Synthesis and catalytic applications of C3-symmetric tris(triazolyl)methanol ligands and derivatives.

Recently introduced tris(1,2,3-triazol-4-yl)methanols and derivatives (TTM ligands) have become a valuable subclass of C3-symmetric tripodal ligands for transition metal-mediated reactions. TTM-based ligand architectures are modularly constructed through regioselective, one-pot triple [3+2] cycloaddition of azides and alkynes. Applications of homogeneous systems of this type and of heterogenised (polystyrene- and magnetic nanoparticle-supported) TTM ligands in synthesis and catalysis are compiled in this Feature Article.

Catalytic enantioselective reductive desymmetrisation of achiral and meso compounds.

Herein an overview of reductive catalytic enantioselective desymmetrisation of achiral or meso compounds is provided. The most efficient reductive desymmetrisations described in the literature, which involve the reduction of C=O, C=N, C=C and C-halogen bonds, or reductive ring-opening, are summarised. The structural diversity of the valuable highly enantioenriched intermediates prepared by reductive desymmetrisation is highlighted.

Rhodium-catalysed asymmetric hydrogenation as a valuable synthetic tool for the preparation of chiral drugs.

During the last few decades, rhodium-catalysed asymmetric hydrogenation of diverse alkene classes has emerged as a powerful synthetic tool in the pharmaceutical industry, contributing to the manufacturing of chiral drugs, recent drug candidates for clinical trials, and major synthetic precursors of drugs. Numerous efficient chiral rhodium complexes, most of which are derived from enantiopure phosphorus ligands, have been employed for the preparation of chiral drugs and intermediates thereof. This review article is intended to provide an updated overview of the most striking contributions in this field, organised according to substrate class: acrylate derivatives, itaconate derivatives, α-substituted enamides, α-arylenol acetates, and minimally functionalised olefins.

Recent advances in enantioselective organocatalyzed anhydride desymmetrization and its application to the synthesis of valuable enantiopure compounds.

Recent years have witnessed increasing interest in the field of asymmetric organocatalysis. In particular, efforts in this field have been devoted to the use of small organic molecules in asymmetric processes based on enantiotopic face discrimination and, only recently, efforts have also been devoted to asymmetric organocatalytic desymmetrization of prochiral substrates-a process based on enantiotopic group discrimination. This critical review documents the advances in the use of organocatalysis for the enantioselective desymmetrization of achiral and meso anhydrides and its application to the synthesis of valuable compounds as reported until 2010 (134 references).

Asymmetric homologation of ketones. A new entry to orthogonally protected (2R,4R)-piperidine-2,4-dicarboxylic acid.

A new conformationally constrained analogue of glutamic acid has been synthesized efficiently in seven steps from a chiral 2-alkyl-4-piperidone. The synthesis is based on (a) the unprecedented asymmetric one-carbon homologation of the ketone controlled by the size of the N-substituent and (b) the appropriate manipulation of substituents at positions 2 and 4 of the piperidine ring, a step that involves two independent oxidation processes.

Base-controlled diastereodivergent synthesis of (R)- and (S)-2-substituted-4-alkylidenepiperidines by the Wadsworth-Emmons reaction.

Significant base and reaction time effects have been observed in the Wadsworth-Emmons reaction between a chiral 2-substituted-4-oxopiperidine and phosphonates. In the reactions carried out using a large excess of DBU as the base and prolonged reaction times, the initially formed 2R products epimerized into thermodynamically more stable products through a retro-conjugate/conjugate addition sequence and 2-substituted-4-alkylidenepiperidines of 2S configuration were selectively synthesized. In contrast, when the reaction was carried out using LDA as the base, epimerization did not occur and 2-substituted-4-alkylidenepiperidines of 2R configuration were obtained with excellent yields.

Unexpected epimerization at C2 in the Horner-Wadsworth-Emmons reaction of chiral 2-substituted-4-oxopiperidines.

The observed epimerization at C2 in the Horner-Wadsworth-Emmons (HWE) reaction of chiral 2-substituted-4-oxopiperidines has been investigated and, on the basis of the experimental results, a mechanism for this unexpected process has been proposed.