Organocatalytic enantio- and diastereoselective synthesis of 1,2-dihydronaphthalenes from isobenzopyrylium ions.

A highly efficient asymmetric synthesis of dihydronaphthalenes is disclosed. The process represents a new addition to the limited asymmetric reactions of isobenzopyryliums, a family of versatile 10π-electron aromatic species. Excellent asymmetric induction is achieved for the first time without an anchoring group in the 4-position or a metal catalyst, both of which were required previously in these reactions. The success is attributed to the unusual chiral counteranion (meanwhile also the nucleophile) generated in situ from the chiral phosphate and the boronic acid as well as the leaving group. Preliminary control experiments provided important insight into the reaction mechanism.