Photochemical Deconjugation of Chiral 3-Methyl-2-butenoates Derived from Carbohydrate-Based Alcohols: The Influence of the Sugar Backbone on the Facial Diastereoselectivity
作者:Thorsten Bach、Frank Höfer
DOI:10.1021/jo001740t
日期:2001.5.1
The photodeconjugation of the alpha-(4-trimethylsilyl-3-butynyl)-substituted senecio acid esters 7 was studied. Chiral alcohols ROH (9) were employed as auxiliaries to control the facial diastereoselectivity of the protonation step. The conversion of the four sugar alcohols diacetone-D-glucofuranose, diacetone-D-allofuranose, diacetone-D-gulofuranose, and diacetone-D-fructopyranose (9a-d) to the esters
研究了α-(4-三甲基甲硅烷基-3-丁炔基)取代的千里光酸酯7的光解共轭。手性醇ROH(9)被用作助剂来控制质子化步骤的面部非对映选择性。通过使用4-碘-四步反应的四个步骤,将四种糖醇双丙酮-D-葡萄糖呋喃糖,双丙酮-D-氟呋喃糖,双丙酮-D-古呋喃糖和双丙酮-D-果糖吡喃糖(9a-d)转化为酯7。 1-三甲基甲硅烷基丁-1-炔(3)作为烷基化剂(总产率为27-45%)。他们的光解共轭得到相应的β,γ-不饱和(R)-酯14a-d,具有中等至优异的非对映异构体过量。以双丙酮-D-葡萄糖呋喃糖和双丙酮-D-果糖吡喃糖作为辅助剂(> 95%de)可获得最佳结果。为了合成具有(S)构型的目标化合物1,用双丙酮-L-果糖吡喃糖(ent-9d)衍生的酯ent-7d进行了脱偶联。从L-山梨糖(15)以改进的程序制备L-果糖(20),其允许分离中间体。构型的2倍倒置很好地进行,并且从L-山梨糖以19%的产