Aldol Addition of Lithium and Boron Enolates of 1,3-Dioxan-5-ones to Aldehydes. A New Entry into Monosaccharide Derivatives
作者:Marek Majewski、Pawel Nowak
DOI:10.1021/jo0002238
日期:2000.8.1
of stereoselectivity in aldol reactions of enolates derived from 1,3-dioxan-5-ones (4) are described. Boron enolates, generated in situ, react with benzaldehyde to give the corresponding anti aldol selectively (the anti:syn ratio of up to 96:4) and in high yield. Lithium enolates give high anti selectivity only with aldehydes branched at the alpha-position. Enantioselective deprotonation of C(S) symmetrical
描述了可控制衍生自1,3-二恶烷-5-酮(4)的烯醇酯在醛醇缩合反应中立体选择性的方法。原位生成的硼烯醇化物与苯甲醛反应,以高产率选择性地产生相应的抗羟醛(反∶syn比例高达96:4)。烯醇锂仅在α位分支的醛才具有较高的抗选择性。使用具有一般结构PhCH(Me)N(Li)R的手性锂酰胺碱,对映体过量C可以高效地完成C(S)对称二恶烷(例如4b)的对映选择性去质子化反应(9,10)如果R基团足够大(例如,R =金刚烷基)或被氟化(例如,R = CH 2 CF 3)。二恶烷酮硼和烯醇锂易于与甘油醛衍生物(19)反应,生成受保护的酮己糖(20和21)。