<i>E</i>–<i>Z</i> isomerization in Suzuki cross-couplings of haloenones: ligand effects and evidence for a separate catalytic cycle
作者:Navneet K. Chehal、Peter H. M. Budzelaar、Philip G. Hultin
DOI:10.1039/c7ob02925j
日期:——
we were surprised to observe extensive isomerization. More surprisingly, the ligand employed strongly influenced the degree of isomerization: DPEphos and Xantphos led to 96% isomerized cross-coupled product whereas reactions in the absence of a phosphine ligand, or reactions employing t-BuXantphos, gave 94% retention of stereochemistry. While E–Z isomerization in Pd-catalyzed vinylic couplings has previously
一般认为卤代烯烃的Suzuki交叉偶联在保留烯烃立体化学的情况下发生。在研究E -1,2-二氯乙烯基苯基酮上的Suzuki交叉偶联时,我们惊讶地观察到广泛的异构化。更令人惊讶的是,所使用的配体极大地影响了异构化程度:DPEphos和Xantphos导致96%的异构化交叉偶联产物,而在没有膦配体的情况下进行反应,或使用t- BuXantphos进行反应,则保留了94%的立体化学。当E – Z Pd催化的乙烯基偶联中的异构化以前已归因于交叉偶联催化循环内的事件,我们为这些反应中单独的Pd催化的异构化过程提供了实验和计算证据。