title: Synthesis of Chiral Tertiary Boronic Esters by Oxime-Directed Catalytic Asymmetric Hydroboration.
abstract: Chiral boronic esters are useful intermediates in asymmetric synthesis. We have previously shown that carbonyl-directed catalytic asymmetric hydroboration (CAHB) is an efficient approach to the synthesis of functionalized primary and secondary chiral boronic esters. We now report that the oxime-directed CAHB of alkyl-substituted methylidene and trisubstituted alkene substrates by pinacolborane (pinBH) affords oxime-containing chiral tertiary boronic esters with yields up to 87% and enantiomeric ratios up to 96:4 e.r. The utility of the method is demonstrated by the formation of chiral diols and O-substituted hydroxylamines, the generation of quaternary carbon stereocenters through carbon-carbon coupling reactions, and the preparation of chiral 3,4,4-trisubstituted isoxazolines.
authors.affiliation: Department of Chemistry, University of Nebraska-Lincoln, 807 Hamilton Hall, Lincoln, NE, 68588-0304, USA.
authors.forename: Veronika M
authors.initials: VM
authors.lastname: Shoba
authors.affiliation: Department of Chemistry, University of Nebraska-Lincoln, 807 Hamilton Hall, Lincoln, NE, 68588-0304, USA.
authors.forename: Nathan C
authors.initials: NC
authors.lastname: Thacker
authors.affiliation: Department of Chemistry, University of Nebraska-Lincoln, 807 Hamilton Hall, Lincoln, NE, 68588-0304, USA.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Bochat
authors.affiliation: Department of Chemistry, University of Nebraska-Lincoln, 807 Hamilton Hall, Lincoln, NE, 68588-0304, USA. jtakacs1@unl.edu.
authors.forename: James M
authors.identifier: http://orcid.org/0000-0002-1903-6535
authors.initials: JM
authors.lastname: Takacs
mesh_terms: D001895:Boron / Q000737:chemistry*; D002384:Catalysis; D004952:Esters / Q000138:chemical synthesis*; D010084:Oxidation-Reduction; D010091:Oximes / Q000737:chemistry*
chemical_list: D004952:Esters; D010091:Oximes; D001895:Boron
keywords: asymmetric catalysis; homogeneous catalysis; hydroboration; oximes; rhodium