Under optimized conditions, 3-substitutedthiophenes (EWG = COOEt, PO(OEt)2) undergo a facile and regioselective oxidative coupling reaction at carbon atom C4. The reactions were performed with various aryl boronic acids as nucleophiles in the presence of silver oxide (2.0 equiv), cesium trifluoroacetate (tfa) (1.0 equiv), benzoquinone (BQ) (0.5 equiv), and catalytic amounts of Pd(tfa)2 (10 mol %)
Reaction orders for the key components in the palladium(II)‐catalyzedoxidativecross‐coupling between phenylboronic acid and ethyl thiophen‐3‐yl acetate were obtained by the method of initial rates. It turned out that the reaction rate not only depended on the concentration of palladium trifluoroacetate (reaction order: 0.97) and phenylboronic acid (reaction order: 1.26), but also on the concentration
通过初始速率法获得了钯(II)催化的苯基硼酸与乙基噻吩-3-乙酸乙酯之间的氧化交叉偶联中关键组分的反应顺序。结果表明,反应速率不仅取决于三氟乙酸钯(反应顺序:0.97)和苯基硼酸(反应顺序:1.26)的浓度,还取决于噻吩(反应顺序:0.55)和氧化银(浓度)的浓度。反应顺序:-1.27)。NMR光谱滴定研究确定了银盐与苯基硼酸和噻吩-3-基乙基乙酸乙酯之间存在1:1的络合物。低反向动力学同位素效应(k H / k D= 0.93)是通过使用乙基噻吩-3-乙酸乙基酯的4氘代异构体并监测其与4-苯基取代产物的反应而确定的。用对位取代的2-苯基噻吩进行的Hammett分析得出与苯基硼酸的氧化交叉偶联的负ρ值。根据动力学数据和其他证据,提出了一种机制,该机制可以将苯基从苯基硼酸转移到三氟乙酸钯和噻吩的1:1络合物中,作为速率确定步骤。提出并讨论了有关中间体的结构。