Highly Functionalised Cyclopentanes by Radical Cyclisation of Unsaturated Bromolactones III. Preparation of Carbaaldohexofuranoses. Determination of the Relative Configuration at C-4/C-5 of 2,3-Unsaturated Heptono-1,4-lactones by Means of 1H NMR Spectroscopy
作者:Anne Marie Horneman、Inge Lundt
DOI:10.1055/s-1999-3384
日期:1999.2
Two new carbaaldohexofuranoses, carba-β-d-glucofuranose and carba-α-l-mannofuranose, have been prepared using 5,6-O-isopropylidene-d-glycero-l-galacto-heptono-1,4-lactone (6) as the starting material. The key step was a highly stereoselective intramolecular 5-exo-trig radical cyclisation of C-2 substituted 2,3-unsaturated 7-bromo-7-deoxyheptono-1,4-lactones promoted by tributyltin hydride. Assignment of the configuration of the unsaturated lactones was based upon NMR data of related compounds. The starting material, compound 6, was obtained by chain elongation of d-gulose, and a facile method for separation of the epimers from the chain elongation has been developed. Thus 5,6-O-isopropylidene-d-glycero-l-galacto-heptono-1,4-lactone (6) and d -glycero-l-talo-heptono-1,4-lactone (5) were isolated crystalline in ca. 30% and 10% yield, respectively.
以 5,6-O-isopropylidene-d-glycero-lalacto-heptono-1,4-lactone (6) 为起始原料,制备了两种新的carbaaldohexofuranose,carba-δ-d-glucofuranose 和carba-δ-l-mannofuranose。关键步骤是在氢化三丁基锡的促进下,对 C-2 取代的 2,3-不饱和 7-溴-7-脱氧庚-1,4-内酯进行高度立体选择性的分子内 5-外三自由基环化。不饱和内酯的构型是根据相关化合物的核磁共振数据确定的。起始原料 6 号化合物是通过 d-古洛糖的链延伸获得的,而且还开发出了一种从链延伸中分离表聚物的简便方法。因此,5,6-O-异亚丙基-d-缩水甘油-l-半乳糖庚-1,4-内酯(6)和 d-缩水甘油-l-半乳糖庚-1,4-内酯(5)分别以约 30% 和 10% 的产率分离出晶体。