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.