Methyl-pyridines side-chain substitution

Pyridine itself can be converted into 3-nitropyridine only inefficiently by direct nitration even with vigorous conditions, however a pair of methyl groups facilitate electrophilic substitution sufficiently to allow nitration to compete with side-chain oxidation. Steric or/and inductive inhibition of A-nitration allows C-substitution using nitronium tetrafluoroborate, an example is 2,6-dichloropy-ridine dehalogenation of 2,6-dichloro-3-nitropyridine provides a practicable preparation of 3-nitropyridine. ... 

The palladium-catalysed reaction of the pyrazolo-pyrimidine derivative (141) with 3-bromotoluene may result in arylation at the 3-position in the pyrazole ring or at an sp hybridized site in the 7-methyl side-chain depending on the base and ligands used. After initial insertion of the palladium catalyst into the aryl halide bond, palladation of (141) occurs by a concerted metalation-deprotonation pathway and is followed by reductive elimination. Concerted metalation-deprotonation is also likely in the palladium-acetate-catalysed reaction of imidazo[l,2-a]pyridines with aryl bromides to give 3-substituted derivatives such as (142). A careful mechanistic study of the arylation of pyridine A-oxide by bromotoluene, catalysed by palladium acetate and t-butylphosphine, has shown that direct reactions of an aryl palladium complex with... 

The first use of chiral helical polymers bearing no chiral side chains for chiral reaction induction was realized by Reggelin et at. in 2002 [69]. Two poly(methyl methacrylate)-based chiral polymers (40) was prepared by hehx-sense selective anionic polymerization of sterically congested methacrylates with a chiral base mixture as initiator. The pyridine moieties in helical polymers allowed various metal coordinations [70] or formation of ionic pairs [71]. Their complexes with palladium precursor were found to be active catalysts for the allyHc substitution reaction of l,3-diphenylprop-2-enyl acetate (Figure 4.36). Although the ee values were only moderate (<33%), this research opened up a new area for asymmetric catalysis with unnatural helical chiral polymers. 

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