obtain syn-cyclobutane isomers, the targeted formation of anti-cyclobutane isomers has not been addressed yet. Herein, using NMR analyses and DFT calculations, we demonstrate that the acetone photosensitized excitation of the 4-tetrazolouracil motif in the nucleoside series specifically provides anti-cyclobutane photoproducts in 51% yield. In addition, the cis stereomer formation is preferred over
efficient photochemical nitrogen elimination and ringexpansion to 1,3,5-triazepin-2,4-dione nucleosides whose structure has been confirmed by X-ray crystallography. In contrast, when the photolysis was attempted under anhydrous conditions in the presence of a nucleophile, a ring contraction reaction occurred, affording 2-oxoimidazolone nucleosides. A mechanism to account for the formation of ring expansion
在水性条件下,4-叠氮尿嘧啶/四唑并[1,5 - c ]嘧啶-5(6 H)-one核苷经历了非常有效的光化学除氮并扩环成1,3,5-triazepin-2,4-dione X射线晶体学已证实其结构的核苷。相反,当在无水条件下在亲核试剂存在下尝试光解时,发生环收缩反应,得到2-氧代咪唑啉酮核苷。提出了一种解释环膨胀和收缩反应的形成并涉及碳二亚胺中间体的机制,其使人联想到2-叠氮基吡啶/四唑并[1,5- a ]吡啶的已知光化学行为。
The Chemistry of 4-Azido-2-pyrimidinone Nucleosides Revisited
作者:Frédéric Peyrane、Pascale Clivio
DOI:10.1021/jo0479765
日期:2005.3.1
Treatment of 4-azido-2-pyrimidinone nucleoside 1 with MeOH/K2CO3 or ammonium hydroxide led to derivatives 2 and 3, respectively. Both compounds derived from a nucleophilic addition at the modified base 2-position. These results contrast with the previously reported sensitivity of the 4-azido-2-pyrimidinone nucleoside 6-position to nucleophiles.