Abstract
The catalyst generated in situ from RuH2(CO)(PPh3)3, (S)-SEGPHOS, and a chiral phosphoric acid promotes asymmetric hydrohydroxyalkylation of butadiene and affords enantioenriched α-methyl homoallylic alcohols. The observed diastereo- and enantioselectivities are determined by both the chiral phosphine and chiral phosphate ligands. Density functional theory calculations (M06/SDD-6-311G(d,p)–IEFPCM(acetone)//B3LYP/SDD-6-31G(d)) predict that the product distribution is controlled by the kinetics of carbon–carbon bond formation, and this process occurs via a closed-chair Zimmerman–Traxler-type transition structure (TS). Chiral-phosphate-dependent stereoselectivity arising from this TS is enabled through a hydrogen bond between the phosphoryl oxygen and the aldehyde formyl proton present in TADDOL-derived catalysts. This interaction is absent in the corresponding BINOL-derived systems, and the opposite diastereo- and enantioselectivity is observed. Additional factors influencing the stereochemical control are determined.
Supporting Information
Complete list of authors in the Gaussian 09 reference (ref 19); Cartesian coordinates, energies, free energies, and numbers of imaginary frequencies for all stationary points and values of the imaginary frequencies for all transition structures. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/jacs.5b04844.
