Brønsted Acid-Catalyzed,\nAsymmetric Allenoate\nClaisen Reaction

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