Recent Advancements in Stereoselective Olefin Metathesis Using Ruthenium Catalysts

Abstract

Olefin metathesis is a prevailing method for the construction of organic molecules. Recent advancements in olefin metathesis have focused on stereoselective transformations. Ruthenium olefin metathesis catalysts have had a particularly pronounced impact in the area of stereoselective olefin metathesis. The development of three categories of Z-selective olefin metathesis catalysts has made Z-olefins easily accessible to both laboratory and industrial chemists. Further design enhancements to asymmetric olefin metathesis catalysts have streamlined the construction of complex molecules. The understanding gained in these areas has extended to the employment of ruthenium catalysts to stereoretentive olefin metathesis, the first example of a kinetically E-selective process. These advancements, as well as synthetic applications of the newly developed catalysts, are discussed.

Helicenes as Chirality‐Inducing Groups in Transition‐Metal Catalysis: The First Helically Chiral Olefin Metathesis Catalyst

“…It has, for instance, been demonstrated that the reactivity of Ru-metathesis catalysts with unsaturated NHC ligands can be improved by increasing the s-donor capacity of the ligand through introduction of donor substituents in the backbone. [29,30] As ap roof-of-concept we investigated the feasibility of asymmetrico lefin metathesis reactions, [14,[31][32][33][34][35] catalyzed by a helicallyc hiral metathesis initiator,w hich was designed according to the general principles outlined above and summarized in Figure 1. [9] On the downside, opportunitiesf or steric and electronic modulation through backbones ubstituentsa re restricted for thesel igand systems.…”

“…[24] This strategy has in the meantime been successfully applied to the synthesis of enantiopure aminohelicenes, [25,26] which we in turn expect to open the door to NHC ligands with helically chiral N-substituents and transitionmetal catalysts derivedt hereof. [29,30] As ap roof-of-concept we investigated the feasibility of asymmetrico lefin metathesis reactions, [14,[31][32][33][34][35] catalyzed by a helicallyc hiral metathesis initiator,w hich was designed according to the general principles outlined above and summarized in Figure 1. In addition, few other helicene substituted imidazolium salts have been synthesized through different routes, but not ligated to transition metals.…”

“…Literature precedence for transition-metal NHC complexes with N-helicenyl substituents is scarce, [27,28] and these have not been investigated in asymmetric catalysis. [29,30] As ap roof-of-concept we investigated the feasibility of asymmetrico lefin metathesis reactions, [14,[31][32][33][34][35] catalyzed by a helicallyc hiral metathesis initiator,w hich was designed according to the general principles outlined above and summarized in Figure 1. [29,30] As ap roof-of-concept we investigated the feasibility of asymmetrico lefin metathesis reactions, [14,[31][32][33][34][35] catalyzed by a helicallyc hiral metathesis initiator,w hich was designed according to the general principles outlined above and summarized in Figure 1.…”

A Simple Nickel Catalyst Enables Broad E-Selective Alkyne Semihydrogenation

“…No reduction of ester (12 c,s ee also 12 g)o rnitrile (12 d)g roups or dehalogenation (12 e)w as detected.T he investigationo fp otential alcohol protecting groups in 11 h-j established that for ab enzyl or silyl ether (12 h and 12 i), somewhat diminished stereoselectivity was found, whereas the acetate 12 j was formed with the usual high E-selectivity (E/Z = 97:3). [25] It has to be noted that noncyclic dialkyl alkynes( thus lacking electronic predisposition through conjugation) lead to significant alkene isomerization and/or cyclotrimerization. [18] Heterocyclic substrates 12 k and 12 l were also converted equally well.…”

Stereoretentive Olefin Metathesis: An Avenue to Kinetic Selectivity

“…Recent studies using ruthenium-based olefin metathesis catalysts have succeeded at developing Z-selective ruthenium catalysts. [28,29,77] One of these systems, using ruthenium catalysts bearing catechothiolate ligands, used stereoretention to provide Z-olefins. Additional investigations revealed this catalyst to also kinetically generate E-olefins.…”