title: Stereoselective synthesis of (E)-mannosylidene derivatives using the Wittig reaction.
abstract: Stabilized ylides Bu(3)P=CH(EWG), where EWG is an ester or nitrile group, react with 2,3,4,6-tetra-O-benzylmannono-1,5-lactone giving high yields of mannosylidene derivatives; in contrast to the glucose and galactose analogues, the (E)-mannosylidenes are predominant (E:Z > 9:1), thus minimizing dipole-dipole repulsions in the Wittig reactions. NMR indicates chair-like conformations for solutions of the (E)-mannopyranosylidenes, but not for those (Z)-isomers where data are available (EWG = CN or CO(2)Et). X-ray crystallography shows an approximately twist-boat conformation for the tetra-O-benzyl-protected (Z)-mannosylideneacetonitrile.
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS, UK.
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Coumbarides
authors.forename: Majid
authors.initials: M
authors.lastname: Motevalli
authors.forename: Warda A
authors.initials: WA
authors.lastname: Muse
authors.forename: Peter B
authors.initials: PB
authors.lastname: Wyatt
mesh_terms: D018360:Crystallography, X-Ray; D007783:Lactones / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008358:Mannose / Q000031:analogs & derivatives* / Q000138:chemical synthesis; D008968:Molecular Conformation; D012996:Solutions; D013237:Stereoisomerism
chemical_list: D007783:Lactones; D012996:Solutions; D008358:Mannose