Palladium complexes pyridine oxides

Figure 6.16. Aerobic oxidation of 1-phenylethanol catalysed by palladium complexes of a fluorous pyridine...

The asymmetric Baeyer-Villiger oxidation using a palladium complex of 2-(phosphinophenyl)pyridine ligand provides a useful procedure for the synthesis... 

Pd(II) catalysts have been widely used for aerobic oxidation of alcohols. The catalytic systems Pd(OAc)2-(CH3)2SO [14] and Pd(OAc)2-pyridine [15] oxidize allylic and benzylic alcohols to the corresponding aldehydes and ketones. Secondary aliphatic alcohols, with relatively high water solubility, have been oxidized to the corresponding ketones by air at high pressure, at 100 °C in water, by using a water-soluble bathophenanthroline disulfonate palladium complex [PhenS Pd(OAc)2] [5d]. The Pd catalyst has also been successfully used for aerobic oxidative kinetic resolution of secondary alcohols, using (-)-sparteine [16]. 

Oxidative decomplexation of palladium complexes obtained via methanol addition to norbor-nadiene with Collin s reagent [chromium(Vl)oxide-pyridine)2] leads to norbornenones 32 and nortricyclenones 33. ... 

Intramolecular oxidative aminations of olefins have alsobeen studied, and many of these intramolecular processes were observed prior to the analogous intermolecular variants. The oxidative aminations of alkenes with arylamines and arylamine derivatives catalyzed by palladium complexes were shown by Hegedus to form indoles (Equation 16.120). These reactions were conducted with orf/io-allylaniline and ort/zo-allylaniline derivatives as substrate, Pd(NCMe)jCl2 as catalyst, and benzoquinone as oxidant. Intramolecular reactions of N-tosylated aliphatic amines were reported by Larock. ° For example, the tosylamide in Equation 16.121 imdergoes cyclization in high yield in the presence of dioxygen with Pd(OAc)j as catalyst in DMSO. A related reaction (Equation 16.122) was reported recently in toluene solvent with added pyridine. ... 

The C—H activation of pyridines has been coupled with a P—C bond-forming reaction to provide a selective method for the formation of arylphosphine oxides (Scheme 4.206) [342]. The catalyst system was comprised of a common palladium complex along with... 

High-oxidation-state palladium complexes are frequently involved in oxidative C-H functionalization processes [43]. Generally, a Pd(II) intermediate that is formed via CH activation or oxidative addition to C-X is oxidized further to the corresponding high-oxidation-state Pd intermediate (see Figure 4.11). For C-H to C-C or C-X bond transformations, mononuclear Pd(IV) and also dinuclear Pd(III)-Pd(III) complexes have been proposed to be involved for substrates based on the 2-phenyl pyridine framework [44]. The irreversible C-C or C-X... 

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... 

Palladium. Flame AAS analysis of Pd is described in P CAM 173 however, it would probably be preferred to use graphite furnace atomization as in S-191 Pt, soluble salts. An oxidizing air-acetylene flame is used for Pd AAS to minimize interferences from Al, Co, Ni, Pt, as well as Rh and Ru. These interferences may be minimized by complexation of Pd as the bis-pyridine-dithiocyanate (13) and extraction into hexone (3). Interferences may be minimized by the addition of 1000 ppm La. The 244.8 and 247.6 nm lines have equal sensitivity however, the 247.6 nm line is generally preferred ( 3). No Federal standard exists for Pd however, in analogy to Ni and Pt, Pd should be treated with caution. 

A Pd-catalyzed oxidative cyclization of phenols with oxygen as stoichiometric oxidant in the noncoordinating solvent toluene has been developed for the synthesis of dihydrobenzo[ ]furans (Equation 136). Asymmetric variants of this Wacker-type cyclization have been reported by Hayashi and co-workers employing cationic palladium/2,2 -bis(oxazolin-2-yl)-l,l -binaphthyl (boxax) complexes <1998JOC5071>. Stoltz and co-workers have reported ee s of up to 90% when (—)-sparteine is used as a chiral base instead of pyridine <2003AGE2892, 2005JA17778>. Attempts to effect such a heteroatom cyclization with primary alcohols as substrates, on the other hand, led to product mixtures contaminated with aldehydes and alkene isomers, which is in contrast to the reactions with the Pd(ii)/02 system in DMSO <1995TL7749>. 

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