Alkynylations

Alkynylations are chemical reactions that introduce an alkynyl group (–C≡C–R or –C≡CH) into a substrate, forming a new carbon–carbon bond with a sp-hybridized carbon. They provide a straightforward route to propargyl and other alkynyl-substituted products, which are valuable in further elaboration and functional materials.

Several general approaches are used:

- Nucleophilic alkynylation: alkynyl anions or organometallic reagents (such as acetylides) add to carbonyl compounds to give propargyl alcohols after workup. This broad class also includes additions to electrophiles under catalytic conditions to forge C–C bonds.

- Electrophilic alkynylation: electrophilic alkynyl sources, including alkynyl halides or hypervalent iodine reagents, transfer the alkynyl moiety to nucleophiles or electron-rich substrates.

- Radical alkynylation: alkynyl radicals generated from suitable precursors add to alkenes or arenes, enabling hydroalkynylation or C–H alkynylation under various conditions.

Transition-metal-catalyzed methods:

- The Sonogashira reaction is the most widely used alkynylation, coupling terminal alkynes with aryl or vinyl halides under palladium catalysis, often with copper co-catalyst, yielding aryl- or vinyl-alkynes.

- Additional metal-catalyzed alkynylations broaden the scope to coupling alkynyl partners with carbonyls, alkenes, or heteroatoms.

Applications and scope:

Alkynylations are employed in the synthesis of natural products, pharmaceuticals, and functional materials. They enable rapid construction of alkynyl motifs with ongoing efforts to improve milder conditions, selectivity, and substrate tolerance.