title: Metal-free catalytic C-Si bond formation in an aqueous medium. Enantioselective NHC-catalyzed silyl conjugate additions to cyclic and acyclic α,β-unsaturated carbonyls.
abstract: A metal-free method for enantioselective conjugate addition of a dimethylphenylsilyl group to α,β-unsaturated carbonyls is reported. Transformations are catalyzed by a chiral N-heterocyclic carbene (NHC), performed in an aqueous solution (3:1 mixture of water and tetrahydrofuran) and are operationally simpler to perform than the NHC-Cu-catalyzed variant. The chiral catalyst is generated from an enantiomerically pure imidazolinium salt (prepared in three steps) and a common organic amine base (dbu). NHC-catalyzed processes proceed with 5.0-12.5 mol % catalyst loading at 22 °C within 1-12 h, affording the desired β-silyl carbonyls in 85:15 to >98:2 enantiomeric ratio and in 50% to >98% yield. Cyclic enones or lactones and acyclic α,β-unsaturated ketones, esters, and aldehydes can be used as substrates.
authors.affiliation: Department of Chemistry, Merkert Chemistry Center, Boston College, Chestnut Hill, Massachusetts 02467, USA.
authors.forename: Jeannette M
authors.initials: JM
authors.lastname: O'Brien
authors.forename: Amir H
authors.initials: AH
authors.lastname: Hoveyda
mesh_terms: D002244:Carbon / Q000737:chemistry*; D002384:Catalysis; D007659:Ketones / Q000737:chemistry*; D012825:Silicon / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D007659:Ketones; D014867:Water; D002244:Carbon; D012825:Silicon