Current Organic Chemistry - Volume 13, Issue 5, 2009

With this part of the special issue on “Synthetic Organic Chemistry”, inserted in the Volume 13, Number 5, March 2009 of Current Organic Chemistry, my second activity, as Guest Editor, comes to an end. It has indeed been a pleasure to be involved with this work including three reviews which deal with the cycloaddition methodology for biologically active heterocycles, recent developments on rotaxane-based shuttles and an update until 2008 on regeneration of carbonyl compounds from the corresponding oximes. I hope that this special issue will be appreciated by chemists who deal with the organic synthesis. The first review, written by U. Chiacchio, A. Padwa, and G. Romeo of Catania (Italy), Emory (USA), and Messina (Italy) Universities, respectively, includes 66 references and contains a representative sampling from the last 10 years on the syntheses of biologically active heterocycles using the 1,3-dipolar cycloaddition and Diels-Alder reactions. Some of these cycloadditions have been sequenced into a cascade process and the use of click chemistry have been also outlined. Using this methodology a wide variety of bio-compounds have been prepared such as aza-sugars, natural and modified nucleosides, ace inhibitors and different macromolecules containing the triazole ring. The many structures diverse and highly successful examples of heterocyclic ring formation indicated that cycloaddition methodology as evolved as an important strategy in heterocyclic synthesis. The second review, written by A. Rescifina and C. Zagni of Catania University, D. Iannazzo of Messina University and P. Merino of Zaragoza University deals with the recent progress occurred in the development of new and more functional molecular shuttles based on bistable [2]rotaxane chemistry covering the years 2006-2008, and includes 89 references. After a concise but exhaustive introduction on the utility and chemistry of this type of mechanically interlocked molecules, the paper prosecutes separately treating the three most important typologies of the energy inputs utilized to power their mechanical motions: chemical, photochemical and electrochemical ones. In each of these paragraphs, the authors described the synthesis, the working and the possible practical applications, in case they exist, of these intriguing systems. Regeneration of Carbonyl Compounds from the Corresponding Oximes: an Update Until to 2008, is the title of the third review written by A. Corsaro, M. A. Chiacchio and V. Pistara of Catania University. This work, which contains 221 references, is an update within the research progress in regeneration of carbonyl compounds from the corresponding oximes starting from 2001 until today and concerns deoximations of aldo- and keto-oximes under mild conventional conditions in aqueous and nonaqueous solution and under ultrasound, ultraviolet and microwave irradiation. Special importance has been given to heterogeneous and solvent-free reactions which, among their different peculiarities, were imperative with the increasing environmental concern that requires new eco-friendly reagents to be developed.

The present review contains a representative sampling from the last 10 years on the synthesis of biologically interesting compounds, prepared by the use of the 1,3-dipolar cycloaddition and Diels-Alder reactions, that have been eventually sequenced into cascade processes to assemble heterocyclic molecules. The important role of click chemistry for the synthesis of bio-inspired compounds have been also outlined.

Artificial molecular machines capable of converting chemical, photochemical and electrochemical energy into mechanical motion represent a high-impact, fast-growing field of interdisciplinary research. These molecular-scale systems utilize a “bottom-up” technology centered upon the design and manipulation of molecular assemblies and are potentially capable of delivering efficient actuation at length scales dramatically smaller than traditional microscale actuators. Much of the inspiration to construct molecular devices and machines comes from the outstanding progress in molecular biology that has begun to reveal the secrets of the natural nanodevices that constitute the material base of life. Mechanically interlocked molecules, such as rotaxanes are one of the most suitable candidates for molecular machines because (i) the mechanical bond allows a large variety of mutual arrangements of the molecular components, while conferring stability on the system; (ii) the interlocked architecture limits the amplitude of the intercomponent motion in the three dimensions; (iii) the stability of a specific arrangement is determined by the strength of the intercomponent interactions; and (iv) such interactions can be modulated by external stimulation. These systems, initially gained interest due to their interesting topology and associated synthetic challenge, but recent efforts have showed that they, by virtue of their electrical properties and bi- or multistable behaviour, are also attractive as nanoscale switches for molecular electronics and nanoelectromechanical systems. This reivew will focused on the recent progress occurred in the development of new and more functional molecular shuttles based on rotaxane chemistry.

Following the previous review of the same title and authors, this up-date deals with the research progress in regeneration of carbonyl compounds from oximes starting from 2001 until today, including some additional deoximation methods appeared during the publication of the previous review. In these years, this topic was dealt together with that of other carbonyl compound derivatives only three times of which one in the presence of microwaves. In particular, this review concerns deoximations of aldo- and keto-oximes under mild conventional conditions and under ultrasound, ultraviolet and microwave irradiation. Special importance has been given to heterogeneous and solvent-free reactions which, among their different peculiarities, were imperative with the increasing environmental concern that requires new eco-friendly reagents to be developed. The initial part of the review, however, is referred to the methods relative to conventional deoximation reactions in aqueous and non-aqueous solution.

This work presents the main methods of synthesis for [4.n]cyclophanes and reveals the possibilities to use common methods or peculiar ones in order to obtain more efficient access to different cyclophanes which exhibit a four membered bridge. The conformational behavior of [4.n]cyclophanes involving the flexibility of the bridges and the rotational behavior of the aromatic rings is discussed in correlation with the length of the bridges and with the nature of the aromatic rings. The complexation ability of the named cyclophanes, their reactivity and applications are also discussed.