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.