Preparation of New Binaphthol-Based Tridentate Ligands for Enantioselective Synthesis

Abstract

A versatile method for resolution of 2,2'-dihydroxy-[1,1'-binaphthalene]-3-carboxylic acid has been developed. Four enantiomerically pure tridentate ligands, namely 3-(hydroxy- methyl)[1,1'-binaphthalene]-2,2'-diol (3), 3-[(2-hydroxyethoxy)[1,1'-binaphthalene]-2,2'-diol (4), 3-(2-hydroxy-5-methylbenzyl)[1,1'-binaphthalene]-2,2'-diol (5), and 3-(2-hydroxy-4,6-di-tert-butyl-benzyl)[1,1'-binaphthalene]-2,2'-diol (6), were synthesised in excellent yields and used as chiral modifiers of LiAlH4. A modest enantioselectivity was found for the reduction of acetophenone with LiAlH4 modified with ligand 4.