Current Organic Chemistry - Volume 12, Issue 10, 2008

Aziridines constitute a reactive and versatile class of molecules and in the present review Dr Chebanov and his co-workers form the National Academy of Science of Ukraine in Kharkiv demonstrate have useful the subclass C-acylated aziridines can be. Compounds with triazepine skeletons have attracted considerable attention due their interesting biological properties. The subclass triazepandiones has now been reviewed in depth by Drs G. Léna and G. Guichard form the Institute of Molecular and Cell Biology, Strasbourg, France. The use of microwaves is becoming more and more frequent and Drs S. Bajaj and R. Jindal from the College of Pharmacy, Ram Nagar, India have contribute a review featuring applications of microwaves in the synthesis of bioactive heterocycles. Prof. M. Sollner, from the University of Ljubljana, Slovenia, has contributed to this journal previously and now she is coming back, together with Dr Z. Jakopin with a comprehensive review on 1,2,4 and 1,2,4-oxadiazoles.

The present review is devoted to heterocyclizations of α,β-unsaturated carbonyl compounds which result in the formation of three-membered partially hydrogenated nitrogen containing heterocyclic systems - aziridinyl ketones, biand tricyclic aziridines. Scientists are interested in these classes of heterocyclic compounds first of all by their photochromic properties and high sensitivity towards UV-VIS irradiation. From the other hand, these compounds are interesting from the viewpoint of classical problems of organic chemistry, among them reactivity, chemo- and regio-selectivity, stereochemistry and many other. The main aim of the publication is a comprehensive review and organization of the known literature data devoted to the reactions of α,β-unsaturated ketone derivatives utilized in the synthesis of aziridines and their chemical and photochemical properties. The first part of the review deals with synthesis and chemical properties of aziridinyl ketones. Two main groups of the reactions leading to target compounds - one-pot synthesis directly from unsaturated carbonyl compounds and step-by-step pathway including their initial modification - are described as well as chemical transformation of azyridinyl ketones. In the second section several synthetic pathways to bi- and tricyclic aziridines like dihyrdoazireno[1,2-c]imidazoles, tetrahydroazireno[ 1,2-a]pyrazines and dihydroazireno[1,2-a]quinoxalines are described and some aspects of stereo- and regoselectivity of appropriate reactions are discussed. The last part of the review is concerned with chemical behavior of aziridinyl aniles in numerous organic reactions including photochemical transformations, cycloadditions, rearrangements, cross-couplings and other. Stereochemistry of such processes and their mechanisms are touched as well.

Compounds with triazepine skeletons have attracted much attention as a result of their interesting biological properties. Triazepandiones represent a particular subset that includes sixteen possible functional isomers, of which nine have been reported in the literature and patents. A survey of the literature indicates that intramolecular cyclization reactions and transformation of other heterocyclic systems are the two main synthetic approaches employed to prepare triazepandiones. This review covers both synthetic methods and applications of compounds with triazepandione skeletons.

Over the past decade, use of microwave energy, to heat chemical reactants on a laboratory scale, has evolved as a well-demonstrated alternative to traditional heating. Clean chemistry, reduction in reaction times, improved yields, and applicability to wide range of reactions, greatly improved efficiency with better quality, safety and tremendous scope for automation are some of the benefits of this emerging technology. Association of biological activity with heterocyclic motifs is well known and is important from drug discovery viewpoint. This article gives an account of the recent applications of microwaves in the synthesis of biologically active heterocyclic compounds with synthesis schemes and/or comprehensive review of reaction conditions and biological importance of over 50 such applications.

The synthesis of peptidomimetics is an area of research that has gained a lot of attention in recent years. Peptidomimetics are compounds designed to mimic the natural peptide but retain its activity with increased stability and bioavailibility, as a result of the structural changes introduced into the parent molecule. The most frequent of these changes are peptide bond surrogates, which contribute to the hydrolytic resistance of peptidomimetics. 1,2,4- and 1,3,4- oxadiazoles are commonly employed as bioisosteric replacements of the amide bond thus constituting these heterocycles as an important structural motif for the pharmaceutical industry. The article will therefore provide an insight into the synthetic methodologies leading to 1,2,4- and 1,3,4-oxadiazole formation to give the reader an appreciation of the field. This review covers all recent developments achieved in the classical synthesis. Additionally, it focuses on the emerging methodologies of microwave-assisted and solid phase synthesis, thus revealing the scope of influence that these methodologies have in the synthesis of 1,2,4- and 1,3,4- oxadiazoles.