Brønsted Acid-Catalyzed, Asymmetric Allenoate Claisen Reaction

An auxiliary-based protocol is described for an asymmetric allenoate Claisen rearrangement. Silicated tosic acid (10 mol %) was used as an inexpensive, user-friendly catalyst. Stereochemical analysis revealed a preferential attack at the si face of prostereogenic olefin. The amine auxiliary was readily hydrolyzed and can be isolated from the reaction mixture (85–87% recovery). The resulting unsaturated β-keto esters were isolated in ≤99% yield and 98% ee. Diastereoselective examples provided a 96:4 syn:anti ratio of the resulting vicinal stereocenters.