Enantioselective Polyene Cyclization Catalyzed by a Chiral Brønsted Acid.

Abstract: The first enantioselective polyene cyclization initiated by a BINOL‐derived chiral <italic>N</italic>‐phosphoramide (NPA) catalyzed protonation of an imine is described. The ion‐pair formed between the iminium ion and chiral counter anion of the NPA plays an important role for controlling the stereochemistry of the overall transformation. This strategy offers a highly efficient approach to fused tricyclic frameworks containing three contiguous stereocenters, which are widely found in natural products. In addition, the first catalytic asymmetric total synthesis of (−)‐ferruginol was accomplished with an NPA catalyzed enantioselective polyene cyclization, as the key step for the construction of the tricyclic core, with excellent yield and enantioselectivity. [ABSTRACT FROM AUTHOR]