Thiazolium Ylide‐Catalyzed Intramolecular Aldehyde-Ketone Benzoin‐Forming Reactions: Substrate Scope

The scope and limitations of intramolecular benzoin‐forming reactions of aldehydes and ketones catalyzed by the combination of a thiazolium salt and a base are described. After optimization of the reaction conditions, five‐ and six‐membered cyclic acyloins were obtained in good to excellent yields and competing reactions such as intramolecular aldol reactions were suppressed. The analogous closure of seven‐membered rings proved difficult.