Undirected, Selective Csp2-H Alkynylation of Five-membered Heteroarenes

The functionalization of Csp2-H bond of heteroarene with an alkyne represents one of the most attractive procedures for the late-stage functionalization of the aromatic core due to the structural characteristics and synthetic versatility given by a triple carbon-carbon bond. The aim of this review is to cover the most significant results reported in the literature regarding the synthesis of alkynyl-substituted five-membered heteroarenes by selective direct Csp2-H alkynylation with 1-haloalkynes and analogs, or by cross-dehydrogenative alkynylation (CDA) with terminal alkynes, without making use of directing groups.