Bromination using catalytic pyridine

Reduetive alkylation of heteroaromatic rings is possible using catalytic hydrogenation. 34 Cyclization of the substituted pyridine 442 was induced by treatment with triphenylphosphine bromine, and generated pyridinium salt 443. Isolation of 443 by Sonnet was followed by hydrogenation with platinum, generating the trail pheromone of the Pharaoh ant (3-butyl-5-methyloctahydroindolizine, 444). 35... 

Bromine(iii) fluoride has been shown to form a colourless 1 1 adduct with pyridine in CFCI3 solution at —78°C this new compound is stable up to ca. 110°C in the absence of water.Naumann and Lehmann have also demonstrated that BrF, disproportionates in CFCI3 into BrFj and BrF in the presence of a catalytic amount of CsF. The fluorination of Br2 by F2 in an electric glow discharge produces BrF, almost quantitatively. When NF, was used as the fluorinating agent a mixture of BrF, and BrF, resulted, rather than bromodi-fluoroamine. 

The asymmetric bromination of (3-dicarbonyl compounds was accomplished using a catalytic amount of a chiral primary amine catalyst, with pyridine dicarboxylic acid (PDA) as the co-catalyst and 3,3-dibromo-5,5-dimethylcyclo-hexa-l,3-dione as the bromine source (Scheme 13.25) [55]. The substrate scope was quite broad and included cyclic and acyclic (3-ketoesters, acycfic p-diketones, and the cyclic ketones cyclopentanone and cyclohexanone. Additionally, the conditions for chlorination of (3-dicarbonyl compounds using the benzoylquinidine catalyst depicted in Scheme 13.15 were adapted for the bromination of two substrates [35]. 

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