Selective Ru-Catalyzed C3–H Alkenylation of Furan-2- and Thiophene-2-carboxylic Acids with Internal Alkynes

A new approach for the preparation of 3-alkenyl furans and thiophenes by selective C3–H alkenylation of furan-2- and thiophene-2-carboxylic acids with internal alkynes has been developed, and novel 3-alkenylated furans and thiophenes have been synthesized and characterized. The main advantages of the developed approach are the use of readily available substrates in which the COOH function serves as a traceless in situ removable directing group, the high regioselectivity of the C3–H alkenylation, which provides easy access to C3-alkenylated furans and thiophenes with highly reactive C2–H and C5–H bonds that are difficult to access by previously reported methods, and the use of a relatively inexpensive [RuCl2(p-cymene)2] precatalyst in the absence of copper and silver promoters.