Organofluorine Compounds and Fluorinating Agents; 29:Stereoselective Synthesis and Reactivity of 2-Chlorodifluoromethyl-Substituted Monosaccharides
作者:Ralf Miethchen、Stefan Tews、Helmut Reinke
DOI:10.1055/s-2003-38076
日期:——
Chlorodifluoromethyl groups were introduced into the 2-position of the glycals 1, 5, 8, and 11 by dithionite-mediated addition of CF2ClBr. The reaction proceeded stereoselectively, i.e. the CF2Cl-group is always found trans to the neighbouring substituent at C-3 in the products. Because the primarily formed glycosyl bromides hydrolyse easily, the corresponding 2-chlorodifluoromethyl-2-deoxypyranoses 3, 6, 9, and 12 were isolated. Only 3,4,6-tri-O-acetyl-2-chlorodifluoromethyl-2-deoxy-d-glucopyranosyl bromide (2) was stable enough for chromatographic separation. The unprotected anomeric pyranoses 3, 6, 9, and 12 were acetylated by acetic anhydride/pyridine yielding the 1-O-acetyl derivatives 4, 7, 10, and 13. These compounds are suitable glycosyl donors, just as the anomeric phenyl thioglycosides 16 and 17 generated from 1,3,4-tri-O-acetyl-2-chlorodifluoromethyl-2-deoxy-d-arabinopyranside (7) and thiophenol (BF3-catalysis). Furthermore, the reactivity of glucosyl bromide 2, 6-deoxy-l-glucose derivative 13 and thioglycosides 16, 17 was investigated. On treatment of glucosyl bromide 2 with pyridine, the 2-chlorodifluoromethyl substituted glycal 14 is formed as the result of HBr elimination. Furthermore, the chlorodifluoromethyl group of compounds 14 and 16 was converted into a methoxycarbonyl group by refluxing in methanolic sodium methoxide (products 15 and 19, respectively). Finally, the thioglycosides 16 and 17 were subsequently deacetylated by CsF on alumina (yielding the dihydroxy derivatives 18 and 20) and acetalized with chloral/DCC (18 forming acetal 21 and carbonate 22) and acetone (20 forming acetal 23), respectively. X-ray analyses are given for the 1-O-acetate 4 and the thioglycosides 21 and 24.
通过连二亚硫酸盐介导的 CF2ClBr 加成,将氯二氟甲基引入糖醛 1、5、8 和 11 的 2 位。该反应以立体选择性方式进行,即 CF2Cl 基团始终与产物中 C-3 处的相邻取代基呈反式。由于最初形成的糖基溴很容易水解,因此分离出了相应的2-氯二氟甲基-2-脱氧吡喃糖3、6、9和12。只有 3,4,6-三-O-乙酰基-2-氯二氟甲基-2-脱氧-d-吡喃葡萄糖基溴 (2) 足够稳定,适合色谱分离。未保护的异头吡喃糖 3、6、9 和 12 通过乙酸酐/吡啶乙酰化,得到 1-O-乙酰基衍生物 4、7、10 和 13。这些化合物是合适的糖基供体,就像异头苯基硫代糖苷 16 一样1,3,4-三-O-乙酰基-2-氯二氟甲基-2-脱氧-d-阿拉伯吡喃苷(7)和苯硫酚(BF3-催化)生成17和17。此外,还研究了葡萄糖基溴2、6-脱氧-L-葡萄糖衍生物13和硫代糖苷16、17的反应性。用吡啶处理葡萄糖基溴 2 时,由于 HBr 消除而形成 2-氯二氟甲基取代的糖醛 14。 此外,化合物14和16的氯二氟甲基通过在甲醇钠的甲醇溶液中回流而转化为甲氧基羰基(分别为产物15和19)。最后,硫代糖苷16和17随后被氧化铝上的CsF脱乙酰化(产生二羟基衍生物18和20),并分别用氯醛/DCC(18形成缩醛21和碳酸酯22)和丙酮(20形成缩醛23)缩醛化。对 1-O-乙酸酯 4 以及硫代糖苷 21 和 24 进行了 X 射线分析。