Mini-Reviews in Organic Chemistry - Volume 11, Issue 2, 2014

The use of proline as catalyst for the aldol process has given a boost to the development of organocatalysis as a research area. Since then, a plethora of organocatalysts of diverse structures have been developed for this and other organic transformations under different reaction conditions. The use of an organic molecule as catalyst to promote a reaction meets several principles of Green Chemistry. The implementation of solvent-free methodologies to carry out the aldol reaction was soon envisaged. These solvent-free processes can be performed using conventional magnetic stirring or applying ball milling techniques and are even compatible with the use of supported organocatalysts as promoters, which allows the recovery and reuse of the organocatalysts. In addition, other advantages such as the reduction of the required amount of nucleophile and the acceleration of the reaction are accomplished by using solvent-free conditions leading to a “greener” and more sustainable process.

The careful selection of a suitable chiral backbone is vital for the preparation of any modern ligand for asymmetric catalysis, where binaphthyl based ligands are considered paradigmatic and systematically used in a diversity of asymmetric catalysed reactions, with emphasis for organocatalysis. Due to the vastness of possible organocatalytic applications, this review article is mainly focused on the asymmetric aldol and vinylogous aldol reactions organocatalysed by binaphthyl-based molecules. Special attention is given to catalytic results, particularly on enantio- and diastereoselectivity obtained by the use of the above binaphthyl chiral inductors.

This mini-review reports an overview of the most promising applications of chiral ionic liquids as organocatalysts for asymmetric reactions such as the asymmetric direct aldol, Michael addition, Diels-Alder and Baylis-Hillman reactions, as well as future perspectives for industrial applications. Recent publications have reported the development of novel chiral ionic liquids and their potential application as unique chiral reaction media or just as alternative chiral organocatalysts. The number of chiral ionic liquids efficiently tested for asymmetric catalysis to date is small but new perspectives can be considered in the future. The peculiar properties of ionic liquids, including chiral ones, combined with the possibility to recycle and reuse them, can be particularly relevant for some catalytic reactions.

In this non-comprehensive short review, we will highlight the usefulness of organocatalyis for the asymmetric synthesis of biological active compounds, ranging from apparently simple molecules to complex natural products.

Chiral phosphonates find many applications in medicine, agriculture, materials science and also in organic synthesis. The rapid growth of asymmetric organocatalysis in the last decade has sparkled the interest of organophosphorus chemists, and a wealth of new methodologies to obtain chiral phosphonic acid derivatives has been developed in recent years. This review surveys the last five years, and it includes methodology to synthesize hydroxyphosphonates, aminophosphonates, asymmetric aldol reactions and Michael addition reactions, cycloadditions and domino processes, as well as applications in target-oriented synthesis involving the Horner-Wadsworth-Emmons olefination reaction and the use of chiral phosphonates as acylating agents.

The current work discussed the criteria that control the non-enzymatic and enzymatic antioxidant activity from a chemical point of view. Two tunable strategies were classified to emphasize the reactivity of non-enzymatic one from the thermodynamic and kinetic perspectives. On the other hand, the non-covalent interactions and the intermediacy of reactive compounds formation were found to be the most efficient tools to modulate the activity of enzymatic antioxidant. Furthermore, the light has been shed on the pro-oxidant behavior of some antioxidants.

Pfitzinger reaction is the formation of derivative of 4-quinoline carboxylic acids from isatins or its analogs under alkaline condition. This reaction was first discovered by Pfitzinger at the end of 19th century hence it is known as Pfitzinger reaction. This reaction has attracted a great deal of attention in the last few decades because of biological significance of quinoline carboxylic acid derivatives. The utility of Pfitzinger reaction has been proved time to time by its involvement in the synthesis of drugs or drug intermediates. The present review is focused on brief aspects of the synthesis of 4-quinoline carboxylic acids from isatins and its different derivatives. It also covers the literature on modification of original Pfitzinger reaction and its application for the synthesis of different bioactive molecules. Different 4-quinoline carboxylic acids analogs synthesized by Pfitzinger reaction or modified Pfitzinger reaction have been tested for varied pharmacological activities. The review encompasses all literature reports of Pfitzinger reaction in the synthesis of different pharmacologically active molecules. This reaction with some modification has been widely used for the synthesis of a number of drugs or drug intermediates. The review also discusses the different chemistry aspects of Pfitzinger reaction.