Terruhedron: Asynunerry Vol. 1, No. 12, pp.913-930.1990 Printed in Greia Britain C957-4166/90 $3.00+.00 Pergmm Press plc Novel Chiral Water Soluble Phosphines II. Applications in Catalytic Asymmetric Hydrogenation Imre TOth, Brian E. Hanson,* Mark E. Davis Department of Ghemistry and L+artment of Chemical Engineezing Virginia PoIylechnic Instituteand StateUa~ersi~, Blacksburg, VA 24061 (Received 16 October 1990) Abstract: The results of the homogeneous asymmetric hydrogenation of several dehydroamino acids by rhodium-diene complexes of the chiral ligands; 2,3-0-isopropylidene-2,3-dihydroxy-1,4- bis(-bis(-p-N,N-dimethylaminophenyl)phosphino)butane, 2a; 2,4-bis(-bis(-p-N,N- dimethylaminophenyl)phosphino)pentane, 3a; and 2,3-bis(-bis(-p-N,N- dimethylaminophenyl)phosphino) butane, 4a; and their N-protonated and N-Me quatemized analogues are reported. The ligands comprise a versatile set which can be used both in organic and aqueous solvents. A detailed investigation of solvent and substituent effects is provided. The presence of p-NMe2 groups enhances the rate of reaction in all cases. For the DIOP derivative, 2a, the presence of the dimethyla~no group causes a reversal in the observed dominant product antipode. This is at~bu~ p~o~nant~y to a change in preferred ligand ~nfo~tion rather than to a kinetic difference between the two ~~t~~~~ of a single ligand coronation. The recently prepared tetrakis-(p-quatemary amino)phenyl derivatives of DIOP, BDPP (Skewphos) and Chiraphos (Scheme 1) represent the first examples of chiral water soluble ligands with more than one cationic functional gr0up.t The presence of four ionic groups in the quatemized versions of these ligands provides unlimited water solubility to their rhodium complexes in a fashion similar to the sulfonated derivatives of &ii chelating phosphines2 Complexes of the cationic ligands show negligible solubility in moderately polar organic solvents such as ethyl acetate, dichloromethane, benzene, etc., and thus can serve as catalysts for the enantioselective two-phase hydrogenation of prochiral organic substrates. Water sohtbihzation by the quatemization method is more favorable than direct sulfonaticm for sensitive ligands, such as DIOP, which caunot bo subjected to Water sotuble complexes with ionic ligands C~SI provide significantly different enantioselectivities compared to the non-functionalized derivatives in methanol or other organic solvents.23 Substitution at the aryl rings of the ligands alone is sufficient to alter the enantioselectivity in non-aqueous solvents. 4-* The effect of water on euantioselectivity has been investigated recently and it was proposed that enantioselectivity is a function of solvent solvophobicity.9 In many cases, however, it is difftcult to separate substituent effects from solvent effects. 913