Preparation and Structural Analysis of Several New α,α,α′,α′-Tetraaryl-1,3-dioxolane-4,5-dimethanols (TADDOL's) and TADDOL analogs, their evaluation as titanium ligands in the enantioselective addition of methyltitanium and diethylzinc reagents to benzald
作者:Yoshio N. Ito、Xavier Ariza、Albert K. Beck、Andrej Boháč、Camille Ganter、Robert E. Gawley、Florian N. M. Kühnle、Juraj Tuleja、Yan Ming Wang、Dieter Seebach
DOI:10.1002/hlca.19940770802
日期:1994.12.14
Preparation and screening of twenty new ligands, all analogs of α,α,α′,α′-tetraaryl-1,3-dioxolane-4,5-dimethanol (TADDOL), for the Ti-catalyzed asymmetric addition of methyltri(isopropoxy)titanium and diethylzinc to benzaldehyde are described. These ligands have the dioxolane ring of the TADDOL's replaced by cyclobutane, cyclopentane, cyclohexene, cyclohexane, bicyclo[2.2.1]heptene and -heptane and
Ti催化不对称加成甲基三(异丙氧基)的二十种新配体的制备和筛选,这些配体是α,α,α',α'-四芳基-1,3-二氧戊环-4,5-二甲醇(TADDOL)的所有类似物描述了钛和二乙基锌与苯甲醛。这些配体具有被环丁烷,环戊烷,环己烯,环己烷,双环[2.2.1]庚烯和-庚烷以及双环[2.2.2]辛烯和-辛烷部分取代的TADDOL的二氧戊环。一些具有取代芳基的H原子或烷基,并且其中九个具有C 2对称性。X射线晶体学和分子力学用于分析配体的结构,并且两个结构特征似乎与选择性相关:(i)螯合O原子和邻位原子的扭转角轴向Ph族的-C原子(小,约19°,最佳角度,图8),以及(ii)轴向Ph族的“垂直度”(图9)。竞争实验表明,TADDOL 1a催化甲基钛和二乙基锌的添加速度比相关的二氧戊环类似物12a,12c和12e快50倍以上(方案7),表明配体需要轴向和赤道芳基(见脚注6)这些反应的加速催化。提出了完