Paquette Leo A, Fabris Fabrizio, Gallou Fabrice, Dong Shuzhi
Evans Chemical Laboratories, The Ohio State University, Columbus, Ohio 43210, USA.
J Org Chem. 2003 Oct 31;68(22):8625-34. doi: 10.1021/jo030196w.
Methodology based on the concept of thionium ion-initiated pinacolic ring expansion has been developed for accessing C4'-spirocyclic thionucleosides. The readily available racemic ketones 6 and 37 are conveniently resolved via their acetals with (R)-mandelic acid. Subsequent reactions beginning with utilization of the Pummerer rearrangement lend themselves to functionalization of the spirocyclic core and ultimately incorporation of the nucleosidic bases. Limitations to this strategy are pointed out. Acquisition of the alpha- and beta-isomers at C4' is equally facile. Absolute configurational assignments have been made possible by X-ray crystallography.
基于硫鎓离子引发的频哪醇环扩张概念的方法已被开发用于合成C4'-螺环硫代核苷。容易获得的外消旋酮6和37可通过它们与(R)-扁桃酸的缩醛方便地拆分。随后从利用Pummerer重排开始的反应有助于螺环核心的官能化，并最终引入核苷碱基。指出了该策略的局限性。在C4'处获得α-和β-异构体同样容易。通过X射线晶体学已能够进行绝对构型归属。
