Palladium catalysis bromination

Lopez-Rodriguez and co-workers prepared a number of serotonin 5-HTia receptor ligands using palladium catalysis [133]. The Spanish group used both DPPP- and BINAP-based systems to couple bromine-substituted benzimidazoles with piperazines. For example, the reaction of the protected heterocycle below with M-methylpiperazine proceeds in excellent yield, Eq. (166). 

It has been shown that C-H bond activation in bromothiophenes may be readily achieved by palladium catalysis in the presence of the reagent combination AgNOa/KF, for instance as illustrated by the synthesis of the 2,2 -bithiophene 45 from 2-bromothiophene 46, providing access to a variety of brominated thiophene derivatives suitable for further functionalization <050L5083>. 

Amination under palladium-catalysis is possible using hydroxylamines as electrophiles.Bromination and chlorination can be performed with N-halosuccinimides or PhICb, while iodine can be used directly. In case of PhICl2, the catalytic cycle involves palladium(III) intermediates.A diastereoselective method for the iodination of aromatic compounds was used by the Yu group (Scheme 5-196). 

The C—I bond is very unstable and more reactive than C—Br, C—Cl and C—F bonds. Iodine is the most expensive of the common halogens and is much less frequently used in synthesis than bromine, chlorine or fluorine. Organometallic reactions proceed with iodinated aliphatic or aromatic compounds more easily than with the other halogens. Noble metal catalysis with palladium complexes is most effective with iodinated compounds. A useful synthetic procedure is the facile reduction of iodinated derivatives under mild conditions. Replacement of iodine by hydrogen at an sp carbon is an exothermic reaction with A// = -25 kJ mol . ... 

Keywords Aromaticity Bromination Diels-Alder reaction Electrophilic substitution Furan Indophenine Isatin Metallatimi Palladium(O) catalysis Pyrrole S-oxidation Sulfur lone pair Thiophene numbering Viktor Meyer TT-System... 

P-aminoacyliron complexes in moderate yield and good diastereomeric excess. Deallylation of these products using palladium(O) catalysis gives the corresponding homochiral secondary amines. On oxidative demetalation with bromine or -bromo-succinimide, concomitant cycli2ation occurs to afford P-lactams (Scheme 4-48). ... 

---