Catalytic asymmetric oxidative couplings of 2-naphthols by tridentate N-ketopinidene-based vanadyl dicarboxylates.

[reaction: see text] A series of oxovanadium(IV) complexes derived from tridentate N-ketopinidene-alpha-amino acids were synthesized. They serve as efficient catalysts for the enantioselective oxidative couplings of various 3-, 6-, or 7-substituted 2-naphthols. The best scenario involves the use of a vanadyl complex arising from L-tert-leucine in CCl4. The asymmetric couplings of 2-naphthols can be conducted smoothly at 40-45 degrees C under a stream of gaseous oxygen, leading to 2,2'-dihydroxy-1,1'-binaphthyls in good yields (61-99%) and with enantioselectivities of up to 87%.