已经实现了以区域选择性方式将苯乙烯与 CO2 和芳基卤化物进行可见光驱动的还原碳芳基化的第一个例子。广泛的芳基碘化物和溴化物与该反应相容。此外,吡啶基卤化物、烷基卤化物甚至芳基氯化物也适用于该方法。这些发现可能会激发对新型可见光驱动的 Meerwein 芳基化加成反应的探索,该反应以用户友好的芳基卤作为自由基来源和 CO2 的光催化利用。
Reactions of chlorine substituted (E)-2,3-diphenylpropenoic acids over cinchonidine-modified Pd: Enantioselective hydrogenation versus hydrodechlorination
摘要:
The effect of the chlorine position on the C-Cl bond hydrogenolysis and the enantioselective hydrogenation of Cl substituted (E)-2,3-diphenylpropenoic acid derivatives has been studied over cinchonidine-modified Pd/Al2O3. In contrast to the fast hydrodechlorination of the beta-phenyl-para-Cl substituted acids the Cl on the alpha-phenyl ring was barely hydrogenolized. These observations were interpreted by the different arrangements of the two phenyl rings on the surface, with the alpha- and beta-phenyl rings adsorbed tilted and parallel, respectively. The results confirmed the beneficial effect of the alpha-phenyl-ortho-substituents on the chiral discrimination, thus the 2,3-diphenylpropionic acids substituted by Cl on the alpha-phenyl ring could be prepared in good yields and optical purities. The conclusions were used for the rational design of an acid, i.e. (E)-2-(2-methoxyphenyl)-3-(3,4-difluorophenyl)propenoic acid, which afforded the best optical purity (ee up to 95% at 295 K) described until now in this heterogeneous system. (C) 2010 Elsevier B.V. All rights reserved.