Current Organic Chemistry - Volume 20, Issue 13, 2016

The 2-unsubstituted 1H-imidazole 3-oxides, considered as ‘nitrone-like’ azaheterocycles, are well known as versatile building blocks, useful for the preparation of more complex systems containing an imidazole moiety. Their applications in diverse reactions, such as isomerization to corresponding imidazol-2-ones, [3+2]-cycloadditions, sulfur transfer reactions leading to imidazole-2-thiones, heterocyclizations leading to fused heterocyclic systems, as well as cross coupling reactions are discussed. New methods for the preparation of enantiomerically pure 1Himidazole 3-oxides and their applications in asymmetric reactions, synthesis of room temperature ionic liquids and biologically active compounds are also reviewed.

Amidines and guanidines are prominent privileged motifs present in many biologically active synthetic compounds as well as natural products. Introduction of an aryl or heteroaryl group at a nitrogen atom of amidines and guanidines attenuates the basic properties of these cores, allows for appending various lipophilic groups and has, in turn, given rise to many new compounds endowed with diverse biological activities. This clearly validates N-aryl amidines and guanidines as an emerging privileged structure. The present review provides an update on the recent (2011-2015) developments in N-arylation chemistry, with a particular emphasis on the examples involving compounds with biological activity.

TEMPO functionalized polymers have been widely applied as cathode-active materials for organic radical batteries, recoverable catalysts for selective oxidation of alcohols and inhibitors for the synthesis of acrylate monomers. This review mainly presents the significant advances which have been made in the last decade, including their synthesis methods and application fields.

Polyoxometalates (POMs) and their hybrid systems are green and efficient catalysts which have found a wide range of application, due to their outstanding properties such as high thermal stability, Redox potential, strong Bronsted acidity, non-corrosive nature and sensitivity to electricity and light. They are able to catalyze various organic reactions as well as being involved in photocatalytic processes. In this review, we try to highlight the recent advances (2009-2015) in the applications of POMs both in their actual structural forms and in the form of hybrid/ composite as catalysts in divergent chemical processes including, organic synthesis, biomass conversion, petrochemical processes, photocatalytic degradation and fuel cell.

The immobilization of Rh/phosphorus complexes in MCM-41 was performed using two different methodologies. The first synthetic strategy was based on the covalent attachment of a new binaphthyl-based phosphoramidite ligand through a trimethoxysilyl linkage, followed by its complexation with the rhodium(I) precursor Rh(CO)2(acac). The resulting heterogeneized Rh(I)/phosphoramidite complex was characterized by FT-IR, N2 adsorption and TG-DSC techniques, which indicated its effective bonding to the mesoporous material. A second approach was based on the physical adsorption of Rh(CO)2(acac) in MCM-41, followed by addition of tris[(R)-2'-(benzyloxy)-1,1'-binaphthyl-2- yl]phosphite, to generate in situ a Rh(I)/phosphite complex, whose rhodium content was determined by chemical analysis (ICP). The two hybrid materials were applied as catalysts in styrene hydroformylation, where both achieved high conversions and regioselectivity for the branched aldehyde, under moderate reaction conditions. The covalent immobilization strategy allowed the reutilization of the Rh/phosphoramidite catalyst, without loss of activity after four runs, while the physically adsorbed Rh/phosphite catalyst lost most of its activity, with occurrence of rhodium leaching.