Deoxy-nitrosugars. 6th communication. Stereoelectronic control in the reductive denitration of tertiary nitro ethers. A synthesis of ?C-glycosides?
作者:Franz Baumberger、Andrea Vasella
DOI:10.1002/hlca.19830660733
日期:1983.11.2
The separate, radical denitration with Bu3SnH of the pyranose derivatives 3, 4, 9, and 10 gave in good yields exclusively the ‘C-glycosides’ 5 and 11, respectively (Scheme 1). Similar reduction of the cyclohexyl derivatives 15, 16, 19 and 20 gave 4:1 mixtures of 17, 18, 21 and 22, respectively, always with predominant formation of an axial C,H-bond. In the furanose series a divergent behaviour was
与卜分开的,自由基的脱硝3吡喃糖衍生物的SNH 3,4,9,和10以良好产率得到专门的“ Ç -glycosides” 5和11,分别(方案1)。环己基衍生物15、16、19和20的相似还原反应分别得到17、18、21和22的4:1混合物,并且始终主要形成轴向C,H键。在呋喃糖系列中,观察到D-甘露糖衍生的硝基醚25和27和D-核糖衍生的硝基醚的发散行为分别如图30和31所示,因为前两者给出了异构体均一的还原产物(分别为26和28;方案3),而后者为非对映异构体32和33的1∶1混合物(方案4)。立体化学结果是基于环O原子的立体电子效应,在三氧杂双环[3.3.0]辛烷环体系中中间的金字塔形烷氧基烷基的优选构型和空间效应进行解释的。