Catalytic enantioselective epoxidation with arabinose-derived uloses containing tunable steric sensors

Synthesis and Applications of Carbohydrate-Based Organocatalysts

Organocatalysis is a very useful tool for the asymmetric synthesis of biologically or pharmacologically active compounds because it avoids the use of noxious metals, which are difficult to eliminate from the target products. Moreover, in many cases, the organocatalysed reactions can be performed in benign solvents and do not require anhydrous conditions. It is well-known that most of the above-mentioned reactions are promoted by a simple aminoacid, l-proline, or, to a lesser extent, by the more complex cinchona alkaloids. However, during the past three decades, other enantiopure natural compounds, the carbohydrates, have been employed as organocatalysts. In the present exhaustive review, the detailed preparation of all the sugar-based organocatalysts as well as their catalytic properties are described.

Turning the Nitrogen Atoms of an Ar2 P-CH2 -N-N-CH2 -PAr2 Motif into Uniquely Configured Stereocenters: A Novel Diphosphane Design for Asymmetric Catalysis

Hexahydropyridazines with CH₂ PAr₂ groups at both N atoms are newly designed 1,4-diphosphanes and were synthesized for the first time. Their N atoms assume a single configuration under the influence of stereocenters at C-5 and C-6. In the solid state, these N-atoms bind the CH₂ PAr₂ substituents axially. Combined with Pd⁰ , N,N'-chiral diphosphanes of this kind catalyzed Tsuji-Trost type allylations of dialkyl malonates with racemic 1,3-diphenylallyl acetate efficiently and with up to 91 % ee.

Chiral ketone and iminium catalysts for olefin epoxidation

Organo-catalyzed asymmetric epoxidation has received much attention in the past 30 years and significant progress has been made for various types of olefins. This review will cover the advancement made in the field of chiral ketone and chiral iminium salt-catalyzed epoxidations.

Carbohydrates as Synthetic Tools in Organic Chemistry

While amino acids, terpenes and alkaloids have found broad application as tools in stereoselective organic synthesis, carbohydrates have only lately been recognised as versatile starting materials for chiral auxiliaries, reagents, ligands and organocatalysts. The structural diversity of carbohydrates and the high density of functional groups offer a wide variety of opportunities for derivatization and tailoring of synthetic tools to a specific problem.

A Fascination with 1,2-Diacetals

1,2-Diacetals are readily prepared, rigid structural motifs that provide a wide range of opportunities for applications in natural product assembly. These uses encompass selective 1,2-diol or alpha-hydroxy acid protection, enantiotopic recognition and desymmetrization methods, chiral memory applications, and reactivity control in oligosaccharide synthesis, as well as functioning as templating components, chiral auxiliaries, and building blocks. 1,2-Diacetals are often more stable and lead to products with enhanced crystallinity compared to their five-ring acetonide counterparts. Many 1,2-diacetals have favorable NMR parameters, which facilitate structural assignment, particularly during asymmetric reaction processes.