Chiral Betaine Catalyzed Steglich Rearrangement

Significance

A highly enantioselective betaine 1 catalyzed Steglich rearrangement of 5-oxazolyl carbonates is presented. Differently substituted substrates were converted into the corresponding azlactones in high yields and excellent enantioselectivities. The mechanistic rationalization, including a productive versus counter-productive reaction cycle, depending on the substrate concentra-tion, intriguingly correlates with the actual results. Control experiments involving binaphthol ammonium salts as catalysts further revealed the nature of this type of organocatalysis.