Vinyl compounds cross-metathesis

Ruthenium-catalyzed olefin cross-metathesis (ring-closing metathesis, RGM) between terminal alkenes and vinyl-boronic acid or esters has recently been developed for the synthesis of ( )-l-alkenylboron compounds from alkenes.459,460 The efficiency of protocol was proved in the synthesis of a key intermediate of epothilone 490 292 461 (Equation (84)). The vinyl boronate was given almost exclusively the trans-adduct. 

Grubbs used (4a) to efficiently install functional groups that might otherwise be added via C H activation or allylic oxidation pathways (Scheme 12). Among the breadth of compound types accessible through these cross metathesis strategies were substituted vinyl-phosphonic, boronic, and carbonyl esters, which were synthesized in good to excellent yields. ... 

Summary Two catalytic reactions, i.e. silylative coupling (mms-silylation) (SC) catalyzed by complexes containing or generating Ru-H and/or Ru-Si bonds (I, II, V, VI) and cross-metathesis (CM) catalyzed by mthenium-carbene (i.e. 1st and 2nd generation mthenium Grubbs catalyst (ID, IV)) of vinyl and allyl-substituted hetero(N,S,B)organic compounds with conunercially available vinyltrisubstituted silanes, siloxanes, and silsesquioxane have been overviewed. They provide a universal route toward the synthesis of well-defined molecular compounds with vinylsilicon functionality. 

We first synthesized suitably functionalized amides in four steps from the corresponding alkenyl bromides (Scheme 11). The allylsilane function was introduced by cross-metathesis between the terminal alkenes and allyltri-methylsilane. Then, the bromide was substituted by an azide and the latter was reduced to the primary amine by the action of LiAlELj. As before, a pep-tidic coupling with vinyl acetic acid led to the desired starting compound with a diastereomeric ratio /Z=70/30. 

Silylative Coupling and Cross-Metathesis of Alkenes and Dienes with Vinyl-Silicon Derivatives — New Catalytic Routes to Synthesis of OrganosUicon Compounds ... 

Summary Recent achievements in two catalytic reactions, i.e., silylative coupling and cross-metathesis of alkenes and dienes with vinyl-silicon compounds, which resulted in new synthetic routes to organosilicon molecular and macromolecular compounds are presented. The silylative coupling, also called dehydrogenative or trans-silylation and silyl group transfer, is catalyzed by metal complexes which either contain or initiate the formation of M-H and M-Si bonds, where M = Ru, Rh, Co and Ir. Cross-metathesis, which was developed very recently, proceeds in the presence of metallacarbenes, mainly those of rathenium (e.g., Grabbs catalyst). 

Vinylsiloxanes of the type illustrated in Figure 3 are model compound for poly(vinyl)siloxanes. Therefore, a series of vinylsiloxanes (Figure 3) was synthesized and the reactivity of these compounds in cross-metathesis with styrenes and 1 -decene was studied [21],... 

Apart from halogen substituted alkenes, heteroatoms normally deactivate catalytic systems. However the synthetic utility of such reactions has encouraged further research in this field. Chlorine substitution at vinylic positions deactivates the double bond but halogen substituted alkenes in which the double bond is in an position undergo cross metathesis with internal alkenes. For example, 5-bromo-l-pentene undergoes cross metathesis with 2-pentene. Unsaturated compounds containing ester groups also react, e.g. methyl-9-octadecenoate is converted to 9-octadiene and dimethyl-9-octadecenedioate by the WCl —Sn(CH3)4 catalytic combination [15]. 

Allylsilanes can be prepared by a wide array of methods, including (1) the reaction of allyl metals with ClSiRs, (2) the reaction of silylanions (MSiRs) with allylic substrates, (3) the Kumada coupling of Me3SiCH2MgBr with vinyl halides, catalyzed by Pd or Ni species, (4) the Wittig reaction of P-silylated Wittig reagents, (5) the cross-metathesis of olefins with allylsilanes, and (6) the reductive silylation of unsaturated compounds. ... 

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