Synthesis of the dibenzofuran-based diphosphine ligand BIFAP and its water-soluble derivative BIFAPS and their use in ruthenium-catalyzed asymmetric hydrogenation.

The syntheses of both enantiomers of the novel diphosphine ligand 2.2'-bis( diphenylphosphanyl)-1,1'-bidibenzofuranyl (BIFAP, 1) and the water-soluble analogue (-)-2,2'-bis(diphenyl-phosphanyl)-1,1'-bidibenzofuranyl-8,8'-disul fonic acid dipotassium salt (BIFAPS, 2) are reported. Advantage is taken of the very high regioselectivity in ring functionalisation of the 1,1'-bidi- benzofuranyl backbone. These ligands are used in the ruthenium-catalysed h ydrogenation of methyl acetoacetate and (Z)-acetamidocinnamic acid in metha nol and water. In methanol both BIFAP and BIFAPS give the products in very high enantiomeric excess. With BIFAPS in water a slight drop in the ee of t he products is observed. When BIFAPS is used with either water or methanol as the solvent the addition of a small amount of acid turns out to be essen tial for a fast reaction and high asymmetric induction.