Synthesis and Characterization of New, Chiral P−N Ligands and Their Use in Asymmetric Allylic Alkylation

Application of mixed phosphorus/sulfur ligands based on terpenoids in Pd-catalyzed asymmetric allylic substitution and Rh-catalyzed hydrogenation

A small library of easily prepared diamidophosphite-sulfides based on 1,3-thioether alcohols, primarily of terpenoid nature, was developed. Upon complexation with Pd(II) ions, these hemilabile ligands showed the ability to form both P,S-chelates and complexes with two ligands P-monodentately bonded to the metal. The structures of the ligands and their complexes were determined by 2D NMR spectroscopy and X-ray diffraction. The use of these stereoselectors provided up to 95% ee in the classic Pd-catalyzed asymmetric allylic substitution reactions of (E)-1,3-diphenylallyl acetate with C- and N-nucleophiles and up to 80% ee in the Pd-mediated allylic alkylation of cinnamyl acetate with β-ketoesters. In addition, ee values of up to 90% with quantitative conversion were achieved in the Rh-catalyzed asymmetric hydrogenation of methyl esters of unsaturated acids. The effects of the structural parameters, reaction conditions and ligand-to-metal ratio on the catalytic results are discussed.

Synthesis and catalytic properties of palladium(II) complexes with P,π-chelating ferrocene phosphinoallyl ligands and their non-tethered analogues

Hybrid phosphines usually combine a phosphine moiety with another heteroatom secondary donor group in their structures while compounds equipped with hydrocarbyl π-donor moieties remain uncommon. This contribution reports the synthesis and structural characterization of the first P/π-allyl-chelating complexes that were obtained using the structurally flexible and redox-active ferrocene unit as the scaffold, viz. [PdCl(R2PfcCHCHCH2-η3:κP)] (1R; R = Ph and cyclohexyl (Cy); fc = ferrocene-1,1'-diyl). These compounds were synthesized from the respective phosphinoferrocene carboxaldehydes R2PfcCHO via reaction with vinylmagnesium bromide to generate 1-(phosphinoferrocenyl)allyl alcohols, which were subsequently acetylated. The resulting allyl acetates reacted smoothly with [Pd2(dba)3]/[Et3NH]Cl (dba = dibenzylideneacetone) to produce the target compounds. Complexes 1R and their nontethered analogues [PdCl(η3-C3H5)(FcPR2-κP)] (5R; Fc = ferrocenyl) were evaluated as pre-catalysts for the Pd-catalysed allylic amination of cinnamyl acetate with aliphatic amines and Suzuki-Miyaura-type cross-coupling of 4-tolylboronic acid with benzoyl chloride. In these reactions, better results were achieved with compounds 5R (particularly with 5Ph), presumably because they form more stable LPd(0)-type catalysts.

P,S-Bidentate Phosphoramidites with (Ra)-BINOL Core in Palladium-Catalyzed Asymmetric Allylic Substitution

Abstract

New P,S-bidentate phosphoramidite ligands, including these having a stereogenic phosphorus atom in the 1,3,2-dioxaphosphepine ring, have been synthesized on the basis of (Ra)-BINOL and its adamantanyl derivatives. With their participation in the Pd-catalyzed asymmetric allylic alkylation of (E)-1,3-diphenylallyl acetate with dimethyl malonate and the amination with pyrrolidine involving these ligands have afforded selectivity up to 84 and 75% ee, respectively.

Recent Advances in Enantioselective Pd-Catalyzed Allylic Substitution: From Design to Applications

This Review compiles the evolution, mechanistic understanding, and more recent advances in enantioselective Pd-catalyzed allylic substitution and decarboxylative and oxidative allylic substitutions. For each reaction, the catalytic data, as well as examples of their application to the synthesis of more complex molecules, are collected. Sections in which we discuss key mechanistic aspects for high selectivity and a comparison with other metals (with advantages and disadvantages) are also included. For Pd-catalyzed asymmetric allylic substitution, the catalytic data are grouped according to the type of nucleophile employed. Because of the prominent position of the use of stabilized carbon nucleophiles and heteronucleophiles, many chiral ligands have been developed. To better compare the results, they are presented grouped by ligand types. Pd-catalyzed asymmetric decarboxylative reactions are mainly promoted by PHOX or Trost ligands, which justifies organizing this section in chronological order. For asymmetric oxidative allylic substitution the results are grouped according to the type of nucleophile used.

Diamidophosphites from β-hydroxyamides: readily assembled ligands for Pd-catalyzed asymmetric allylic substitution

Novel diamidophosphites based on β-hydroxyamides were prepared, and their individual and in situ formed complexes were tested in Pd-mediated allylations.

Oxalamide-based bisdiamidophosphites: synthesis, coordination, and application in asymmetric metallocatalysis

A new group of P*-chiral bisdiamidophosphites has been developed for Pd- and Rh-catalyzed asymmetric reactions with good to excellent enantioselectivities.

Unusual Water-Soluble Imino Phosphine Ligand: Enamine and Imine Derivatives of 1,3,5-Triaza-7-phosphaadamantane (PTA)

A series of water-soluble and air-stable E-enamine derivatives of 1,3,5-triaza-7-phosphaadamantane (PTA), PTA═C(R)NH₂, 1-4, are reported along with data on E-Z isomerization and tautomerization to the imine form (PTA-CR═NH). Reaction of 1,3,5-triaza-7-phosphaamantane-6-yl lithium, PTA-Li, with aromatic nitriles afforded E-enamine derivatives of PTA in good yield (49-91%). Phosphines 1-4 are stable toward water and air, and do not appear to isomerize or tautomerize, unless coordinated to a metal or oxidized. The corresponding oxides, O═PTA═C(R)NH₂ (5-8), were observed as ∼55/45 mixtures of E and Z isomers. Kinetic data on the E-Z isomerization is reported. Upon coordination of 1-4 to W(CO)₄(pip)₂, a κ¹- P enamine is formed, [W(CO)₄(pip)(κ¹- P-PTA═CRNH₂)]. Enamine-imine tautomerization of the metal bound phosphine was observed resulting in κ²- P, N imine complexes, [W(CO)₄(κ²- P, N-PTA-CR═NH)], 9-12. The crystal structures of the κ¹- P enamine 11a, κ²- P, N imine 9 and 12, phosphines 1 and 3, as well as phosphine oxide 8a were obtained. DFT calculations on the various isomers of the phosphines and phosphine oxides are also reported.

Synthesis of ferrocene derivatives with planar chirality via palladium-catalyzed enantioselective C-H bond activation

The first catalytic and enantioselective C-H direct acylation of ferrocene derivatives has been developed. A series of 2-acyl-1-dimethylaminomethylferrocenes with planar chirality were provided under highly efficient and concise one-pot conditions with up to 85% yield and 98% ee. The products obtained could be easily converted to various chiral ligands via diverse transformations.

Ferrocene phosphane-heteroatom/carbon bidentate ligands in asymmetric catalysis

A review of chiral ferrocene ligands featuring a combination of phosphorus and other elements as donor atoms in the asymmetric catalysis.

Allylic alkylations catalyzed by palladium-bis(oxazoline) complexes derived from heteroarylidene malonate derivatives

A series of simple heteroarylidene malonate-type bis(oxazoline) ligands 4 and 5 were applied to the palladium-catalyzed allylic alkylation reaction, and the ligand 4a bearing a phenyl group afforded excellent enantioselectivity (up to 96% ee) for the allylic alkylation product. Other substrates were also examined, giving the allylic alkylated products in high yield but with poor ee values.