Denmark Scott E, Fujimori Shinji, Pham Son M
Department of Chemistry, Roger Adams Laboratory, University of Illinois, Urbana, Illinois 61801, USA.
J Org Chem. 2005 Dec 23;70(26):10823-40. doi: 10.1021/jo051930+.
[structures: see text] The consequences of double diastereodifferentiation in chiral Lewis base catalyzed aldol additions using chiral enoxysilanes derived from lactate, 3-hydroxyisobutyrate, and 3-hydroxybutyrate have been investigated. Trichlorosilyl enolates derived from the chiral methyl and ethyl ketones were subjected to aldolization in the presence of phosphoramides, and the intrinsic selectivity of these enolates and the external stereoinduction from chiral catalyst were studied. In the reactions with the lactate derived enolate, the strong internal stereoinduction dominated the stereochemical outcome of the aldol addition. For the 3-hydroxyisobutyrate- and 3-hydroxybutyrate derived enolates, the catalyst-controlled diastereoselectivities were observed, and the resident stereogenic centers exerted marginal influence. The corresponding trimethylsilyl enol ethers were employed in SiCl4/bisphosphoramide catalyzed aldol additions, and the effect of double diastereodifferentiation was also investigated. The overall diastereoselection of the process was again controlled by the strong external influence of the catalyst.
[结构：见正文] 研究了在手性路易斯碱催化的羟醛加成反应中，使用源自乳酸、3-羟基异丁酸和3-羟基丁酸的手性烯醇硅烷进行双重非对映体分化的结果。将源自手性甲基和乙基酮的三氯硅基烯醇化物在磷酰胺存在下进行羟醛缩合反应，并研究了这些烯醇化物的固有选择性以及来自手性催化剂的外部立体诱导作用。在与源自乳酸的烯醇化物的反应中，强烈的内部立体诱导作用主导了羟醛加成反应的立体化学结果。对于源自3-羟基异丁酸和3-羟基丁酸的烯醇化物，观察到了催化剂控制的非对映选择性，且存在的立体中心产生的影响较小。相应的三甲基硅基烯醇醚用于SiCl4/双磷酰胺催化的羟醛加成反应中，同时也研究了双重非对映体分化的影响。该过程的总体非对映选择性再次由催化剂的强烈外部影响控制。
