Palladium phenylation

Palladium compounds are also useful catalysts for oligomerisation and co-oligomerisation reactions. Dimerisation or co-dimerisation of olefins catalysed by palladium(n) chloride or, better, PdCl2(C6H5CN)2 involves a palladium(ii)-hydride intermediate as the catalytically active species. A similar reaction to dimerisation is coupling, e.g. of benzene to give biphenyl, which is also catalysed by palladium(ii) chloride and proceeds via palladium-phenyl u-bonded species. The nature of intermediates in... 

Catalytic reduction of 3-nitro-7-phenyl-l,8-naphthyridin-2(lH)-one (136) with palladium on carbon in 2-ethoxyethanol gave the l,2-di(l,8-... 

Cacchi and Palmier (83T3373) investigated a new entry into the quinoline skeleton by palladium-catalyzed Michael-type reactions. They found that phenyl mercurial 134 was a useful intermediate for the synthesis of quinoline derivatives, and that by selecting the reaction conditions the oxidation level of the heterocyclic ring in the quinoline skeleton can be varied. On such example is shown in Scheme 16. PdCla-catalyzed coupling between organomercurial reagent 134 and enone 135 delivered adduct 136 which was subsequently cyclized to quinoline 137 under acidic conditions. 

Treatment of 4-arylamino-8-iodoquinoline 268 with propargyl alcohol in presence of iodo(phenyl)bis(triphenylphosphine) palladium and copper (I)iodide afforded 269 which upon catalytic reduction using Linder s catalyst gave 4//-pyrrolo[3,2,l-(/]quinoline 270 (97H2395) (Scheme 48). 

The acetate (1) and its mosylate analog (79) have been shown to undergo cydoad-dition with the CN double bond of alkyl imines to generate substituted pyrrolidines in the presence of nickel or palladium catalyst [35]. For example, both the phenyl imine (80) and the diazene (81) gave reasonable yields of adducts (82) and (83) respectively (Scheme 2.23). 

A more expected difference between platinum oxide and palladium-on-carbon was found in the hydrogenolysis of 5-phenyI-2-(3,4-dimethoxybenzyI)-2-oxazoline. Cleavage occurred at the benzyl-oxygen bond over both catalysts, but over platinum, the less substituted phenyl group was saturated as well (78). 

Hydrogenolysis of cxo-2-phenyl-9-oxabicyclo[3.3, l]nonan-2-ol proceeds exclusively with retention over Raney nickel and with inversion over palladium. No reduction with palladium occurred at all until a drop of perchloric acid was added (36). 

Palladium-mediated catalysis has only been exploited relatively recently in the synthesis of substituted PPV derivatives. The use of aryl dibromides as monomers is particularly useful as it allows the synthesis of PPVs substituted with alkyl rather than alkoxy sidechains. The Suzuki [53, 54], Heck [55], and Stille [56] reactions have been used in the synthesis of new PPV derivatives, but attaining high molecular weight PPV derivatives by these methodologies has proved problematic. A phenyl-subslilutcd PPV material PPPV 31 was synthesized by a Suzuki coupling (Scheme 1-10) of dibromoethene and fo/.v-boronic acid 30. Its absorption (2ni ix=385 nm) and emission (2max=475 nm) maxima were strongly... 

Complete reduction of the azepine ring to hexahydroazepine has been effected with hydrogen and palladium,40 or platinum,135 239 catalysts. For example, ethyl 1 f/-azepine-l-carboxylate is reduced quantitatively at room temperature to ethyl hexahydroazepine-l-carboxylate (92% bp 118 —120 3C).134 136 TV-Phenyl-S/Z-azepin -amine (1), however, with platinum(IV) oxide and hydrogen in methanol yields the hexahydroazepine 2 in which the amidine unit is preserved in the final product.34 The same result is obtained using 5% palladium/barium carbonate, or 2 % palladium/Raney nickel, as catalyst. 

At 260 C with palladium on charcoal in an atmosphere of carbon dioxide, 3-benzoyl-l-phenyl-7, 8-dimethoxy-4,5-dihydro-3//-3-benzazepine undergoes dehydrogenation to 3-bcnzoyl-7,8-di-methoxy-l-phenyl-3//-3-benzazepine (mp 166 C) in poor yield (19%)."1... 

Nitro-phenyl)-aerylsaureester und -propansaureester reagieren mit Natriumboranat in Gegenwart von Palladium/Kohle als Katalysator zu cyclischen Hydroxamsau-ren mit Chinolin-Struktur z.B. ... 

An einer mit Palladium bedeckten Graphit-Kathode wird Phenylacetonitril in methano-lischer Salzsaure in einer geteilten Zelle zu 2-Phenyl-athylamin (85% d.Th.) reduziert9. 

Other examples that involve intermediate allyl cations are illustrated in Scheme 1.4. The cationic palladium(II) complex [Pd(dppp)(PhCN)2](BF4)2 coordinates the carbonyl oxygen of benzaldehyde and the activated carbonyl carbon attacks the isoprene, forming the allyl cation 10 which then cyclizes to give the 4-methyl-6-phenyl-5,6-dihydro-2H-pyran [22]. 2-Oxopropyl acrylate 11, in the presence of trimethylsilyltrifluoromethane sulfonate (TMSOTf) and methoxytrimethylsilane (MeOSMT), generates the cation 11a which is an efficient dienophile that reacts easily with the cyclohexadiene to give the Diels-Alder adduct in good yield [23]. 

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