Chiral Ammonium Betaines as Ionic Nucleophilic Catalysts

Abstract

Catalyst debut: The chiral ammonium betaine 1 has been successfully applied to the asymmetric Steglich rearrangement as an ionic nucleophilic catalyst. The catalyzed reaction results in record levels of product enantioselectivity, and has a broad substrate scope. M.S.=molecular sieves, Troc=2,2,2‐trichloroethoxycarbonyl.

The Steglich Rearrangement of 2‐Oxindole Derivatives Promoted by Anion‐based Nucleophilic Catalysis

“…To the best of our knowledge, only one example of the use of an ionic catalyst has been reported for this transformation: Ooi et al . disclosed an elegant example involving the rearrangement of 1 (Figure A) to its C ‐acylated analogue 2 in the presence of the ammonium phenoxide catalyst 3 with excellent enantiomeric excess .…”

ChemInform Abstract: Chiral Ammonium Aryloxides: Efficient Multipurpose Basic Organocatalysts

“…In 2010, the nucleophilic character of the aryloxy anion of chiral ammonium betaines was smartly exploited by Ooi and co-workersw ho reported the Steglich rearrangemento f5 -oxazoly 2,2,2-trichloroethyl carbonate derivatives 43 by meanso f C 1 -symmetric chirala mmonium betaines B2 (Scheme 21). [37] The idea behind the use of betaines versus simple ammonium aryloxylates was to take advantage of ap seudo-intramolecular acyl transfer within the ion pair C that should result in ac ooperativee ntropic activation and ah igh level of stereocontrol (RouteA). Initial attempts to achieve the Steglich rearrangement from 43 (R = C 6 H 5 CH 2 )b ym eanso fB2b as the catalyst failed.T he absence of catalytic activity was ascribed to the Scheme19.…”

Chiral Ammonium Aryloxides: Efficient Multipurpose Basic Organocatalysts

“…In 2010, the nucleophilic character of the aryloxy anion of chiral ammonium betaines was smartly exploited by Ooi and co‐workers who reported the Steglich rearrangement of 5‐oxazoly 2,2,2‐trichloroethyl carbonate derivatives 43 by means of C 1 ‐symmetric chiral ammonium betaines B2 (Scheme ) . The idea behind the use of betaines versus simple ammonium aryloxylates was to take advantage of a pseudo‐intramolecular acyl transfer within the ion pair C that should result in a cooperative entropic activation and a high level of stereocontrol (Route A).…”