Influence of the β-Alkoxy Group on the Diastereoselectivity of Aldol Reactions of Tetrahydro-4<i>H</i>-thiopyran-4-one with 4-Alkoxytetrahydro-2<i>H</i>-thiopyran-3-carboxaldehydes
作者:Dale E. Ward、Marcelo Sales、Chuk C. Man、Jianheng Shen、Pradip K. Sasmal、Cheng Guo
DOI:10.1021/jo016291r
日期:2002.3.1
(14a) diastereomers. Similar aldol reactions of 3 with the cis and trans isomers of 4-(methoxy)methoxytetrahydro-2H-thiopyran-3-carboxaldehyde (9b and 9c) were examined to probe the influence of the ketal protecting group in 9a on the observed aldol diastereoselectivity. The results are rationalized by applying Evans' stereochemical model for merged 1,2- and 1,3-asymmetric induction (non-chelation), with
在各种条件下,研究了四氢-4H-硫代吡喃-4-酮(3)与1,4-二氧杂-8-硫杂螺[4.5]癸烷-6-甲醛(9a)的醛醇缩合反应的非对映选择性。在最佳条件下,可以选择性地(3-16:1)从该醛醇缩合反应中获得四种可能的非对映异构体中的三种。9a与3的Li,B,Mg(II)和Ti(IV)的烯酸酯以及相应的三甲基甲硅烷基烯醇醚4b在BF(3)x OEt(2),SnCl(4)或TiCl(4)作为促进剂仅以合成的(11a)和反(12a)非对映体混合物形式提供Felkin加合物(> 95%)。与使用由二异丙基氨基锂生成的3烯酸锂(3∶1; 3∶1; 2; 3∶1; 3∶3∶1; 3∶3∶1; 2∶3; 2∶3; 1∶3)相比,使用3的“无胺”烯醇酸锂得到的12a具有更高的非对映选择性(9∶1)和产率(70%)。 15-40%)。TiCl(4)促进4b与9a的反应生成具有出色选择性(16:1)的11a。相比之下,MgBr(2)x