approaches include the use of multicomponent reactions (MCRs), and solid and reusable catalysts. Through MCRs it is possible to work without isolating intermediate products, so the use of auxiliary solvents is minimized. Furthermore, catalysis by heteropolycompounds is a field of increasing importance worldwide. Heteropolycompounds are effective, reusable and stable solid catalysts that have intrinsic multifunctionality: they can be designed in order to enhance their redox or superacidic properties by varying the atoms in their formula. The present review presents recent advances in the synthesis of organic compounds through multicomponent reactions by using heteropolycompounds as catalysts. Some of these compounds are: dihydropyrimidinones, quinazolinones, naphthol derivatives, pyridines, xanthenones, azabicyclo[2.2.2]octan-5-ones, dispiroheterocycles, imidazoles, spirofused heterocycles, and 1,4-dihydropyridines.

Alkyl nitrites are inexpensive, mild, relatively stable and easy-to-handle alkyl esters of nitrous acid, that can be prepared simply and used in various synthetic reactions. Alkyl nitrites were discovered in the 19th century and were initially used as medical vasodilators. After several years it was observed, that alkyl nitrites are useful chemical reagents, especially as efficient NO source, consequently these were used for diazotization and as nitrating agent or oxidant. In this review several important and novel applications of alkyl nitrites in organic transformations are reported.

Intramolecular Diels-Alder reactions have become commonly employed transformations in the repertoire of the synthetic organic chemist. Variants of this reaction, which incorporate heteroatoms in the diene and dienophile, are also popular. Surprisingly, one of the least utilized intramolecular Diels-Alder cycloadditions utilizes a carbonyl (either an aldehyde or ketone) as a dienophile. While aldehyde dienophiles are routinely used in intermolecular Diels-Alder reactions, the intramolecular variant is significantly rarer. In this mini-review we will examine the known examples of intramolecular Diels-Alder reactions utilizing aldehyde or ketone dienophiles and evaluate the advantages and challenges associated with these reactions.

Glycerol, a major co-product in the process of biodiesel production, is a promising precursor to a variety of high value fine chemicals such as glyceric acid, dihydroxyacetone, lactic acid and tartronic acid via the corresponding chemoselective oxidation reactions. One of the prospective routes to selectively oxidize glycerol and yield products with good selectivity is the use of nano-sized metal particles as heterogeneous catalysts. In this short review, recent developments in chemoselective oxidation of glycerol to specific products over nano-sized metal catalysts are described. Attention is drawn to various reaction parameters such as the type of the support, the size of the metal particles, and the acid/base properties of the reaction medium which were illustrated to largely influence the activity of the nanocatalyst and selectivity to the target product.

Benzimidazoles and its derivatives are an important group of heterocyclic compounds that show a wide range of pharmacological properties such as antitumor, antimicrobial, antihypertensive, antiviral, antiulcer, anticonvulsant, antiinflammatory activities etc. These diverse biological applications of benzimidazole compounds have motivated new efforts in search for novel derivatives with improved biological activity and diverse applications in pharmaceutical industry. Outstanding to the importance of this structure, the aim of this review is to highlight aspects reported on the chemistry and biological activity of benzimidazoles during the past few years (2000-2013).

This review covers novel cyclopeptides isolated from marine organisms published in literature since 2007, together with the relevant structure, biological activity, source organisms and country of origin. Structure- activity relationship, biosynthetic studies, isolation procedures, and chemical synthesis, have been included.