Palladium(0)-catalyzed allylic alkylation of diketoester-dioxinones with allyl acetates under neutral conditions: synthesis of hexasubstituted benzene derivatives

Intermolecular palladium(0)-catalyzed allylic alkylation of diketoester-dioxinones was performed under neutral conditions with 2-alkenyl and 2-cycloalkenyl acetates. Subsequent aromatization using cesium carbonate gave rise to isopropylidene-protected hexasubstituted resorcylates.     

Palladium(0)-catalyzed regioselective and multicomponent synthesis of 1,2,3-trisubstituted 1H-indenes

A multicomponent synthesis of biologically important indenes bearing three substituent groups at the 1-, 2-, and 3-positions from available o-ethynylbenzaldehyde derivatives and organoboron reagents under palladium(0) catalysis is described. A two-component coupling reaction in methanol provides 1H-indenols, whereas a three-component reaction involving secondary aliphatic amines as the third component in DMF affords 1H-indenamines. This method allows combinatorial preparation of unsymmetrically substituted 1H-indenes that cannot be prepared via previous synthetic routes.     

Palladium(0)-catalyzed synthesis of medium-sized heterocycles by using bromoallenes as an allyl dication equivalent

We have developed a highly regio- and stereoselective synthesis of medium-sized heterocycles containing one or two heteroatoms via cyclization of bromoallenes bearing an oxygen, nitrogen, or carbon nucleophilic functionality in the presence of a palladium(0) catalyst and alcohol. In this reaction, bromoallenes act as an allyl dication equivalent, and the intramolecular nucleophilic attack takes place exclusively at the central carbon atom of the allene moiety. Interestingly, bromoallenes having a carbon nucleophile with a five-atom tether afford eight-membered rings with trans-configuration, while those having an oxygen or a nitrogen nucleophile give the corresponding cis-rings selectively. This is the first example that demonstrates the synthesis of medium-sized rings via cyclization of bromoallenes, and this reaction provides a very useful method for a catalytic synthesis of seven- and eight-membered heterocycles without using high dilution conditions.     

Palladium(0) nanoparticle catalyzed cross-coupling of allyl acetates and aryl and vinyl siloxanes

The cross-coupling of allyl acetates and aryl and vinyl siloxanes proceeds readily by the catalysis of in situ generated palladium(0) nanoparticles. The reactions are stereoselective, and (E)-coupling products are obtained both from cis and trans allyl acetates. The coupling with vinyl siloxanes provides a novel protocol for the synthesis of 1,4-pentadienes.     

Palladium(0)-catalyzed cascade one-pot synthesis of isoxazolidines

A highly diastereoselective cascade reaction protocol has been developed for the synthesis of isoxazolidine derivatives utilizing aryl halides, O-homoallyl hydroxylamine and palladium(0) in a one-pot reaction.     

Palladium(O) catalyzed azidation and amination of allyl acetates. Selective synthesis of allyl azides and primary allylamines

Palladium catalyzed reaction of allyl acetates with azide ion gives allyl azides, which are readily converted into the corresponding primary allylamines upon treatment with PPh₃/NaOH.     

Palladium(0)-catalyzed synthesis of chiral ene-allenes using alkenyl trifluoroborates

Enantioenriched allenes serve as chiral transfer reagents, making them attractive synthetic targets. Herein, the synthesis of enantioenriched allenes utilizing a Pd(0)-catalyzed cross-coupling reaction of propargylic carbonates and phosphates with alkenyl trifluoroborates is reported. Di-, tri-, and tetrasubstituted allenes were synthesized in moderate to high optical yields. Several racemic allenes possessing various functional groups were also synthesized.     

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.     

Cu(I)-catalyzed regioselective synthesis of polysubstituted furans from propargylic esters via postulated (2-furyl)carbene complexes

Polysubstituted furan derivatives are regioselective obtained from (bis-alkynyl)methyl carboxylates in the presence of catalytic amounts of copper(I) salts. This multistep process is consistent with the intermediacy of a copper(I) (2-furyl)carbene complex which is intercepted by suitable trapping reagents.     

Palladium(II)-catalyzed intramolecular aminoacetoxylation of sugar derived alkenyl tosylsulfonamide: Total synthesis of l-deoxyallonojirimycin

Palladium catalyzed intramolecular aminoacetoxylation of d-ribose derived alkenyl tosylsulfonamide to deliver l-deoxyallonojirimycin in an overall yield of 19%. The preliminary screening of l-deoxyallonojirimycin against carbohydrate processing enzymes showed moderate inhibitory activity against α-glucosidase (yeast) and α-mannosidases.     

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 cyclization of electron-deficient enynes and enediynes

In the presence of a Pd(0) precatalyst, Pd2(bq)2(nbe)2 or Pd2(dba)3, 1,6-enyne esters were heated in refluxing benzene to give cyclodimers as single regioisomers. On the other hand, the combination of the Pd(0) precatalyst and triphenyl phosphite gave rise to various cycloisomerization products depending on the substitution pattern of the enyne esters. Six-membered ring cycloisomerization products were predominantly obtained from enyne esters bearing methallyl or 2-phenyl-2-propenyl moieties, while other enyne esters afforded normal five-membered ring cycloisomerization products. Intramolecular [2 + 2 + 2] cyclocotrimerization of enediyne esters also proceeded in the presence of the Pd(0) precatalyst and triphenylphosphine to give fused cyclohexadienes.     

Palladium(0)-catalyzed cross-benzannulation between conjugated enynes. reactivity-controlled synthesis of multifunctionalized benzenes

The synthesis of multifunctionalizbenzenes such as polysubstituted alkoxycarbonyl- or cyanostyrenes was carried out by the regioselective cross-benzannulation between conjugated enynes in the presence of Pd(PPh(3))(4).     

Palladium(II)-catalyzed double carbonylation of organic halides in the presence of amines: α-Ketoamide synthesis

Aryl, hetero-aryl, and vinylic halides react with carbon monoxide (40 atm pressure or less) and a secondary amine at 60–100°C in the presence of a catalytic amount of palladium compound to form α-ketoamides, in addition to simple amides as by-products. When a primary amine was used in place of a secondary one, an imine of the α-ketoamide was readily obtained.     

Chiral Palladium(II)-catalyzed asymmetric glyoxylate-Ene reaction: alternative approach to the enantioselective synthesis of alpha-hydroxy esters

An effective chiral palladium catalyst [Pd(CH(3)CN)(2)(S)-Tol-BINAP](SbF(6))(2) (2b) is developed for asymmetric glyoxylate-ene reactions. This palladium dicationic catalyst provides a simple but efficient approach to the asymmetric synthesis of alpha-hydroxy esters in excellent yields with high enantioselectivities at relatively higher reaction temperature (60 degrees C).     

Palladium(0)-catalyzed rearrangement of allyl enol ethers to form chiral quaternary carbon centers via asymmetric allylic alkylation

Herein we report the first palladium(0)-catalyzed asymmetric allylic alkylation (AAA) of allyl enol ether via π-allylpalladium intermediate using Trost chiral diphosphine. This unprecedented reaction produced very rare α-aryl quaternary aldehydes with multi-functional groups. The main novelty in the chemistry demonstrates that enol ethers can be used as precursors for π-allylpalladium intermediates, an observation that is certainly rare and to the best of our knowledge, perhaps without prior precedent. Chiral ligand (R,R)-L3 was found to be optimal in this Pd-AAA reaction and provided good to excellent yield (80–95%) and enantioselectivity (70–90%) with a range of analogs.     

Palladium(II)-catalyzed sequential hydroxylation-carboxylation of biphenyl using formic acid as a carbonyl source

[reaction: see text] A simultaneous hydroxylation-carboxylation of biphenyl occurred to give 4'-hydroxy-4-biphenylcarboxylic acid, which has wide potential application as a polyester monomer.     

Palladium(0)-catalyzed Mizoroki-Heck reaction and Rh(I)-catalyzed asymmetric hydrogenation of polymer-supported dehydroalanine system

We have developed a practical route for the synthesis of peptides containing unnatural amino acids. Mizoroki-Heck reaction of polymer-supported dehydroalanine, followed by asymmetric hydrogenation was accomplished using Pd(0) and Rh(I)-DuPHOS catalysts, respectively, leading to 36 dipeptides containing phenylalanine derivatives with high stereocontrol.