Ikuko Abe

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

Abstract 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.

Catalytic use of chiral phosphine ligands in asymmetric Pauson–Khand reactions

Abstract Catalytic asymmetric Pauson–Khand reactions with chiral bidentate phosphines as ligands have been successfully accomplished. The catalytic use of ( S )-BINAP as a ligand was demonstrated to be the most effective in the cobalt-catalyzed reactions of 1,6-enynes, providing a facile entry to optically active 2-cyclopentenone derivatives with high enantioselectivity. A plausible mechanism for the asymmetric induction is proposed on the basis of the stereochemical outcome obtained.

(S)-Proline-derived new chiral ligands with phosphino, organosulfur or organoselenenyl functionality as an enantiocontrollable coordinating element

Abstract The synthesis of ( S )-proline-derived chiral ligands bearing phosphino, organosulfur or selenenyl groups and their use as chiral ligands in palladium-catalyzed asymmetric allylic alkylations has been accomplished. In particular, the ( S )-proline-derived phosphine ligands bearing alkylsulfenyl groups provided high enantioselectivity, and the degree of asymmetric induction was dependent upon the steric bulk of the alkyl substituents in sulfenyl groups. The stereochemical results are rationalized by a plausible mechanism involving the assistance of chelates formed by the participation of the two preferred heteroatoms involved.

Asymmetric catalytic Pauson–Khand reactions with chiral phosphine ligands: Dramatic effects of substituents in 1,6-enyne systems

Abstract A cobalt-catalyzed reaction of 1,6-enyne systems under a carbon monoxide atmosphere using chiral phosphine ligands provides a facile entry to optically active 2-cyclopentenone derivatives. (S)-BINAP was demonstrated to be the most effective in the cobalt-catalyzed cyclization of 1,6-enynes among various chiral bidentate phosphine ligands employed, affording chiral 2-cyclopentenone derivatives with high enantioselectivity. The dramatic effects of the substituents in the 1,6-enynes were observed in this asymmetric synthesis. A plausible mechanism for the asymmetric induction is proposed on the basis of the stereochemical outcome obtained.

Chiral sulfoxide ligands bearing nitrogen atoms as stereocontrollable coordinating elements in palladium-catalyzed asymmetric allylic alkylations

Abstract Palladium-catalyzed asymmetric allylic alkylations were studied by using chiral sulfoxide ligands bearing nitrogen atoms as coordinating elements, such as chiral α-sulfinylacetamides, β or γ-amino sulfoxides, and β-sulfinyl sulfonamides. The effects of the chiral sulfinyl functions on the asymmetric induction were demonstrated. Use of ( S )-2-pyrrolidinophenyl p -tolyl sulfoxide or ( S )-2-( N -butyl- N -methylaminomethyl)phenyl p -tolyl sulfoxide as chiral ligands in the palladium-catalyzed asymmetric allylic alkylations provided the highest enantioselectivity (50 or 58% e.e., respectively) among chiral sulfoxide ligands examined by us. The participation of the sulfinyl groups in these catalytic asymmetric reactions is rationalized, and the mechanism for the asymmetric induction is proposed on the basis of the stereochemical outcome obtained.

New chiral sulfoxide ligands in catalytic asymmetric Diels–Alder reactions: double acceleration by the chiralities of the sulfoxides and oxazolines

Abstract New chiral sulfoxide ligands which are useful for catalytic asymmetric Diels–Alder reactions have been developed. The new ligands involve a chiral sulfinyl function and a 1,3-oxazoline ring with an asymmetric carbon center, in which the chiral sulfinyl group has been revealed to play a crucial role in achieving high enantioselectivity in asymmetric Diels–Alder reactions. Among the Lewis acid catalysts employed, magnesium iodide provided the highest chemical and stereochemical efficiency in the cycloaddition reactions. A mechanistic pathway for the asymmetric synthesis is proposed on the basis of the stereochemical outcomes obtained.

A novel direct catalytic asymmetric synthesis of cyclic indole derivatives by intramolecular carbopalladation of allenes and subsequent intramolecular amination

Abstract A novel asymmetric synthetic method allowing a facile entry to chiral cyclic indole compounds has been developed by means of asymmetric carbopalladation–amination of allenes using a palladium catalyst with chiral phosphine ligands: intramolecular carbopalladation of allenes, which bear o -iodophenyl amino groups, was followed by intramolecular amination of the resultant π-allylpalladium intermediates. The enantioselectivity of the asymmetric reactions were found to be dependant on the chiral phosphine ligands and the solvent used; N -methylpyridone was the most effective solvent for achieving efficient enantioselectivity with high chemical yields, and ( S )-(−)-BINAP or ( S )-Tol-BINAP were revealed to be the most useful of the chiral phosphine ligands examined, depending on the substrate employed.

Palladium-catalyzed asymmetric reactions enantiocontrolled by chiral organosulfur functionality

Abstract Participation of chiral sulfinyl functionality in palladium-catalyzed asymmetric reactions is demonstrated by using chiral sulfoxides as chiral ligands or chiral substrates. New chiral ligands, o-(phosphinoamino)phenyl and o-phosphinophenyl sulfoxides, have been developed. The structure of an intermediary palladium complex was determined by X-ray crystallographic analysis. The palladium-catalyzed asymmetric 1,3-rearrangements of (1,3-butadienyl)cyclopropanes bearing chiral sulfinyl groups to cyclopentenes are described. The participation of the chiral sulfinyl group to the palladium catalyst is described.