Highly Effective and Diastereoselective Synthesis of Axially Chiral Bis-sulfoxide Ligands via Oxidative Aryl Coupling

Bifunctional Squaramide-Catalyzed Oxidative Kinetic Resolution: Simultaneous Access to Axially Chiral Thioether and Sulfoxide

Axially chiral thioethers and sulfoxides emerge as two pivotal classes of ligands and organocatalysts, which have remarkable features in the stereoinduction of various asymmetric transformations. However, the lack of easy methods to access such molecules with diverse structures has hampered their broader utilization. Herein, an oxidative kinetic resolution for sulfides using a chiral bifunctional squaramide as the catalyst with cumene hydroperoxide as the terminal oxidant is established. This asymmetric approach provides a variety of axially chiral thioethers as well as sulfoxides bearing both axial and central chirality, with excellent diastereo- and enantioselectivities. This catalytic system also successfully extends to the kinetic resolution of benzothiophene-based sulfides. Preliminary mechanism investigation indicates that the multiple hydrogen bonding interactions between the bifunctional squaramide catalyst and substrates play a crucial role in determining the enantioselectivity and reactivity.

Enantioselective Synthesis of Tertiary α,α-Diaryl Carbonyl Compounds Using Chiral N,N'-Dioxides under Umpolung Conditions

Brønsted acid-catalyzed addition of the chiral N,N'-dioxide into ynamides generated enolonium ions in situ which underwent enantioselective alkylation by indoles, pyrroles, and phenols, without racemization of the formed tertiary center. This external oxidant approach allows for the use of unmodified nucleophiles and does not leave trace groups from the oxidant, which significantly increases the synthetic efficiency and the product diversity. Furthermore, the byproduct of the N,N'-dioxide could be efficiently recycled into an optically pure form.

Regioselective and oxidant-free sulfinylation of indoles and pyrroles with sulfinamides

An unexpected time-controlled highly selective C3- or C2-sulfinylation of pyrroles with sulfinamides is reported for the first time. The sulfinylation of indoles with sulfinamides using this protocol is oxidant-free and can be performed under obviously more feasible conditions (1.2 equiv. of indoles, 10 min) in comparison with the precedent procedure (3-20 equiv. of indoles, 16-18 h, ammonium persulfate as oxidant, hv). A variety of functional groups were tolerated, and various C2-thioindoles and C2/3-thiopyrroles were obtained in moderate to excellent yields.

Traceless point-to-axial chirality exchange in the atropselective synthesis of biaryls/heterobiaryls

A strategy for establishing a chiral axis from stereogenic centers via elimination or oxidative aromatization with a high level of chirality transfer was developed.

An isotetramolybdate-supported rhenium carbonyl derivative: synthesis, characterization, and use as a catalyst for sulfoxidation

We successfully synthesized an isotetramolybdate-supported rhenium carbonyl derivative, [(CH₃)₄N]₄[{Re(CO)₃}₄(Mo₄O₁₆)]·H₂O, which showed excellent catalytic activity in the selective oxidation of sulfides under comparatively mild reaction conditions.

Synthesis and characterization of a Sb(v)-containing polyoxomolybdate serving as a catalyst for sulfoxidation

A Sb-containing Anderson-based polyoxomolybdate cluster, [(CH₃)₄N]₄H₈[Na₅Sb₃(Sb₂Mo₁₂O₅₇)]·17H₂O [1; (CH₃)₄N⁺ = TMA⁺], has been successfully synthesized by using an aqueous solution method and structurally characterized.

Cooperativity of axial and centre chirality in the biaryl disulfoxide/Rh(i)-catalysed asymmetric 1,4-addition of arylboronic aids to 2-cyclohexenone: a DFT study

Atropisomeric biaryl disulfoxides contain two independent chiral elements. Previously, the (M,S,S)-diastereomer showed very high catalytic activity and selectivity in the Rh-catalyzed asymmetric 1,4-addition of arylboronic acids to α,β-enones whereas the (M,R,R) counterpart - none. Herein, DFT computations on the key transmetallation (turnover-determining) and carborhodation (enantioselectivity-determining) steps of the catalytic cycle show that the (M,S,S)-ligand gives rise to lower reaction barriers for these elementary steps. However, the barriers for the (M,R,R)-ligand are not sufficiently high to explain the lack of reactivity. Hence, this phenomenon is most likely due to the failure of catalyst formation from the ligand and the dimeric Rh precatalyst complex. The hitherto unknown (M,S,R)-ligand shows predicted enantioselectivity similar to the (M,S,S)-ligand as a consequence of lower reaction barriers associated with those isomers whose key features resemble the (M,S,S)-ligand.

Chiral Organosulfur Ligands/Catalysts with a Stereogenic Sulfur Atom: Applications in Asymmetric Synthesis

Asymmetric synthesis, in which chiral organocatalysts or metal complexes with chiral ligands are used, has become the most valuable methodology for the preparation of enantiomerically pure organic compounds. Among such catalysts/ligands, a growing number constitute various organosulfur compounds. This Review provides comprehensive and critical information on the plethora of sulfur-based chiral ligands and organocatalysts used in asymmetric synthesis, which have been published within the last 15 years. However, it is confined to the presentation of only those chiral catalysts/ligands that possess a stereogenic sulfur atom and includes sulfoxides, sulfinamides, N-sulfinyl ureas, sulfoximines, and some related S-chiral derivatives.

Metal- and additive-free oxygen-atom transfer reaction: an efficient and chemoselective oxidation of sulfides to sulfoxides with cyclic diacyl peroxides

Metal- and additive-free sulfoxidation was developed using cyclic diacyl peroxides as oxygen sources and a single two-electron transfer mechanism was suggested.

C-H Coupling Reactions Directed by Sulfoxides: Teaching an Old Functional Group New Tricks

Sulfoxides are classical functional groups for directing the stoichiometric metalation and functionalization of C-H bonds. In recent times, sulfoxides have been given a new lease on life owing to the development of modern synthetic methods that have arisen because of their unique reactivity. They have recently been used in catalytic C-H activation proceeding via coordination of an internal sulfoxide to a metal or through the action of an external sulfoxide ligand. Furthermore, sulfoxides are able to capture nucleophiles and electrophiles to give sulfonium salts, which subsequently enable the formation of C-C bonds at the expense of C-H bonds. This Review summarizes a renaissance period in the application of sulfoxides arising from their versatility in directing C-H functionalization.

Efficient and selective oxidation of sulfides in batch and continuous flow using styrene-based polymer immobilised ionic liquid phase supported peroxotungstates

Good conversion and high selectivity for sulfoxidation have been achieved under segmented and continuous flow using a polystyrene-based polymer immobilised ionic liquid phase (PIILP) peroxotungstate.

Pseudo enantiomeric mixed S/P ligands derived from carbohydrates for the 1,4-addition of phenyl boronic acid to cyclohexenone

Mixed S/P ligands 3 and 10, good catalyst precursors for the Rh(i)-catalysed 1,4-addition of phenylboronic acid to cyclohexenone behave as enantiomers even though both derived from d-sugars.

The emergence of sulfoxides as efficient ligands in transition metal catalysis

Sulfoxides are capable of forming stable complexes with transition metals and there have been many comprehensive studies into their binding properties. However, the use of sulfoxides, particularly chiral sulfoxides, as ligands in transition metal catalysis is rather less well developed. This review aims to describe these catalytic studies and covers new developments that are showing very promising results and that have led to a renewed interest in this field.

Recent advances and new concepts for the synthesis of axially stereoenriched biaryls

Over the past decade the field of the synthesis of axially chiral compounds has been rapidly expanding. Not only key advances have been achieved concerning the already established strategies but also new synthetic routes have been devised. This review showcases the recent developments in this domain.

Atroposelective synthesis of axially chiral P,S-ligands based on arynes

An unprecedented atropo-diastereoselective aryl–aryl coupling via arynes allows for the modular synthesis of enantiopure P,S-ligands.

Computational modelling of the enantioselectivity in the asymmetric 1,4-addition reaction catalyzed by a Rh complex of a S-chiral disulfoxide

Computational chemistry is a powerful tool for understanding chiral catalysis and can also aid future catalyst design.

Ruthenium-catalyzed highly regio- and stereoselective hydroarylation of aromatic sulfoxides with alkynes via C–H bond activation

A ruthenium-catalyzed hydroarylation of aromatic sulfoxides with alkynes in the presence of AgSbF₆ and pivalic acid yielding trisubstituted alkenes is described.

A class of benzene backbone-based olefin-sulfoxide ligands for Rh-catalyzed enantioselective addition of arylboronic acids to enones

A class of readily available and easily tunable benzene backbone-based olefin-sulfoxide ligands was developed for the rhodium-catalyzed asymmetric conjugate addition reaction of arylboronic acids to enones with up to 97% yield and 97% ee.

Design of chiral sulfoxide-olefins as a new class of sulfur-based olefin ligands for asymmetric catalysis

The design and development of a novel class of chiral sulfur-olefin hybrid ligands with high synthetic feasibility are described. These new sulfoxide-olefin ligands showed excellent catalytic activities and enantioselectivities (up to 98% ee) in rhodium-catalyzed asymmetric 1,4-addition reactions of aryl boronic acids to α,β-unsaturated carbonyl compounds.

Sulfoxide-alkene hybrids: a new class of chiral ligands for the Hayashi-Miyaura reaction

Sulfoxide-alkene hybrids are introduced as a new class of chiral heterodentate ligands for the Hayashi-Miyaura reaction. The synthesis of these ligands was achieved without the use of protecting groups. A chiral resolution was performed via simple column-chromatographic separation of the diastereomeric ligands. Both diastereomers proved to be excellent ligands in Rh-catalyzed 1,4-addition reactions, furnishing chiral products with high enantioselectivities and, remarkably, opposite stereoconfigurations.

Sequential aldol condensation-transition metal-catalyzed addition reactions of aldehydes, methyl ketones, and arylboronic acids

Sequential aldol condensation of aldehydes with methyl ketones followed by transition metal-catalyzed addition reactions of arylboronic acids to form β-substituted ketones is described. By using the 1,1'-spirobiindane-7,7'-diol (SPINOL)-based phosphite, an asymmetric version of this type of sequential reaction, with up to 92% ee, was also realized. Our study provided an efficient method to access β-substituted ketones and might lead to the development of other sequential/tandem reactions with transition metal-catalyzed addition reactions as the key step.