New asymmetric vanadium catalyst for highly selective oxidative coupling polymerization

Novel oxovanadium(IV)-bisoxazoline catalysts, such as vanadyl sulfate (VOSO4)-(R)-2,2'-isopropylidenebis(4-phenyl-2-oxazoline) [(R)Phbox], for the asymmetric oxidative coupling polymerization (AOCP) of 2,3-dihydroxynaphthalene were developed. For example, the AOCP with VOSO4-(R)Phbox in CH2Cl2-MeOH [7/1 (v/v)] at room temperature for 24 h under an O-2 atmosphere, followed by acetylation of the hydroxyl groups, afforded a polymer in a 58% yield with a specific rotation of [alpha](D) = -147. The enantioselectivity during the polymerization was estimated to be 80% enantiomeric excess (S), a value much higher than that observed for the polymerizations with the copper(l)-based catalyst systems and the typical oxovanadium(IV) catalysts reported for the asymmetric oxidative coupling producing the 1,1'-bi-2-naphthol derivatives. (c) 2005 Wiley Periodicals, Inc.