Asymmetric Induction via the Structural Indenyl Effect

Abstract

Constrained geometry, planar chiral, dichloro[η5:κS-indenyl-sulfanyl]rhodium complex (pS)-1 reacts with (E)-2-pentene in the presence of silver hexafluoroantimonate to afford syn,syn-1,3-dimethyl-π-allyl complex (pS)-2 in 88% yield. Reaction of (pS)-2 with the sodium or tetrabutylammonium salts of dimethyl malonate anion provided dimethyl 2-[(1R,2E)-1-methyl-2-buten-1-yl]-1,3-propanedioate ((R)-3) in 68–70% yield and 66–68% enantiomeric excess. NMR analysis and density functional theory calculations establish that asymmetric induction is substantially determined by the electronic asymmetry of the indenyl ligand polarizing the preferred site of nucleophilic attack on the π-allyl ligand toward the terminal carbon that is syn to the indenyl benzo-ring.