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[摘要]：Pradimicins are structurally intriguing natural products that possess potent biological activity as antifungal and antiviral agents through a unique mode of action as carbohydrate binding agents. A preliminary synthetic approach towards pradimicin A has focused on a model study of the core tricyclic ring system. The route features an alkoxyallylboration/cycloisomerization/DielsAlder cycloaddition sequence as the key steps. The alkoxyallylboration was critical for differentiating the hydroxy groups in the central cyclohexadienediol unit of pradimycins, which will ensure a regiocontrolled glycosylation. For the cycloisomerization reaction, various substrates and conditions were tested for a ring-closing enyne metathesis reaction. With enyne substrate 23, dimerization-prone bicyclic diene 24 was isolated as the major product under the conditions of both ruthenium-catalyzed metathesis and palladium-catalyzed cycloisomerization. In the end, the optimal route found for the synthesis of the model functionalized tricyclic ring system 31 features a one-pot sequential palladium-catalyzed cycloisomerization, DielsAlder reaction, and oxidative aromatization. |
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