title: Phosphine-catalyzed asymmetric synthesis of β-lactones from disubstituted ketenes and aldehydes.
abstract: In this article we describe a general catalytic procedure for the formation of β-lactones bearing two stereogenic centers, from disubstituted ketenes and achiral aldehydes. BINAPHANE was found to display excellent enantioselectivity (≥90% ee for eight examples) and good diastereoselectivity (≥90:10 for 13 examples) in catalyzing the formation of β-lactones bearing two stereogenic centers from achiral aldehydes (both aromatic and aliphatic) and alkylarylketenes or dialkylketenes. A preference for formation of the trans diastereomer was observed in these reactions. For those reactions where BINAPHANE failed as a catalyst, tri-n-butylphosphine was found to be an effective achiral nucleophilic catalyst, effecting good yield and diastereoselectivity in racemic β-lactone formation. Evidence for the involvement of phosphonium enolate intermediates in the reaction mechanism was obtained through reaction monitoring by (31)P NMR spectroscopy and by comparison with previously characterized intermediates observed in the phosphine-catalyzed ketene homodimerization reaction.
authors.affiliation: Department of Chemistry, Oakland University , 2200 North Squirrel Road, Rochester, Michigan 48309-4477, United States.
authors.forename: Shi
authors.initials: S
authors.lastname: Chen
authors.forename: Mukulesh
authors.initials: M
authors.lastname: Mondal
authors.forename: Ahmad A
authors.initials: AA
authors.lastname: Ibrahim
authors.forename: Kraig A
authors.initials: KA
authors.lastname: Wheeler
authors.forename: Nessan J
authors.initials: NJ
authors.lastname: Kerrigan
mesh_terms: D000447:Aldehydes / Q000737:chemistry*; D002384:Catalysis; D003516:Cycloparaffins / Q000737:chemistry*; D019281:Dimerization; D005030:Ethylenes / Q000737:chemistry*; D007659:Ketones / Q000737:chemistry*; D007783:Lactones / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D010720:Phosphines / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D000447:Aldehydes; D003516:Cycloparaffins; D005030:Ethylenes; D007659:Ketones; D007783:Lactones; D010720:Phosphines; C043255:tri-n-butylphosphine; C044646:phosphine; C008223:ketene