ZedPhos Ru(II)/Diamine complexes in asymmetric reduction of carbonyl groups.

The asymmetric catalysis by transition metal complexes is recognized an alternative strategy for the preparation of compounds which were believed to be impossible to carry out by conventional methods. The greater part of the transition metals known as excellent catalysts for asymmetric synthesis have optically active diphosphine as source of chiality but in spite of the great variety of chiral ligands available, there is still demand for the development of catalysts which display the requirements of high enantioselectivity, diastereoselectivity and productivity in fine chemicals, fragrances, flavours, agrochemicals1. We have recently prepared two ligands derived from chiral olefins in Z-geometry2, nicknamed ZedPhos by ourselves(a (R,R)-ZedPhos and b(R,R)-Xilyl ZedPhos). We have investigated the stereodifferentiating ability of these ligands in Hydrogen Transfer (HT) and Asymmetric Hydrogenation (AH) of carbonyl compounds in the presence of achiral diamine (ampy), and chiral (R,R) or (S,S)-1,2-diphenyletylen diamine (DPEN). By comparison we have prepared the hydrogenated analogous3, (2R,5R) -2,5-bis(diphenylphosphino)hexane c, to investigate the possible fate of the the double bound on the ligand. e.e.% up to 82% was obtained in the reduction of acetophenone. [1] H.U. Blaser, Asymmetric catalysis on industrial scale, E. SHMIDT Eds., 2004. [2] Cesarotti, Edoardo; Rimoldi, Isabella; Spalluto, Paola; Demartin, Francesco. Chiral 1,4-bis-diphosphine ligands from optically active (Z)-olefins. Tetrahedron: Asymmetry 2007, 18(11), 1278-1283. [3] Yan, Yuan-Yong; RajanBabu, T. V. Ligand substituent effects on asymmetric induction. Effect of structural variations of the DIOP ligand on the Rh-catalyzed asymmetric hydrogenation of enamides. Organic Letters 2000, 2(26), 4137-4140.