Palladacycles intramolecular coupling

Acceleration of the intramolecular coupling of phenol and aryl halide moieties that is effected with a fJC-palladacycle by a base is realized. o-AminophenyIdiphenylphosphine is a ligand that forms effective Pd complexes for the Heck reaction. ... 

This conversion of an acyclic bisdiene to a cychzed enediene constitutes a new Pd-mediated reaction mode, which can be rationalized as outlined in Scheme 7. Com-plexation of bisdiene 17 following oxidative cyclization (i.e., oxidative addition with intramolecular coupling of the diene moieties) affords palladacycle 20. Protonation in an... 

Intramolecular Pd-catalyzed aryl-aryl coupling reactions under dehydrohalogenation are assumed to proceed via palladacycles as illustrated by the example in Scheme Several mechanistic pathways may explain the cyclopalladation step... 

The first step of the catalytic cycle proposed for this complex reaction consists of the oxidative addition of the aryl iodide reactant to palladium(O) (Scheme 19.11). Subsequent reversible insertion of norbornene into the Pd-Ar bond gives rise to complex 9, which undergoes base-mediated intramolecular C-H activation to give palladacycle 10. Oxidative addition of the primary alkyl iodide furnishes palladium(IV) complex 11, which, after reductive elimination and deinsertion of norbornene, generates a paUadium(II) species (12) able to undergo cross-coupling reactions such as the Mizorold-Heck coupling, as illustrated in Scheme 19.10. 

There has been a summary of computational and experimental studies of the use of palladium complexes with A -heterocyclic carbenes (NHCs) in the asymmetric coupling of -hybridized carbon-hydrogen bonds with aryl halides. It has been shown that the electronic and catalytic properties of NHCs fused to porphyrins may be modified by varying the inner metal in the porphyrin. A DPT study of the use of palladium-NHC complexes in the asymmetric intramolecular a-arylation of 2-bromoaryl amides to give 3,3-disubstituted oxindoles (101) has been reported. The likely pathway involves insertion of the palladium into the arene-bromine bond to form a palladacycle which deprotonates to give an (9-enolate. Conversion into the C-enolate followed by reductive elimination gives the product. The intramolecular reaction of 0 a cyclopropane carbon-hydrogen bond in a 2-bromoanilide derivative has been used to form cyclopropyloxindoles, (102), in a palladium-catalysed, silver-mediated reaction. 

Intramolecular Pd-catalyzed aryl-aryl coupling reactions under dehydrohalogenation are assumed to proceed via palladacycles as illustrated by the example in Scheme 47.[33]-P7] Several mechanistic pathways may explain the cyclopalladation step including the C,H-activation however, a reaction of an electrophilic arylpalladium bromide with the electron-rich phenolate in the sense of an electrophilic aromatic substitution is certainly a plausible explanation. C—C bond formation finally takes place by reductive elimination. 

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