Rhodium-Catalyzed Enantioselective 1,2-Addition of ArylboronicReagents to α-Ketoesters using Chiral Diene Ligands
本研究是以「tert-butyl 2-oxo-2-phenylacetate 進行 1,2-不對稱加成製備成 tert-butyl 2-hydroxy-2,2-diphenylacetate之最適化實驗」做為實驗目標，在起始物的苯環上添加不同的取代基進行反應，以探討不同的 tert-butyl 2-oxo-2-phenylacetate 衍生物產率及鏡像超越值的差異。研究結果顯示，在以取代基位置為操作變因的實驗中，間位、對位擁有 48% 及 43% 的產率，鄰位產率則僅有 12% ，但鏡像超越值皆能達 >90% ee。由此可推論鄰位因有較大的立體阻礙，使得反應不易發生；間位雖比對位有較高的立體阻礙，但因與反應處相距較遠，故影響較小；而鏡像選擇性不受立體阻礙影響。為了使間位和對位反應的差異更為明顯，故決定在間位及對位以不同電子效應的基團做為取代基進行反應。研究結果也顯示，當間位具有一個拉電子特性的 CF3取代基，能使 α–ketoester 之加成產物產率>99%。未來若能進一步以更多不同的推拉電子基做為取代基，則可望使立體阻礙大小與推拉電子效應被量化，進而預測產率，協助進行最適化製備的研究過程中，更有效率的找到最適化條件。
The change in NaCl crystals from cubic to octahedral～Sodium polyacrylate stabilizes the {111} face of Miller indices～
When adding 2% or 4% sodium polyacrylate as habit modifier, standard milky-white octahedral NaCl crystals grew gradually in saturated NaCl solution on the bottom of the container. [1] [2] Sodium polyacrylate is well known as a highly water-absorbable polymer with many carboxylate anions. In the case of low concentration (0.01%, 0.02%, 0.05%, 0.1% and 0.5%) sodium polyacrylate many small or microscopic crystals whose shapes were nearly octahedrons and had {111} faces were observed with an optical microscope on the bottoms of the solution containers. In low concentration sodium polyacrylate, octahedral NaCl crystals made up of electrostatically unstable {111} faces grew similarly to crystals in high concentrations of 2% or 4% NaCl. Therefore, by adding sodium polyacrylate to saturated NaCl solution, cleaved rock salt crystals in this sol were observed to find out whether or not a change in crystal morphology from cuboids of {100} faces to octahedrons of {111} faces would occur. Regardless of the sodium polyacrylate concentrations of 0.01%, 0.02%, 0.05%, 0.1%, 0.5% and 2%, all cuboid crystals changed into a pyramidal shape in which four of the side surfaces formed an equilateral triangle. When one side of each equilateral triangle face was rotated so the square face of the crystal was soaked in the NaCl sol, all crystals grew into octahedrons of high transparency. Sodium polyacrylate, even under a low concentration, caused morphological change in the NaCl crystals. Many carboxylate anions in the sodium polyacrylate attracted sodium ions and the repulsive force between the carboxylate anions became weak, excluding the water in the internal space of the polymer. We considered that the stabilizing {111} faces of gathered sodium ions attached to carboxylate anions. Chloride and sodium ions coordinated continuously to minimize the NaCl surface area, growing into an octahedral and lowering the surface energy of the NaCl crystal. [3]