Direct palladium(II)-catalyzed synthesis of arylamidines from aryltrifluoroborates

A fast and convenient synthesis of arylamidines starting from readily available potassium aryltrifluoroborates and cyanamides is reported. The coupling was achieved by Pd(II)-catalysis in a one step 20 min microwave protocol using Pd(O(2)CCF(3)), 6-methyl-2,2'-bipyridyl, TFA, and MeOH, providing the corresponding arylamidines in moderate to excellent yields.     

The palladium(II)-catalyzed Nazarov reaction

The PdCl(2)-catalyzed cyclization of alpha-alkoxy dienones leads to 2-hydroxycyclopentenones, whereas the Pd(OAc)(2)-catalyzed reaction leads to cross-conjugated cyclopentenones through an oxidative process. [reaction: see text]     

Pt(II)-catalyzed synthesis of 1,2-dihydropyridines from aziridinyl propargylic esters

Pt(II)-catalyzed cycloisomerization of aziridinyl propargylic esters affords 1,2-dihydropyridines with regiodefined installation of substituents. A mild conversion of the 1,2-dihydropyridines to the corresponding substituted pyridines as well as chirality retention from the aziridinyl propargylic ester substrates have been demonstrated.     

Diversity synthesis using the complimentary reactivity of rhodium(II)- and palladium(II)-catalyzed reactions

Rhodium(II)-catalyzed reactions of aryldiazoacetates can be conducted in the presence of iodide, triflate, organoboron, and organostannane functionality, resulting in the formation of a variety of cyclopropanes or C-H insertion products with high stereoselectivity. The combination of the rhodium(II)-catalyzed reaction with a subsequent palladium(II)-catalyzed Suzuki coupling offers a novel strategy for diversity synthesis.     

Cu(II)-aza(bisoxazoline)-catalyzed asymmetric benzoylations

[reaction: see text] Racemic 1,2-diols and alpha-hydroxy carbonyl compounds can be asymmetrically benzoylated in a kinetic resolution in the presence of various Cu(II)-aza(bisoxazoline) catalysts. A novel bisbenzyl-substituted aza(bisoxazoline) ligand proved to be especially effective when immobilized on MeOPEG(5000), giving from 91 to > or = 99% ee in 37-49% yield for each of five sequential reactions.     

The renaissance of palladium(II)-catalyzed oxidation chemistry

Palladium(II)-catalyzed oxidations constitute a paramount reaction class but have remained immature over the past few decades. Recently, this field has reappeared at the forefront of organometallic catalysis. This emerging area article outlines recent developments in palladium(II)-catalyzed oxidation chemistry with discussion of potential future growth.     

Cationic palladium(II)-catalyzed stereoselective glycosylation with glycosyl trichloroacetimidates

The development of a new method for stereoselective glycosylation with glycosyl trichloroacetimidate donors employing cationic palladium(II), Pd(CH(3)CN)(4)(BF(4))(2), is described. This process employs Pd(CH(3)CN)(4)(BF(4))(2) as an efficient activator, providing access to a variety of disaccharides and glycopeptides. This reaction is highly stereoselective and proceeds under mild conditions with low catalyst loading. Interestingly, this palladium catalysis directs beta-glucosylations in the absence of classical neighboring group participation.     

Mild and efficient palladium(II)-catalyzed racemization of allenes

Allenes undergo racemization in the presence of catalytic amounts of Pd(OAc)2/LiBr under mild conditions; the reaction proceeds via a bromopalladation-debromopalladation sequence and tolerates various functional groups.     

Direct synthesis of chiral tertiary diphosphines via Pd(II)-catalyzed asymmetric hydrophosphination of dienones

A highly diastereo- and enantioselective Pd(II)-catalyzed hydrophosphination of dienones with Ph(2)PH involving formation of double C*-P bonds has been developed, providing a series of chiral tertiary diphosphines (chiral PCP pincer ligands) in high yields. A catalytic cycle for the reaction was proposed.     

1,2-Oxopalladation versus pi-allyl palladium route. A regioconvergent approach to a key intermediate for cyclopentanoids synthesis. New insights into the Pd(II)-catalyzed lactonization reaction

Regioconvergent synthesis of the key lactone 1 from an equimolar mixture of the two olefins 4 and 5 was achieved by unique Pd(II) chemistry. The synthetic versatility of lactone 1 has been demonstrated in the synthesis of iridoids and of the endo-Corey lactone 2, which is a key intermediate for the F(2)-isoprostane synthesis. Upon exposure of the sodium salts of 4 and 5 to a catalytic amount of Pd(OAc)(2) under oxygen, in the presence of AcOH, an isomeric lactone 12 was obtained in addition to the title compound 1. The Pd(II) lactonization was optimized by fine-tuning all the factors participating in the catalytic cycle: solvent, oxidant, co-oxidant, and Pd(II) source. The Hosokawa's heterobimetallic couple emerged as the catalyst of choice. With a Cu(II)-Pd(II) couple, the redox process was transferred to copper, and the formal oxidation state of palladium remained constant during the reaction. By virtue of this new methodology, lactone 1 was obtained in a rewarding 60% yield, along with isomeric lactone 12 in 30% yield. A detailed mechanistic study was carried out in order to elucidate the formation of lactones 1 and 12. Lactone 1 was formed from either olefin 8 or olefin 10; on the other hand, lactone 12 was formed exclusively from olefin 10. An intramolecular 1,2-acyloxypalladiation was invoked for the transformation of 8 into 1, whereas the pi-allyl complexes 13 and 11 were involved in the transformation of olefin 10 into 12 and 1, respectively.     

Atroposelective synthesis of N-aryl peptoid atropisomers via a palladium(ii)-catalyzed asymmetric C–H alkynylation strategy

The introduction of chirality into peptoids is an important strategy to determine a discrete and robust secondary structure. However, the lack of an efficient strategy for the synthesis of structurally diverse chiral peptoids has hampered the studies. Herein, we report the efficient synthesis of a wide variety of N-aryl peptoid atropisomers in good yields with excellent enantioselectivities (up to 99% yield and 99% ee) by palladium-catalyzed asymmetric C–H alkynylation. The inexpensive and commercially available l-pyroglutamic acid was used as an efficient chiral ligand. The exceptional compatibility of the C–H alkynylation with various peptoid oligomers renders this procedure valuable for peptoid modifications. Computational studies suggested that the amino acid ligand distortion controls the enantioselectivity in the Pd/l-pGlu-catalyzed C–H bond activation step.

The introduction of chirality into peptoids is an important strategy to determine a discrete and robust secondary structure.     

Efficient synthesis of 2-(2′-hydroxyphenyl)benzoxazole by palladium(II)-catalyzed oxidative cyclization

An efficient method for the synthesis of 2-(2′-hydroxyphenyl)benzoxazole has been developed by using palladium-mediated oxidative cyclization.     

Pd(II)-catalyzed asymmetric addition of malonates to dihydroisoquinolines

We have developed a highly efficient reaction for catalytic asymmetric addition of malonates to dihydroisoquinolines using chiral Pd(II) complexes. In the reactions, substrates with various substitution patterns were available, and the reactions were complete within several hours (<3 h in most cases) under mild reaction conditions, affording various optically active C1-substituted tetrahydroisoquinoline derivatives (up to 98% yield, up to 97% ee). Furthermore, slow addition of DDQ allowed the in situ generation of the reactive intermediate from the corresponding N-Boc-protected amine, and dehydrogenative addition reaction was successfully demonstrated.     

Pd(II)-catalyzed intermolecular 1,2-diamination of conjugated dienes

A Pd(II) chloride precatalyst, in the presence of 1 equiv of benzoquinone, effects highly efficient, regioselective 1,2-diamination of 1,3-dienes using dialkyl ureas under mild conditions. There is no requirement for a large excess of diene.     

Homogeneous nucleation of bis(1,2-cyclohexanedionedioximato)palladium(II)

Precipitation from homogeneous solution has been applied to the drop technique for the study of the homogeneous nucleation of bis(1,2-cyclohexanedionedioximato)palladium(II). It was found that under the experimental conditions employed the interfacial energy of the chelate was 47 ergs.cm(-2) and the critical radius size 11 A.     

A route for the synthesis of novel asymmetric binuclear pentafluorophenyl derivatives of palladium(II)

Binuclear halogen-bridged complexes of the type (C₅F₅)₂Pd(μ-Cl)₂ML₂ (M  Ni, Pd (L₂  dpe), Pt (L  PEt₃)] have been prepared by reaction of cis-Pd(C₆F₅)₂(PhCN)₂ with the corresponding halo complexes, MCl₂L₂, in dichloromethane, IR and NMR structural data are discussed.     

Rhodium(II)-catalyzed asymmetric sulfur(VI) reduction of diazo sulfonylamidines

Diazo sulfonylamidines readily undergo enantioselective oxygen transfer from sulfur to carbon atom in the presence of chiral rhodium(II) carboxylates resulting in chiral sulfinylamidines. This unusual asymmetric atom transfer "reduction" occurs rapidly under mild conditions, and sulfinylamidines are obtained in excellent yield.     

Palladium(II)-catalyzed asymmetric synthesis of (Z)-alpha-alkylidene-gamma-butyrolactams from (Z)-N-allylic 2-Alkynamides. Total synthesis of (-)-isocynometrine

Pd(OAc)2 combined with nitrogen-containing ligands catalyzed the cyclization of (Z)-N-allylic 2-alkynamides in acetic acid to afford the alpha-(Z)-acetoxyalkylidene-gamma-butyrolactams in high yield and high stereoselectivity. When chiral nitrogen-containing ligands were used, the catalytic asymmetric protocol was achieved with moderate enantioselectivity (up to 80 degrees C). The utility of this new methodology was exemplified by the total synthesis of (-)-isocynometrine.