Nucleosides and Nucleotides. 151. Conversion of (<i>Z</i>)-2‘-(Cyanomethylene)-2‘-deoxyuridines into Their (<i>E</i>)-Isomers <i>via</i> Addition of Thiophenol to the Cyanomethylene Moiety Followed by Oxidative <i>Syn</i>-elimination Reactions<sup>1</sup>
作者:Abdalla E. A. Hassan、Naozumi Nishizono、Noriaki Minakawa、Satoshi Shuto、Akira Matsuda
DOI:10.1021/jo960577s
日期:1996.1.1
Wittig reaction of 1-[3,5-O-(1,1,3,3-tetraisopropyldisiloxane-1,3-diyl)-beta-D-erythro-pentofuranos-2-ulosyl]uracil (6) with Ph(3)P=CHCN afforded (Z)-2'-cyanomethylene derivative 7 exclusively. The (E)-isomer was accessed from its (Z)-isomer through a sequence of addition of thiophenol to the 2'-cyanomethylene moiety of the (Z)-isomer from the alpha-face, selectively, and stereoselective oxidative syn-elimination
1- [3,5-O-(1,1,3,3-四异丙基二硅氧烷-1,3-二基)-β-D-赤型戊呋喃并-2-脲基]尿嘧啶(6)的Wittig反应与Ph( 3)P = CHCN仅得到(Z)-2′-氰基亚甲基衍生物7。从(Z)异构体通过(α)面选择性地和立体选择性氧化合消除苯硫酚向(Z)异构体的2'-氰基亚甲基部分中添加(E)异构体生成的加合物。发现苯硫醇酯加到氰基亚甲基部分上的非对映选择性受2-部分羰基在碱部分的参与和糖保护基的空间位阻的影响。尽管众所周知在6的2'位发生亲核加成反应是选择性地从α面发生的,用LiSPh在THF中处理7意外地得到几乎相等比例的α-和β-苯硫基衍生物8和9的混合物。此外,在用CHS(2)Cl(2)中的PhSAlMe(2)或在THF中存在Mg(ClO(4))(2)的情况下用LiSPh处理7时,观察到异常的β面部选择性添加。另一方面,当用LiSPh处理(Z)-2′-(氰基亚甲