Mini-Reviews in Organic Chemistry - Volume 7, Issue 3, 2010

This review is intended to cover the developments in the chemistry of poly(azolyl)borates, derived from triazoles, imidazoles, oxazolines, thioimidazoles and related systems, based on the main synthetic methods, coordination properties, spectroscopic and structural features of this important class of ligands. The subject matter has been divided into the main categories: (i) N-donor boron-centered ligands, (ii) soft S-donor boron-centered ligands and (iii) hybrid scorpionate ligands. In this review we provide essential information to allow the reader to probe more deeply into the main aspects of the chemistry of these fascinating and flexible ligands. This review would also demonstrate the enormous potential of poly(azolyl)borates chemistry by discussing the future perspectives in this field.

Besides the well-known role of ultrasound in initiation and acceleration of radical reactions, this low-energy acoustic field has recently become a valuable tool for physico-chemical investigations of solvation phenomena in homogeneous ionic reactions in aqueous and aqueous-organic solutions. In this mini-review we summarize these experimental data, showing that the application of classical quantitative methods, such as reaction kinetics and correlation analysis, if combined with sonication of the reaction medium, can reveal subtle hydrophobic interactions that remain hidden in the conventional experiments. Correlation of kinetic sonication effects with substrate hydrophobicity has revealed that independent of the reaction mechanism the decrease in reaction rate with the increasing content of different hydrophobic co-solvents can be explained by the reaction ground-state stabilization, which is largely of hydrophobic origin. When ultrasound suppresses this hydrophobic stabilization of reagents, it accelerates the reaction. On the contrary, if sonication perturbs the stabilization of encounter complexes between reagents, it hinders the reaction. Many of the conclusions reviewed in this article make a contribution to the chemistry of solutions and physical organic chemistry.

The Morita-Morita-Baylis-Hillman reaction (MMBHR) is one of the most important carbon-carbon bond forming reactions, and involves the selective atom-economical construction of a carbon-carbon bond at the α-position of an activated alkene, providing densely functionalized molecules. One of the major drawbacks of the MBHR is the low reaction rate, requiring long reaction times. In this review, the MBHR, in combination with microwave irradiation is summarized for the synthesis of highly functionalized molecules with the advantages of green process and shorter reaction times.

Most receptors are designed to explore the anion-binding affinities for medical, biological, environmental relevant anions. Of the major types of receptors, sensors related to hydrogen bond have been studied widely by numerous researchers. Both hydrogen-bond-induced π-delocalization and anion-triggered deprotonation govern the signal transduction of the binding events in these systems. An overview of the inclusion of the (thio)urea and pyrrole groups within synthetic receptor molecules is presented in this article.

The quinone/hydroquinone sesquiterpenes of drimane or rearranged drimane skeletons constitute a wide and diverse group of secondary metabolites of mixed biogenesis. These compounds are mainly of marine origin and their interest is not only for the variety of isolated structure but for the interesting biological activities that they present. In this paper a series of quinone/hydroquinone sesquiterpenes of natural origin that have been reported to date is presented. The structures of these compounds are gathered into eight groups with reference to their biological activities and compounds synthesised.