2-Quinoxalinol Salen Copper Complexes for Oxidation of Aryl Methylenes

A copper(II) complex of the 2-quinoxalinol salen ligand (salquCu) 1 has been tested for use in catalysis. Here, an optimized method for oxidation of aryl methylenes and its potential applications are described. In organic solvents, the yields obtained are higher than with other commonly used catalytic methods. Because this methods does not require high heat or increased pressure, this presents an opportunity for more environmentally friendly or green chemistry in a single-phase system. Using this method, a key fragment of natural products Vitamin K-1 and K-2, 1,4-naphthoquinone, can be easily synthesized from 1,2,3,4-tetrahydronaphthalene in increased yield (65%) as compared to established methods (30-40 % yield) that require higher temperatures and increased pressure. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)