5 catalysed allylation

Another more specific characteristic can allowed the differentiation between homogeneous and colloidal catalysts. In Pd-catalysed allylic alkylation rac-3-acetoxy-1,3-diphenyl-l-propene with dimethyl malonate, homogeneous and colloid species reacts at different rates with both substrate enantiomers, obtaining in the case of Pd colloids an excellent kinetic resolution (see Section 4) [44]. 

Enriched I (more than 75% (5)-I) was used as substrate for Pd-catalysed allylic alkylation, using both colloidal [Pd/l]coii and molecular [Pd/lj oi catalysts. As observed in Scheme 3, the colloidal system reacts more slowly with (S)-I enantiomer only 8% of (R)-l is present in the starting substrate, leading to a substrate conversion of ca. 10% with an ee of the remained substrate higher than 99% (S), in agreement with the relative rate calculated previously, k((/J)-I)/k((S)-I) 12 (see above). This relative rate is actually smaller for the molecular catalyst (see above) and consequently a higher conversion was obtained in this case 67% conversion is achieved after 30 h of reaction from a starting substrate constituted by 88.5 R)-I and 11.5(5)- . 

Scheme 3. Pd-catalysed allylic alkykation using an enriched substrate (a) colloidal catalyst (Pd/l/I = 1/1.05/100) (b) molecular catalyst (Pd/l/I = 1/1.25/10,000).

Scheme 1.1 Mechanism for Pd-catalysed allylic substitution with soft nucleophiles.

Scheme 1.2 Test reaction Pd-catalysed allylic alkylation of 1,3-diphenylpropenyl acetate with dimethyl malonate.

Scheme 1.4 Pd-catalysed allylic alkylations with dithioether ligands.

Scheme 1.10 Mixed S/P ligands for Pd-catalysed allylic alkylations and aminations.

Since carbohydrates constitute an inexpensive and highly modular chiral source for preparing chiral ligands," Claver et al. have reported the use of a series of thioether-phosphite" and thioether-phosphinite furanoside ligands" in the test palladium-catalysed allylic substitution reaction. In the first type of ligand, a systematic variation of the donor group attached to the carbon atom C5 indicated that the presence of a bulky phosphite functionality had a positive effect on the enantioselectivity. Indeed, the enantioselectivity was controlled mainly by the phosphite moiety. This was confirmed by the use of a ligand... 

Furanoside thioether-phosphinite ligand for Pd-catalysed allylic substitutions of acyclic and cyclic allylic substrates. 

Scheme 1.64 Cu-catalysed allylic substitution of cinnamyl phosphate with ZnEt2 in the presence of P-aminosulfonamide ligands.

Scheme 1.66 Cu-catalysed allylic alkylations of allylic phosphates with vinylalumi-num reagents in the presence of sulfur-containing diaminocarbene ligands.

Scheme 1.79 Phosphinamidite-thioether ferrocenyl ligands for Pd-catalysed allylic...

Scheme 1.80 N/S/P-ferrocenyl ligand for Pd-catalysed allylic alkylations of indoles.

Scheme 10.84 Pd-catalysed allylic amination with phosphinite thioglycoside ligands.

They have also been implicated (45) in the HC1 catalysed allyl activated reinitiation of thermal"-degradation as well as in the "Schlimper" type complexes which have been thought to contribute to the color of degraded PVC (46). 

Figure 6.18. Palladium catalysed allylic alkylation using fluorinated ligands.[60, 61]...

One of the beauties of transition metal-catalysed allylic alkylation is the existence of a relatively high degree of mechanistic understanding, enabling fea-... 

B. M. Trost, D. L. Van Vranken, Asymmetric Transition Metal-Catalysed Allylic Alkylations, Chan. Rev. 1996, 96, 395-422. 

Furthermore, the use of a Lewis acid promoter leads to increased stereoselectivities (Table 19, entry C)252,254. Compared to the aprotic reaction, where allyl silane was used instead of allyl bromide and indium chloride, an almost complete reversal of the diastereos-electivity was found. It was demonstrated recently that the Lewis acid catalysed allylation reaction can be carried out efficiently without any organic solvent in saturated ammonium chloride solution255. Finally, Lewis acid catalysed Mannich reactions can be carried out conveniently in mixtures of organic solvents and water. However, the exact role of the Lewis acid catalyst has not been clarified (Table 19, entry D)253. The same reaction can be carried out in pure water with catalysis by indium trichloride256. 

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