On the Role of Planar Chirality in Asymmetric Catalysis:  A Study toward Appropriate Ferrocene Ligands for Diethylzinc Additions

Abstract

Employing a directed ortho-metalation route, chiral ferrocene-based hydroxyloxazolines have been synthesized, and their capability to serve as bidentate ligand precursors in the diethylzinc addition to benzaldehyde has been investigated. On the basis of the X-ray crystal structures of two ferrocenes, (S,R p )-6 and (S,S p )-10, it became possible to determine the general importance of the element of planar chirality for diastereomeric ferrocene complexes in this process. Comparison of the assumed transition states revealed a preferential catalyst conformation which led to the design of an adequate arene compound [(S)-20] that displayed catalytic activity similar to that of (S,R p )-6.

Ferrocene-derived P,N ligands: synthesis and application in enantioselective catalysis

“…In addition, oxazolines have been shown by various groups to be excellent ortho -directing groups [44][45][46][47]. The origin of diastereoselection is shown in Figure 3.…”

Structurally Diverse Second‐Generation [2.2]Paracyclophane Ketimines with Planar and Central Chirality: Syntheses, Structural Determination, and Evaluation for Asymmetric Catalysis

“…The introduction of central chirality by incorporation of chiral amine side-chains is also possible. The interaction of planar and central chirality, usually referred to as chiral cooperativity, [22][23][24][25][26] was thus studied in a ligand system that has elements of both planar and central chirality.…”

The application of ligands with planar chirality in asymmetric synthesis

“…A comparison of the ferrocene derived ligands with the corresponding benzene derived ligands reveals that the ferrocene template (planar chirality) plays an essential role in this reaction. Recently, Bolm reported the chiral ferrocene-based hydroxyloxazolines catalyzed asymmetric diethylzinc addition to benzaldehyde [7]. The ferrocene derivatives (S, R p )-1 and (S, S p )-2 are diastereomer with the identical central chirality but opposite in planar chirality, while (R p )-3 have only single planar chirality, the results of Scheme 1 indicated the differences in catalytic ef®ciency and enantioselectivity.…”