Wing-Sze Lee

NEW CHIRAL 2,2'-BIPYRIDINE DIOLS AS CATALYSTS FOR ENANTIOSELECTIVE ADDITION OF DIETHYLZINC TO BENZALDEHYDE

Abstract New C 2 -symmetric chiral 2,2′-bipyridine diols were prepared from readily available homochiral materials such as menthone and camphor. Their catalytic activities in the reaction of diethylzinc with benzaldehyde to give 1-phenyl-1-propanol were studied. In all cases, the yields were good and enantioselectivities up to 95% were observed.

First enantioselective catalyst based on a chiral terpyridine: synthesis of new C2-symmetric 2,2′:6′,2′′-terpyridine ligands and copper-catalyzed enantioselective cyclopropanation of alkenes

Abstract New C2-symmetric chiral 2,2′:6′,2′′-terpyridines were prepared from readily available homochiral materials. Copper complexes of these ligands were prepared in situ and their catalytic activities in cyclopropanations of alkenes with alkyl diazoacetate to give cyclopropyl esters were studied. In all cases, the cyclopropyl ester yields were excellent and enantioselectivities up to 94% ee were observed. Competition experiments revealed that electron-donating substituents on styrene accelerate the reaction. Hammett plot exhibited a good linearity with negative ρ+ value (−0.79).

Chiral bipyridine-copper(I) complex-catalyzed enantioselective allylic oxidation of cyclic alkenes †

Abstract Chiral copper(I)–bipyridine complexes were prepared and used as catalysts in the enantioselective allylic oxidation of cyclic alkenes with tert -butyl perbenzoate. The yields ranged from moderate to good and enantioselectivities up to 70% were observed.

New chiral 2,2′:6′,2″-terpyridine ligands from the chiral pool: synthesis, crystal structure of a rhodium complex and uses in copper- and rhodium-catalyzed enantioselective cyclopropanation of styrene

Abstract A number of chiral C 2 -symmetric 2,2′:6′,2″ terpyridines L 1 – L 4 were synthesized in moderate to good yields from commercially available chiral materials. Copper(II) and rhodium(III) chloride complexes of these ligands were prepared in good yields. The Rh( L 2 )Cl 3 complex was isolated as a yellow crystalline solid and characterized by X-ray crystallography. Both Cu( L )(OTf) 2 and Rh( L )(OTf) 3 were found to be active catalysts in the cyclopropanation of styrene with ethyl diazoacetate. Enantioselectivity up to 82% e.e. was observed.

Chiral zinc(II) bipyridine complex. Crystal structure and catalytic activity in asymmetric allylation reaction

A chiral bipyridine zinc(II) complex, Zn(L)Cl2 (L=chiral bipyridine), has been prepared and characterized by usual spectroscopic means and X-ray crystallography. Reaction of Zn(L)Cl2 with AgCF3SO3 gave Zn(L)(CF3SO3)2insitu; this complex is an active catalyst for allylation of aldehydes with enantiomeric excesses up to 60%.

Ruthenium catalyzed asymmetric transfer hydrogenation based on chiral P,N,O Schiff base ligands and crystal structure of a ruthenium(II) complex bearing chiral P,N,O Schiff base ligands

Abstract A ruthenium catalyst, generated in situ by heating the chiral P,N,O Schiff base ligand L (L = (S)-Ph2PC6H4CNCHPhCH2OH) with Ru(DMSO)4Cl2 in 2-propanol, is active for asymmetric transfer hydrogenation with best enantioselectivity up to 81%. A ruthenium complex of formula RuL2Cl2 is prepared and its crystal structure revealed that the two chiral P,N,O Schiff ligands are in meridional configuration. This complex is also an active catalyst for asymmetric transfer hydrogenation. However, the ‘[Ru(DMSO)4]Cl2 + chiral P,N,O ligand’ protocol displays better enantioselectivity.

Synthesis of new chiral terpyridine mono-N-oxide and di-N-oxide ligands and their applications in copper-catalyzed asymmetric cyclopropanation

Abstract New families of chiral terpyridine mono- N -oxides L 1 – L 3 and di- N -oxides L 4 – L 6 , were synthesized in moderate to good yields by simple oxidation of their corresponding terpyridines with m -CPBA. The copper(II) triflate complexes of these ligands were found to be highly effective catalysts for asymmetric cyclopropanation of styrene with ethyl diazoacetate. The isolated yields of cyclopropane were excellent and the enantiomeric excesses of up to 83% were observed. Competition experiments with substituted styrenes showed good σ + correlations with ρ =−0.70 for mono- N -oxide L 3 and ρ =−0.69 for di- N -oxide L 6 .

Copper Complexes of Chiral Tetradentate Binaphthyl Schiff‐Base Ligands: Syntheses, X‐ray Crystal Structures and Activity in Catalytic Asymmetric Cyclopropanation of Alkenes

A number of new chiral monomeric binaphthyl Schiff-base ligands H2L [where H2L = 2,2′-bis(3-R1-5-R2-2-hydroxybenzylideneamino)-1,1′-binaphthyl] and a series of chiral copper(II) complexes [CuL] were prepared in good or nearly quantitative yields. Some of the free ligands and the [CuL] complexes were structurally characterized by X-ray crystallography. Almost all the [CuL] complexes were found to be active catalysts for the asymmetric cyclopropanation of alkenes with ethyl or tert-butyl diazoacetate. Enantioselectivities of up to 77% ee were observed. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Enantioselective palladium catalyzed allylic substitution using chiral P,N,O Schiff base ligands

Abstract Palladium complexes prepared in situ from [Pd(η3-C3H5)Cl]2 and a number of chiral Schiff ligands having hard and soft donor atoms were evaluated as catalysts for allylic substitution reaction. Enantioselectivity of up to 92% was observed.

Stereoselective formation of a single-stranded helicate : Structure of a bis(palladium-allyl)quaterpyridine complex and its use in catalytic enantioselective allylic substitution

Chiral C2-symmetric quaterpyridine L reacts with [Pd(eta3-C3H5)Cl]2 to form a chiral single-stranded helical binuclear palladium complex of formula [Pd2(eta3-C3H5)2(L)]2+; the complex can efficiently catalyze allylic substitution of 1,3-diphenylprop-2-enyl acetate with dimethyl malonate with enantioselectivity up to 85%.