Enantioselective Hydroarylation or Hydroalkenylation of Benzo[b]thiophene 1,1-Dioxides with Organoboranes

Catalytic Enantioselective Electrophilic Difunctionalization of Unsaturated Sulfones

An efficient protocol of enantioselective thiolative azidation of sulfone-tethered alkenes via a chiral chalcogenide catalyzed electrophilic reaction is disclosed. A series of enantioenriched sulfones bearing remote stereogenic centers was achieved with good yields and high enantioselectivities with linear unsaturated sulfones and cyclic unsaturated sulfones. Mechanistic studies revealed the importance of the sulfone group in the improvement of the reactivity and enantioselectivity of the reaction.

Regiodivergent and Enantioselective Synthesis of Cyclic Sulfones via Ligand-Controlled Nickel-Catalyzed Hydroalkylation

Cyclic sulfones have demonstrated important applications in drug discovery. However, the catalytic and enantioselective synthesis of chiral cyclic sulfones remains challenging. Herein, we develop nickel-catalyzed regiodivergent and enantioselective hydroalkylation of sulfolenes to streamline the synthesis of chiral alkyl cyclic sulfones. The method has broad scope and high functional group tolerance. The regioselectivity can be controlled by ligands only. A neutral PYROX ligand favors C3-alkylation whereas an anionic BOX ligand favors C2-alkylation. This control is kinetic in origin as the C2-bound Ni intermediates are always thermodynamically more stable. Reactivity study of a wide range of relevant Ni intermediates reveal a NiI/NiIII catalytic cycle with a NiII-H species as the resting state. The regio- and enantio-determining step is the insertion of this NiII-H species into 2-sulfolene. This work provides an efficient catalytic method for the synthesis of an important class of organic compounds and enhances the mechanistic understanding of Ni-catalyzed stereoselective hydroalkylation.

Asymmetric Hydroarylation Reactions Catalyzed by Transition Metals: Last 10 Years in a Mini Review

Hydroarylation reactions play a pivotal role in organic chemistry due to their versatility and efficiency. In the last 10 years, the scientific production around this reaction has been very high, but in its asymmetric version, the results are less. In this mini review, selected literature examples are considered to draw attention to directions of the asymmetric hydroarylation reaction mediated by transition metal catalysts. The selected works were grouped in two main sections. In the first, we reported examples relating the narrower definition of hydroarylation, namely the metal-catalyzed processes where inactivated aryl moiety undergoes a direct functionalization via insertion of an unsaturated compound. In the second part, hydroarylation reactions take place with the use of pre-activated aryl substrates, usually aryl-iodides or aryl-boronated.

Chiral Diene Ligands in Asymmetric Catalysis

Asymmetric catalysis has emerged as a general and powerful approach for constructing chiral compounds in an enantioselective manner. Hence, developing novel chiral ligands and catalysts that can effectively induce asymmetry in reactions is crucial in modern chemical synthesis. Among such chiral ligands and catalysts, chiral dienes and their metal complexes have received increased attention, and a great progress has been made over the past two decades. This review provides comprehensive and critical information on the essential aspects of chiral diene ligands and their importance in asymmetric catalysis. The literature covered ranges from August 2003 (when the first effective chiral diene ligand for asymmetric catalysis was reported) to October 2021. This review is divided into two parts. In the first part, the chiral diene ligands are categorized according to their structures, and their preparation methods are summarized. In the second part, their applications in asymmetric transformations are presented according to the reaction types.

Catalytic Enantioselective Synthesis of α-Difunctionalized Cyclic Sulfones

As saturated heterocyclic building blocks become increasingly popular in medicinal chemistry and drug discovery programs, expansion of the synthetic toolkit to novel stereofunctionalized heterocycles is a priority. Herein, we report the development of a palladium-catalyzed decarboxylative asymmetric allylic alkylation reaction to access a broad range of enantioenriched α-difunctionalized 5- and 6-membered sulfones from easily accessible racemic starting materials. The allylic alkylation step was found to occur with high levels of enantioselectivity as a result of a palladium-mediated dynamic kinetic resolution of E/Z enolate intermediates. This methodology paves the way to hitherto unexplored stereodefined cyclic sulfones for medicinal chemistry applications.

Base-Mediated Annulation of Electrophilic Benzothiophene with Naphthols and Phenols: Accessing Benzothiophene-Fused Heteroacenes

A base-mediated annulation of 2-nitrobenzothiophenes with naphthols was realized for the synthesis of hitherto unknown class of heteroacenes, namely benzothieno[2,3-b]naphthofurans. By using naphthols with a hydroxyl group positioned at 1st or 2nd position, we could synthesize two positional isomers, benzothieno[2,3-b]naphtho[2,1-d]furans or benzothieno[2,3-b]naphtho[2,3-d]furans. The annulation was found to be general with a range of substituted 2-nitrobenzothiophenes and naphthols. This heteroannulation of benzothiophene was extended using a range of phenols affording the corresponding benzothieno[2,3-b]benzofurans in moderate yields. The basic photophysical properties of these heteroacenes were evaluated, and we also demonstrated the applicability of this annulation on the gram scale.