Thiazolium ylide-catalyzed intramolecular aldehyde-ketone benzoin-forming reactions: Substrate scope

The scope and limitations of intramolecular benzoin-forming reactions of aldlehydes 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.