Chiral thioether ligands: coordination chemistry and asymmetric catalysis

Sterically Congested, "Roofed" .BETA.-Iminodisulfides as New Chiral Ligands for Palladium-Catalyzed, Asymmetric Allylic Alkylation

“…Steric repulsion between the disulfide moiety of the 2-iminothioether ligand and the phenyl ring of the p-allyl substrate appears greater than that from the "roof " moiety of the ligand, rendering the intermediate (12) more feasible than 11. Nucleophilic attack at the p-allyl complex would occur at a transposition relative to the sulfur atom, which is a better electron acceptor, to preferentially give the (S)-alkylated product (8).…”

“…Chiral b-aminosulfides and their derivatives, 8,9) which are principally prepared from the corresponding 2-amino alcohols and/or a-amino acids, are used less frequently in this reaction system. However, Anderson et al, 10,11) Page and colleagues, 12) Braga et al, 13,14) and Tokuda et al 15) have reported good to excellent chemical yields and enantioselectivities using these compounds, indicating that chiral baminosulfides have potential as effective chiral ligands.…”

“…20) We initially tested the catalytic activity of the symmetrical "roofed" b-iminodisulfide 5a-Pd(II) complex, prepared in situ. The Pd(II)-catalyzed allylic alkylation of 1,3-diphenyl-2-propenyl acetate (7) with dimethyl malonate under standard conditions, in the presence of N,O-bis(trimethylsilyl)acetamide (BSA) as a base and a catalytic amount of KOAc in CH 2 Cl 2 , did not proceed well, and gave the corresponding product (8) in only 6% yield and 12% ee ( Table 1, entry 1).…”

Synthesis and characterization of four new unsymmetrical potentially pentadentate Schiff base ligands and related Zn(II) and Cd(II) complexes

“…Transition metal complexes with nitrogen, oxygen and sulfur donors ligands have been prepared since the beginning of the development of coordination chemistry and there is continuing interest in these complexes [1][2][3]. It has attracted more attention in metal complexes of unsymmetrical Schiff bases ligands with nitrogen, oxygen and sulfur atoms in recent years due the fact that the ligands around central metal ions in natural systems are unsymmetrical [4,5].…”

“…It has attracted more attention in metal complexes of unsymmetrical Schiff bases ligands with nitrogen, oxygen and sulfur atoms in recent years due the fact that the ligands around central metal ions in natural systems are unsymmetrical [4,5]. The presence of both hard and soft donor atoms in the backbones of unsymmetrical Schiff bases ligands, they readily coordinate with a wide range of transition metal ions [1][2][3][4][5][6][7][8]. Most of these unsymmetrical Schiff bases ligands obtained by the condensation of different types of primary amines with various ketones and aldehydes [9,10] by metal-templated [11][12][13] or by direct syntheses [14,15].…”