Regioselective Formation of Enol Esters from the Ruthenium-Catalyzed Markovnikov Addition of Carboxylic Acids to Alkynes
作者:Janine Jeschke、Christian Gäbler、Heinrich Lang
DOI:10.1021/acs.joc.5b02293
日期:2016.1.15
selectivities with up to 99% of the Markovnikov product were achieved. The electronic influence of the substrates on the reaction rate was quantified by Hammett plots. By the use of electron-rich alkynes or highly acidic carboxylic acids, the reaction rate could be increased. Hence, the addition of highly acidic pentafluorobenzoic acid to electron-rich 4-methoxyphenylacetylene can even be carried out
钌络合物[Ru(CO)2(P(p -C 6 H 4 -X)3)2(O 2 CPh)2 ](1a,X = CF 3 ; 1b,X = Cl; 1c,X = H ;1d,X = Me;1e,X = OMe)已成功应用于末端区域炔烃的区域选择性马尔可夫尼可夫加成反应,生成了有价值的烯醇酯。催化剂筛选显示出膦的电子性质对活性和选择性有重大影响。催化剂1a达到最高活性,具有最吸电子的膦配体。通过添加催化量的AgOTf,可以进一步提高选择性和活性。此外,Markovnikov产品的选择性高达99%。底物对反应速率的电子影响通过哈米特图定量。通过使用富电子炔烃或高酸性羧酸,可以提高反应速率。因此,甚至可以在25°C下在4小时内定量地向富含电子的4-甲氧基苯基乙炔中添加高酸性五氟苯甲酸。此外,在温和的反应条件下(25–70°C),可以分离出种类繁多的简单的,电子或空间上具有挑战性的底物,具有良好的产率,具有很高的区域选择性。