Silicon‐Directed Nazarov Reactions II. Preparation and Cyclization of β‐Silyl‐substituted Divinyl Ketones

Two general methods for the preparation of β‐silyl‐substituted divinyl ketones have been developed starting from either α, β‐unsaturated aldehydes or simple ketones. Anhydrous FeCl₃ induces the cyclization to cyclopentenones under mild conditions and in good yields with predictable and complete control over the position of the double bond in the five‐membered ring. The observed effects of substituents on rate can be explained by a rate‐determining cationic electrocyclization. Silyl substitution has been shown to retard the reaction.