Organic Synthesis in Water Utilizing Inorganic Porous Materials

虽然使用PTC在水介质中进行反应是一种通用的方法，但基于硅胶的吸附性质，我们设计了另一种在水中的势能过程。虽然硅胶在有机合成中的应用已经得到了广泛的研究，但就我们所知，它在水介质中的有机反应中的应用还没有被开发。在水中，由于二氧化硅表面与有机分子之间的疏水作用，作为底物的有机分子会被吸附到二氧化硅上，因此二氧化硅是一种有效的有机反应介质。在硅胶-水体系中，我们研究了碘催化氯胺-T(CT)催化烯烃的氮杂环化反应及其产物氮杂环丙烷的开环反应，其中硅胶(硅胶与MCM-41)的使用显示了独特的结果。例如，在水中硅胶60存在下，用CT、K_2CO_3和催化量的I_2处理苯乙烯，可以高产率地得到N-(对甲苯磺酰基)-2-苯基氮杂环丁烷。在碘催化剂-CT体系中，多种烯烃被成功地用于水中二氧化硅催化的烯烃叠氮化反应。考察了N-(对甲苯磺酰基)-2-正己基氮杂环丁烷与NaN_3或KCN的开环反应。在没有二氧化硅的情况下，氮杂环丙烷与NaN_3或KCN在水中的反应不同于上述的氮杂环化反应。然而，当加入硅胶60时，所需的反应继续进行，分别得到区域选择性开环产物。为了得到扩环产物，反应中加入了硫氰酸钾。正如预期的那样，以两个非对映异构体的混合物以良好的产率合成了由一个硫氰酸酯和两个氮杂环丙烷部分组成的扩环产物--噻唑烷衍生物。

Although the use of PTC to permit the reaction in aqueous media is a general method, an alternative potential process in water was devised, based on the adsorptive nature of silica gel. While the application of silica gel to organic synthesis has been widely investigated, its use in organic reactions in aqueous media has not been exploited, to the best of our knowledge. Silica would be effective as organic reaction media in water because the organic molecule as a substrate would be adsorbed to the silica by hydrophobic interactions between the surface of the silica and the organic molecule. We investigated here on the iodine-catalyzed aziridination of olefins using Chloramine-T (CT) and the ring opening of the resulting aziridine in a silica-water system, in which the use of silica (silica gel vs. MCM-41) showed unique results. For example, when styrene was treated with CT, K_2CO_3, and a catalytic amount of I_2 in the presence of Silica Gel 60 in water, N-(p-toluenesulfonyl)-2-phenylaziridine was obtained in good yield. A variety of olefins were successfully employed in this silica-mediated olefin aziridination in water using the iodine catalyst-CT system. To show the generality of the present media in organic synthesis, the ring opening of N-(p-toluenesulfonyl)-2-n-hexylaziridine with NaN_3 or KCN was examined. The reaction of aziridines with NaN_3 or KCN in water in the absence of silica did not proceed similarly to the case of the aziridination described above. When Silica Gel 60 was added, however, the desired reaction proceeded to afford the regioselective ring-opening products, respectively. To obtain a ring expansion product by the system, potassium thiocyanate was employed in the reaction. As was expected, a ring expansion product, thiazolidine derivative consisting of one thiocyanate and two aziridines moieties was produced in good yield as a mixture of two diastereomers.