Crandell Douglas W, Mazumder Shivnath, Evans P Andrew, Baik Mu-Hyun
Department of Chemistry , Indiana University , 800 E. Kirkwood Ave. , Bloomington , IN 47405 , USA . Email:
Department of Chemistry , Queen's University , 90 Bader Lane , Kingston , ON K7L 3N6 , Canada . Email:
Chem Sci. 2015 Dec 1;6(12):6896-6900. doi: 10.1039/c5sc02307f. Epub 2015 Aug 25.
Density functional theory calculations demonstrate that the reversal of regiochemical outcome of the addition for substituted methyl propiolates in the rhodium-catalyzed [(2 + 2) + 2] carbocyclization with PPh and ()-xyl-binap as ligands is both electronically and sterically controlled. For example, the ester functionality polarizes the alkyne π* orbital to favor overlap of the methyl-substituted terminus of the alkyne with the p-orbital of the alkenyl fragment of the rhodacycle during alkyne insertion with PPh as the ligand. In contrast, the sterically demanding xyl-binap ligand cannot accommodate the analogous alkyne orientation, thereby forcing insertion to occur at the sterically preferred ester terminus, overriding the electronically preferred orientation for alkyne insertion.
密度泛函理论计算表明，在以三苯基膦（PPh）和（）-联萘二酚二甲苯酯（xyl-binap）为配体的铑催化[(2 + 2) + 2]碳环化反应中，取代丙炔酸甲酯加成的区域化学结果的反转是由电子效应和空间效应共同控制的。例如，酯官能团使炔烃的π*轨道极化，有利于在以三苯基膦为配体的炔烃插入过程中，炔烃的甲基取代端与铑环烯基片段的p轨道重叠。相比之下，空间位阻较大的xyl-binap配体无法容纳类似的炔烃取向，从而迫使插入发生在空间位阻较小的酯端，优先于炔烃插入的电子效应取向。
