Dispiroketals in synthesis. Part 25.1 Further reactions of dispiroketal protected glycolate to afford optically active 1,2,3,4-tetraols
作者:Morifumi Fujita、Dramane Lainé、Steven V. Ley
DOI:10.1039/a900951e
日期:——
Glycolic acid can be converted to optically active 1,2,3,4-tetraols using a dispiroketal unit as a protecting group and chiral auxiliary. Aldol reactions of dispiroketal protected glycolate with aldehydes afford one diastereoisomer preferentially with two newly formed stereogenic centres. To extend the polyol chain, the carbonyl group of the aldol product is converted to a vinyl ether by the Tebbe reagent after protection of the free alcohol. A subsequent hydroboration–oxidation protocol affords the dispiroketal protected tetraol. The final deprotection of the tetraol occurs selectively without epimerisation or migration of the silyloxy protecting groups.
使用二螺酮单元作为保护基团和手性辅助剂,可将乙醇酸转化为具有光学活性的 1,2,3,4-四醇。受二酮保护的羟基乙酸酯与醛发生醛醇反应,可产生一种非对映异构体,并优先获得两个新形成的立体中心。为了延长多元醇链,在保护游离醇后,醛醇产物的羰基会通过 Tebbe 试剂转化为乙烯基醚。随后通过氢硼化合-氧化反应生成受二环酮保护的四元醇。四醇的最终脱保护作用是有选择性地进行的,不会出现硅烷氧基保护基团的外延或迁移。