炔丙型硫Ylide环丙烷化反应及其立体选择性

炔丙型硫Ylide与丙烯酸酯的反应是一个多反应竞争的复杂反应, 通常环丙烷化产物收率很低. 本文通过对反应底物的优化, 成功获得了高收率、高选择性的反式环丙烷化产物. 同时利用Gaussian 03程序, 选择密度泛函BHHLYP方法, 6-31G**基组对反应路径及过渡态模型进行了计算, 进而采用密度泛函理论中的B3LYP方法, 选择6-31G**基组, 对顺、反式产物的热稳定性进行了分析, 明确了该反应的高非对映选择性是由过渡态的能量差异和产物的热稳定性两个因素共同决定的, 而过渡态的能量差异可以归于分子内弱的立体电子效应的不同.

Cyclopropanation Reaction and Diastereoselectivity of Propargyl Sulfur Ylide with Acrylates

The cyclopropanation of propargyl sulfur Ylide with acrylate usually gave poor yield because of several competing reactions such as 2,3]-σ atropic rearrangement were also involved in this system. In our research, a higher yield(75%) and high diastereoselectivity(96%d.e.) for trans-2-ethynyl cyclopropane carboxylate were obtained by changing the structure of sulfur ylide and optimizing the reaction conditions. The mechanism and diastereoselectivity of the reaction were studied via the density functional theory method. High selectivity toward trans cyclopropanes are predicted on the basis of the relative activation energies of diastereomeric torsional transition states and the thermodynamic satbility of products. The energy differences between these transition states could be rationalized with the help of weak intramolecular stereoelectronic interactions.