C-Glycosidations of a 2-Ketohexosyl Bromide with Electrophilic, Radical, and Nucleophilic Anomeric Carbons
作者:Frieder W. Lichtenthaler、Matthias Lergenmüller、Sabine Schwidetzky
DOI:10.1002/ejoc.200300152
日期:2003.8
susceptibility of acylated 2-ketohexosyl halides to C-homologation is demonstrated with the easily accessible tri-O-benzoyl-α-D-arabino-hexos-ulosyl bromide 1 as the model compound. C-Glycosidation with an electrophilic anomeric carbon requires prior carbonyl protection, to avoid carbonyl addition by the C-nucleophile, for example, as the cyanohydrin. Silver triflate-promoted reaction with the silylenol ether of
酰化的 2-酮己糖基卤化物对 C-同系化的敏感性用易于获得的三-O-苯甲酰基-α-D-阿拉伯-己糖-ulosyl bromide 1 作为模型化合物来证明。具有亲电异头碳的 C-糖苷化需要事先羰基保护,以避免 C-亲核试剂的羰基加成,例如,作为氰醇。三氟甲磺酸银促进与苯乙酮的甲硅烷醇醚反应,然后有效地产生 β-苯甲酰基产物。通过热 (AIBN) 或光化学诱导,1 平滑地生成异头自由基——由于其封端取代,相对亲电——它在三丁基锡和缺电子烯烃存在的情况下专门捕获氢。然而,它与烯丙基三丁基锡烷以高立体选择性反应生成 α-C-烯丙基糖苷糖。ulosyl bromide 1 中的 α-溴酮官能团易受 Reformatsky 条件的影响:用锌-铜对处理很容易产生 1,2-烯醇化物,这是一种最简单的异头亲核试剂,可有效地添加到醛中以产生 α-C-羟烷基糖苷糖或具有高度双立体选择的α-C-二糖(含糖醛)。(©