Synthesis of Isocoumarins through Three‐Component Couplings of Arynes,Terminal Alkynes,and Carbon Dioxide Catalyzed by an NHC–Copper Complex

A copper‐catalyzed multicomponent coupling reaction between in situ generated ortho‐arynes, terminal alkynes, and carbon dioxide was developed to access isocoumarins in moderate to good yields. The key to this CO₂‐incorporating reaction was the use of a versatile N‐heterocyclic carbene/copper complex that was able to catalyze multiple transformations within the three‐component reaction.     

Regio‐ and Stereoselective Chlorocyanation of Alkynes

A variety of terminal and internal alkynes were converted regio‐ and stereoselectively into (Z )‐3‐chloroacrylonitriles by treatment with BCl₃ in the presence of stoichiometric amounts of imidazolium thiocyanates. These products could be readily functionalized to provide useful building blocks, thus demonstrating the synthetic value of the method. Preliminary mechanistic studies suggest initial activation of the cationic thiocyanate by the Lewis acid, followed by electrophilic attack of the alkyne. The syn addition of a chloride to the vinyl cation intermediate and final elimination of the thiourea unit afford the desired chloroacrylonitriles.     

Nickel‐Catalyzed Stereoselective Dicarbofunctionalization of Alkynes

A nickel‐catalyzed three‐component reaction involving terminal alkynes, boronic acids, and alkyl halides is presented herein. Trisubstituted alkenes can be obtained in a highly regio‐ and stereocontrolled manner by the simultaneous addition of both aryl and alkyl groups across the triple bond in a radical‐mediated process. The reaction, devoid of air‐ and moisture‐sensitive organometallic reagents and catalysts, is operationally simple and offers a broad scope and functional‐group tolerance.     

Dual Photoredox/Nickel‐Catalyzed Three‐Component Carbofunctionalization of Alkenes

The potential of merging photoredox and nickel catalysis to perform multicomponent alkene difunctionalizations under visible‐light irradiation is demonstrated here. Secondary and tertiary alkyl groups, as well as sulfonyl moieties can be added to the terminal position of the double bond with simultaneous arylation of the internal carbon atom in a single step under mild reaction conditions. The process, devoid of stoichiometric additives, benefits from the use of bench‐stable and easy‐to‐handle reagents, is operationally simple, and tolerates a wide variety of functional groups.     

Highly Regio‐ and Stereoselective Hydrosilylation of Alkynes Catalyzed by Tridentate Cobalt Complexes

Several cobalt complexes bearing tridentate (NNN) ligands were synthesized and served as precatalysts for alkyne hydrosilylation with Ph₂SiH₂. For terminal alkynes, the catalyst L2 b‐CoCl₂ was selected, and resulted in the corresponding α‐vinylsilanes with high (Markovnikov) regioselectivity and extensive functional‐group tolerance. For internal diaryl alkynes, the catalyst L2 c‐CoCl₂ exhibited the best activity, and afforded E‐selective vinylsilanes through syn‐addition in excellent yield under mild conditions.     

Silver‐Catalyzed Stereoselective Aminosulfonylation of Alkynes

A silver‐catalyzed intermolecular aminosulfonylation of terminal alkynes with sodium sulfinates and TMSN₃ is reported. This three‐component reaction proceeds through sequential hydroazidation of the terminal alkyne and addition of a sulfonyl radical to the resultant vinyl azide. The method enables the stereoselective synthesis of a wide range of β‐sulfonyl enamines without electron‐withdrawing groups on the nitrogen atom. These enamines are found to be suitable for a variety of further transformations.     

Highly Chemo‐, Regio‐, and Stereoselective Cobalt‐Catalyzed Markovnikov Hydrosilylation of Alkynes

A highly chemo‐, regio‐ and stereoselective cobalt‐catalyzed Markovnikov hydrosilylation of alkynes was developed. Various functionalized groups, such as halides, free alcohols, free aniline, ketones, esters, amides, and nitriles are tolerated, which may lead to further applications and late‐stage derivatizations. To date, this is the most efficient cobalt catalytic system (TOF=65 520 h^?1; TOF=turnover frequency) for hydrosilylation of alkynes. The Hiyama–Denmark cross‐coupling reactions of vinylsilanes with aryl iodides underwent smoothly to afford 1,1‐diarylethenes. A unique regioselectivity‐controllable hydrosilylation/hydroboration reaction of alkynes was also described.     

Regio‐ and Enantioselective Cobalt‐Catalyzed Sequential Hydrosilylation/Hydrogenation of Terminal Alkynes

A highly regio‐ and enantioselective cobalt‐catalyzed sequential hydrosilylation/hydrogenation of alkynes was developed to afford chiral silanes. This one‐pot method is operationally simple and atom economic. It makes use of relatively simple and readily available starting materials, namely alkynes, silanes, and hydrogen gas, to construct more valuable chiral silanes. Primary mechanistic studies demonstrated that highly regioselective hydrosilylation of alkynes with silanes occurred as a first step, and the subsequent cobalt‐catalyzed asymmetric hydrogenation of the resulting vinylsilanes showed good enantioselectivity.