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.

Ungeahnte Qualitäten: Das chirale Ammoniumbetain 1 war als ionischer nucleophiler Katalysator in der asymmetrischen Steglich‐Umlagerung erfolgreich. Die Umsetzung ergab rekordverdächtige Enantioselektivitäten und war auf vielfältige Substrate anwendbar. M.S. = Molekularsieb, Troc = 2,2,2‐Trichlorethoxycarbonyl.

Chiral Ammonium Betaines as Ionic Nucleophilic Catalysts. -Chiral betaine NAB is a highly enantioselective catalyst for the Steglich rearrangement of oxazolyl trichloroethyl carbonates (I) providing oxazolones bearing a quaternary stereogenic carbon atom. -(URAGUCHI, D.; KOSHIMOTO, K.; MIYAKE, S.; OOI*, T.; Angew.