Simple oxidation of 3-O-silylated glycals: application in deblocking 3-O-protected glycals
作者:Andreas Kirschning、Ulrike Hary、Claus Plumeier、Monika Ries、Lars Rose
DOI:10.1039/a807479h
日期:——
A high yielding allylic oxidation of 3-O-silylated glycals 5–10 with the reagent system PhI(OAc)2–TMSN3 is presented. The iodine(III) species generated under these conditions is a lot more effective for generating carbohydrate-derived 3-trialkylsiloxy-2,3-dihydro-4H-pyran-4-ones 11–15 than is [hydroxy(tosyloxy)iodo]benzene, the Koser reagent. Even disaccharide 9 containing the oxidation-labile phenylseleno group is smoothly oxidized to the corresponding enone 15. The hypervalent azido iodine reagent is complementary to the Koser reagent, because 3-O-benzylated or -acylated glycals cannot be oxidized. When the iodine(III)-mediated oxidation of 3-O-silylated or -benzylated glycals is followed by a reduction step, the formal 3-O-deblocking of glycals is achieved. In particular, the Luche reduction of enones obtained from the oxidation of lyxo-configured glycals 24 and 26 is highly selective and exclusively affords the corresponding lyxo-configured glycals 28 and 30. In some cases, these products can be transformed under Mitsunobu conditions into glycals with inverted configuration at C-3 in moderate yield.
提出了一种高产率的3-O-硅烷化糖醇5–10的烯丙氧化反应,使用的试剂系统为PhI(OAc)2–TMSN3。在这些条件下生成的碘(III)物种相比于Koser试剂[羟基(托芳基羟基)碘]苯,更有效地生成以碳水化合物为基础的3-三烷基硅氧基-2,3-二氢-4H-吡喃-4-酮11–15。即使是含有易氧化的苯基硒基的二糖9,也能平稳地氧化成相应的烯酮15。超价的叠氮碘试剂与Koser试剂互补,因为3-O-苄基化或-酰基化的糖醇无法被氧化。当3-O-硅烷化或-苄基化的糖醇进行碘(III)介导的氧化后再进行还原步骤时,可以实现糖醇的形式性3-O-去堵功能。特别是,从lyxo构型的糖醇24和26氧化得到的烯酮进行Luche还原反应时,选择性极高,专门生成相应的lyxo构型的糖醇28和30。在某些情况下,这些产物可以在Mitsunobu条件下转化为C-3配置反转的糖醇,且产率适中。