A regio- and stereoselective entry to (Z)-β-halo alkenyl sulfides and their applications to access stereodefined trisubstituted alkenes

Controlling Selectivity in Shuttle Hetero-difunctionalization Reactions: Electrochemical Transfer Halo-thiolation of Alkynes

Shuttle hetero-difunctionalization reaction, in which two chemically distinct functional groups are transferred between two molecules, has long been an unmet goal due to the daunting challenges in controlling the chemo-, regio-, and stereoselectivity. Herein, we disclose an electrochemistry enabled shuttle reaction (e-shuttle) to selectively transfer one RS^- and one X^- group between β-halosulfides and unsaturated hydrocarbons via a consecutive paired electrolysis mechanism. The preferential anodic oxidation of one anion over the other, which is controlled by their distinct redox potentials, plays a pivotal role in controlling the high chemoselectivity of the process. This easily scalable methodology enables the construction of a myriad of densely functionalized β-halo alkenyl sulfides in unprecedented chemo-, regio-, and stereoselectivity using benign surrogates, e.g., 2-bromoethyl sulfide, avoiding the handling of corrosive and oxidative RS-Br reagents. In a broader context, these results open up new strategies for selective shuttle difunctionalization reactions.

Synthetic Applications of Sulfonium Salts

This minireview aims to cover the developments over the past two decades in the chemistry of sulfonium salts. Specifically, insight is provided into the synthetic strategies available for the preparation of these compounds, the different reactivity patterns that are expected depending on their structural features or the reaction conditions applied, and the diversity of organic scaffolds that can thereby be synthesized. Additionally, the pros and cons derived from the use of sulfonium salts are presented and critically compared, when possible, in relation to reagents not based on sulfur but depicting similar reactivity.

The Alkyne Moiety as a Latent Electrophile in Irreversible Covalent Small Molecule Inhibitors of Cathepsin K

Irreversible covalent inhibitors can have a beneficial pharmacokinetic/pharmacodynamics profile but are still often avoided due to the risk of indiscriminate covalent reactivity and the resulting adverse effects. To overcome this potential liability, we introduced an alkyne moiety as a latent electrophile into small molecule inhibitors of cathepsin K (CatK). Alkyne-based inhibitors do not show indiscriminate thiol reactivity but potently inhibit CatK protease activity by formation of an irreversible covalent bond with the catalytic cysteine residue, confirmed by crystal structure analysis. The rate of covalent bond formation ( kinact) does not correlate with electrophilicity of the alkyne moiety, indicative of a proximity-driven reactivity. Inhibition of CatK-mediated bone resorption is validated in human osteoclasts. Together, this work illustrates the potential of alkynes as latent electrophiles in small molecule inhibitors, enabling the development of irreversible covalent inhibitors with an improved safety profile.

5-(Alkynyl)dibenzothiophenium Triflates: Sulfur-Based Reagents for Electrophilic Alkynylation

The synthesis of a series of 5-(alkynyl) dibenzothiophenium triflates, prepared from dibenzo[b,d]thiophene 5-oxide and the corresponding trimethylsilyl-substituted alkynes is reported. Their structures were determined by X-ray crystallography, and their reactivities as electrophilic alkynylation reagents evaluated. Their broad substrate scope and functional-group tolerance illustrate their potential to become an alternative to the broadly used EBX reagents. Isotope labeling studies reveal that alkynyldibenzothiophenium salts may undergo attack by nucleophiles at either the α- or β-carbon atom depending on the nature of their substitution pattern. Subsequent elimination of the dibenzothiophene unit and 1,2-migration of one of the groups (in case of β-attack) affords the desired alkynes.

A rhodium(i)–oxygen adduct as a selective catalyst for one-pot sequential alkyne dimerization-hydrothiolation tandem reactions

An air-stable rhodium(i)–oxygen adduct featuring a CNC-pincer ligand, based on 1,2,3-triazol-5-ylidenes, catalyzes the homo-dimerization and hydrothiolation of alkynes, affording the gem-enyne and α-vinyl sulfide isomers, respectively, with excellent selectivity.

Heck–Mizoroki coupling of vinyliodide and applications in the synthesis of dienes and trienes

Vinyliodide reacts chemoselectively under Heck–Mizoroki conditions with terminal alkenes to give diene products, including vinyl boronate esters, and the resulting dienylboronate undergoes Suzuki–Miyaura coupling with aryl, heteroaryl and alkenyl halides to access dienes and trienes.

Indium(iii) catalysed regio- and stereoselective hydrothiolation of bromoalkynes

Hydrothiolation of bromoalkynes has been reported for the first time under metal catalysed conditions. Indium(iii) trifluoromethanesulfonate was demonstrated as the first catalyst which can catalyse the hydrothiolation of bromoalkynes with absolute regio- and stereoselectivity to generate synthetically valuable (Z)-β-bromo vinyl sulfides in good yields.