Ruthenium-Induced Cyclization of Heteroatom-Functionalized Alkynes: Progress, Challenges and Perspectives.

Metal-induced cyclization of functionalized alkynes represents one of the most general approaches to prepare organic heterocycles. Although RuII centers are well-established to promote alkyne to vinylidene rearrangements and many RuII -mediated alkyne cyclizations have been rationalized to be the results of post-vinylidene transformations, recent discoveries indicate that RuII centers can serve as electrophiles and induce alkyne cyclizations without vinylidene intermediacy. In this Minireview, an overview of the RuII -induced cyclization of heteroatom-functionalized alkynes in the last decade is provided, with an emphasis on the discoveries and validations of the unconventional "non-vinylidene-involving" pathways.