Palladium(0)-catalyzed cycloisomerization of enallenes

A novel palladium(0)-catalyzed cycloisomerization of enallenes has been developed. This reaction, catalyzed by [Pd(dba)2] (dba=dibenzylideneacetone) in acetic acid, results in the formation of cyclopentene derivatives and [n.3.0]bicyclic systems (n=3, 4) in good to high yields. The carbon-carbon bond-forming step is highly stereoselective to give cis-fused bicyclic systems. The presence of acetic acid as solvent and dba as ligand for palladium(0) turned out to be essential for the reaction in order to provide good reactivity and regioselectivity.     

Palladium(II)-catalyzed synthesis of functionalized indenes from o-alkynylbenzylidene ketones

An efficient method for the synthesis of functionalized indenes from o-alkynylbenzylidene ketones under palladium(II) catalysis was developed. The reaction is initiated by trans-nucleopalladation of alkynes, followed by conjugate addition and quenched by protonolysis of the carbon-palladium bond. With acetate and halide ions as nucleophiles, 3-acetoxy- and 3-halogen-substituted indenes could be obtained in high yields.     

Palladium(0)-catalyzed amination of allylic natural terpenic functionalized olefins

The palladium(0) catalyzed amination of allylic acetates and carbonates derivatives from terpenic olefins was carried out under mild conditions. The reaction offers a very good method for the preparation of allylic amines and thus to provide a useful entry to new functionalized terpenic olefin products. The mechanism involving a formation of p-allyl-palladium intermediate complex is in good agreement with the results obtained with the optically active substrates, as well as via an analysis of the observed regio-and stereoselectivity.      

Palladium(II)-catalyzed Amination of Isoprene with Aniline

The reaction of isoprene with aniline, catalyzed by the Pd(acac)₂-(RO)₃P-CF₃CO₂H system, 1 : 4 : 4 [R = Me, Et; acac = (CH₃CO)₂CH], in MeCN provides N-(3-methylbut-2-en-1-yl)aniline with a high selectivity (up to 84%) and a nearly quantitative yield (75%). At 1 : 4 : 20 and 1 : 4 : 40 molar component ratios in the catalytic system, up to 28–31% of N,N-(2,3-dimethylprop-2-en-1-yl)aniline is formed. Telomeric reaction products appear at 1 : 2 : 4 and 1 : 1 : 10 ratios.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 6, 2005, pp. 963–968.Original Russian Text Copyright © 2005 by Petrushkina, Mysova, Orlinkov.     

Palladium(II)-catalyzed intramolecular diamination of unfunctionalized alkenes

Intramolecular diamination reactions are described which yield cyclic ureas as direct products of an oxidative alkene transformation in the presence of palladium acetate and iodosobenzene diacetate as terminal oxidant. The reaction is truly catalytic in metal catalyst and represents the proof of principle for this elusive type of alkene oxidation.     

Palladium(II)-catalyzed transfer vinylation of protected monosaccharides

A method for the catalytic vinylation of protected monosaccharides bearing a single free hydroxyl function has been developed. Reaction of representative primary, secondary, and anomeric sugar hydroxyl functions with butyl vinyl ether as the reactant and solvent and (phen)Pd(OAc)(2) (phen = 1,10-phenanthroline ligand) as the catalyst gives the corresponding vinylated sugar products in 36-79% yield. The catalyst requires the presence of traces of oxygen in the reaction mixture to prevent decomposition to Pd(0).     

Palladium(II)-catalyzed direct alkenylation of nonaromatic enamides

A mild and efficient method for the direct alkenylation of nonaromatic enamides was achieved through a palladium(II)-catalyzed C-H functionalization. The reaction scope includes cyclic and acyclic enamides and a range of activated alkenes. This approach represents the first successful direct C(3)-functionalization of nonaromatic cyclic enamides.     

Palladium(II)-catalyzed direct intermolecular alkenylation of chromones

A new efficient method for the direct alkenylation of chromones via a palladium(II)-catalyzed C-H functionalization reaction was developed. The use of pivalic acid with Cu(OAc)(3)/Ag(2)CO(3) provided superior reactivity in the cross-coupling of chromones with alkene partners. This approach represents a significant advance over the existing two-step method and afforded various 3-vinylchromone derivatives, which are privileged structures in many biologically active compounds and versatile synthetic building blocks.     

Palladium(II)- and mercury(II)-catalyzed rearrangements of propargyl acetates

The scope and utility of the metal-catalyzed rearrangement of propargyl acetates first reported by Rautenstrauch were expanded. Treatment of a series of appropriate acetate substrates with Pd(II)- and Hg(II)-catalysts afforded synthetically useful fused 5,6-bicyclic-1,4-cyclopentadienyl acetates and 2-cyclopentenones. It was found that the substituents at the terminal alkynyl and alkenyl positions of the acetate substrate had a significant impact on the outcome of the reaction.     

Palladium(II)-catalyzed oxidative homo-coupling of 1,3-dimethyluracil derivatives

A palladium-catalyzed oxidative homo-coupling of 1,3-dimethyluracil was examined. Two types of uracil dimer, C5–C5′ linked dimer and C5–C6′ linked dimer were obtained in variable yields depending on the conditions along with a low yield of C5–C5′ and C6–C5′ linked uracil trimer.     

Palladium(II)-catalyzed isomerization of olefins with tributyltin hydride

A new efficient method for the synthesis of geometrically pure (E)-alkenes from (Z)-alkenes is described. The reaction of aryl- or alkyl-substituted (Z)-alkenes with tributyltin hydride and triethylamine in the presence of a catalytic amount of palladium acetate afforded the corresponding (E)-alkenes in good yields.     

Palladium(II)-catalyzed claisen rearrangement of allyl vinyl ethers

The Claisen rearrangement of allyl vinyl ethers is catalyzed by PdCl₂(CH₃CN)₂, provided that alkyl substituents protect the vinyl ether double bond from coordination by the metal catalyst.     

Palladium(II)-catalyzed addition of arylboronic acid to nitriles

The addition of arylboronic acid to nitriles catalyzed by palladium(II) species in the presence of bipyridine as the ligand was developed. The use of bipyridine is crucial for changing the properties of arylpalladium species from more electrophilic to more nucleophilic making the reaction possible.     

Palladium(II)-catalyzed conjugate addition of arylsiloxanes in water

Palladium-phosphinous acids catalyze the conjugate addition of arylsiloxanes to a wide range of alpha,beta-unsaturated substrates in water. A microwave-assisted procedure is described that uses 5 mol % of POPd1 to afford beta-substituted ketones, aldehydes, esters, nitriles, and nitroalkanes in 83% to 96% yield within 4 h. This method eliminates the need for stoichiometric additives and an excess of arylsiloxane, and does not require an inert atmosphere.     

Palladium(II)-catalyzed direct arylation of enaminones using organotrifluoroborates

A Pd(II)-catalyzed reaction for the direct arylation of cyclic enaminones is reported. The reactivity of electron-rich, electron-poor, and sterically encumbered organotrifluoroborates was investigated. This reaction represents a unique use for organotrifluoroborates as coupling partners and discloses the utility of enaminones for direct-functionalization reactions. It provides immediate access to arylpiperidine, indolizidine, and quinolizidine scaffolds from the corresponding mono- and bicyclic, unattenuated enaminones.     

Bi(OTf)3-catalyzed cycloisomerization of aryl-allenes

Intramolecular hydroarylation of allenes was achieved under very mild conditions using bismuth(III) triflate as the catalyst. Efficient functionalization of activated and nonactivated aromatic nuclei led to C-C bond formation through a formal Ar-H activation. A tandem bis-hydroarylation of the allene moiety was also developed giving access to various interesting polycyclic structures.     

Room temperature Au(I)-catalyzed exo-selective cycloisomerization of acetylenic acids: an entry to functionalized gamma-lactones

A highly efficient gold-catalyzed cyclization reaction of various functionalized acetylenic acids is described. The cyclizations are conducted in the presence of Au(I) catalyst in acetonitrile at room temperature in a short reaction time. The reaction conditions are compatible with several functional groups, such as ester, alkene, alkyne, chloro, and free or protected alcohol, and lead to original gamma-lactones in good to excellent yields.     

Palladium(II)-catalyzed oxidative Heck coupling of thiazole-4-carboxylates

Oxidative Heck coupling of thiazole-4-carboxylates via palladium(II)-catalyzed C-H bond activation has been achieved in moderate to good yields. No ligand, and no acidic additive were used in the reaction. The results showed that this protocol tolerated a series of substitutions on the thiazole ring. A preliminary attempt of direct arylation with p-xylene via Pd(II)-catalyzed C-H bond activation has also been done.     

Palladium(II)-catalyzed ring expansion of a 1-alkenyl cyclopentanol

7,7-Dimethyl-2-methylenenorbornan-1-ol, a strained bicyclic 1-alkenyl cyclopentanol, undergoes Wagner-Meerwein rearrangement to fenchone under treatment with a catalytic amount of PdCl₂(PPh₃)₂ in refluxing N-methylpyrrolidin-2-one. The described reaction constitutes the first example of the palladium(II)-catalyzed ring expansion of 1-alkenyl cyclopentanols to the corresponding cyclohexanones.