Laboratory of Applied Chemistry, Institute of Organic Chemistry (IOC), Karlsruhe Institute of Technology (KIT), Straße am Forum 7, 76131 Karlsruhe, Germany.
Laboratory of Applied Chemistry, Institute of Biological and Chemical Systems, Functional Molecular Systems (IBCS-FMS), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
Philos Trans A Math Phys Eng Sci. 2020 Jul 24;378(2176):20190267. doi: 10.1098/rsta.2019.0267. Epub 2020 Jul 6.
Seeking a sustainable and selective approach for terpene modification, a catalyst deconvolution approach was applied to the Meinwald rearrangement of (+)-limonene oxide as a model substrate to yield dihydrocarvone. In order to identify the most suitable catalyst and reaction conditions, different Lewis acids were evaluated. Bismuth triflate proved to be the most active catalyst under mild reaction conditions, with a low catalyst loading (1 mol%) and a relatively short reaction time (3 h). The optimized reaction conditions were subsequently transferred to other terpene-based epoxides, yielding different bio-based biscarbonyl structures, which constitute interesting and valuable substances, e.g. for polymer synthesis or as fragrances. Monoepoxides derived from ()-(-)-carvone and (+)-dihydrocarvone rearranged to the desired products with high selectivities and yields. γ-Terpinene dioxide could be transformed in a double rearrangement to the respective biscarbonyl in moderate yields. A better result was achieved for limonene dioxide after further adjustment of the protocol to reach acceptable yields with a low catalyst loading of 0.1 mol% using 2-methyl tetrahydrofuran as a sustainable solvent. Compared to many procedures described in the literature, this procedure represents a step towards an increased sustainability in terpene modification by considering several principles of Green Chemistry, such as renewable resources, catalysis and mild reaction conditions for elementary chemical transformations. This article is part of a discussion meeting issue 'Science to enable the circular economy'.
为了寻求一种可持续且具有选择性的萜烯修饰方法，我们应用催化剂解卷积方法对（+）-柠檬烯氧化物的 Meinwald 重排反应进行了研究，以生成二氢大马酮。为了确定最合适的催化剂和反应条件，我们评估了不同的路易斯酸。三氟甲磺酸铋被证明是最有效的催化剂，在温和的反应条件下，催化剂的负载量低（1 mol%），反应时间相对较短（3 小时）。随后，将优化后的反应条件转移到其他基于萜烯的环氧化物上，得到了不同的生物基双羰基结构，这些结构构成了有趣且有价值的物质，例如用于聚合物合成或作为香料。（）-（-）-蒈烯和（+）-二氢大马酮衍生的单环氧化物以高选择性和产率转化为所需产物。γ-松油烯二氧化物可以通过双重重排以中等产率转化为相应的双羰基化合物。通过进一步调整方案，使用 2-甲基四氢呋喃作为可持续溶剂，以低至 0.1 mol%的催化剂负载量达到可接受的产率，对于柠檬烯二氧化物的结果更好。与文献中描述的许多程序相比，该程序通过考虑绿色化学的几个原则，如可再生资源、催化和温和的化学反应条件，代表了在萜烯修饰方面朝着提高可持续性迈出的一步。本文是关于“科学促进循环经济”的讨论文章的一部分。
