Optically Active Tripodal Dendritic Polyoxometalates: Synthesis, Characterization and Their Use in Asymmetric Sulfide Oxidation with Hydrogen Peroxide

Asymmetric Synthesis of S(IV) and S(VI) Stereogenic Centers

Sulfur can form diverse S(IV) and S(VI) stereogenic centers, of which some have gained significant attention recently due to their increasing use as pharmacophores in drug discovery programs. The preparation of these sulfur stereogenic centers in their enantiopure form has been challenging, and progress made will be discussed in this Perspective. This Perspective summarizes different strategies, with selected works, for asymmetric synthesis of these moieties, including diastereoselective transformations using chiral auxiliaries, enantiospecific transformations of enantiopure sulfur compounds, and catalytic enantioselective synthesis. We will discuss the advantages and limitations of these strategies and will provide our views on how this field will develop.

Molybdenum/Tungsten-Based Heteropoly Salts in Oxidations

Oxidation represents one of the most important and practical chemical transformations for both organic synthesis, material science and pharmaceutical area. Among the existing strategies, molybdenum/tungsten-based heteropoly salts involved oxidations with low-cost and environmentally benign terminal oxidant and thus have attracted considerable attention in recent years. In this review, we have summarized the recent development of heteropoly salts utilized in oxidations, mainly the peroxomolybdates and peroxotungstates. We wish to highlight the progress made in the past 20 years of this field. Three categories are classified according to the aggregation state of metal oxides. Special attention is paid to the catalytically active peroxometalate species generated during the oxidation process. It is helpful to shed light on the common features that enable highly efficient and selective oxidations. We aim to inspire fellow chemists to explore more functional metalates for catalytic oxidations, especially asymmetric versions. Meanwhile, we attempt to understand the design principles for the discovery of more efficient, selective and economical catalytic systems.

Bisguanidinium dinuclear oxodiperoxomolybdosulfate ion pair-catalyzed enantioselective sulfoxidation

Catalytic use of peroxomolybdate for asymmetric transformations has attracted increasing attention due to its catalytic properties and application in catalysis. Herein, we report chiral bisguanidinium dinuclear oxodiperoxomolybdosulfate [BG]²⁺[(μ-SO₄)Mo₂O₂(μ-O₂)₂(O₂)₂]²⁻ ion pair, as a catalyst for enantioselective sulfoxidation using aqueous H₂O₂ as the terminal oxidant. The ion pair catalyst is isolatable, stable and useful for the oxidation of a range of dialkyl sulfides. The practical utility was illustrated using a gram-scale synthesis of armodafinil, a commercial drug, with the catalyst generated in situ from 0.25 mol% of bisguanidinium and 2.5 mol% of Na₂MoO₄·2H₂O. Structural characterization of this ion pair catalyst has been successfully achieved using single-crystal X-ray crystallography.

Peroxomolybdates can be used as catalysts, but to date have not been employed in catalytic asymmetric transformations. Here the authors report that peroxomolybdates with a chiral bisguanidinium salts are active catalysts for asymmetric sulfoxidation, and furthermore identify the catalytic species.

Counterion-dominating chirality transfer between chiral and achiral polyoxometalates

The chirality transfer between inorganic polyoxometalate clusters is realized by the suitable mediation of counterions through multi-interactions in aqueous solution.

Asymmetric catalytic sulfoxidation by a novel VIV8 cluster catalyst in the presence of serum albumin: a simple and green oxidation system

Enantioselective oxidation of a series of alkyl aryl sulfides catalyzed by a novel VIV8 cluster is tested in an aqueous medium in the presence of serum albumin. The procedure is simple, environmentally friendly, selective, and highly reactive.

Enantioselective extraction mediated by a chiral cavitand–salen covalently assembled on a porous silicon surface

A chiral organic–inorganic hybrid device shows enantioselection properties in water solution towards bromine-marked alkyl-ammonium salts.