Oxypalladation carboxylic acid/alcohol reactions

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. 

Thereafter, a serial of palladium-catalyzed intramolecular C-ff activation of allylic C-H bonds (Scheme 2.4) was reported by White [9], who first developed a novel route for accessing chiral syn-l,2-amino alcohols enabled through the discovery of a Pd/sulfoxide-catalyzed diastereoselective allylic C-H activation reaction of chiral homoallylic Af-tosyl carbamates. The author discovered that the addition of bis-sulfoxide ligands (L-1) to Pd(OAc)2 promoted allylic C-H cleavage of a-olefins versus oxypalladation in the presence of weak oxygen nucleophiles (i.e., carboxylic acids). Evidences presented that the mechanism proceeds via Pd(ll)/sulfoxide-promoted allylic C-H cleavage to furnish a n-allylic palladium intermediate followed by counterion-promoted functionalization with the tethered Af-tosyl carbamate nucleophile. 

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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