Allylic Alkylation Products Research Articles

Palladium-Catalyzed Asymmetric Allylic Substitutions by Axially Chiral P,S-, S,S-, and S,O-Heterodonor Ligands with a Binaphthalene Framework.

Axially chiral P,S-heterodonor ligand L1 is effective in the asymmetric allylic substitution of 1,3-diphenylpropenyl acetate with dimethyl malonate. its bidentate coordination pattern to a I'd metal center with both P and S atoms has been unambiguously established by X-ray diffraction and NMR spectroscopic analyses. Herein, we further disclose that axially chiral S,S-heterodonor ligands L2-L4 are also effective in the same reaction to give the allylic alkylation product in moderate to good ee. However, the corresponding S,O-heterodonor ligands are not as effective as the corresponding P,S- or S,S-heterodonor ligands in the same asymmetric reaction. (C) 2004 Elsevier Ltd. All rights reserved.

Palladium-catalyzed asymmetric allylic substitutions by axially chiral P,S-, S,S-, and S,O-heterodonor ligands with a binaphthalene framework

Axially chiral P,S-heterodonor ligand L1 is effective in the asymmetric allylic substitution of 1,3-diphenylpropenyl acetate with dimethyl malonate. Its bidentate coordination pattern to a Pd metal center with both P and S atoms has been unambiguously established by X-ray diffraction and NMR spectroscopic analyses. Herein, we further disclose that axially chiral S,S-heterodonor ligands L2– L4 are also effective in the same reaction to give the allylic alkylation product in moderate to good ee. However, the corresponding S,O-heterodonor ligands are not as effective as the corresponding P,S- or S,S-heterodonor ligands in the same asymmetric reaction.

Novel Ferrocenylphosphine‐imines Containing a Pyridine Unit as a New Family of Chiral Ligands: The Important Influence of the Position of the Pyridine N‐Atom on the Reactivity and Enantioselectivity in Palladium‐Catalyzed Asymmetric Allylic Alkylations.

A new class of ferrocene based phosphine-imine ligands with a pyridine moiety was used in the Pd-catalyzed asymmetric allylic alkylation of 1,3-diphenylprop-2-en-1-yl ester 5 and cyclohexenyl acetate 8, and it was found that the position of pyridine N-atom had an important influence on the catalytic activity and enantioselectivity of the Pd-complex. The Pd-complex derived from ligand (R,S-P)-1c with a 3-pyridine N-atom turned out to be an efficient catalyst, affording an allylic alkylation product with an ee of up to 99%, while the Pd-complex derived from ligand (R,S-P)-1a with a 2-pyridine N-atom surprisingly showed no activity. Using ligand (R,S-P)-1b with a 4-pyridine N-atom, an ee of 95% with 91% yield was obtained in the allylic alkylation of 1,3-diphenylprop-2en-1-yl pivalate, but no allylic alkylation product of cyclohexenyl acetate was obtained. (C) 2004 Elsevier Ltd. All rights reserved.

Highly Regioselective Asymmetric Copper‐Catalyzed Allylic Alkylation with Dialkylzincs Using Monodentate Chiral Spiro Phosphoramidite and Phosphite Ligands.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Novel ferrocenylphosphine-imines containing a pyridine unit as a new family of chiral ligands: the important influence of the position of the pyridine N-atom on the reactivity and enantioselectivity in palladium-catalyzed asymmetric allylic alkylations

A new class of ferrocene based phosphine-imine ligands with a pyridine moiety was used in the Pd-catalyzed asymmetric allylic alkylation of 1,3-diphenylprop-2-en-1-yl ester 5 and cyclohexenyl acetate 8, and it was found that the position of pyridine N-atom had an important influence on the catalytic activity and enantioselectivity of the Pd-complex. The Pd-complex derived from ligand ( R, S P)- 1c with a 3-pyridine N-atom turned out to be an efficient catalyst, affording an allylic alkylation product with an ee of up to 99%, while the Pd-complex derived from ligand ( R, S P)- 1a with a 2-pyridine N-atom surprisingly showed no activity. Using ligand ( R, S P)- 1b with a 4-pyridine N-atom, an ee of 95% with 91% yield was obtained in the allylic alkylation of 1,3-diphenylprop-2-en-1-yl pivalate, but no allylic alkylation product of cyclohexenyl acetate was obtained.

Highly regioselective asymmetric copper-catalyzed allylic alkylation with dialkylzincs using monodentate chiral spiro phosphoramidite and phosphite ligands

The copper complexes of chiral spiro phosphoramidite and phosphite ligands were found to be effective catalysts in the asymmetric allylic alkylations of cinnamyl halides with dialkylzincs. The allylic alkylation products were obtained in high regioselectivities (S N2′/S N2 up to 98:2) and enantiomeric excesses of up to 74% for S N2′ products.

Regioselective rhodium-catalyzed allylic alkylation/ring-closing metathesis approach to carbocycles

Treatment of the allylic carbonates 1a– c with the sodium anion of the α-substituted malonates ( n=0–2) and Wilkinson's catalyst modified with a triorganophosphite, furnished the allylic alkylation products 2 / 3a– i in 83–97% yield, favoring 2a– i . The dienes 2a– i were then subjected to ring-closing metathesis using either I or II , to afford the carbocycles 4a– i in 79–99% yield.

Palladium-catalyzed asymmetric allylic substitution using novel phosphino-ester (PHEST) ligands with 1,1′-binaphthyl skeleton

The asymmetric allylic alkylation of rac-1,3-diphenyl-2-propenyl acetate 1 with dimethyl malonate 2a proceeded smoothly in the presence of lithium acetate, BSA ( N, O-bis(trimethylsilyl)acetamide), [Pd(η 3-C 3H 5)Cl] 2, and the chiral ligand ( R)- i-Pr 2N-PHEST ( R)- 5a to give the allylic alkylation product ( R)- 3a in 89% yield with 99% ee. Furthermore, the asymmetric allylic amination of 1 with potassium phthalimide 2c has been carried out using the same ligand to give the allylic amination product ( S)- 3c in 10% yield with 66% ee.

Zr-Catalyzed Olefin Alkylations and Allylic Substitution Reactions with Electrophiles

Disubstituted aryl olefins undergo efficient alkylations in the presence of 5 mol % Cp2ZrCl2, n-BuMgCl, and alkyl tosylates or alkyl bromides. In one class of reactions (Table 1), the resulting alkyl zirconocene (initial alkylation product) undergoes β-hydride abstraction with a hydrogen atom from within the substrate to afford allylic alkylation products (Scheme 5). In another category of reactions, where cyclic allylic ethers (chromenes) are used (Table 2), Zr-alkoxide elimination occurs after the C−C bond formation to effect a net allylic substitution. It is proposed that these reactions involve the nucleophilic attack of substrate-derived zirconates or zirconocene−Grignard reagents on various tosylates and bromides. There is little or no competitive electrophile alkylation by the n-alkyl Grignard reagent. Several mechanistic and synthetic aspects of these Zr-catalyzed C−C bond forming reactions are examined and discussed.

Synthesis and application of novel chiral phosphino-oxazoline ligands with 1,1′-binaphthyl skeleton

C 1-Symmetric phosphino-oxazolines, ( S,S)- and ( S,R)-2-[4-(isopropyl)oxazol-2-yl]-2′-diphenylphosphino-1,1′-binaphthyl, which possess both phosphine and oxazoline moieties, were prepared from racemic binaphthol and enantiomerically pure ( S)-(+)-2-amino-3-methyl-1-butanol in high yields. Reaction of 1,3-diphenyl-2-propenyl acetate with dimethyl sodiomalonate in the presence of 2 mol% of palladium catalysts bearing the new chiral ligands proceeded with high enantioselectivity to give allylic alkylation products of up to 91% ee.

Synthesis and Structures of Low-Valent Tungsten Complexes Bearing Chiral Oxazoline-Derived Ligands

The synthesis of low-valent tungsten (0 and II) complexes bearing chiral bidentate phosphino- oxazoline or bisoxazoline ligands is described. The structures of four of the complexes have been determined by single crystal X-ray analyses. Tungsten(II)-allyl complexes of the type [W(CO)2(PN)(C3H5)Cl] (PN = phosphino-oxazoline) are fluxional in solution, but can be crystallized as single diastereoisomers. The complex [W(CO)3(PN)(CH3CN)], which also crystallizes as a single diastereoisomer, is readily oxidized in solution and solid state, in stark contrast to analogous compounds bearing four carbonyl ligands [W(CO)4(PN)] or [W(CO)4(NN)] (NN = bisoxazoline) which were found to be stable. [W(CO)3(PN)(CH3CN)] functions as a highly enantioselective catalyst in allylic substitution reactions with dimethyl sodiomalonate, whereas complexes of the type [W (CO)2(PN )(Z -C3H4)X)] (Z = H, Ph; X = Cl, Br) failed to yield allylic alkylation products.

Nuclear magnetic resonance and crystallographic studies of chiral η3-allyl palladium(II) complexes and asymmetric allylic alkylation of propen-2-yl acetates

The chiral complexes [Pd(η3-allyl)(P–P′)]X [P–P′= the chiral chelating ligand (S)(N-diphenylphosphino)(2-diphenylphosphinoxymethyl)pyrrolidine; allyl = MeCHCHCHMe, 2; or PhCHCHCHPh 3; X = BF4– or PF–6] have been prepared and analysed by NMR spectroscopy. Their diastereoisomeric composition have been determined on the basis of 1H, 13C, 31P and two-dimensional 1H–X (X =13C or 31P) correlation NMR spectra. Since retention of the preferred syn disposition of the allylic substituents occurs in both cases the reaction product is a mixture of two isomers which differ in allylic chirality. The relative absolute configurations have been assigned by two-dimensional nuclear Overhauser effect measurements and confirmed by the X-ray crystallographic determination of the structure of the major diastereoisomer of 2: the allyl fragments have (1S,3R) absolute configuration. The reaction of racemic 1,3-dimethylprop-2-enyl acetate in the presence of 2 and of 1,3-diphenylprop-2-enyl acetate in the presence of 3 with sodium dimethyl malonate gives the allylic alkylation products in 20 and 30% enantiomeric excess respectively.

ChemInform Abstract: Synthesis, Characterization, and Thermolytic Behavior of η3‐Allyl(methyl)(tertiary phosphine)palladium(II), and X‐Ray Structure of the Cluster (Pd4(μ‐C3H5)2(μ‐Cl)2(μ‐dppm)2)·4 C4H8O (dppm: Ph2PCH2PPh2).

AbstractComplexes such as (IV) decompose thermally with preferential evolution of ethane rather than 1‐butene, the allylic alkylation product.

Synthesis, characterization, and thermolytic behaviour of η3-allyl(methyl)(tertiary phosphine)palladium(II), and X-ray structure of the cluster [Pd4(µ-C3H5)2(µ-Cl)2(µ-dppm)2]·4C4H8O (dppm = Ph2PCH2PPh2)

Complexes of the type [Pd(η3-allyl) Me(L)][allyl = C3H5 or 2-MeC3H4; L = P(C6H11)3, PPh3, PPh2Me, PPhMe2, or PBun3] have been synthesized and characterized by 1H, 13C n.m.r. and mass spectroscopy. The [Pd (η3-C3H5) Me(L)] complexes thermally decompose with preferential evolution of ethane rather than but-1-ene, the allylic alkylation product. The participation of the binuclear methyl-bridged intermediate [Pd2(η3-allyl)2(µ-Me)2](3) is supposed. Indirect support for this is given by the thermolysis of a toluene solution of (3). The effects of phosphines, alkenes, and other additives on the thermolysis products are discussed. The structure of a complex isolated from the [Pd2(η3-allyl)2(µ-Cl)2]–LiMe–Ph2PCH4PPh4(dppm) reaction system in tetrahydrofuran was revealed by X-ray analysis as two µ-chloro-µ-allyl-dipalladium(I) units bridged by two dppm ligands.

Thermolysis of [(η3-allyl)PdMe(PPh3)]: an unexpected evolution of ethane gas as a main product

The novel title complex thermally decomposes with preferential evolution of ethane rather than but-1-ene, the allylic alkylation product, indicating that the binuclear methyl-bridged intermediate formed by phosphine dissociation predominantly participates in this thermolysis.

Asymmetric Allylic Alkylation of 1,3-Disubstituted 2-Propenyl Acetates Catalyzed by a Chiral Ferrocenylphosphine–Palladium Complex

Reaction of racemic 2-propenyl acetates substituted with two different aryl groups at 1 and 3 positions with sodium acetylacetonate in the presence of a palladium catalyst containing an optically active ferrocenylphosphine ligand gave regioisomeric allylic alkylation products of high optical purity (up to 95% ee).

η-Allylmetal chemistry. Part 7. Allylic alkylation catalysed by platinum complexes. Isolation of rigid (σ-allyl)(pentane-2,4-dionato)platinum(II) complexes

Reactions of β-diketo-anions with η3-allylbis(triphenylphosphine)platinum(II) complexes or allyl acetates in the presence of triphenylphosphineplatinum complexes afford high yields of allylic alkylation products. Alkylation of the corresponding η3-but-2-enylplatinum(II) complex gives a larger amount of the product of coupling at the secondary carbon than of that at the primary carbon, while the reversed selectivity is found in the reaction of the η3-but-2-enylpalladium(II) complex. Reactions of η3-allylmono(triphenylphosphine)platinum(II) complexes with thallium(I) pentane-2,4-dionate give stereochemically rigid, thermally stable, (σ-allyl)(pentane-2,4-dionato)-platinum(II) complexes.