Pd-H elimination reactions in palladium(II) allylic complexes

The ease of H elimination from the 4- (beta-) position in a series of allylic complexes [Pd(5-C(6)F(5)-1-3-eta(3)-cyclohexenyl)XL](n+) (X, L = Br, N-, P-donor, C(6)Cl(2)F(3); n = -1, 0, +1) was compared by analyzing their decomposition products at 50 degrees C. Pd-H elimination does not occur for cationic complexes, whereas it is the main decomposition pathway for neutral and anionic complexes. In addition to the charge of the complex, the ease of this Pd-H elimination is determined by the trans influence of the ligands (aryl > PMe(3) > Br, N-donor).     

Ligand control in palladium—catalyzed coupling reactions between organozirconium compounds and allylic species

A (π-allylic)Pd(II) complex can serve as a catalyst precursor for selective coupling between allylic halides or acetates and alkenylsirconium complexes.     

钯配合物催化的芳基-芳基不对称偶联反应

本文以三种匀性膦作配体制成了零价钯配合物, 并分虽试验了由它们催化苯酚得到的α-溴-β-苄氧基萘和进一步衍生而得的格氏试剂的偶联反应, 制成了β'β'-二苄氧基-α', α'-联萘.     

Umpolung in allylic phosphonates. Regioselective reaction of acetoxy allylic phosphonates with nucleophiles catalyzed by palladium(0) complex

Vinylic phosphonates with functional groups can be synthesized regioselectively by the reaction of acetoxy allylic phosphonates with soft carbon nucleophiles in the presence of bis(trimethylsilyl)acetamide (BSA) under palladium(0) catalysis with moderate to good yields.     

Direct palladium(0)-catalyzed amination of allylic alcohols with aminonaphthalenes

The direct activation of CO bonds in allylic alcohols by palladium complexes has been accelerated by carrying out the reactions in the presence of titanium reagents. The palladium-catalyzed amination of allylic alcohols using aminonaphthalenes gave N-allylic naphthylamines in good yields. The monoallylation products are formed in the main.     

Highly regio- and chemoselective palladium(0)-mediated allylic substitution of difunctional allylic halides with phenols

An efficient Pd(0)-mediated, base-assisted reaction of phenols with difunctionalised allylic halides results in the formation of coupled products in good yields. The reactions proceed with excellent stereo-, regio- and chemocontrol. An appropriately functionalised Weinreb amide, synthesised by this methodology, undergoes halogen-lithium exchange and subsequent intramolecular 1,2-carbonyl addition/elimination to give an advanced macrocyclic intermediate with potential use in the synthesis of likonide B.     

One-pot synthesis of tetrahydrofuran derivatives from allylic alcohols and vinyl ethers by means of palladium(II) acetate

Treatment of a mixture of allylic alcohol and vinyl ether in the presence of Pd(OAc)₂ provides 2-alkoxy-4-alkenyltetrahydrofuran in good yield.     

Synthesis of conjugated trienes by palladium(0) catalysed cross coupling

2-Bromo-1-ethenyl-3,4-dihydronaphthalene (1) is subjected to palladium(0) catalysed coupling to a series of vinyl and aryl iodides via a bromozinc intermediate; the products when heated undergo 6π-electrocyclic ring closure.     

Reductive displacement of allylic acetates by hydride transfer via catalytic activation by palladium(0) complexes

Allylic acetates are reduced to alkenes by reductive displacement by hydride reagents via catalytic activation with Pd(0) complexes. In the absence of hydrides, allylic acetates afford conjugated dienes in DMSO solvent.     

Enantioselective synthesis of acyclic allylic esters catalyzed by a palladium/BINAP(S) system

The synthesis of chiral nonracemic acyclic allylic pivalates via the Pd-catalyzed allylic substitution of racemic allylic carbonates is presented. Good to excellent enantioselectivities (up to 90%) were observed in several cases. An extraordinarily high preference for the production of the branched regioisomeric product is seen when starting from 3-buten-2-yl and crotyl substrates. A significant kinetic resolution (k_rel = 38) of the 1,3-dimethylallyl substrate was also observed, leading to the production of esters of both enantiomers of an allylic alcohol with a single enantiomer of catalyst.     

Oxidative addition of N-halosuccinimides to palladium(0): the discovery of neutral palladium(II) imidate complexes, which enhance Stille coupling of allylic and benzylic halides

The Stille coupling of organostannanes and organohalides, mediated by air and moisture stable palladium(II) phosphine complexes containing succinimide or phthalimide (imidate) ligands, has been investigated. An efficient synthetic route to several palladium(II) complexes containing succinimide and phthalimide ligands, has been developed. cis-Bromobis(triphenylphosphine)(N-succinimide)palladium(II) [(Ph₃P)₂Pd(N-Succ)Br] is shown to mediate the Stille coupling of allylic and benzylic halides with alkenyl, aryl and allyl stannanes. In competition experiments between 4-nitrobromobenzene and benzyl bromide with a cis-stannylvinyl ester, (Ph₃P)₂Pd(N-Succ)Br preferentially cross-couples benzyl bromide, whereas with other commonly employed precatalysts 4-nitrobromobenzene undergoes preferential cross-coupling. Furthermore, preferential reaction of deactivated benzyl bromides over activated benzyl bromides is observed for the first time. The type of halide and presence of a succinimide ligand are essential for effective Stille coupling. The type of phosphine ligand is also shown to alter the catalytic activity of palladium(II) succinimide complexes.     

Microwave-assisted aqueous Suzuki coupling reactions catalyzed by ionic palladium(II) complexes

Suzuki coupling is one of the most powerful methods for the synthesis of biaryls. We have prepared and characterized a series of unsymmetrical sulfonated water-soluble Pd(II)-pyridyl imine complexes and investigated them as catalysts for the Suzuki cross-coupling reaction in water under microwave irradiation. The compounds proved to be effective catalysts.     

Oxidative coupling of 5-membered heterocyclic compounds catalyzed by palladium(II)

Coupled heterocycles (bithiophenes, bifurans, furyl thiophenes) have been obtained in high yields via the reaction of thiophene and furan with palladium salts in solution at 50–100°C.

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50–100° (, , ) .

     

Oxidative coupling of furan derivatives to bifurans catalyzed by palladium(II)

Furan and its 2-substituted derivatives (substituents: –CH₃, –CHO, –COOCH₃, –COOC₂H₅, –CH(OOCCH₃)₂) have been shown to react with palladium acetate in solution at 90–130°C giving the corresponding bifuran derivatives in high yields. The following order of activities has been obtained: –H, –CH₃, –CHO>–COOCH₃, –COOC₂H₅, –CH(OOCCH₃)₂>–COOH, which corresponds to the substituent effect in electrophilic substitution in heteroaromatic compounds.

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, 2- (: –CH₃, –CHO, –COOCH₃, –COOC₂H₅, –CH(OOCCH₃)₂) 90–130° . : –H, –CH₃, –CHO>–COOCH₃, –COOC₂H₅, –CH(OOCCH₃)₂>–COOH, .

     

cis-Bis(di­methyl sulfoxide-S)­dinitrato­palladium(II) and cis-dinitratobis(1,4-oxathiane-S)­palladium(II)

The Pd atom in each of the two title compounds, [Pd(NO₃)₂(C₂H₆OS)₂], (I), and [Pd(NO₃)₂(C₄H₈OS)₂], (II), coordinates two O atoms from two nitrate ligands and two S atoms from di­methyl sulfoxide (dmso) and thio­xane (systematic name: 1,4-oxathiane) ligands in a pseudo-square-planar cis-geometry. In the dmso complex, the distances to palladium are Pd—O 2.067 (2) and 2.072 (2) Å, and Pd—S 2.2307 (11) and 2.2530 (8) Å. The corresponding distances in the thio­xane complex are Pd—O 2.053 (3) and 2.076 (2) Å, and Pd—S 2.2595 (9) and 2.2627 (11) Å. Both compounds may be regarded as dimers with an inversion centre, where one of the coordinating nitrate O atoms in one mol­ecule also interacts with the Pd atom in the adjacent mol­ecule, with Pd—O distances of 2.849 (9) and 3.31 (3) Å in (I) and (II), respectively.