Abstracts

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Organocatalytic Domino Reactions
Alba, A-N.; Companyó, X.; Viciano, M.; Rios, R.

Since the rediscovery of proline in 2000 as catalyst in aldol reaction by List, Barbas and Lerner and, soon after, the development of iminium catalysis by D. W. C. MacMillan, the emergence of organocatalysis as an important tool in organic synthesis is outstanding. During the last years, several research groups have worked in the development of new and powerful methodologies that allow us to build difficult molecules with high yields and enantioselectivities in a metal-free environment. Moreover, the possibility to join two or more organocatalytic reactions in one process has become one challenging goal for chemists, probably due to the costly protecting groups and time-consuming purification procedures after each synthetic step that are one of the common issues in organic synthesis. To circumvent these problems, tandem, domino, cascade or multicomponent organocatalytic reactions have been utilized for the efficient diastereo- and enantioselective construction of complex molecules from simple precursors in simple processes. For example, different tandem organocatalytic reactions such as cyclopropanation, aziridination, Michael-aldol, Michael-alkylation, etc. have been developed since 2006 with excellent yields and stereoselectivities. Herein, we describe the last trends and examples of organocatalytic domino reactions. This review aims to cover and discuss the current development of this fast growing field.


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Recent developments on rotaxane-based shuttles
Rescifina A., Zagni C., Iannazzo D., Merino P.

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 intercomponout 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.


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Advances in bioconjugation
Kalia J., Raines R.T

Bioconjugation is a burgeoning field of research. Novel methods for the mild and site-specific derivatization of proteins, DNA, RNA, and carbohydrates have been developed for applications such as ligand discovery, disease diagnosis, and high-throughput screening. These powerful methods owe their existence to the discovery of chemoselective reactions that enable bioconjugation under physiological conditions-a tremendous achievement of modern organic chemistry. Here, we review recent advances in bioconjugation chemistry. Additionally, we discuss the stability of bioconjugation linkages-an important but often overlooked aspect of the field. We anticipate that this information will help investigators choose optimal linkages for their applications. Moreover, we hope that the noted limitations of existing bioconjugation methods will provide inspiration to modern organic chemists.


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Rational design of functional DNA with a Non-Ribose acyclic scaffold
Kashida H., Liang X., Asanuma H.

The growing field of DNA technology requires new modified DNAs that can perform advanced functions. No matter how we optimize the length and sequence of DNA using only the four naturally occurring nucleotides, potential performance is limited. In this review, we describe a facile and effective method of rationally designing new functional DNA by focusing on acyclic scaffolds, especially threoninols, which are utilized to incorporate functional molecules into DNA. Wedge-type insertion of a functional molecule with a planar structure of proper size in D-threoninol to DNA does not destabilize the duplex, although the backbone structure is changed. Rather, intercalation offsets such distortions and significantly raises the melting temperature of the DNA duplex. Based on the wedge-type insertion, photoresponsive DNA (tethering azobenzenes) and fluorescent probes that can detect single nucleotide polymorphisms (SNPs) and insertion/deletion (indel) polymorphisms have been designed. Furthermore, a variety of molecular clusters of dyes have also been prepared from acyclic scaffolds tethering dyes.


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New synthetic strategies for medium-sized and macrocyclic compounds by palladium-catalyzed cyclization
Majumdar K.C., Chatopadhyay B.

This brief review article describes the progress made in the synthesis of medium- and large-sized carbocyclic and heterocyclic rings by the application of the palladium-catalyzed reactions.


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Multi-component heterocycle syntheses via catalytic generation of alkynones
Willy B., Muller T.J.J

Alkynones are versatile three-carbon building blocks in heterocyclic chemistry. They are easily and efficiently prepared by a modified Sonogashira coupling of acid chlorides and terminal alkynes. As a consequence of the mild reaction conditions the stage is set for new diversity-oriented routes to heterocycles by sequential and consecutive transformations. Hence, isoxazoles, indolizines, pyrazoles, pyridimines, 1,5-benzoheteroazepines, furans, oxazoles, pyrroles, tetrahydro-β-carbolines, 4H-thiochromen-4-ones and 4H-thiopyrano[2,3-b]pyridin-4-ones are readily accessible by multicomponent coupling-cycloaddition, coupling-addition-cyclocondensation, or coupling-addition-substitution reactions in a one-pot fashion.


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Copper-catalyzed multicomponent reactions: Securing a catalytic route to ketenimine intermediates and their reactivities
Yoo E.J., Chang S.

A new type of Cu-catalyzed multicomponent reaction has been developed relying on the in situ generation of N-sulfonyl- or N-phosphorylketenimine intermediates, which are obtained from the cycloaddition of 1-alkynes and sulfonyl-or phosphoryl azides followed by ring-opening rearrangement of the initially formed copper triazole species. This facile and versatile route to ketenimines has led to develop a range of highly efficient multicomponent reactions by employing diverse nucleophiles such as amines, alcohols, water, pyrroles, and thiolates. Additionally, intramolecular version and cycloadditions of the ketenimines with imines or their derivatives have also been developed on the basis of the same strategy.


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Recent advances in the use of unsymmetrical palladium pincer complexes
Moreno I., SanMartin R., Ines B., Herrero M.T., Dominguez E

Palladacycles containing tridentate ligands have become a very promising family of complexes due to an excellent balance between stability and reactivity that enables them to catalyze a number of organic reactions. Moreover, special chemical properties of such interesting compounds have been considered as keys to determine the mechanisms of many palladium-catalyzed reactions. Although the most commonly employed are those with two identical donor groups, that is, symmetrical pincers, the interest in the preparation and synthetic applications of unsymmetrical ones has considerably increased because the presence of two different donor groups provides them unique properties and reactivity. In fact, high efficiency in terms of outstanding turnover numbers and frequencies has been achieved by using this emerging class of palladacycles. In this article it is projected to compile the advances achieved in the synthesis and catalytic applications of unsymmetrical palladium pincer complexes with a special focus on cross-coupling reactions, the processes in which the catalytic activity of such specially designed catalysts has been mainly evaluated.


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Biological properties of schiff bases and azo derivatives of phenols
Przybylski P., Huczynski A., Pyta K., Brzezinski B., Bartl F.

Aza-derivatives of phenols such as Schiff bases and hydrazones are an important and interesting group of chemical compounds. They exhibit a number of biological activities and play an important role in the regulation of many biochemical processes. Due to these properties, these compounds are potentialy useful for the design and production of novel anticancer, antimalaria, antivirus and antimicrobial drugs. The primary aim of the present review is to compare selected groups of phenol-derivatives containing azo-, heterocyclic, aromatic, alkyl and sugar moieties in view of their potential use and undesired effects, since some of them are widely used as dyes in the industry. Despite the vast number of azo derivatives of phenols which were synthesized and tested with respect to their biological activities, there is a continuous search for compounds of this group which might exhibit interesting, new biological effects.