Asymmetric Counteranion‐Directed Catalysis

Abstract

Exceedingly high enantioselectivity in a catalytic reaction can be realized even when the chirality resides only in the counteranion of the catalyst. A salt (1) composed of an achiral ammonium cation and a chiral phosphate counteranion catalyzes asymmetric transfer hydrogenations of aromatic and aliphatic α,β‐unsaturated aldehydes with a Hantzsch ester in excellent enantioselectivities (see scheme).

Die katalytische asymmetrische Acetalisierung

“…Zunächst führt die reversible Addition der primären Alkoholfunktion des Diols an den Aldehyd zur Bildung eins Halbacetal-Intermediats A. Protonierung seiner OH-Funktion durch den Katalysator führt zur Eliminierung von Wasser und der Entstehung des entscheidenden Oxocarbeniumionen-Intermediats B. Das chirale Imidodiphosphat-Gegenanion sorgt für eine chirale Umgebung des Oxocarbeniumkations [13] und wirkt als Base, die den nucleophilen Angriff der zweiten Alkoholgruppe auf die si-Seite des Oxocarbeniumions dirigiert, wodurch das Skonfigurierte cyclische Acetal entsteht.…”

A Powerful Chiral Counteranion Motif for Asymmetric Catalysis

“…[23,24] In addition, their corresponding bases should be useful in applications of asymmetric counteranion-directed catalysis (ACDC). [25][26][27] Recently, a highly acidic binaphthyl-derived chiral disulfonic acid catalyst has been designed and synthesized. [28][29][30] The corresponding chiral cyclic disulfonimides have been unknown but appeared to us as a particularly promising chiral catalyst motif.…”

NH-Isoxazolo-bicycles; new molecular scaffolds for organocatalysis

“…Prior to testing the enantiocontrol with catalytic systems based on the resolved bicycles we explored the possibility for counter ion directed organocatalysis. 5,30,31 Control experiments confirmed that rac-5a, in combination with either (þ)-or (À)-CSA, furnished products with essentially with no enantioenrichment. Similarly, no enhancement was observed with (þ)-or (À)-1,1 0 -binaphthyl-2,2 0 -diyl hydrogen phosphate 9 nor with the more sterically demanding (R)-TRIP 13 as co-catalyst with rac-5a; in the case of (R)-TRIP, limited solubility of the co-catalyst is reflected in the poor chemical yield, results are summarised in Table 4, entries 1e5.…”

“…1e3 A range of catalyst architectures with varying modes of operation have been developed and whilst SOMO 4 and counter ion catalysis 5 are at early stages of development many applications of enamine, 6 iminium 7 and hydrogen bonding catalysis 8 have been reported. To-date the most successful catalysts are derivatives of the five-membered, secondary amine heterocycles proline 9 and imidazolidinone.…”