Frontispiece: The Broensted Acid-Catalyzed, Enantioselective Aza-Diels-Alder Reaction for the Direct Synthesis of Chiral Piperidones

The Rapid Assembly of Molecular Complexity... ...ranks among the most important challenges in modern organic chemistry. In their communication on page513ff. , Schneider etal. have developed a 3-component, formal aza-Diels Alder reaction of aldehydes, para-anisidine, and a silyl dienolate which assembles a broad range of 2-piperidones in one synthetic step with excellent enantioselectivity when catalyzed by a chiral phosphoric acid. DFT-calculations of this process point to a stepwise mechanism comprising a domino-vinylogous Mannich lactamization reaction. The products were shown to be readily manipulated to furnish poly-alkylated piperidines. That strategy might prove highly useful in the context of stereoselective alkaloid synthesis.