Stereoselectivity ring-closing metathesis

Chiral imidazolinylidenes with N-aryl substituents have been employed by Grubbs and coworkers in the stereoselective ring closing metathesis of olefins [52]. The introduction of the aryl groups as N-substituents was achieved by a palladium catalyzed Buchwald-Hartwig coupling (Scheme 16) [53]. 

Fig. 17. Tandem and stereoselective ring closing metathesis using two different Grubbs catalysts.

Catalytic ring-closing metathesis makes available a wide range of cyclic alkenes, thus rendering a number of stereoselective olefin functionalizations practical. The availability of effective metathesis catalysts has also spawned the development of a variety of methods that prepare specially-outfitted diene substrates that can undergo catalytic ring closure. The new metathesis catalysts have already played a pivotal role in a number of enantioselective total syntheses. 

An interesting application of the cydization of alkenyl thioacetals is the stereoselective preparation of olefmic diols. Thus, oxidative cleavage of the silicon—carbon bond [32] in the ring-closed metathesis products, i.e. cyclic allylsilanes such as 35 and 36, affords (Z)-alk-2-ene-1,5-diols 37 and 38 (Scheme 14.18) [33],... 

A concise stereoselective synthesis of a myoinositol derivative has been achieved by ring-closing metathesis of diene 21 prepared from a readily available bis-Weinreb amide 20 of D-tartrate [Eq. (6.19)]. ... 

The stereoselective construction of nitrogen heterocycles remains a topic of intense synthetic interest [39]. Evans and Robinson described the combination of the stereospecific aUylic amination with ring-closing metathesis as a strategy for the constmction of mono- and disubstituted azacycles, which they demonstrated with the stereospecific construction of cis- and tra s-2,5-disubstituted pyrrolines [40]. Furthermore, this approach provided an ideal system for the determination of whether the enantiospecific rhodium-catalyzed aUyhc amination with an enantiomerically enriched nucleophile experiences a matched and a mismatched reaction manifold. 

Cycloalkynes may be formed by applying ring-closing metathesis to diynes.214 Partial hydrogenation of the product provides a stereoselective route to cis cyclo-alkenes that cannot be directly prepared in pure form by ring-closing metathesis ... 

Singh, V., Praveena, G.D., Karki, K., and Mobin, S.M. (2007) Cydoaddition of cydohexa-2,4-dienones, ring-closing metathesis, and photochemical reactions a common stereoselective approach to duprezianane, polyquinane and... 

A ring-closing metathesis (RCM) strategy was utilized in the synthesis of 5-hydroxypiperidin-2-ones <03JOC2432>. Stereoselectivity is observed with optically active amino acid derivatives as starting materials. 

Holt, D J, Barker, W D, Jenkins, P R, Panda, J, Ghosh, S, Stereoselective preparation of enantiomeri-cally pure annulated carbohydrates using ring-closing metathesis, J. Org. Chem., 65,482-493,2000. 

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