title: Silyl fluoride electrophiles for the enantioselective synthesis of silylated pyrrolidine catalysts.
abstract: Chiral silylated pyrrolidine catalysts are obtained in high yield and enantioselectivity by sparteine-mediated lithiation of N-Boc-pyrrolidine and addition to silyl fluoride electrophiles. The activity and enantioselectivity of a new tert-butyldiphenylsilylpyrrolidine catalyst has been demonstrated for various asymmetric Michael reactions at 5 mol % catalyst loading and affords up to 99% ee for asymmetric Michael reactions with aldehydes and nitro-olefins. Acetaldehyde donors proceed with yields up to 77% and enantioselectivities up to 96% ee, avoiding common side reactions that often lower yields. Insight into the mechanism of pyrrolidine-based catalysts is provided by demonstrating ESI mass spectrometry evidence for activation of a nitro acceptor by formation of a hydrogen-bonding adduct with the catalyst amine. Analysis of reaction intermediates using mass spectrometry provides evidence that the pyrrolidine catalyst also plays a role in activating nitro-olefins through hydrogen-bonding.
authors.affiliation: Department of Chemistry, University of California, One Shields Avenue, Davis, California 95616, USA.
authors.forename: Kaleb I
authors.initials: KI
authors.lastname: Jentzsch
authors.forename: Taewoo
authors.initials: T
authors.lastname: Min
authors.forename: Jennifer I
authors.initials: JI
authors.lastname: Etcheson
authors.forename: James C
authors.initials: JC
authors.lastname: Fettinger
authors.forename: Annaliese K
authors.initials: AK
authors.lastname: Franz
mesh_terms: D002384:Catalysis; D005459:Fluorides / Q000737:chemistry*; D015394:Molecular Structure; D011759:Pyrrolidines / Q000737:chemistry*; D012821:Silanes / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D013237:Stereoisomerism
chemical_list: D011759:Pyrrolidines; D012821:Silanes; D005459:Fluorides