Isomerization‐Asymmetric Hydrogenation Sequence Converting Racemic β‐Ylidenecycloalkanols into Stereocontrolled β‐Substituted Cycloalkanols Using a Ru Catalytic System with Dual Roles
作者:Noriyoshi Arai、Yuki Okabe、Takeshi Ohkuma
DOI:10.1002/adsc.201901269
日期:2019.12.17
Racemic β‐ylidenecycloalkanols were transformed into the cis‐β‐substituted cycloalkanols with high enantio‐ and diastereoselectivities through an isomerization‐asymmetric hydrogenation sequence with the (4,4′‐bi‐1,3‐benzodioxole)‐5,5′‐diylbis[di(3,5‐xylyl)phosphine (DM‐Segphos)/2‐dimethylamino‐1‐phenylethylamine (DMAPEN)‐ruthenium(II) catalyst; such transformation hardly proceeded by single‐step asymmetric
外消旋β-亚烷基环烷醇通过异构化-不对称加氢序列(4,4'-bi-1,3-苯并二恶唑)-5,5'-二基双被转化为对映异构和非对映选择性高的顺式-β-取代的环烷醇[二(3,5-二甲苯基)膦(DM-Segphos)/ 2-二甲基氨基-1-苯乙胺(DMAPEN)-钌(II)催化剂;这种转化很难通过一步不对称加氢进行。该反应通常在4至10 atm的H 2下以500的底物与催化剂的摩尔比进行,以提供顺式/反式产物比率高达99:1和98%ee。机理实验表明,该催化体系通过钌环酰胺中间体可逆地形成了两个反应性物种(I)和(II)。酰胺络合物与烯丙醇反应生成烯丙基醇盐络合物,并部分或全部除去二胺((I)型),并且这种(I)络合物催化将烯丙醇异构化为外消旋α-取代的酮。酰胺络合物与氢反应形成的具有二胺螯合的RuH 2络合物(II)(II)通过动态动力学拆分促进外消旋α-取代的酮不对称加氢成立体控制的β-取代的环烷醇。