Carbon-hydrogen bonds palladium© bromide

Step 6. Reductive elimination. Sodium carbonate is present in the reaction mixture in stoichiometric amounts. Carbonate reacts with the palladium-hydrogen bond, and bromide is released. At the end of step 6, the catalyst is regenerated as Pd(0), and the reaction cycle starts again. Base is required in the reductive elimination step. 

Catalytic hydrogenation of (23-12) over palladium on charcoal results in the scission of the weak N—O bond and the formation of amino alcohol (24-1). This is converted to a pyrrolidine by an internal alkylation reaction. Thus, reaction of the intermediate with carbon tetrabromide and triphenyl phosphine presumably converts the alcohol to a bromide internal displacement by the primary amine forms the five-membered ring (24-2). Alkylation of that amine with the complex bromo amide (24-3) then affords the endothehn antagonist atrasentan (24-4) [25]. 

Examples of the formylation of aryl halides with synthesis gas catalyzed by palladium complexes are summarized in Equation 19.90. These reactions relied upon the development of ligands with particular steric and electronic properties. The dia-damantyl-n-butyl phosphine shown in the equation, in combination with palladium acetate, leads to the formation of aromatic aldehydes in high yields from electron-rich and electron-poor aryl bromides. Reactions of nitroarenes and 2-bromopyridine provided the aldehydes in low yield, but other examples occurred in satisfactor) yield with only 0.1-0.75 mol % catalyst. The identity of the base is important in this process, and TMEDA was the most effective base. The mechanism of this process was not proposed in the initial work, but is likely to occur by oxidative addition of the aryl halide, insertion of the carbon monoxide into the palladium-aryl bond, and a combination of hydrogenolysis of the acyl intermediate and elimination of hydrogen halide to regenerate palladium(O). The base would then be involved in the hydrogenol5 sis and consumption of hydrogen halide. 

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