Quantitative Dihydroxylation Of Δ~5-Steroids And Gel Properties Of Steroidal Epoxides

In this dissertation, quantitative and stereospecific dihydroxylation of Δ⁵-steroids, and the investigation of gelation properties and reactions in gels are reported. In the research, the gelators of gels are a series of novel epoxy-functionalized dehydroepiandrosterones.We have developed a one-pot procedure to convert 15 Δ⁵-steroids to corresponding 5α,6β-dihydroxylated steroids using H₂O₂ and catalyzed by H₂SO₄ and KI. The yield is quantitative and the stereochemistry is specific. The reaction mechanism is proposed by comparing with the literature procedures and oxidizing non-steroidal alkenes. This methodology should have wide applications in the agriculture, food and pharmaceutical industries because of its simplicity, its inexpensiveness, its high effectiveness and its compatibility with numerous functional groups.10 Epoxy-functionalized dehydroepiandrosterones and 1 dehydroepiandrosterone aldol condensation product were synthesized and their gelation properties were investigated. In gealtion tests, we found that hydroxyl, epoxy and aromatic groups are all necessary for gel formations. The CGC values of the gels are almost below 1 wt%, which can be termed super-gelators. The corresponding xerogels and reference gelators were characterized with FTIR spectroscopy, SEM and XRD technique. Nanofiber structures were observed in all the organic gels. The results indicated that the large differences in morphologies are mainly attributed to the diversity of gelator structures and different gel solvents. Based on the FTIR and XRD studies, the primary driving forces of gel formations are hydrogen bonding and the gelators adopt hexagonal aggregation modes. A possible model was proposed to describe the process of self-assembly.According to the structures of gelators and the properties of gels, the reductions of carbonyl group and epoxidations of double bonds were studied. In the non-gel medium, the carbonyl group in gelators can not be reduced by NaBH₄, on the contrary NaBH4 can realize quantitative and stereospecific reduction of carbonyl group in gelators in the gel medium. Furthermore, granular PTFE have obvious promotion effects on the reduction rate. Based on the control experiments, a hydrogen bonding activating carbonyl group mechanism was proposed and the stereochemistry of reduction was explained. In the study of the epoxidation reactions, the following conclusions can be drawn.（1） Comparing with the non-gel medium, the epoxidation in the gel medium exhibits higher stereoselectivity.（2） The addition of granular PTFE can increase the reaction rate and stereoselectivity.（3） The higher stereoselectivity in the gel medium attributed to the ordered arrangements in space of gelator molecules.