Free radical bromination and nucleophilic fluorination allows the conversion of methyl sorbate into the 6-fluoro analogue which undergoes sequential asymmetric dihydroxylation reactions. A range of 6-deoxy-6-fluorosugars were prepared by using different combinations of ligands. While the enantiomeric excesses obtained were comparable to those from other 6-substituted sorbates, the regioselectivity of dihydroxylation was moderate, with both 2,3- and 4,5-diols being obtained. A successful temporary persilylation strategy was evolved to convert the products of dihydroxylation rapidly to the fluorosugars 6-deoxy-6-fluoro-L-idose, 6-fluoro-L-fucose and 6-deoxy-6-fluoro-D-galactose, which were obtained in overall yields of 4%, 6% and 8% from methyl 6-fluoro-hexa-2E,4E-dienoate 6.
自由基
溴化和亲核
氟化可将
山梨酸甲酯转化为 6-
氟类似物,并进行连续的不对称二羟基化反应。通过使用不同的
配体组合制备了一系列 6-脱氧-6-
氟糖。虽然获得的对映体过量与其他 6-取代
山梨酸酯的对映体过量相当,但二羟基化的区域选择性适中,同时获得了 2,3- 和 4,5- 二醇。开发了一种成功的临时全
硅烷化策略,将二羟基化产物快速转化为
氟糖6-脱氧-6-
氟-L-艾糖、6-
氟-
L-岩藻糖和6-脱氧-6-
氟-
D-半乳糖,这由 6-
氟-六-2E,4E-二烯酸甲酯 6 得到的总产率为 4%、6% 和 8%。