NEW DEVELOPMENTS IN ENANTIOSELECTIVE HYDROGENATION

A broad variety of atropisomeric biphenyl diphosphines have been synth esized via optically active 6,6'-dimethoxybiphenyl-2,2'-diyl-bis(dip p hosphonates), -bis(phosphonic dichlorides), -bis(phosphonous dichlorid es) and -bis(primary diphosphines). The usefulness of diphosphine vari ety in enantioselective hydrogenation was demonstrated by application to substrates of unconventional and unprecedented type such as an alph a-pyridyl ketone, gamma-keto olefins, an alpha-pyrone and an enol ethe r of a beta-keto lactam. Enantioselectivities and rates in these hydro genations were markedly influenced by the electronic and steric proper ties of the diphosphine ligands. Of particular utility were the biphen yl diphosphines with alpha-furyl and 3,5-di-t-butylphenyl groups on th e P atoms. A synthesis of a tetrasulfonated biphenyl diphosphine carry ing the sulfonato substituents in the para position of the P-phenyl ri ngs has also been developed. Ruthenium catalysts derived from this lig and proved highly efficient for several enantioselective hydrogenation s in aqueous systems.