构型转换法制备赤式紫胶桐酸及反应机理分析

Preparation of erythro aleuritic acid by configuration transformation method and analysis of reaction mechanism

以苏式紫胶桐酸为原料,通过构型转换法制备赤式紫胶桐酸。采用FTIR、质谱、核磁(1HNMR/13CNMR)、TG、DSC、XRD、手性拆分、比旋光度等表征手段对所得产物进行了分析确证。对紫胶桐酸苏式到赤式构型的转换机理进行了初步探究。结果表明:FTIR、质谱、核磁显示,产物与苏式紫胶桐酸结构一致;XRD、DSC、TG结果表明,苏式紫胶桐酸与产物具有相同晶型,但产物熔点更高,晶胞尺寸更小;手性拆分结果显示,产物为紫胶桐酸的光学异构体,从而确定产物为赤式紫胶桐酸。对中间产物的结构表征表明,苏式紫胶桐酸到赤式紫胶桐酸构型转换的机理为卤素和羟基之间双分子亲核取代(SN2)和双分子消除反应(E2)同时发生的反应,羟基和卤素间的两次SN2反应是发生构型转换反应(Walden转换)的关键;羟基/卤素间的E2反应是苏式紫胶桐酸能够彻底转化为赤式紫胶桐酸的原因。

Erythro aleuritic acid was prepared by configuration transformation method from thero aleuritic acid. The products were characterized by FTIR, mass spectrometry, nuclear magnetic resonance(1HNMR and 13CNMR), TG, DSC, XRD, chiral resolution and specific rotation. The transformation mechanism of thero aleuritic acid into erythro aleuritic acid was primary explored. FTIR, mass spectrometry and nuclear magnetic resonance results showed that the structure of the product was consistent with thero aleuritic acid. XRD, DSC and TG results suggested that thero aleuritic acid and the product had the same crystal type, but the product had higher melting point and smaller crystal cell structure. The chiral resolution result showed that the product was an optical isomer of aleuritic acid, which was determined to be erythro aleuritic acid. Based on the structural characterization of the intermediates, the mechanism of configuration transformation from thero aleuritic acid to erythro aleuritic acid was the simultaneous reaction of nucleophilic substitution(SN2) and elimination reaction(E2) between the halogens and hydroxyl. The twice SN2 reactions between the hydroxyl and halogens were the key to the configuration transformation reaction(Walden transformation). The E2 reaction of hydroxyl/halogen was the reason for the complete transformation of thero aleuritic acid into erythro aleuritic acid.