Oxypalladation palladium compounds

However, if in nonaqueous solutions (discussed next) the oxidations also proceed through oxypalladation adducts, then the two mechanisms of decomposition of the oxypalladation adducts would predict diflFerent products. First, let us consider the mechanism of Jira, Sedlmeier, and Smidt (Reactions 50-53). In this case OH in II (Reaction 52) is replaced by OR. Decomposition via Reaction 55 is impossible, so II must decompose by solvolysis. This would give 1,1-disubstituted ethanes from ethylene oxidation. On the other hand, the first suggestion (Reaction 48) would probably be more consistent with formation of the vinyl compounds since hydride elimination should be completed if a rapid rearrangement of electrons to give acetaldehyde cannot occur. Evidence exists that 1,1-disubstituted ethanes are the initial products in methanol, and in acetic acid it is claimed that both vinyl acetate and 1,1-diace-toxyethane are initial products this suggests that in this solvent competition exists between palladium (II) hydride elimination and acetate attack. However, until now there have been no detailed studies of the oxidation under conditions where 1,1-disubstituted products are formed. More work is needed before the course of the reaction under these conditions is completely understood. 

The electron-transfer reactions from the palladium(0) cenme to the cotndinated quinone in [Pd(ii -COD)(l,4-quinone)] compounds have been studied. Addition of acid was found to initiate a redox reaction to afford a palladium(II) diene compound and hydroquinone. In some cases, further reacticm to give oxypalladated derivatives was observed. 

B.i.b. Alkynes Containing Proximate 1,3-Dicarbonyl Groups. 2-Propargyl-1,3-dicarbonyl compounds react with alkenyl triflates or alkenyl/aryl/heteroaryl halides to give 2,3,5-trisubstituted-furans (Scheme 4). The process probably proceeds through an oxypalladation step that involves a nucleophilic attack of a stabilized enolate across the activated carbon-carbon triple bond, reductive elimination of a palladium(0) species from the resultant oxypalladation adduct, and isomerization of the initially formed alkylidene derivative. 

The oxidative addition reactions to alkenes promoted or catalyzed by PdCl2(CH3CN)2 have been classified based on the nature of the attacking species. Oxygen nucleophiles such as water, alcohols and carboxylic acids undergo oxypalladation, while ammonia, amines and their derivatives are typical nucleophiles for aminopalladation. Carbopalladation with active methylene compounds is also discussed The palladium-catalyzed intramolecular hetero- and carbopalladation of olefins is extensively used as the ring-forming step in the synthesis of a variety of heterocyclic and carbocyclic systems, and representative examples are provided. 

The palladium(II)-catalyzed olefin carbonylation reaction was first reported more than 30 years ago in studies by Stille and co-workers and James et al. The reaction of carbon monoxide with cis- and tra 5-but-2-ene in methanol in the presence of palladium(II)-chloride and copper(II)-chloride yielded threo- and eryt/zro-3-methoxy-2-methyl-butanoate, respectively. The transformation that was based on the well-known Wacker process for oxidation of ethylene into acetaldehyde in water " is now broadly defined as the Pd(II)-catalyzed oxycarbonylation of the unsaturated carbon-carbon bonds. This domino reaction includes oxypalladation of alkenes, migratory insertion of carbon monoxide, and alkoxylation. Since the development of this process, several transformations mediated by palladium(II) compounds have been described. The direct oxidative bisfunctionalization of alkenes represents a powerful transformation in the field of chemical synthesis. Palladium(II)-promoted carbonylation of alkenes in the presence of water/alcohol may lead to alkyl carboxylic acids (hydrocarboxylation), diesters [bis(aIkoxycarbonyla-tion)], (3-alkoxy carboxylic acids (alkoxy-carboxylation), or (3-alkoxy esters (alkoxy-carbonylation or alkoxy-alkoxy-carbonylation). Particularly attractive features of these multitransformation processes include the following ... 

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