Wanbin Zhang

C–N Bond Cleavage of Allylic Amines via Hydrogen Bond Activation with Alcohol Solvents in Pd-Catalyzed Allylic Alkylation of Carbonyl Compounds

Hydrogen-bond-activated C-N bond cleavage of allylic amines was realized in Pd-catalyzed allylic alkylation to form the C-C bond product. The method could be expanded to a series of allylic amines and carbonyl compounds with excellent results. It provides a new and convenient access to C-C bond formation based on Pd-catalyzed allylic alkylation of allylic amines by using only inexpensive alcohol solvents.

Interesting and effective P,N-chelation of tetrasubstituted ferrocene ligands for palladium-catalyzed asymmetric allylic substitution

Abstract The complexation of 1,1′-bis(diphenylphosphino)-2,2′-bis(oxazolinyl)-ferrocene with palladium(II) in solution was studied and with this kind of P,N-chelating tetrasubstituted ferrocene compounds as chiral ligands, up to 99% ee was given to the palladium-catalyzed asymmetric allylic substitution of 1,3-diphenyl-2-propenyl acetate with sodium dimethyl malonate.

A Palladium-Catalyzed Enantioselective Addition of Arylboronic Acids to Cyclic Ketimines†

Sly as Nicox: A palladium-catalyzed addition of arylboronic acids to ketimines has been developed to efficiently provide products in up to 99 % yield and 96 % ee. The reactions could be run under aerobic conditions and with unpurified trifluoroethanol (TFE). A pyrrolidine compound bearing a chiral α-tertiary amine was synthesized in several steps without loss of enantioselectivity. TFA = trifluoroacetate.

Efficient palladium-catalyzed asymmetric allylic alkylation of ketones and aldehydes

Palladium-catalyzed asymmetric allylic alkylation of ketones, via enamines generated in situ as nucleophiles, were carried out smoothly with chiral metallocene-based P,N-ligands. Under the same conditions, however, reactions of aldehydes could hardly be observed. Subsequently, this obstacle was resolved by using chiral metallocene-based P,P-ligands. Both ketones and aldehydes afforded excellent enantioselectivities with up to 98% ee and 94% ee, respectively.

Palladium-Catalyzed Allylic Alkylation of Simple Ketones with Allylic Alcohols and Its Mechanistic Study†

Allylic alcohols were directly used in Pd-catalyzed allylic alkylations of simple ketones under mild reaction conditions. The reaction proceeded smoothly at 20 °C by the concerted action of a Pd catalyst, a pyrrolidine co-catalyst, and a hydrogen-bonding solvent, and does not require any additional reagents. A computational study suggested that methanol plays a crucial role in the formation of the π-allylpalladium complex by lowering the activation barrier.

Chemoselective transfer hydrogenation of α,β-unsaturated ketones catalyzed by pincer-Pd complexes using alcohol as a hydrogen source.

A pincer-Pd complex was utilized in the chemoselective transfer hydrogenation of α,β-unsaturated ketones using n-BuOH as a hydrogen source and solvent. Good to excellent yields were obtained for various substrates even with reducible groups. Based on deuterium-labeling experiments, the reaction mechanism is proposed to occur via a pincer-Pd-hydride intermediate.

An Asymmetric Aerobic Aza-Wacker-Type Cyclization: Synthesis of Isoindolinones Bearing Tetrasubstituted Carbon Stereocenters†

Its all in the solvent: An enantioselective variant of an aza-Wacker-type cyclization that gives isoindolinones containing tetrasubstituted carbon centers α to the nitrogen atom has been developed (see scheme; tfa=trifluoroacetate). The use of a highly coordinating solvent is crucial for the activity of the catalyst and the stereoselectivity the reaction (up to 99 % ee).

Diphenylphosphinooxazoline ligands with a chiral binaphthyl backbone for Pd-catalyzed allylic alkylation

Novel diphenylphosphinooxazoline ligands with a chiral binaphthyl backbone were prepared. It was interestingly found that the two diastereomeric ligands afforded two enantiomeric products, respectively, with excellent catalytic activities and enantioselectivities for the palladium-catalyzed allylic alkylation, regardless of the identical (S)-oxazoline ring existing in both ligands. This is the first example using an (S)-oxazoline ligand to afford an (R)-product for this reaction.

Chiral Bicycle Imidazole Nucleophilic Catalysts: Rational Design, Facile Synthesis, and Successful Application in Asymmetric Steglich Rearrangement

A new type of chiral bicycle imidazole nucleophilic catalyst was rationally designed, facilely synthesized, and successfully applied in an asymmetric Steglich rearrangement with good to excellent yield and enantioselectivity at ambient temperature. Moreover, it can be easily recycled with almost no reduction of catalytic efficiency. This is the first example for the successful chiral imidazole nucleophilic catalyst without H-bonding assistance.

Novel chiral P,N-ferrocene ligands in palladium-catalyzed asymmetric allylic alkylations

Abstract Novel chiral P,N-ferrocene ligands, 1-diphenylphosphino-1′-oxazolinylferrocenes, were prepared from ferrocene via 1,1′-bis(tributylstannyl)ferrocene and 1-diphenylphosphino-1′-methoxycarbonylferrocene as intermediates, and with this new kind of ligand up to 91% ee with 99% chemical yield was afforded for the palladium-catalyzed allylic alkylation of 1,3-diphenyl-2-propenyl acetate with dimethylmalonate anion. The complexation behavior of this kind of ligand with dichlorobis(acetonitrile)palladium and bis(μ-chloro)(1,3-diphenyl-η 3 -allyl)dipalladium was investigated.