Breit Bernhard, Heckmann Golo, Zahn Stephan K
Albert-Ludwigs-Universität Freiburg Institut für Organische Chemie und Biochemie Albertstrasse 21, 79104 Freiburg, Germany.
Chemistry. 2003 Jan 20;9(2):425-34. doi: 10.1002/chem.200390044.
2-Substituted secondary alcohol o-DPPB esters (o-DPPB=ortho-diphenylphosphanylbenzoyl) have been prepared and their o-DPPB-directed diastereoselective hydroformylation examined. It was found that the diastereoselectivity increased as a function of the steric demand of the substituents both at the stereogenic center and in the alkene 2-position. Hydrolytic cleavage of the o-DPPB group afforded-via the lactols 29-the corresponding lactones 30, the relative configurations of the vicinal stereogenic centers of which were ascertainable by 2D-NOESY spectroscopy. In addition, a crystal structure analysis of the hydroformylation product 2 d provided further confirmation of the relative configuration. Replacement of the ester carbonyl group of the o-DPPB by a methylene unit resulted in significantly worse diastereoselectivity in the course of the hydroformylation (34-->35), which indicates a decisive role for the ester carbonyl function. All the experimental observations were combined in a model of the origin of the 1,2-asymmetric induction during the title reaction. The key feature is the consideration of diastereomeric trigonal-bipyramidal rhodium-hydrido-olefin complexes I and II, capable on the basis of the Hammond postulate of acting as good models for the transition states of the selectivity-determining hydrometalation step. Investigation of these complexes by force-field methods indicated good correlation between theoretically predicted and experimentally determined diastereoselectivities.
已制备出2-取代仲醇邻二苯基膦酰基苯甲酸酯（o-DPPB = 邻二苯基膦酰基苯甲酰基），并对其o-DPPB导向的非对映选择性氢甲酰化反应进行了研究。发现非对映选择性随着立体中心以及烯烃2-位取代基的空间需求的增加而提高。o-DPPB基团的水解裂解通过内消旋醇29得到相应的内酯30，其邻位立体中心的相对构型可通过二维NOESY光谱确定。此外，氢甲酰化产物2 d的晶体结构分析进一步证实了相对构型。将o-DPPB的酯羰基替换为亚甲基单元会导致氢甲酰化过程中非对映选择性显著变差（34→35），这表明酯羰基官能团起决定性作用。所有实验观察结果都纳入了标题反应中1,2-不对称诱导起源的模型。关键特征是考虑了非对映体三角双锥铑-氢化物-烯烃配合物I和II，根据哈蒙德假说，它们能够作为选择性决定氢金属化步骤过渡态的良好模型。通过力场方法对这些配合物的研究表明，理论预测的非对映选择性与实验测定的非对映选择性之间具有良好的相关性。
