Synthesis, conformation, and glycosidic coupling reactions of highly active substituted 2,7-dioxabicyclo[4.1.0]heptanes: 1,2-anhydro-3,4-di-O-benzyl-α-d-xylopyranose
作者:Guangbin Yang、Fanzuo Kong、Robert R. Fraser
DOI:10.1016/0008-6215(94)84074-1
日期:1994.5
8 by ring closure with potassium tert -butoxide. Comparison of the observed vicinal coupling constants for 8 with the results obtained from calculations by molecular mechanics suggested that the conformation of the pyranose ring is close to a 4 H 5 half chair. The anhydro sugar was highly reactive, its condensation with 1,2:3,4-di- O -isopropylidene-α- d -galactopyranose proceeding in reasonable yield
摘要以d-木糖为原料合成了标题的1,2-脱水糖(8)。合成的关键中间体是2-O-乙酰基-3,4-二-O-苄基-β-d-吡喃吡喃糖基氟,其通过叔丁醇钾的闭环转化为晶体8。将观察到的8的邻位偶合常数与通过分子力学计算得到的结果进行比较表明,吡喃糖环的构型接近4 H 5半椅。脱水糖具有高反应活性,在没有任何路易斯酸催化剂的情况下,它与1,2:3,4-二-O-异亚丙基-α-d-吡喃半乳糖的缩合反应可进行合理的收率,并在分子筛存在下定量地给出β-连接的二糖为主要产物。缩合的立体化学结果几乎不受溶剂或反应温度变化的影响。某些路易斯酸催化剂的存在导致β:α比值降低,而当高氯酸三苯甲基酯为催化剂时,主要获得的是α-连接的二糖。