Regio- and stereoselective synthesis of (E)-1-bromo-2-iodoalkenes through iodobromination of internal alkynes

Synthesis of Tetrasubstituted 1,4-Dicarbonyl (Z)-2,3-Dihaloalkenes via Electrophilic Halogenation of Alkynyl Hydrazones

A highly practical and stereoselective route to 1,4-dicarbonyl 2,3-dihaloalkenes is presented. The strategy involves bench-stable unprotected alkynyl hydrazones and commercially available N-halosuccinimides that provide γ-oxo-α,β-(Z)-dihaloenoates in excellent yields with complete Z-selectivity. The protocol also furnishes vicinal dihaloalkenes with two different halogen atoms. Also, a straightforward one-pot synthesis of dihaloenoates from readily accessible 2-oxo-3-butynoate is demonstrated. In addition, potential synthetic transformations of 4-oxo-2,3-dibromoenoates are explored, which include the synthesis of valuable five- and six-membered heterocycles.

Widely applicable (radio)dihalogenation of alkynes and alkenes using two different nucleophilic alkali metal halides

A hydrogen bond donor solvent-assisted highly regio- and stereoselective difunctionalization of alkynes and alkenes using two nucleophilic alkali metal salts as halogenation reagents.

Recent advances in the stereoselective synthesis of acyclic all-carbon tetrasubstituted alkenes

Alkenes bearing four carbon-based groups are ubiquitous motifs in chemical sciences due to their various applications from medicinal to materials chemistry, and as chemical platforms for the synthesis of complex, chiral molecules. As such, tremendous research efforts are currently ongoing in order to develop general procedures for the challenging stereoselective synthesis of all-carbon tetrasubstituted alkenes, especially for acyclic structures. Since classical approaches to carbon-carbon double bonds are not suitable for the high steric demand around tetrasubstituted alkenes, a variety of unique approaches to access these privileged functional groups have been developed in recent years. This review article highlights the most significant developments in the field from 2007 to 2020, with an emphasis on the mechanisms and remaining limitations of these contemporary methods. Specifically, recent advances in internal alkyne carbofunctionalizations, in multicomponent couplings or other cross-couplings from nucleophilic or electrophilic alkenyl partners, and in the development of miscellaneous methods, are discussed.

Regio- and Stereoselective Synthesis of 1,2-Dihaloalkenes Using In-Situ-Generated ICl, IBr, BrCl, I2, and Br2

We describe a catalyst-free 1,2-trans-dihalogenation of alkynes with an unprecedented substrate scope and exclusive regio- and stereoselectivity. This versatile dihalogenation system-a combination of NX¹S electrophile and alkali metal halide (MX²) in acetic acid-is applicable for diverse categories of alkynes (electron-rich or poor alkynes, internal and terminal alkynes, or heteroatoms such as O-, N-, S-substituted alkynes). The hydrogen bonding donor solvent acetic acid is essential for the in-situ generation of X¹X² electrophile, including ICl, IBr, BrCl, I_2, and Br₂.

Hydrogen-Bonding-Assisted Brønsted Acid and Gold Catalysis: Access to Both (E)- and (Z)-1,2-Haloalkenes via Hydrochlorination of Haloalkynes

We have developed an efficient synthesis of both (Z)- and (E)-chlorohaloalkenes via hydrochlorination of haloalkynes, based on two distinct hydrogen-bond-network-assisted catalytic systems: Brønsted acid catalysis and gold catalysis. Both systems offer high stereoselectivity, good chemical yields, and diverse functional group tolerance.

Regio- and Stereoselective Radical Perfluoroalkyltriflation of Alkynes Using Phenyl(perfluoroalkyl)iodonium Triflates

A method for regio- and stereoselective anti-addition of the perfluoroalkyl and the triflate group of phenyl(perfluoroalkyl)iodonium triflates to alkynes is presented. The radical reaction uses cheap CuCl as a smart initiator and can be conducted in gram scale. The perfluoroalkyltriflated products are readily further functionalized, rendering this transformation valuable.

Triphenylphosphine promoted regio and stereoselective α-halogenation of ynamides

Metal free α-halogenation of ynamides at room temperature.