Selective mono-claisen rearrangement of carbohydrate glycals. A chemical consequence of the vinylogous anomeric effect
作者:Dennis P. Curran、Young-Ger Suh
DOI:10.1016/s0008-6215(00)90885-1
日期:1987.12
second apparently similar Claisen rearrangement required significantly higher temperatures in all cases. Thus, similar hydroxy groups were differentiated without resort to selective protection. A stereoelectronic rationale based on the newly-introduced vinylogous anomeric effect (VAE) is put forth to explain the accelerated Claisen rearrangements of these glycals. Molecular orbital and resonance descriptions
碳水化合物糖的单克莱森重排被证明是合成上有用的并且在机理上有意义的反应。将过-O-乙酰基缩水甘油基叔丁基二甲基氯硅烷混合物加到二异丙基氨基锂中,生成双(或三)烯酮甲硅烷基乙缩醛,加热后,进行平滑的单克莱森重排以在甲基化后提供C-糖基化合物。在所有情况下,第二次明显相似的Claisen重排都需要明显更高的温度。因此,相似的羟基被区分而无需借助选择性保护。提出了基于新引入的乙烯基异头作用(VAE)的立体电子原理,以解释这些糖类的加速克莱森重排。包括了VAE的分子轨道和共振描述,VAE还用于合理化碳水化合物糖基态的构象偏好。通过单克莱森重排产生的C-糖基化合物适用于Pd(0)催化的烯丙基烷基化,从而提供了异常容易地进入假单酸环系统的通道。据报道,假单酸C的已知前体的九步合成。