Current Organic Chemistry - Volume 9, Issue 6, 2005

Transition-metal-catalyzed or -mediated intramolecular [2 + 2 + 2] alkyne cyclotrimerizations are one of the most efficient method to construct highly substituted arene frameworks in a single operation. The recent developments of novel catalyst systems as well as new strategies render the intramolecular cyclotrimerizations more and more attractive tools in practical organic synthesis. This review surveys most recent research works on the intramolecular alkyne cyclotrimerizations published from 2000 to 2004. The synthetic potential of the intramolecular alkyne cyclotrimerization is also discussed with respect to the recent applications to the synthesis of natural products and artificial functional molecules.

The construction of biomolecular, supramolecular, nano-molecular structures and host-guest interaction occurs by composite of many interactions, i.e., electrostatic, cation-dipole, hydrogen bond, van der Waals, π-_π , cation-π, XH-π, etc. Some of these can be seen in host-guest chemistry, sometimes in almost pure form: the convergence of binding sites and rigid geometry, and isolated environments make it possible. In this review, the author shows several interactions observed in host-guest complexes. The macropolycyclic compounds, composed of aromatic rings and hetero atoms, formed various kinds of inclusion complexes and these contain several interaction, i.e., cation-dipole (-O×××M+, -N×××M+, CF ×××M+), hydrogen bond (-N×××HX, C-F×××HX), Ag-Ag metal bond, cation-π, and coordination bond.

Suzuki coupling is probably the most versatile approach among the cross-coupling reactions and the reaction has long been the subject of intensive work in the area of transition-metal chemistry. From both scientific and environmental points of view, various modifications have recently been developed that the Suzuki reactions involve catalysts, substrates, reaction media, reaction conditions and synthetic techniques. This review will focus on describing both the seminal early work and the exciting recent development in the area of the environmentally friendly Suzuki arylaryl coupling reaction. Transformations that will be covered include the use of green media such as water, ethanol, poly(ethylene glycol), supercritical carbon dioxide, ionic liquids and solvent-free etc.; the design of recoverable and reusable polymer-supported catalysts and entrapment or intercalation of metal species; and the development of synthetic methodology involving ultrasound irradiation and microwave heating technique.

The account highlights an important approach to supramolecular self-assembly via “vector-manipulation at metal centers” ranging from Werner-system to Cotton-system coordination compounds. The approach has been successfully employed in the architecture of container molecules like metal analogues of the bowl-shaped calixarenes and metal-linked calixarene-based carcerands and carceplexes. The concepts of metal vector and vector-manipulation at metal centers were further interpreted based upon the stereochemistry and trans- or cis-effect of ligands in the substitution reactions at metal centers.

The redox chemistry of different nitro compounds of biological significance is focused to understand how the reduction of the nitro group can play an active role in several aspects as: electroanalytical determinations, free radical generation and stability and free radical reactivity. We have focused our studies to a lot of pharmaceuticals belonging mainly to the following families: calcium antagonists as nitrobenzene substituted 1,4-dihydropyridines, antibacterial and anti protozoan agents as nitroimidazoles and nitrofurans. The formation of the nitro radical anion as the product of the one electron reduction of nitro compounds generates a series of important consequences passing from chemical to biological aspects. We have used electrochemical techniques to study the formation, stability and reactivity of this nitro radical anion in different media. From cyclic voltammetric experiments it is possible qualitatively to visualize the formation of the nitro radical anion through the one-electron reversible couple due to the redox system nitro / nitro radical anion . Furthermore also is possible the quantitative determination of the kinetic rate constant of the nitro radical anion decay and the interaction constants with other molecules. Although substituents may affect the redox potential and consequently the stability or reactivity of the nitro radical anions, other factors are important in regulation of these properties. Among these factors, it is possible to mention the nature of the reaction media making possible the occurrence of intermolecular reactions of the father-son type between the nitro radical anion and an acidic hydrogen present in the molecules.