作者:Kiyoshi Kudo、Yuji Oida、Koichi Mitsuhashi、Sadayuki Mori、Koichi Komatsu、Nobuyuki Sugita
DOI:10.1246/bcsj.69.1337
日期:1996.5
The palladium(II)-catalyzed carbonylation of various enol esters in the presence of methanol under pressurized carbon monoxide was investigated. As typical results, the carbonylation of isopropenyl acetate afforded a cyclocarbonylation product, 2-methoxy-2,5,5-trimethyl-1,3-dioxolan-4-one, in 46% yield under carbon monoxide of 150 atm at 100 °C, whereas vinyl acetate selectively gave an α-hydroesterification product, methyl 2-acetoxypropionate, in 56% yield under 250 atm at 100 °C. On the contrary, the reaction of 3,3-dimethyl-1-buten-2-yl acetate gave exclusively a β-hydroesterification product, methyl 3-acetoxy-4,4-dimethylpentanoate, in 64% yield. The yields of these products show a maximum as a function of the base/palladium ratio and of the carbon monoxide pressure. The effects of the reaction variables, such as the MeOH/substrate ratio, the structure of the base, the base/Pd ratio, the CO pressure, and the reaction temperature, were examined for optimizing the process. The mechanisms for the unique cyclocarbonylation and highly regioselective hydrocarbonylation of enol esters involving hydridopalladium(II) intermediate are discussed.
研究了在加压一氧化碳和甲醇存在下,钯(II)催化的各种烯醇酯的羰基化反应。作为典型结果,在150大气压、100°C的条件下,异丙烯基乙酸酯的羰基化反应得到了环状羰基化产物,2-甲氧基-2,5,5-三甲基-1,3-二氧杂环己烷-4-酮,产率为46%;而乙烯基乙酸酯在250大气压、100°C的条件下,选择性地得到了α-羟基酯化产物,乙酸甲酯-2-乙酰氧基丙酸酯,产率为56%。相反,3,3-二甲基-1-丁烯-2-基乙酸酯反应得到了唯一的β-羟基酯化产物,乙酸甲酯-3-乙酰氧基-4,4-二甲基戊酸酯,产率为64%。这些产物的产率作为碱/钯比的函数和一氧化碳压力的函数达到最大值。为了优化过程,考察了反应变量,如甲醇/底物比、碱的结构、碱/钯比、一氧化碳压力和反应温度等的影响。讨论了含氢钯(II)中间体参与的烯醇酯独特环羰基化和高度区域选择性羟基羰基化的机理。