Nucleosides and Nucleotides. 156. Chelation-Controlled and Nonchelation-Controlled Diastereofacial Selective Thiophenol Addition Reactions at the 2‘-Position of 2‘-[(Alkoxycarbonyl)methylene]-2‘-deoxyuridines: Conversion of (<i>Z</i>)-2‘-[(Alkoxycarbonyl)methylene]-2‘-deoxyuridines into Their (<i>E</i>)-Isomers<sup>1</sup>
作者:Abdalla E. A. Hassan、Satoshi Shuto、Akira Matsuda
DOI:10.1021/jo9613601
日期:1997.1.1
gave the (Z)-isomer 13 in 92% yield. The oxidativesyn-elimination of the (2'R)-2'-[(tert-butoxycarbonyl)methyl]-2'-deoxy-2'-thiophenoxy-5'-O-(triisopropylsilyl)uridine (17), which was obtained from 14 in two steps, exclusively gave the desired (E)-[(tert-butoxycarbonyl)methylene] derivatives 18 in 90% yield. Deprotection of 18 gave the (E)-(carboxymethylene)-2'-deoxyuridine (3). The (Z)-(carboxyme
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(4)的Wittig反应与Ph( 3)P = CHCO(2)R(R =乙基或叔丁基)分别高产率分别得到(Z)-2′-[((烷氧羰基)亚甲基]衍生物5和13。观察到苯硫酚向5和13的2'-[((烷氧基羰基)亚甲基]部分加成的异常的β面部选择性,发现该面部选择性受硫醇盐抗衡阳离子和烷氧基部分的体积的影响。在THF中在PhSH存在下用LiSPh(1.5当量)处理2'-[((乙氧基羰基)亚甲基]衍生物5]选择性高产率地得到2'β-(苯硫基)衍生物11和痕量的2'α-(苯硫基) )导数10。另一方面,当2' 在二恶烷/ DMF中,在PhSH的存在下,用KSPh处理-[[(叔丁氧基羰基)亚甲基]衍生物13,反转面部选择性以选择性生成2'α-(苯硫基)加合物14(α:beta,77:23)收率达