Strategies for the development of enantioselective catalysts

Abstract

Novel C 2 -symmetric diiminosphosphoranes and diketimines are useful ligands for Pd-and Cu-catalyzed C±C bond forming reactions, Angermund's molecular modeling based on accessible molecular surface serving as a guide in predicting catalyst activity. The ®rst highly enantioselective diphosphites as ligands in Rh-catalyzed hydrogenation are also described, the selectivity principle being based on in situ selection of conformational enantiomers. Finally, a systematic study of chiral diphosphonites reveals that ferrocene-based derivatives are ideal in hydrogenation and certain conjugate addition reactions. These methods are compared to biocatalytic strategies based on the creation of enantioselective biocatalysts by in vitro evolution, a rational process which is independent of the catalyst structure or mechanism.

Copper‐catalyzed Enantioselective Conjugate Addition Reactions of Organozinc Reagents

“…7.2), with various bridging units were introduced by the groups of Reetz, Chan, and Waldmann [48][49][50]. Excellent enantioselectivities -up to 96% for ligand 23, for instance -were found.…”

“…Excellent enantioselectivities (96% ee) for 2-cyclohexenone were also obtained with the ligands 22, 23, and 29, introduced by the groups of Pfaltz [47], Reetz [48], and Alexakis [63], respectively. Ees in the range of 90-92% were found with ligands 24, 25, 30, and 35 [49, 55, 60].…”

“…7.5) [47,48]. It appears that the structural requirements of the chiral ligands are not especially limited.…”

Peptidic Amidomonophosphane Ligand for Copper‐Catalyzed Asymmetric Conjugate Addition of Diorganozincs to Cycloalkenones

“…[16] These phosphorus ligands were shown to be applicable in the conjugate addition reaction of nitroalkenes [17][18][19][20][21] and a,b-unsaturated lactones. [22,23] Copper-catalyzed conjugate arylation, [24,25] vinylation [26] and kinetic resolution [27] have been the topics of the recent brilliant studies. [28] It is natural for us to apply the amidophosphane 1 in the copper-catalyzed asymmetric conjugate addition of diorganozincs, because 1 was really effective in the conjugate alkylation of Grignard reagents [6] as well as the Rh(I)-catalyzed conjugate arylation of arylboronic acids.…”

Enantioselective Hydrogenations with Chiral Titanocenes

“…One the most effective routes for the enantioselective synthesis of amines, alcohols and alkanes is the transition-metal-complex-catalyzed hydrogenation of the corresponding prochiral compounds. Among numerous known catalysts for these reactions, metallocenes are one of the most promising types [3,4,5,6], as they are strongly unsymmetrical and, thus, reduce the number of possible isomeric catalyst-substrate complexes, leading to excellent enantiocontrol in many cases. In addition, the possibility of restricting the conformational flexibility and the steric bulk by adding substituent or bridges allows the rational design and tailoring of catalytic activity and selectivity.…”