Nucleophilic reactions palladium

In the Wacker process, the coordinated ethene undergoes nucleophilic attack by OH-. In the course of the redox reaction, palladium(II) is reduced... 

Sakai s elegant application of Pd-induced nucleophilic reactions of allylic acetates provides the first experimental support for the biogenesis of the koumine alkaloid skeleton and is an excellent concluding illustration of the power of palladium in indole chemistry. 

Diethylamine (11) is an inexpensive base that removes fluorenylmethyl-based protectors without forming an adduct with the liberated moiety, and it can be eliminated by evaporation. It has been employed as nucleophile for palladium-catalyzed allyl-transfer reactions (see Section 3.13). 

The speculative mechanism(20-21) as outlined in Equation 2 involves initial reaction between palladium(II) and butadiene to form a -complex 2 followed by a nucleophilic reaction with carbon monoxide and methanol to give 3. 

The analogous reaction of 5-iodopyridazin-3(2H)-one led to the formation of pyridazino[4,5-6]indoles (3.82.) in a two step nucleophilic substitution, palladium catalysed intramolecular carbon-carbon bond formation sequence. The same reaction has also been carried out in one-... 

Palladium-catalyzed allylic oxidations, in contrast, are synthetically useful reactions. Palladium compounds are known to give rise to carbonyl compounds or products of vinylic oxidation via nucleophilic attack on a palladium alkene complex followed by p-hydride elimination (Scheme 9.16, path a see also Section 9.2.4). Allylic oxidation, however, can be expected if C—H bond cleavage precedes nucleophilic attack 694 A poorly coordinating weak base, for instance, may remove a proton, allowing the formation of a palladium rr-allyl complex intermediate (89, path by694-696 Under such conditions, oxidative allylic substitution can compete... 

Caiboxylate ions are also effective nucleophiles in palladium-catalyzed reactions of alkenes and several classes of lactones including 7-pyrones (equation 11)17 and isocoumarins (equation 12)18 have been made in this manner. These early studies used stoichiometric amounts of palladium salts, since efficient redox systems had not yet been developed. However, with more modem techniques catalysis in these systems should be relatively straightforward. The more recent catalytic cyclization-caibonylation process in equation (13) is indicative of this.19... 

Fischer-type carbenes can also be modified via transition metal catalyzed reactions. Fischer chromium aminocarbene complexes can be used as nucleophiles in palladium-catalyzed allyUc substitution reactions with aUylic acetates and carbonates, alFording the corresponding allyl-substituted aminocarbenes. For example, reaction of the Uthiated carbene (15) gives (16) in good yield (Scheme 25). ... 

These peptide enolates could also be used as excellent nucleophiles in palladium-catalyzed allylic alkylations. Reactions of numerous dipeptides (e.g. 263) with different allylic substrates (e.g. 264) and [AllPdClja as catalyst delivered (S,/f)-configured peptides with y,5-unsaturated side chains (265), usually in high yields and diastereoselectivities (equation 69). 

This methodology has been used to provide efficient protocols for the asymmetric allylic alkylation of p-keto esters, ketone enolates, barbituric acid derivatives, and nitroalkanes. Several natural products and analogs have been accessed using asymmetric desymmetrization of substrates with carbon nucleophiles. The palladium-catalyzed reaction of a dibenzoate with a sulfonylsuccinimide gave an advanced intermediate in the synthesis of L-showdomycin (eq 3). ... 

Reactions with Nitrogen Nucleophiles. The palladium(O)-catalyzed asymmetric desymmetrization of cw-3,5-dibenzoyloxy-1-cyclopentene, with 6-chloropurine and 2-amino-6-chloropurine as nucleophiles, has been utilized in the synthesis of (-)-carbovir and (—)-neplanocin. In these examples, the diphenylethanediamine and the anthracenyldiamine based ligands were found to be superior to the standard ligand. 

Cyclic 1,2-diketones, such as3-methylcyclopentane-l,2-dione, act as oxygen nucleophiles in palladium(0)-catalyzed reactions with a range of cyclic and acyclic allylic esters. The products of these reactions were subjected to a lanthanide-catalyzed Claisen rearrangement to access the C-alkylated products. 

Reactions with Sulfur Nucleophiles. The use of sulfur nucleophiles in palladium-catalyzed allylic substitution reactions is less well documented than that of carbon, nitrogen and oxygen nucleophiles. The asymmetric synthesis of allylic sulfones utilizing a catalytic phase transfer system has been used to produce (35)-(phenylsulfonyl)cyclohex-l-ene on a 45 g scale (eq 10). In many cases, it has been reported that allylic carbonates are more reactive than allylic acetates in asymmetric allylic substitution... 

It is interesting that in essence complex (XX) is the result of cyclopentadienyl transfer from nickel to the iron atom. In Maitlis s opinion (180) the reaction mechanism resembles the tetraphenylcyclobutadiene transfer from palladium to the iron atom. In terms of CO substitution in the Fe and Ni carbonyls these are nucleophilic reactions in which nickelocene plays the role of a nucleophile. 

Jutand, A. Dual role of nucleophiles in palladium-catalyzed Heck, Stille, and Sonogashira reactions. Pure Appl. Chem. 2004, 76, 565-576. Li, C.-J., Slaven, W. T., John, V. T., Banerjee, S. Palladium catalyzed polymerization of aryl diiodides with acetylene gas in aqueous medium a novel synthesis of areneethynylene polymers and oligomers. Chem. Commun. 1997,1569-1570. 

The research group of Trost has shown that stabilized enolates derived from -diesters and a-phe-nylsulfonyl esters are excellent nucleophiles for palladium(0)-catalyzed reactions with allylic acetates. Since these reactions involve ir-allylpdladium intermediates, they proceed with net retention of configuration and, therefore, differ from traditional displacement reactions where inversion is the rule. Moreover, the transition metal imposes a template effect on intramolecular versions of these reactions and... 

Wacker-type oxidative reactions of olefins with nucleophiles, reactions of zr-allyl-palladium complexes with nucleophiles, reactions based on chelation, and trans-metallation of organomercury compounds. 

Although anionic species have proven useful in the preparation of C-glycosides and C-disaccharides, substantial versatility is available from the use of neutral palladium mediated couplings discussed in Chapter four and presented in Scheme 8.8.1. Such reactions, applied to non-aromatic systems, were demonstrated by Engelbrecht, et al.,30 in the reaction of electron deficient species with glycosidic carbonates. The reactions, shown in Scheme 8.9.4, incorporate diethyl malonate as the nucleophilic species. Palladium was used to effect the coupling of this compound to unsaturated sugars. When the more... 

Palladium-catalyzed reactions have been widely investigated and have become an indispensable synthetic tool for constructing carbon-carbon and carbon-heteroatom bonds in organic synthesis. Especially, the Tsuji-Trost reaction and palladium(II)-catalyzed cyclization reaction are representative of palladium-catalyzed reactions. These reactions are based on the electrophilic nature of palladium intermediates, such as n-allylpalladium and (Ti-alkyne)palladium complexes. Recently, it has been revealed that certain palladium intermediates, such as bis-7i-allylpalladium, vinylpalladium, and arylpalladium, act as a nucleophile and react with electron-deficient carbon-heteroatom and carbon-carbon multiple bonds [1]. Palladium-catalyzed nucleophilic reactions are classified into three categories as shown in Scheme 1 (a) nucleophilic and amphiphilic reactions of bis-n-allylpalladium, (b) nucleophilic reactions of allylmetals, which are catalytically generated from n-allylpalladium, with carbon-heteroatom double bonds, and (c) nucleophilic reaction of vinyl- and arylpalladium with carbon-heteroatom multiple bonds. According to this classification, recent developments of palladium-catalyzed nucleophilic reactions are described in this chapter. 

A number of nucleophilic reactions of the olefins (CFs)2C CX CFs (X = CF3.H, or F) have been described. Addition of methanol yields (CF3)aCH CX(CFs) OMe, in a reaction which requires triethylamine as basic catalyst, except where the substituent is fluorine, substitution of fluorine by a dimethylamino-group occurring upon reaction of (CF3)2C CF-CF3 with dimethylamine and water, and metfaylamine adds to (CF3)2C CF CF3. Chlorine readily adds photochemically to the olefins, and all except the most hindered (CF3)sC C(CF3)3 undergo ready hydrogenation in the presence of palladium on alumina (see pp. 63,83 for other catalytic reductions). 

Allylic aeetates or carbonates can undergo nucleophilic substitutions via palla-dium(0)-catalysis (11). In this paper, we report on the extension of this reaction to unsaturated fatty aeids by the preparation of allyl carbonates and acetates of oleic, linoleic, and 10-undecenoic acid and their substitution with carbon- and heteroatom-nucleophiles by palladium(0)-catalysis. In this way, different substituents can be in-trodueed into the alkyl chain of fatty acids. This leads to fatty acid derivatives in which the properties of biologically active compounds may possibly be combined with the amphiphilic property of the fatty acid. 

---