Kunio Hiroi

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.

New chiral o-(phosphinoamido)phenyl sulfoxide ligands in palladium-catalyzed asymmetric allylic alkylations

Abstract A new chiral o -(phosphinoamido)phenyl sulfinyl functionality was demonstrated as efficient ligands in palladium-catalyzed asymmetric allylic alkylations. Especially, chiral o -(phosphinoamido)phenyl 2-methoxy-1-naphthyl sulfoxide was concluded to be the most effective ligand for the asymmetric induction among the known ligands bearing a chiral organosulfur group as the sole chiral source. The mechanism of the asymmetric induction is proposed.

Chiral β-phosphino sulfoxides as chiral ligands in palladium-catalyzed asymmetric allylic nucleophilic substitution reactions

Abstract The first attempt to use chiral β-phosphino sulfoxides as chiral ligands was successfully accomplished in a palladium-catalyzed asymmetric allylic alkylation and amination, providing extremely high enantioselectivity with chiral 2-(diphenyl-phosphino)phenyl 2-methoxy-1-naphthyl sulfoxide. The structure of the intermediary palladium complex chelated by the ligand was determined by the X-ray crystallographic analysis. The mechanism for the asymmetric induction is proposed on the basis of the stereochemical results obtained.

Catalytic asymmetric oxidative lactonizations of meso-diols using a chiral iridium complex

A chiral amino alcohol/Ir complex catalyzes the asymmetric oxidative lactonizations of meso-diols to give the corresponding lactones in up to 81% ee.

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.

Transition metal-catalyzed asymmetric vinylcyclopropane-cyclopentene rearrangements. Asymmetric synthesis of cyclopentane derivatives using chiral sulfoxides as chiral sources

Abstract Optically active α-olefinic cyclopropane derivatives, prepared by Michael addition of sodium bromomalonate to chiral vinylic sulfoxides followed by intramolecular asymmetric alkylation, led to facile transformation into chiral cyclopentane derivatives upon treatment with transition metals such as palladium, nickel, and platinum. The stereospecificity of the rearrangements was dependent on the catalysts and the reaction conditions employed. The palladium catalysts represented the highest stereospecificity.