Synthesis of sialic acid derivatives based on chiral substrate-controlled stereoselective aldol reactions using pyruvic acid oxabicyclo[2.2.2]octyl orthoester
accomplished based on substrate-controlled asymmetric aldol reactions between sterically complicated aldehydes easily prepared from commercially available carbohydrates and a novel pyruvic acid oxabicyclo[2.2.2]octyl orthoester. Systematic aldol reactionstudies using chiral aldehydes revealed that α,β,γ-benzyloxy-substituted aldehydes with an α,β-anti relative configuration preferentially provided the
唾液酸及其类似物的合成是基于易于从市售碳水化合物制备的空间复杂醛与新型丙酮酸草酸双环[2.2.2]辛基原酸酯之间的受底物控制的不对称醛醇缩合反应完成的。使用手性醛的系统羟醛反应研究表明,具有α,β-反相对构型的α,β,γ-苄氧基取代的醛优先为Felkin产物提供具有高非对映选择性的4,5-抗构型。具有α,β-顺式排列的α,β,γ-苄氧基取代的醛中的相对β,γ构型对醛醇缩合反应中形成的立构中心的非对映选择性具有次要作用。syn - β ,γ-抗苄氧基醛显示出比α,β- syn - β ,γ- syn苄氧基醛更高的非对映选择性,从而生成Felkin产物。
Practical Synthesis of Methyl Z-2-(N-Acetylamino) but-2-Enoate. An Intermediate to D- and L-2-Aminobutyric Acid
作者:William A. Nugent、John E. Feaster
DOI:10.1080/00397919808006866
日期:1998.5
Abstract Treatment of inexpensive L- or DL-threonine methyl ester with acetic anhydride and either pyridine or anhydrous sodium acetate at reflux results in dehydration yielding the N,N-diacetamide of the title compound in >80% yield. Monodeacetylation of the diacetamide with 0.1 equiv of triethylamine in methanol affords the title monoacetamido derivative 1 in nearly quantitative yield.
Asymmetric synthesis. Practical production of D and L threonine. Dynamic kinetic resolution in rhodium and ruthenium catalyzed hydrogenation of 2-acylamino-3-oxobutyrates.
Enantioselective syntheses of D and L threonine are described. Racemic methyl and ethyl 2-acylamino-3-oxobutyrate 1 were synthesized from the corresponding acetoacetates 6 and then hydrogenated stereoselectively via dynamic kinetic resolution with various chiral P * P Rh (I) 8 and Ru (II) 10 catalysts to give syn optically active alcohols which could be converted by hydrolysis and treatment with propylene oxide into threonine. The best results were obtained using (-) CHIRAPHOS Ru and (+) BINAP Ru as catalysts, in the hydrogenation step leading respectively to D threonine (ee: 99 %) and L threonine (ee: 94 %) in 26-34 % overall yields.