Transition-Metal-Catalyzed Selective Alkynylation of C-H Bonds

Alkynylation reactions are one of the most sought-after synthetic methodologies due to the versatility of C-C triple bond diversifications. Sonogashira coupling was widely used for the synthesis of alkynylated molecules; however, this methodology requires the use of previously halogenated substrates, which is a major drawback. To overcome this issue, a complimentary method, transition-metal-catalyzed C-H alkynylation, was emerged as an alternative tool in the recent years. Though the initial reports required the use of either specific directing groups or strong alkynylating agents for effective functionalization, recent studies indicate that transition-metal-catalyzed site selective alkynylations can be carried out using mild and readily available alkynylating agents under moderate reaction conditions. In this review, we explain the transition metal cataluyzed site selective alkynylation both C(sp(2))-H and C(sp(3))-H bonds by emphasizing to the reaction mechanism.