Pyridines olefinations, palladium® acetate

The Heck reactions depicted so far all involve the coupling of halopyridines and other olefins. The alternate approach, coupling of a vinylpyridine with an aryl halide is also feasible, although less commonly employed. 4-Vinylpyridine was coupled successfully with diethyl 4-bromobenzylphosphonate (7.50.) in the presence of a highly active catalyst system consisting of palladium acetate and tn-o-tolylphosphine to give the desired product in 89% yield, which was used for grafting the pyridine moiety onto metal oxides.70... 

The use of palladium and ruthenium as halogen-free carbonylation catalysts has been studied intensively by Shell. The catalysts were principally designed for the carbonylation of olefins in the presence of alcohols in order to yield carboxylic esters [26], but work also well for the synthesis of carboxylic acids or anhydrides. The latter are formed when the reaction is conducted in an acid as a solvent [27]. The palladium systems typically consist of palladium acetate, tertiary phosphines, and strong acids such as mineral acids or acids with weak or noncoordinating anions such as p-toluenesulfonic acid. Remarkable activities are achieved when aromatic phosphines that carry pyridines as substituents are... 

In 2011, the same group reported unprecedented C3-selective functionalization of pyridine derivatives. The oxidative coupling catalyzed by palladium acetate/l,10-phenanthroline/Ag2CO3 under air afforded the desired olefination product in up to good yields (Scheme 9.7). Moreover, a significant kinetic isotope effect was observed, which is consistent with metal-mediated C-H bond cleavage. 

Iodination of 4-amino-3-nitrobenzoic acid 9a with iodine monochloride followed by esterification gives iodide 9b. Acylation of 9b with hot acetic anhydride provides amide 9c. Palladium catalyses coupling of amide 9c with Z-vinylstanne [45], generate cis olefin 9d. Treatment of 9d with osmium tetraoxide followed by acetylation with acetic anhydride in pyridine gives triol 9e. 

The synthesis of uleine (610) required that the stereochemistry of the ethyl side chain be inverted and this was accomplished by thermal (cis) elimination of acetic acid from the acetoxy ketone 625. One of the products was the tetracyclic olefin 628, and reduction with palladium catalyst and a trace of pyridine gave almost exclusively the required cts,c/s-ketone 629. This compound was cyclized and reduced as before to give uleine (610 Scheme 40). 

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