A Facile One-Pot Synthesis of Polymer-Supported 1,1′-Bi(2-naphthol)s

1,1′-Bi(2-naphthol) (BINOL) was readily anchored onto polymer supports via the Suzuki-Miyaura coupling and used as an immobilized chiral ligand in titanium-catalyzed asymmetric oxidation of thioethers. The polymer-supported BINOL 3 was prepared by the Suzuki-Miyaura coupling reaction of cross-linked polystyrene-supported arylboronic acid 1 with (R)-6-bromo-1,1′-bi(2-naphthol) (2, eq. 1). The asymmetric oxidation of the aryl methyl thioethers 4a and 4b with tert-butyl hydroperoxide took place in the presence of a titanium complex derived from titanium tetraisopropoxide and ligand 3 to give sulfoxides 5a and 5b in 61% and 51% yield with 82% and 91% ee, respectively (eq. 2). Polymer-supported BINOL 3 was recovered, retreated with titanium tetraisopropoxide and reused without significant loss of selectivity [81% ee (1st reuse), 79% ee (2nd reuse), 84% ee (3rd reuse)].