C-Glycosylidene derivatives (exo-glycals): their synthesis by reaction of protected sugar lactones with tributylphosphonium ylids, conformational analysis and stereoselective reduction
作者:Miguel Gascón-López、Majid Motevalli、George Paloumbis、Peter Bladon、Peter B Wyatt
DOI:10.1016/j.tet.2003.09.081
日期:2003.11
Stabilised tributylphosphonium ylids Bu3PCHCH(EWG), where EWG is CO2Me, CO2tBu or CN, react with protected sugar lactones under mild conditions to give high yields of glycosylidene derivatives (4 and 5) with good Z/E selectivity. X-Ray crystallography shows that in the solid state the tetra-O-benzyl protected (Z)-glucosylideneacetonitrile (Z)-4c adopts a conformation intermediate between a boat and
稳定化的三丁基内鎓盐卜3 PCHCH(EWG),其中,EWG是CO 2 Me中的CO 2吨卜或CN,用温和的条件下被保护的糖内酯反应,得到glycosylidene衍生物(高产量的4和5具有良好的)ž / E选择性。X射线晶体学表明,在固态下,四-O-苄基保护的(Z)-葡萄糖基亚乙乙腈(Z)-4c在舟皿和扭转舟皿之间采用构象中间体,而同分异构的半乳糖衍生物(Z)-5c作为扭曲的椅子而存在。NMR数据表明,与半乳糖亚基衍生物相比,在溶液中类似椅状的构型再次比其亚糖亚基类似物更受青睐。固溶相核磁共振研究和分子建模表明,即使在半乳糖系列中,(E)-双键几何结构也不利于环的椅状几何结构。这与避免使用1,3-烯丙基应变是一致的。可以通过使用Et 3 SiH–CF 3 CO 2 H或Et 3 SiH–BF 3 ·Et 2 O还原糖基亚烷基双键以形成立体选择性的β- C-糖苷衍生物。