Palladium complexes allyl/enyl

Abstraction of chloride from a vinylpalladium complex by silver acetate has been reported,45 as well as halide abstraction by silver triflate from arylpalladium halides.46 More interestingly in the context of creating C-C bonds, silver perchlorate was able to promote the reaction of (r -aryl)palladium bromide with dienes. Silver-promoted bromide abstraction led to the formation of (r 1-r 2-enyl)palladium complexes, which evolved further through the regioselective formation of a C-C bond between the aryl group and the former diene. Reactions with nonconjugated dienes suggested that the reaction proceeds via carbometallation of the less crowded double bond. Isomerization and (3 elimination led to a (ri3-allyl)palladium complex (Scheme 10.26).47... 

The origin of enantioselectivity which accompanies the allylic acetate substitution reaction of l,3-diphenylprop-2-enyl acetate with dimethyl malonate, catalysed by palladium complexes having chiral imine-sulfide chelate ligands, has been explored. 

Interestingly, the palladium-catalyzed allylic substitution of ( )-l,3-diphenylprop-2-enyl acetate as a model reaction has been performed with a chiral diketimine and dialdimine (eq 44). The Pd complex derived the diketimine turned out to be an active catalyst as the corresponding allylated derivative was isolated in 78% yield and 92% ee. Surprisingly, the Pd complex derived Irom dialdimine showed no activity even after four days at room temperature. This extreme difference in catalyst activity between these two systems can be understood by applying the AMS model. 

An interesting example of enantioselective catalytic alkylation of carbonyl groups by unqiolung of 7r-allyl palladium complexes has been disclosed recently.A number of chiral ligands have been screened in the palladium-catalyzed alkylation of cyclohex-enyl acetate. The best performing ligand was the monodentate... 

The palladium-catalyzed decarboxylative coupling of allyl 2-(benzo[c(jthiazol-2-yl)acetates 118 provides a facile approach to 2-(but-3-enyl)benzo[c(jthiazoles 122 <07JA4138>. The reaction is initiated by nucleophilic attack of Pd(0) on the allyl ester to give Pd-7t-allyl complex 119, which undergoes nucleophilic attack at the less substituted allylic carbon from the benzothiazole nitrogen to produce 120. Decarboxylative dearomatization leads to intermediate 121, and a subsequent aza-Cope rearrangement driven by rearomatization affords the final product 122 and accounts for the unusual regioselectivity. This appears to be the first report of a tandem allylation/aza-Cope reaction driven by decarboxylative dearomatization/ rearomatization. 

The obtained amino functionalised imidazolium salts could be used to generate the corresponding palladium(ll) carbene complexes using the silver(l) complexes as carbene transfer agents. Application of these palladium(ll) complexes (predominantly in situ) in asymmetric allylic alkylation reactions between ( )-l,3-diphenylprop-3-enyl acetate and dimethyl malonate (a standard reaction for this catalytic process [145]) gave up to 80% ee,... 

Enantioselective allylic substitutions catalyzed by transition-metal complexes are a powerful method for constructing complex organic molecules [4f,55]. Palladium-based catalysts have often given excellent results. To expand the scope of the reaction, a new enantioselective allylic alkylation catalyzed by planar-chiral ruthenium complexes was developed [56]. For example, the reaction of l,3-diphenyl-2-propenyl ethyl carbonate with sodium dimethyl malonate in the presence of 5 mol% of a planar chiral (S)-ruthenium complex (Figure 5.3) at 20 °C for 6 h in THE resulted in the formation of the corresponding chiral allylic alkylated product of dimethyl 2-((2 )(lS)-l,3-diphenylprop-2-enyl)propane-l,3-dioate in 99% yield vsdth 96% e.e. (Eq. 5.33). 

An in-depth study of platinum allylic alkylation and subsequent comparison to ligand-identical palladium catalysts was done by Blacker et al. The allylic alkylation of diphenyl-2-enyl acetate with dimethyl malonate, (equation 73), reveals activity for a variety of complexes with activity restricted by the source of zerovalent platinum (Table 1). Nonactive complexes are thought to be less prone to dissociation into coordinatively unsaturated catalytical active species. 

Leitner and co-workers described Pd-catalyzed nucleophilic substitutions ofallylic substrates with different nucleophiles [27]. They used Pd2(dba)3 as the palladium source and phosphane 20 as perfluoro-tagged ligand [Eq. (5)]. Reaction between cinnamyl methyl carbonate (21) and various nucleophiles (Nu-H) were performed in a THF/C7FJ4 biphasic mixture. A decrease in conversion was observed only after the ninth run (with 5 mol% Pd complex). By reducing the amoimt of Pd complex to 1 mol%, five quantitative recyclings were possible. The standard protocol was also applied to the condensation of dimethyl malonate with allyl methyl carbonate, (2-vinyl)butyl carbonate, and cyclohex-2-enyl carbonate. In each case two recyclings were performed without any decrease in conversion. 

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