title: Ruthenium-Catalyzed Asymmetric Hydrohydroxyalkylation of Butadiene: The Role of the Formyl Hydrogen Bond in Stereochemical Control.
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.
authors.affiliation: †Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, United States.
authors.forename: Matthew N
authors.initials: MN
authors.lastname: Grayson
authors.affiliation: ‡Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, Texas 78712, United States.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Krische
authors.affiliation: †Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, United States.
authors.forename: K N
authors.initials: KN
authors.lastname: Houk
mesh_terms: D000478:Alkylation; D002070:Butadienes / Q000737:chemistry*; D002384:Catalysis; D006860:Hydrogen Bonding; D008958:Models, Molecular; D012428:Ruthenium / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D002070:Butadienes; D012428:Ruthenium; C031763:1,3-butadiene