Stereoselective synthesis of (E)-mannosylidene derivatives using the Wittig reaction.
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.
Coumbarides
Gregory S
GS
School of Biological and Chemical Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS, UK.
Motevalli
Majid
M
Muse
Warda A
WA
Wyatt
Peter B
PB
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
D007783:Lactones; D012996:Solutions; D008358:Mannose