Formation of enamides via palladium(II)-catalyzed vinyl transfer from vinyl ethers to nitrogen nucleophiles

Palladium(II) complexes catalyze the formation of enamides via the formal cross-coupling reaction between nitrogen nucleophiles and vinyl ethers. These vinyl transfer reactions proceed in good yields with amide, carbamate, and sulfonamide nucleophiles, and the optimal catalyst is (DPP)Pd(OCOCF(3))(2) (DPP = 4,7-diphenyl-1,10-phenanthroline). [reaction: see text]     

Ni(II)-catalyzed enantioselective Nazarov cyclizations

Nazarov cyclizations are catalyzed by a dicationic Ni(ii) complex containing the chiral tridentate phosphine Pigiphos; the catalyst exerts a high degree of torquoselectivity and affords the products in up to 88% ee.     

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)- and platinum(II)-catalyzed addition of stabilized carbon nucleophiles to ethylene and propylene

PdCl(2)(CH(3)CN)(2) and [PtCl(2)(H(2)C[double bond]CH(2))](2) catalyze the addition of beta-dicarbonyl compounds to ethylene and propylene.     

Platinum(II)-catalyzed cross-coupling of polyfluoroaryl imines

The introduction of fluorine into an organic molecule imparts unique physicochemical properties. Not surprisingly, fluorine is increasingly incorporated into new drugs and agrochemicals. However, aryl fluoride building blocks are only available through synthesis. The ability to cross-couple polyfluoroaromatics selectively could provide a convenient route to functionalized fluoroaromatics. We report herein the first examples of Pt-catalyzed cross-coupling of aryl fluorides. The methylated products can potentially serve as precursors to a wide range of functionalized fluorinated small molecules.     

Radical cascade cyclizations and platinum(II)-catalyzed cycloisomerizations of ynamides

Ynamides are tested as new partners in radical and organometallic transformations. A radical cascade involving a 5-exo-dig cyclization followed by a 6-endo-trig radical trapping transforms ynamides into hetero-polycyclic compounds such as isoindoles, isoindolinones and pyrido-isoindolones. Various ene-tosylynamides react with platinum(II) chloride and lead to bicyclic nitrogenated heterocycles. This unprecedented and easily operated process can be coupled with a hydrolysis of the intermediate cyclic tosylenamides in a one-pot transformation, which provides cyclobutanones.     

Platinum(II)-catalyzed addition of alcohols to alkynes

A simple, high-yielding synthesis of acetals from the platinum(II)-catalyzed addition of alcohols to alkynes is described. The regioselectivity of the method and its mechanism are also discussed.     

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.     

Platinum(II)-catalyzed intermolecular hydroarylation of unactivated alkenes with indoles

Ethylene, alpha-olefins, and vinyl arenes undergo platinum-catalyzed hydroarylation with substituted indoles in moderate to good yield.     

Rh(I)-catalyzed CO gas-free carbonylative cyclization of organic halides with tethered nucleophiles using aldehydes as a substitute for carbon monoxide

The CO gas-free carbonylative cyclization of organic halides, with tethered nitrogen, oxygen, and carbon nucleophiles, with aldehydes as a substitute for carbon monoxide can be achieved in the presence of a catalytic amount of a rhodium complex. The reaction involves the decarbonylation of the aldehyde by the rhodium catalyst, and the successive carbonylation of an organic halide utilizing the rhodium carbonyl that is formed in situ. Aldehydes having electron-withdrawing groups showed a higher ability to donate the carbonyl moiety.     

Gold(I)-catalyzed intermolecular addition of carbon nucleophiles to 1,5- and 1,6-enynes

Gold(I)-catalyzed addition of carbon nucleophiles to 1,6-enynes gives two different type of products by reaction at the cyclopropane or at the carbene carbons of the intermediate cyclopropyl gold carbenes. The 5-exo-dig cyclization is followed by most 1,6-enynes, although those bearing internal alkynes and alkenes react by the 6-endo-dig pathway. The cyclopropane versus carbene site-selectivity can be controlled in some cases by the ligand on the gold catalyst. In addition to electron-rich arenes and heteroarenes, allylsilanes and 1,3-dicarbonyl compounds can be used as the nucleophiles. In the reaction of 1,5-enynes with carbon nucleophiles, the 5-endo-dig pathway is preferred.     

Pd(0)-catalyzed couplings using bromide and chloride derivatives of Baylis-Hillman adducts with triarylbismuths as atom-efficient multi-coupling nucleophiles

Bromide and chloride derivatives of Baylis-Hillman adducts have been demonstrated to react efficiently with triarylbismuths affording allylic arylated products in high yields under palladium-catalyzed conditions. Triarylbismuths have been employed in sub-stoichiometric amounts as multi-coupling and atom-efficient nucleophiles in these reactions. The reactivity of both allylic bromides and chlorides was found to be facile and equally efficient in couplings with triarylbismuths.     

Cu(II)-catalyzed C-H (SP3) oxidation and C-N cleavage: base-switched methylenation and formylation using tetramethylethylenediamine as a carbon source

Base-switched methylenation and formylation using tetramethylethylenediamine (TMEDA) as a carbon source have been achieved under mild conditions, catalyzed by CuCl(2), with atmospheric oxygen as oxidant. Bisindolylmethanes, diphenylmethanes and 3-formylindoles were synthesized with excellent regioselectivity and good yield.     

Platinum(II)-catalyzed intramolecular cyclization of alkynylbenzonitriles: synthesis of 1-alkoxyisoquinolines and isoquinolones

A facile synthesis of a series of 1-alkoxyisoquinolines and (2H)-isoquinolones by an intramolecular 6-endo-dig cyclization of ortho-alkynylbenzonitriles in the presence of a catalytic amount of hydrido(dimethylphosphinous acid-κP)[hydrogen bis(dimethylphosphinito-κP)]platinum(II) in various alcohols at 65-90 °C is described for the first time.     

A mutually pi-facial selective cyclopropanation of chiral enamides using dirhodium(II) carbenoids

A mutually pi-facial selective cyclopropanation of chiral enamides using dirhodium(II) carbenoids is described here. This work illustrates the influence of enamide substituents on stereoselectivity and reveals insights into this cyclopropanation.     

Platinum(II)-catalyzed 1,6-diene cycloisomerizations: turnover in the absence of beta-hydride elimination

Electrophilic pincer-ligated Pt(II)-dications are efficient catalysts for the cycloisomerization of 1,6-dienes, initiated by alkene activation. The tridentate ligands inhibit beta-hydride elimination and thus enable cationic mechanisms that turnover by Pt(II) extrusion. PPP ligands lead to cyclopropane products, while PNP ligands provide cyclohexene products; mechanistic issues are also discussed.     

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.     

2,4,6-Triphenylpyridine as a neutral leaving group in the palladium(0)-catalyzed allylation of nucleophiles

Palladium(0)-catalyzed allylation of nucleophiles such as morpholine, sodium dimethyl malonate and 2,6-dimethylaniline can be achieved under very mild conditions using N-allyl-2,4,6-triphenylpyridinium tetrafluoroborates as allylating reagents in reactions in which 2,4,6-triphenylpyridine acts as the neutral leaving group.     

Cu(II)-catalyzed functionalizations of aryl C-H bonds using O2 as an oxidant

Cu(II)-catalyzed acetoxylation and halogenation of aryl C-H bonds are developed. ortho-Selectivity was observed with a wide range of 2-arylpyridine substrates. Both mono- and difunctionalizations are achieved by tuning the reaction conditions. Excellent functional group tolerance and use of O2 as a stoichiometric oxidant are significant advantages over our recently developed Pd-catalyzed C-H functionalization reactions. These newly discovered reaction conditions are also applicable for cyanation, amination, etherification, and thioetherification of aryl C-H bonds. Mechanistic investigations are carried out to gain insights into the Cu(II)-catalyzed C-H functionalization reactions.