Palladium allylation

Palladium Allyl Cation Complexes with Chiral Ligands 

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

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. 

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]. 

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

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

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

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

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 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. 

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. 

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. 

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). 

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 

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. 

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. 

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. 

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