Stereoselective Synthesis of (<i>E</i>)-Mannosylidene Derivatives Using the Wittig Reaction
作者:Gregory S. Coumbarides、Majid Motevalli、Warda A. Muse、Peter B. Wyatt
DOI:10.1021/jo061178s
日期:2006.9.1
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 CO2Et). X-ray crystallography shows an
稳定的烷基化物Bu 3 P CH(EWG),其中EWG为酯基或腈基,可与2,3,4,6-四-O-苄基甘露糖醛-1,5-内酯反应,得到高产率的甘露烯衍生物。与葡萄糖和半乳糖类似物相比,(E)-甘露糖基占主导地位(E:Z > 9:1),从而使维蒂希反应中的偶极-偶极排斥力最小。NMR表示(E)-甘露聚糖吡喃酮溶液的椅子样构型,但对于有数据可用的那些(Z)异构体则没有(EWG = CN或CO 2 Et)。X射线晶体学显示四氧的大致扭曲构象-苄基保护的(Z)-亚苄基乙腈。