Functionalized Dihydro/Tetrahydrobenzo[ a ]Fluorenes via Interrupted Iso ‐Nazarov Reaction

ABSTRACT Under the catalysis of p ‐TsOH immobilized on silica (PTS‐Si), the iso ‐Nazarov reaction of ( E )‐(2‐stilbenyl)methanol/( E )‐(2‐stilbenyl)imine tosylate bearing a styrene moiety forged the corresponding [5/6] systems with the exclusive trans relationship at the two newly formed adjacent stereogenic centers. The ensuing “interrupted” nucleophilic addition by the pendent styrenyl olefin furnished the dihydro‐11 H ‐benzo[ a ]fluorene with the exclusive cis stereocontrol at the two‐carbon ring junction. Thus, from non‐chiral starting materials, the interrupted iso ‐Nazarov reaction formed two rings and provided the olefin moiety, which can be functionalized to other groups/systems possessing one to two additional chiral centers. Up to five contiguous stereogenic centers on the tetrahydrobenzo[ a ]fluorene could be constructed efficiently.