Synthesis of Concave and Vaulted 2H-Pyran-Fused BINOLs and Corresponding [5] and [7]-Oxa-helicenoids: Regioselective...

Synthesis of concave and vaulted 2H-pyran-fused BINOLs has been achieved. A regioselective, path-breaking concerted cascade route allows the placement of six-membered heteroaromatic rings at the sterically crowded 7,8 and 7',8' positions of BINOL. DFT studies with relative energetics that support the kinetically controlled reaction pathway are preferred, matching the experimental results. The new BINOLs exhibit smaller dihedral angle than BINOL on the diol part; this structural feature can be an assisting factor for better ligation with metals in the metal-catalyzed reactions. Corresponding C₂ symmetric [5] and [7]-oxa-helicenoids have an overlapping, sterically crowded geometry.