Ligands In Palladium-catalyzed Allylic Alkylation Research Articles

Ion-paired Ligands for Palladium-catalyzed Allylic Alkylation under Base-free Conditions

The effectiveness of a catalytic amount of bromide ions for significantly accelerating the palladium-catalyzed allylation of carbonyl compounds with allylic carbonates is reported. In particular, t...

ChemInform Abstract: Spiro‐Fused Carbohydrate Oxazoline Ligands: Synthesis and Application as Enantio‐Discrimination Agents in Asymmetric Allylic Alkylation.

In the present work, we describe a convenient synthesis of spiro-fused D-fructo- and D-psico-configurated oxazoline ligands and their application in asymmetric catalysis. The ligands were synthesized from readily available 3,4,5-tri-O-benzyl-1,2-O-isopropylidene-β-D-fructopyranose and 3,4,5-tri-O-benzyl-1,2-O-isopropylidene-β-D-psicopyranose, respectively. The latter compounds were partially deprotected under acidic conditions followed by condensation with thiocyanic acid to give an anomeric mixture of the corresponding 1,3-oxazolidine-2-thiones. The anomeric 1,3-oxazolidine-2-thiones were separated after successive benzylation, fully characterized and subjected to palladium catalyzed Suzuki–Miyaura coupling with 2-pyridineboronic acid N-phenyldiethanolamine ester to give the corresponding 2-pyridyl spiro-oxazoline (PyOx) ligands. The spiro-oxazoline ligands showed high asymmetric induction (up to 93% ee) when applied as chiral ligands in palladium-catalyzed allylic alkylation of 1,3-diphenylallyl acetate with dimethyl malonate. The D-fructo-PyOx ligand provided mainly the (R)-enantiomer while the D-psico-configurated ligand gave the (S)-enantiomer with a lower enantiomeric excess.

Spiro-fused carbohydrate oxazoline ligands: Synthesis and application as enantio-discrimination agents in asymmetric allylic alkylation.

In the present work, we describe a convenient synthesis of spiro-fused D-fructo- and D-psico-configurated oxazoline ligands and their application in asymmetric catalysis. The ligands were synthesized from readily available 3,4,5-tri-O-benzyl-1,2-O-isopropylidene-β-D-fructopyranose and 3,4,5-tri-O-benzyl-1,2-O-isopropylidene-β-D-psicopyranose, respectively. The latter compounds were partially deprotected under acidic conditions followed by condensation with thiocyanic acid to give an anomeric mixture of the corresponding 1,3-oxazolidine-2-thiones. The anomeric 1,3-oxazolidine-2-thiones were separated after successive benzylation, fully characterized and subjected to palladium catalyzed Suzuki–Miyaura coupling with 2-pyridineboronic acid N-phenyldiethanolamine ester to give the corresponding 2-pyridyl spiro-oxazoline (PyOx) ligands. The spiro-oxazoline ligands showed high asymmetric induction (up to 93% ee) when applied as chiral ligands in palladium-catalyzed allylic alkylation of 1,3-diphenylallyl acetate with dimethyl malonate. The D-fructo-PyOx ligand provided mainly the (R)-enantiomer while the D-psico-configurated ligand gave the (S)-enantiomer with a lower enantiomeric excess.

Synthesis of 1,5- P, N-phosphino-sulfoximines through phospha-Michael reaction of alkenyl sulfoximines and their evaluation as ligands in palladium-catalyzed allylic alkylation

We describe a modular synthesis of cyclic and acyclic 1,5- P, N-phosphino-sulfoximines by using a phospha-Michael reaction of the corresponding alkenyl sulfoximines with HPPh 2/KO tBu as key step, which proceeds with medium diastereoselectivity. The palladium-catalyzed allylic alkylation of racemic 1,3-diphenyl allyl acetate with malonate in the presence of a S S R C R C-configured N-benzyl-substituted cyclic phosphino-sulfoximine gave the corresponding alkene with 97% ee in 98% yield. A comparative study of N-substituted phosphino-sulfoximines showed the selectivity of the Pd(0)-catalyst to be dependent not only on the chiral backbone of the ligand but also on the N-substituent and configuration of the sulfoximine group.

Synthesis and Application of Chiral Cyclopropane-Based Ligands in Palladium-Catalyzed Allylic Alkylation

A series of chiral, cyclopropane-based phosphorus/sulfur ligands have been synthesized and evaluated in the palladium-catalyzed allylic alkylation of 1,3-diphenylpropenyl acetate with dimethyl malonate. Variation of the ligand substituents at phosphorus, sulfur, and the carbon backbone revealed 24d to have the optimal configuration for this reaction, giving the product in high yield and with good enantioselectivity (93%). A model for the observed enantioselectivity is discussed within the context of existing models, using X-ray crystallographic data, solution-phase NMR studies, and the absolute stereochemistry of the products. Selected ligands were also evaluated in the palladium-catalyzed intermolecular Heck reaction and the rhodium-catalyzed hydrogenation of a dehydroamino acid.

Comparative Study of 1,5-Dinitrogen Schiff Bases as Potential Ligands in Palladium-Catalyzed Allylic Alkylation.

1-(2'-Pyrido and 2'-quinolino)-(1R)-arylethylamino)-ethylidenes (7-12) were prepared as potential ligands in Pd Η catalytic complexes for enantioselective allylic alkylation of 1,3-diphenyl-1-acetoxy-propene-2 (15). Alkylation with palladium complexes of 7-12 yielded 1,3-diphenyl-l-dimethylmalonyl-propene-2 (14) with enantioselectivity up to 55 % e.e. Enantioselectivity is discussed in view of the results recently reported for structurally related 1,5-bidentate dinitrogen ligands of C 1 symmetry. Reversal of enantioselectivity observed for the ligands 10 and 11 is attributed to the inversion of steric requirements in the second coordination sphere of their catalytic complexes.

Synthesis of Novel Planar Chiral Ferrocene and Cyclopentadienyl Manganese Tricarbonyl Derivatives and Their Use as Chiral Ligands in the Palladium‐Catalyzed Asymmetric Allylic Alkylation.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of novel planar chiral ferrocene and cyclopentadienyl manganese tricarbonyl derivatives and their use as chiral ligands in the palladium-catalyzed asymmetric allylic alkylation

We have shown that cymantrene derivatives are better P,N-chelate ligands for palladium-catalyzed allylic alkylation than ferrocenes, which have a similar pentagonal ligand structure to cymantrene derivatives. In particular, the PPh 3-substituted cymantrene gave a higher enantioselectivity (>98%).

Palladium-catalyzed asymmetric allylic alkylations of cycloalkenyl acetates with planar chiral phosphino-ferrocene carboxylic acids

New phosphino-ferrocene carboxylic acids with only planar chirality ( Sp)- 3 and ( Sp)- 4 have been synthesized conveniently from ( S, Sp)- 5 and ( S, Sp)- 7. They were used as ligands in palladium-catalyzed allylic alkylation of cycloalkenyl acetates. With ligand ( Sp)- 4, high yield and good ee were given for reactions of a series of cycloalkenyl acetates and nucleophiles.