Asymmetric Allylic Substitution Reactions Research Articles

Construction of P‐Stereogenic Center by Selective Ligation of N—P—N Type Ligands and Application to Asymmetric Allylic Substitution Reactions.

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P,N-Bidentate aryl phosphite ligands based on chiral 2-imino-, 2-oxazolinyl and 2-oxazolidinyl phenols and their catalytic activity

New P,N-hybrid aryl phosphites with distant imino, oxazolino and oxazolidino groups are effective chiral ligands in Pd-catalysed asymmetric allylic substitution reactions.

Construction of P-stereogenic center by selective ligation of NPN type ligands and application to asymmetric allylic substitution reactions

Chiral bisoxazolylphosphine ligands 1 [( S, S)-PhP(Ox-R) 2: R=Me, i Pr, t Bu] with an NPN backbone were prepared from chiral 4-alkyl-2-phenyl-4,5-dihydrooxazole compounds. These ligands coordinated to Pd(II) ion as bidentate ligands selectively to give a stereogenic phosphorus atom. The Pd-( S, S)-PhP(Ox- t Bu) 2 1c catalyst evoked high enantioselectivity in asymmetric allylic substitutions of acyclic substrates using dimethyl sodiomalonate as nucleophile. In the reaction of 3-penten-2-yl acetate, which affords a π-allyl intermediate with a small steric factor, the Pd- 1c catalyst successfully induced very high enantioselectivity (94% ee) indicating the effectiveness of the P-stereogenic center formed by selective ligation of ligand 1. In the reaction of cyclic substrates, moderate to high enantioselectivity was obtained by Pd- 1 catalyst using the sodium salt of dimethyl methylmalonate.

New Enantiopure Cyclic β‐Iminophosphine Ligands: Applications in Pd‐Catalyzed Asymmetric Allylic Substitution.

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1,2‐Aminothioethers Derived from Ephedrine and Pseudoephedrine: Heterobidentate Ligands for the Palladium‐Catalyzed Asymmetric Allylic Substitution Reaction.

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New enantiopure cyclic β-iminophosphine ligands: applications in Pd-catalyzed asymmetric allylic substitution

New enantiopure cyclic β-iminophosphines were applied as ligands in Pd-catalyzed asymmetric allylic substitution reactions.

X-ray crystallographic and NMR spectroscopical characterization of intermediates in the Pd-catalyzed allylic substitution reaction with 4-substituted phosphinooxazolines. Correlation between intermediate structure and product configuration

The novel P,N-ligand 2-[2-(diphenylphosphino)phenyl]-4,5-dihydro-4-methyl-4-phenyloxazole (2a) has been synthesized. The corresponding [PdII(η3-diphenylallyl) (2a)]PF6 (3a) and [PdII(η3-1,3-dimethylallyl) (2a)]PF6 (4a) complexes have been studied by X-ray analysis and NMR spectroscopy. 3a exists as exo–syn–syn isomer in the solid state. In solution, the same isomer predominates. The X-ray structure of 4a reveals that the oxazoline ligand is coordinated in a pseudo-enantiomeric conformation compared with 3a. A syn–anti arrangement of the allyl substituents is favored in the solid state. NMR spectroscopical investigations suggest a formation of six isomers in solution due to endo–exo orientation of the allyl moiety and syn–anti isomerization of the methyl substituents. NMR data of [Pd0(η2-dimethylfumarate)(phosphinooxazoline)] complexes give evidence that two isomers exist in solution. The isomeric ratio is strongly dependent on the steric bulk of the oxazoline substituents. The solid state structures of [Pd0(η2-dmfu) (2c)] and [Pd0(η2-dmfu) (1a)] confirmed the structures of the main isomer found in solution. The asymmetric allylic substitution reaction of 1,3-diphenylallyl acetate with dimethyl malonate catalyzed by 3a proceeds with a selectivity of 97% ee. The ee induced by 2a in catalytic allylic substitution of 1-methylbutenyl acetate is moderate (18%). A comparison of the intermediate 4a and 5a as model of the actual olefinic intermediate suggests that the poor enantioselectivity achieved with ligand 2a is due to the preferred formation of anti-isomers of the allylic intermediate 4a and the conformational instability of the complex.

1,2-Aminothioethers Derived from Ephedrine and Pseudoephedrine: Heterobidentate Ligands for the Palladium-Catalysed Asymmetric Allylic Substitution Reaction

Heterobidentate sulfide-tertiary amine ligands incorporating 1,2-aminothioethers derived from ephedrine and pseudoephedrine have been prepared and used successfully in the palladium-catalysed asymmetric allylic substitution reaction, giving ees of up to 89%. The stereoelectronic effects operating in the reactions are discussed.

Asymmetric allylic substitution reactions of 2-substituted 2-cycloalkenyl carbonates using 9-PBN coordinated palladium

2-Substituted 2-cycloalkenyl carbonates are suitable substrates for asymmetric allylic substitution reaction using 9-PBN coordinated palladium, producing the allylic substituted products with high enantiomeric excess.

ChemInform Abstract: A Novel Amphiphilic Chiral Ligand Derived from D-Glucosamine. Application to Palladium-Catalyzed Asymmetric Allylic Substitution Reaction in an Aqueous or an Organic Medium, Allowing for Catalyst Recycling.

A novel amphiphilic phosphinite−oxazoline chiral compound, 2-methyl-4,5-[4,6-O-benzylidene-3-O-bis{4-((diethylamino)methyl)phenyl}phosphino-1,2-dideoxy-α-d-glucopyranosyl]-[2,1-d]-2-oxazoline (1), has been prepared from natural d-glucosamine hydrochloride. The newly prepared complex, [Pd(2-methyl-4,5-[4,6-O-benzylidene-3-O-bis{(4-((diethylmethylammonium)methyl)phenyl)}phosphino-1,2-dideoxy-α-d-glucopyranosyl]-[2,1-d]-2-oxazoline)(η3-C3H5)]3+·3BF4- (3), is soluble in water and an efficient catalyst for asymmetric allylic substitution reaction in water or an aqueous/organic biphasic medium (up to 85% ee). This catalytic system offers an easy separation of the aqueous catalyst phase from the product phase and allows recycling of the catalyst phase. In addition, compound 1 also works as an effective ligand for the palladium-catalyzed reaction under conventional homogeneous conditions in an organic medium, in which the catalyst (Pd−1 complex) can be recovered by simple acid/base extraction and reused in the se...

A novel amphiphilic chiral ligand derived from D-glucosamine. Application to palladium-catalyzed asymmetric allylic substitution reaction in an aqueous or an organic medium, allowing for catalyst recycling

A novel amphiphilic phosphinite-oxazoline chiral compound, 2-methyl-4,5-[4,6-O-benzylidene-3-O-bis[4-((diethylamino)methyl)phenyl]phosphino-1,2-dideoxy-alpha-D-glucopyranosyl]-[2,1-d]-2-oxazoline (1), has been prepared from natural D-glucosamine hydrochloride. The newly prepared complex, [Pd(2-methyl-4,5-[4,6-O-benzylidene-3-O-bis[(4-((diethylmethylammonium)methyl)phenyl)]phosphino-1,2-dideoxy-alpha-D-glucopyranosyl]-[2,1-d]-2-oxazoline)(eta3-C3H5)]3+ x 3BF4- (3), is soluble in water and an efficient catalyst for asymmetric allylic substitution reaction in water or an aqueous/organic biphasic medium (up to 85% ee). This catalytic system offers an easy separation of the aqueous catalyst phase from the product phase and allows recycling of the catalyst phase. In addition, compound 1 also works as an effective ligand for the palladium-catalyzed reaction under conventional homogeneous conditions in an organic medium, in which the catalyst (Pd-1 complex) can be recovered by simple acid/base extraction and reused in the second reaction.

Synthesis, X‐Ray Crystal‐Structure Analysis, and NMR Studies of (η3‐Allyl)palladium(II) Complexes Containing a Novel Dihydro(phosphinoaryl)oxazine Ligand: Application in Palladium‐Catalyzed Asymmetric Synthesis

The novel chiral P,N-ligand 2-[2-(diphenylphosphino)phenyl]-5,6-dihydro-4-phenyl-4H-1,3-oxazine (4) was synthesized. The corresponding {dihydro[(phosphino-ϰP)aryl]oxazine-ϰN} (η3-diphenylallyl)palladium(II) hexafluorophosphate 5 and the analogous [Pd(η3-1,3-dimethylallyl)] complex 6 were investigated by X-ray analysis and 1D- and 2D-NMR spectroscopy. The complex 5 exists as `exo'-syn-syn isomer in the solid state (Fig. 1). In solution, the same isomer exceeds with 90%. The X-ray crystal structure of 6 reveals that the dihydro(phosphinoaryl)oxazine ligand coordinates in a pseudo-enantiomeric conformation compared with that of 5 (Fig. 3). A syn-anti arrangement of the allyl substituents of 6 is favored in the solid state. 1H-NMR Spectroscopic investigations suggest that the auxiliary 6 adopts two conformations. This conformational instability together with `exo'/`endo' and syn/anti isomerization leads to the formation of 6 isomers (Fig. 4). The asymmetric allylic substitution reaction of 1,3-diphenylallyl acetate with dimethyl malonate in the presence of 4 proceeds with a selectivity of 99% ee. The ee induced by 4 in the catalytic allylic substitution of 1-methylbut-2-enyl acetate is moderate (54%).

New Chiral Sulfoxide Ligands Possessing a Phosphano or Phosphanoamino Functionality in Palladium-Catalyzed Asymmetric Allylic Nucleophilic Substitution Reactions

New chiral sulfoxide ligands possessing a phosphano or phosphanoamino functionality as an alternative coordinating element were developed, and their usefulness was demonstrated by applying them to palladium-catalyzed asymmetric allylic nucleophilic substitution reactions. The structure of the catalyst precursor coordinated by the chiral phosphino sulfoxide was determined by X-ray crystallographic analysis. The possible mechanism for the asymmetric induction using these chiral ligands was proposed on the basis of the stereochemical outcome obtained.

New chiral phosphinooxathiane ligands for palladium-catalyzed asymmetric allylic substitution reactions

New chiral ligands, phosphinooxathianes 3 and 6, were synthesized easily and their ability as ligands were examined in Pd-catalyzed asymmetric allylic alkylation of 1,3-diphenyl-2-propenyl acetate with dimethyl malonate to give an allylation product. Enantiomeric excess of up to 94% has been obtained using 1 mol% of [PdCl(η 3-C 3H 5)] 2 and 2 mol% of 3.

The First Successful Use of Simple 1,2-Aminothioethers as Hybrid Ligands in the Palladium-Catalysed Asymmetric Allylic Substitution Reaction

Hybrid sulfide-tertiary amine ligands incorporating 1,2-aminothioethers have been prepared and used successfully in the palladium-catalysed asymmetric allylic substitution reaction for the first time.

Asymmetric allylic substitution reaction with nitrogen and oxygen nucleophiles using monodentate chiral phosphine, 9-PBN

Asymmetric allylic substitution reactions between 1,3-diphenyl-2-propenyl acetate and various hetero nucleophiles were efficiently carried out using the catalysts derived from the monodentate phosphine ligands, (1 R, 2 S, 5 R, 6 S)-2,6-dimethyl-9-phenyl-9-phosphabicyclo[3.3.1] nonane and its enantiomer ((−)- and (+)-9-PBNs), and palladium (0).

Synthesis of chiral 1′-substituted oxazolinylferrocenes as chiral ligands for Pd-catalyzed allylic substitution reactions

Chiral 1-oxazolinyl-1′-(diphenylphosphino)ferrocenes 4 and 1-oxazolinyl-1′-(phenylthio)ferrocenes 5 were prepared from 1,1′-dibromoferrocene through 1-oxazolinyl-1′-bromoferrocenes 3. The compounds 4 and 5 were employed as chiral ligands in Pd-catalyzed asymmetric allylic substitution reactions. High enantioselectivities (82–99% ee) and high yields (96–99%) were observed in the substitution reactions of 1,3-diphenylprop-2-enyl acetate and dimethyl malonate with the catalysts generated from [(π-allyl)PdCl] 2 and 4, while the use of 5 led to inferior results (20–75% ee and 25–28% yields). 1H-, 13C-, and 31P-NMR data are analyzed for the complexes obtained from the reactions of [(η 3-allyl)PdCl] 2 and [(η 3-1,3-diphenylallyl)PdCl] 2 with 4a and 4b.

New chiral phosphinooxazolidine ligands for palladium-catalyzed asymmetric allylic substitution

New chiral phosphinooxazolidines were prepared and examined as chiral ligands in Pd-catalyzed asymmetric allylic substitution reaction of 1,3-diphenyl-2-propenyl acetate with dimethyl malonate or benzylamine. Enantioselectivity up to 98% was observed.

ChemInform Abstract: Chiral β‐Phosphino Sulfoxides as Chiral Ligands in Palladium‐Catalyzed Asymmetric Allylic Nucleophilic Substitution Reactions.

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Catalytic asymmetric reactions via π-allylpalladium complexes coordinated with chiral monophosphine ligands

Chiral monophosphines (MOPs), whose chirality is due to biaryl axial chirality, are prepared from enantiometrically pure 2,2′-dihydroxy-1,1′-binaphthyl and 3,3′-dihydroxy-4,4′-biphenanthryl. The representatives are 2-(diphenylphosphino)-2′-methoxy-1,1′-binaphthyl (MeO–MOP and 3-(diphenylphosphino)-3′-methoxy-4,4′-biphenanthryl (MOP–phen). The palladium complexes coordinated with the MOP ligands are highly effective catalysts for catalytic asymmetric allylic substitution reactions, where chelating bisphosphine ligands cannot be used because of their low catalytic activity or low selectivity towards the desired reaction pathway. The catalytic asymmetric reactions are: (1) asymmetric reduction of allylic esters with formic acid (93% ee). (2) Regio- and enantioselective alkylation of allyl esters (87% ee).