The Synthesis of Pseudo‐Geminal, Pseudo‐Ortho and Ortho Hydroxy‐oxazolinyl[2.2]paracyclophanes for Use as Ligands in Asymmetric Catalysis

Abstract

Synthetic routes to pseudo-geminal, pseudo-ortho and ortho hydroxy-oxazolinyl-2]paracyclophanes (and the diastereoisomers of each) for use as N,O ligands in asymmetric catalysis have been devised. The substitution pattern was found to have a strong effect on the rate and enantioselectivity of the formed catalyst in the addition of diethylzinc to benzaldehyde.

Synthesis of Planar Chiral Carbazole Derivatives Bearing a [2.2]Paracyclophane Skeleton

“…In continuation of our studies on the synthesis of disubstituted [2.2]paracyclophanes7f–h, 9c, 12 we became interested in planar chiral carbazoles such as 2 a (Figure 1), which we hypothesized to be relevant for polymer and materials science due to the extended π‐system of the carbazole core 13. From a synthetic point of view, their preparation by metal‐catalyzed direct functionalization/arylation was expected to provide new insights and opportunities in the chemistry of [2.2]paracyclophane modifications.…”

Planar Chiral Phosphines Derived from [2.2]Paracyclophane

“…There have only been two studies comparing the activity of regioisomeric [2.2]paracyclophane ligands 47. 48…”

“…In the pseudo‐ortho isomer, the donors are positioned on a C 2 symmetric chiral scaffold and hence the scaffold is more dominant. In a related study on hydroxy‐oxazolinyl[2.2]paracyclophanes, the pseudo‐gem ligand gave the highest enantioselectivity for the matched diastereomer and the lowest for the mismatched diastereomer; the other substitution patterns gave moderate enantioselectivities without such a pronounced matched/mismatched effect 48. It is hard to draw any conclusions on just two studies and it will be interesting to know if the substitution pattern of other, non‐symmetric, bidentate ligands shows similar effects.…”

/ Organic Materials: A. Hirsch awarded / Asymmetric Catalysis: C. Bolm honored / Peptide Chemistry: Prize for S. H. Gellman

“…He recently reported in Angewandte Chemie on solvent‐free asymmetric organocatalysis in a ball mill2a and discussed the synthesis of pseudogeminal, pseudo‐ ortho ‐, and ortho ‐hydroxy‐oxazolinyl[2.2]paracyclophanes as ligands for asymmetric catalysis in Advanced Synthesis & Catalysis , for which he is a board member 2b…”