An efficient and enantioselective synthesis of oxa[9]helicenes has been established via vanadium(V)-catalyzed oxidative coupling/intramolecular cyclization of polycyclic phenols. A newly developed vanadium complex cooperatively functions as both a redox and Lewis acid catalyst to promote the present sequential reaction and afford oxa[9]helicenes in good yields with up to 94% ee.

Enantioselective oxidative-coupling of polycyclic phenols such as 2-anthracenol, 9-or 3phenanthrol, and 5-chrysenol was established by using vanadium(V/IV) catalysis under air or O2 as a co-oxidant. In the vanadium catalyzed reaction, the corresponding coupling products were obtained in good to excellent yields with up to 93% enantiomeric excess.

Vanadium-mediated enantioselective Friedel-Crafts (FC)-type reactions were established using the dinuclear vanadium complex (R(a),S,S)-1a. The vanadium complex promoted the FC-type reaction of imines with 2-naphthols or indoles to give corresponding adducts with high enantioselectivities.

Enantioselective Oxidative-Coupling of Polycyclic Phenols. -Axially chiral vanadium complexes catalyze the enantioselective oxidative-coupling of polycyclic phenols to biphenols. The corresponding phosphoric acids show catalytic activity in the asymmetric aza-hetero-Diels-Alder reaction. -(TAKIZAWA, S.; KODERA, J.; YOSHIDA, Y.; SAKO, M.; BREUKERS, S.; ENDERS, D.; SASAI*, H.; Tetrahedron 70 (2014) 9, 1786-1793, http://dx.