Palladium complexes pyrimidine

X = OCH2. Y = CH2O. Crys (91 N) 18 i Figure 42 Novel palladium complexes of macrocyclic pyrimidine ligands. 

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... 

Thermal decarboxylation of pyrimidylcarboxylic organotin esters is another means to prepare the corresponding stannylpyrimidines [33]. This method obviates the intermediacy of lithiated pyrimidine species that would undergo undesired reactions at higher temperatures. The decarboxylation occurs at the activated positions. Therefore, thermal decarboxylation of tributyltin carboxylate 62, derived from refluxing carboxylic acid 61 with bis(tributyltin) oxide, provided 4-stannylpyrimidine 63. Addition of certain Pd(II) complexes such as bis(acetonitrile)palladium(II) dichloride improved the yields, whereas AIBN and illumination failed to significantly affect the yield. 

Heath and Rees corrected the earlier conclusions of Potts et al. (66JOC265) and Sai et al. [81IJC(B)10] who had reacted 1,2,4-triazolo[4,3-a]pyridine with dimethyl acetylenedicarboxylate in boiling toluene and benzene. The latter believed that 3-substituted triazolopyridines 209 and 210 were the products. Heath and Rees repeated the experiments in refluxing benzene and in refluxing toluene both in the presence and absence of 5% palladium-on-charcoal, and showed that under all sets of conditions 3-cyano-4-oxo-4f/-pyrido[l,2-a]pyrimidine-2-carboxylate 212, 5-(2-pyridyl)pyrazole-3,4-dicarboxylate 213, and an adduct 211 were isolated from the complex reaction mixtures in 20%, 20%, and 1% yields, respectively (82CC1280). When the reaction was carried out in methanol, only 3-cyano-4-oxo-4//-pyrido[ 1,2-a]pyrimidine-2-carboxylate 212 was obtained... 

Ruiz J, Villa MD, Cutillas N, Lopez G, de Haro C, Bautista D, Moreno V, Valencia L (2008) Palladium(II) and Platinum(II) Organometallic Complexes with 4, 7-dihydro-5-methyl-7-oxo[l, 2, 4]triazolo[l, 5-a]pyrimidine. Antitumor activity of the platinum compounds. Inorg Chem 47 4490 1505... 

Figure 3.21 Complexes of nickel(ll), palladium(ll) andplatinum(ll) with pyrimidine functionalised carbene ligands.

The oxidative palladium 1 1-insertion complex intermediates (300) and (301) in the coupling reaction between 2,4-dichloropyrimidine, or 5-bromo-2-methanesulfonylpyrimidine, and tetra-kis(triphenylphosphine)- or tetrakis(triisopropyl phosphite)-palladium can be isolated and purified by conventional methods (Scheme 49). The regioselectivity of the insertion reaction in 2,4-dichloropyrimidine is in accord with the 4-regiochemistry in coupling reactions (Section 6.02.5.5.4). The palladized pyrimidines react readily with organnostannnanes, and may serve as catalysts in coupling reactions between the respective pyrimidine precursor and stannanes <90ACS927>. 

Using this procedure, low yields were however obtained for pyrimidine A -oxides, presumably due to catalyst inhibition resulting from complexation of the palladium species by the heterocycle. To overcome this issue, a variety of additives were investigated and copper cyanide was found to provide a large improvement in the efficiency of the arylation reaction (eq 22). 

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