Regio- and Stereoselective Homodimerization of Monosubstituted Acetylenes in the Presence of the Second Generation Grubbs Catalyst

Abstract

Silyl-and phenylacetylenes undergo efficient homodimerization in the presence of a second generation Grubbs catalyst. The reaction permits fully regio-and stereoselective synthesis of disubstituted 1,3-enynes. The other commonly used ruthenium-based olefin metathesis catalysts remain inactive in the reaction.

Z‐Selective (Cross‐)Dimerization of Terminal Alkynes Catalyzed by an Iron Complex

“…Thus, complex 1 is the first effective iron catalyst reported to date for the cross‐dimerization of terminal alkynes. The regio‐ and stereoselectivity of the reaction, together with its high activity, make complex 1 comparable to catalysts based on precious‐metal complexes –. As compared to the procedure reported by Ozawa and co‐workers for the cross‐dimerization catalyzed by ruthenium, a lower catalyst loading (1 vs. 5 mol %) and a lower excess of ethynyltrimethylsilane were required, under neutral conditions (a base is needed in the case of Ru), for similar catalytic results.…”

Catalytic transformation of phenylacetylene mediated by phosphine-free ruthenium alkylidene complexes

“…Although second-generation phosphine-free ruthenium catalysts have been reported as inactive in the dimerization of silylacetylenes [19], to the best of our knowledge those complexes have not been used as catalysts for the intermolecular cyclotrimerization of 1-alkynes.…”

Piano-Stool Iron Complexes as Precatalysts for gem-Specific Dimerization of Terminal Alkynes

“…The catalytic dimerization of terminal alkynes is an effective synthetic route for conjugated enynes, owing to its unity atom economy and the availability of various alkyne precursors. − The main challenge is to control the regio- and stereoselectivity. The homodimerization of a terminal alkyne may yield up to three isomeric enyne products, − whereas the cross-dimerization of two different terminal alkynes may result in an even more complicated mixture of products. − Moreover, the formations of cumulenes, higher oligomers, and polymers may further complicate the reaction outcome. − A large number of catalysts, mostly precious-metal catalysts and f-block elements, have been extensively investigated. − ,− Meanwhile, there have been increasing research endeavors toward the development of sustainable and environmentally benign alternatives to noble-metal catalysts for alkyne dimerization. − Such an effort is evidenced by the rapid development of iron-based catalysts. For example, a few iron-hydride complexes of P,N,P-pincer ligands have proven effective toward the Z -selective dimerization of arylacetylenes at room temperature without any additive. − The iron complex of a cyclic (alkyl)­aminocarbene ligand has been reported as an E -selective catalyst toward the dimerization of arylacetylenes in the presence of a large excess of KO t Bu at high temperatures .…”