Palladium allylation

The hydrolytic DKR of allyl esters has been studied as a DKR of esters. The first DKR was accomplished through Pd-catalyzed racemization and enzymatic hydrolysis of allylic acetates in a buffer solution. However, the DKR under these conditions was limited to cyclohexenyl acetates to give symmetrical palladium-allyl intermediates. Among them, 2-phenyl-2-cyclohexenyl acetate 9 was the only substrate to have been resolved with good results (81% yield, 96% ee). 

A wide variety of organoalkynyl derivatives of cotarnine hydrochloride, a cyclic iminium salt with rich biological activity, were prepared from the direct alkynylation of cotarnine hydrochloride using silver(l) alkynyls.180 Substituted enynes were prepared from the coupling reactions of silver alkynyls with the palladium allyl intermediates, which was... 

In the presence of certain metals, particularly nickel and palladium, allylic and aryl halides serve as convenient sources of... 

HsCjljN-MgBr 30 25 Bis-[2,4-pentandionato]-palladium Allyl-diethyl-amin 96 8... 

Metal-n-allyl complexes are important in a number of stereoselective catalytic reactions and are therefore attractive for computational chemists (see also Chapter 13, Section 13.2). An empirical force field study based on the MM2 parameterization scheme aimed at predicting stereoselective nickel(0)-catalyzed cycloadditions was recently conducted 56. As in a similar study 57, where a force field for the structure optimization of palladium-allyl systems was developed, dummy atoms were needed to define the structural model. Based on the assumptions required to model a catalytic process, the results obtained have to be interpreted with caution. 

Esters of allylic alcohols with resin-bound carboxylic acids can be converted into palladium allyl complexes by treatment with palladium(O). These allyl complexes react with carbon... 

The palladium-allylation of ambident aromatic heterocycles is covered by Professor Moreno-Mafias and Dr. Pleixats (Barcelona, Spain) in the second chapter of this volume. The preference for carbon versus oxygen, nitrogen, and sulfur allylation is discussed from the diverse viewpoints of regioselectivity, kinetic versus thermodynamic control, mechanisms, stereochemistry, and synthetic targets in the first general survey of this topic. 

Arguably the best, or at least the most versatile, allylic oxidation method is based on Pd [114]. Since the intermediates are palladium-allyl complexes rather than free radicals the number of by-products is limited compared to the preceding examples (Fig. 4.41). Furthermore, a large number of nucleophiles (amines, alcohols, stabilized carbanions, carboxylates or halides) may attack the palladium-allyl complex, giving a wide variety of products. 

Introduction of a bulky pyridyl ligand again results in a reduced ligating ability of the pyridine functionality [41], which this time could be visualised using the rhodium(I) cod complexes instead of the palladium allyl ones (see Figure 3.5). 

Steric protection can be provided by adamantyl wingtip groups that are introduced by the reaction of the l,r-diaminobiphenyl to the Schiff base (with 2-adamantone) followed by reduction with LiAlH [79,80] (see Figure 5.24). Ring closure with triethyl orthoformate to the corresponding azolium salt proceeds as usual and subsequent reaction with [Pd(allyl)Cl]j in the presence of a suitable auxiliary base (potassium tcrt-butylate) yields the respective palladium allyl complex. The paUadium(II) allyl complex can then be reacted with hydrochloric acid to form the [Pd(NHC)Cy dimer. Subsequent reaction with a silver(I) salt predictably breaks up the dimer under chloride abstraction and anion transfer from silver to palladium. 

The reactions of CO with palladium allyl complexes have also been investigated. Ris-i -allylpalladium and hu- -crotylpalladium yield the corresponding carboxylic acids after acidification. A lactone, which has been observed in the analogous nickel reaction, could not be discovered [56]. 

Rhodium and palladium allyl complexes form from the reaction of a Tl(III)allyl compound with a metal halide ... 

Tetrahydro-4-hydroxy-2-vinylfuran (2) can be prepared from 4-acetoxy-5-hexen-l,2-diol (I) with high 1,3-asymmetric induction via nucleophilic displacement on the palladium allyl complex, followed by elimination of a hydride. Thus, treatment of 1 with (dba),Pd2-chloroform and triphenylphosphane at 20 °C for 3 hours gives the tetrahydrofuran in 95 % yield and a 91 9 dia stereomeric ratio, On the basis of mechanistic considerations, the major isomer is assigned trans 1. 

Allenols undergo a palladium(0)-catalyzed cyclization process to yield highly functionalized vinyl oxiranes in a diastereoselective manner (Equation 77) <1999JA7943>. Initial carbon palladation forms a palladium allyl intermediate that suffers subsequent attack by the internal oxygen nucleophile to generate the oxirane fragment. 

Friesen, R. W. Product subclass 2 palladium-allyl complexes. Science of Synthesis 2002, 1,113-264. 

The INS spectra of the a-allyl compound allyl iodide, CH2=CHCH2l, and the r -allyl compound di-p-chloro-bis(r] -allylpalladium), [ Pd(Ti -C3H5) 2(p-Cl)2] [94] and the INS below 800 cm of nickel and palladium allyl complexes [97] have been reported. The structure of the palladium complex is shown in Fig. 7.24 [98]. The INS spectra are shown in Fig. 7.25. Peak positions and assignments are in Table 7.15. 

In chapter 19 you will meet palladium allyl cations as useful reagents and Evans and Robinson38 have combined the Pauson-Khand reaction with allyl cation complexes using rhodium as a compromise between Pd and Co. The enolate 132 combines with the Rh(I) cation complex from the allylic carbonate 133 to give the enyne 134 that gives the Pauson-Khand product 135 in 87% yield with the same catalyst but at higher temperatures. 

Here is an example from the McMurry flexibilene synthesis quoted in chapter 1. An alkyne 127 with a protected aldehyde group reacts with Cp2ZrHCl to give a vinyl zirconium complex 128 which is coupled to a palladium-allyl complex in the next step. The double bond so produced is present with the same E configuration in the final product. It is marked 129 with an arrow in the diagram.28... 

Among the methods available for these reactions, two have gained prominence the use of Claisen-style [3,3]-sigmatropic rearrangements for the selective allylation of enolates and the more general reactions of palladium allyl cation complexes. 

Addition of alkyl organo-zlnc reagents Palladium Allyl Cation Complexes with Chiral Ligands Summary... 

Palladium Allyl Cation Complexes with Chiral Ligands... 

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