Coumbarides Gregory S, Motevalli Majid, Muse Warda A, Wyatt Peter B
School of Biological and Chemical Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS, UK.
J Org Chem. 2006 Sep 29;71(20):7888-91. doi: 10.1021/jo061178s.
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.
稳定的叶立德Bu(3)P=CH(EWG)（其中EWG为酯基或腈基）与2,3,4,6-四-O-苄基甘露糖-1,5-内酯反应，能高产率地生成亚甘露糖基衍生物；与葡萄糖和半乳糖类似物不同，(E)-亚甘露糖基衍生物占主导（E:Z > 9:1），从而使维蒂希反应中的偶极-偶极排斥作用最小化。核磁共振表明，(E)-甘露糖基吡喃亚基溶液呈椅式构象，但对于(Z)-异构体（EWG = CN或CO(2)Et，有数据可用）的溶液则不是。X射线晶体学显示，四-O-苄基保护的(Z)-亚甘露糖基乙腈呈近似扭船式构象。
