Recent Advances in Radical-Involved Alkynylation of Unactivated C(sp(3))-H Bonds by Hydrogen Atom Abstraction

The direct C(sp(3))-H functionalization is one of the major research topics in synthetic chemistry since C(sp(3))-H bonds are ubiquitous in every aspect of chemistry. Despite impressive advances in transition-metal-catalyzed C(sp(3))-H activation, the radical-initiated process via hydrogen atom abstraction (HAA) of C(sp(3))-H bonds represents a more appealing strategy owing to the mild reaction conditions and good regioselectivity. Given the importance of alkynes as versatile synthons in organic synthesis and key structural motifs in drug discovery, great efforts have been made toward their synthesis via the combination of HAA and alkynylation process in recent years. This review summarizes the recent progress in radical-initiated C(sp(3))-H alkynylation reactions with emphasis on the alkynylating reagents and mechanistic discussion.