The hypothesis which explains the diastereoselectivity of the 1,3-dipolar cycloaddition of the N-glycosylnitrones 1–3 leading to the 5,5-disubstituted isoxazolidines 4–6 on the basis of a kinetic anomeric effect predicts that nucleophiles should add to N-glycosylnitrones with a high degree of diastereoselectivity. To test this prediction, the nucleophilic addition of lithium and potassium dialkylphosphites
这解释了的1,3-偶极环加成的非对映选择性的假说Ñ -glycosylnitrones 1 - 3通向5,5-二取代的
异恶唑烷4 - 6的动能端基异构效应的
基础上预测,亲核试剂应该添加到ñ -具有高度非对映选择性的糖基硝
酮。为了检验该预测,已经研究了
锂和二烷基
亚磷酸锂向由
肟9和(苄
氧基)
乙醛制备的结晶(Z)-硝基1的亲核加成反应。
亚磷酸锂的添加使N-glycosyl- Ñ -hydroxyaminophosphonates 12 - 16(78-92 DE%)以高收率(方案4) 。
亚磷酸钾的添加显示出低得多的非对映选择性。糖苷切割,
氢解,和
脱烷基化的12 - 16得到(+) - (小号)-phosphoserine(+) - 19(34-45%来自9)。通过N-(3,3,3-三
氟-
2-甲氧基-
2-甲氧基-2-
苯基丙酰)衍
生物24的X射线分析证实了其绝对构型。类似地,结晶的硝
酮25得到N-糖