title: Stereoselective formation of quaternary stereogenic centers via alkylation of α-substituted malonate-imidazolidinones.
abstract: A new stereoselective alkylation methodology is presented for formation of chiral, nonracemic quaternary centers via a chiral auxiliary protocol involving α-alkylated malonate imidazolidinones. Based on two X-ray structures of quaternized products, the diastereoselectivity observed may be rationalized via a transition-state involving an s-transC-N conformation of the C-N bond of the auxiliary, with the metal cation (K(+)) chelated into the malonate six-membered hole as a Z-enolate. A deprotection protocol involving ethanethiolate exchange of the imide to the corresponding thioester, followed by a standard Fukuyama reduction and a borohydride reduction, furnishes α,α'-quaternized β-hydroxypropionates in high ee overall.
authors.affiliation: Department of Chemistry, University of Cape Town , Rondebosch 7701, South Africa.
authors.forename: Thobela
authors.initials: T
authors.lastname: Bixa
authors.forename: Roger
authors.initials: R
authors.lastname: Hunter
authors.forename: Ana
authors.initials: A
authors.lastname: Andrijevic
authors.forename: Wade
authors.initials: W
authors.lastname: Petersen
authors.forename: Hong
authors.initials: H
authors.lastname: Su
authors.forename: Francis
authors.initials: F
authors.lastname: Dhoro
mesh_terms: D000478:Alkylation; D002384:Catalysis; D048289:Imidazolidines / Q000737:chemistry*; D008314:Malonates / Q000737:chemistry*; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D048289:Imidazolidines; D008314:Malonates; D000644:Quaternary Ammonium Compounds; C004916:ethylene urea; C030290:malonic acid