The neighbouring effect of isosorbide and its epimers in their reactions with dimethyl carbonate
The neighbouring effect of isosorbide and its epimers in their reactions with dimethyl carbonate
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DOI：
10.14293/s2199-1006.1.sor-chem.ab3r7e.v2
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发表时间：
2014-10
影响因子：
--
通讯作者：
F. Aricò;P. Tundo
中科院分区：
文献类型：
--
作者：
F. Aricò;P. Tundo
摘要 本文研究了异山梨醇及其差向异构体、异甘露醇和异艾杜醇与碳酸二甲酯的反应，以便通过无卤素化学方法轻松获得生物基产品。异山梨醇及其差向异构体在与碳酸二甲酯 (DMC) 的双分子亲核取代中表现出不同的反应性。在DMC和弱碱存在下进行羧甲基化反应，高产率合成了二羧甲基衍生物。由于 OH 基团的外位位阻较小，异甘露糖是最具反应性的脱水糖。另一方面，在强碱和DMC存在下进行的异山梨醇及其差向异构体的甲基化显示出内羟基的较高反应性，异艾杜醇是最具反应性的差向异构体。这一结果归因于β位氧与脱水糖结构内分子内氢键结合的邻近效应。以两性催化剂水滑石为溶剂，以DMC为试剂和溶剂，在高压釜中进行甲基化反应。在这种情况下，差向异构体的反应性结果完全不同，异山梨醇是最具反应性的试剂，可能是由于水滑石的结构同时包含酸性和碱性位点。在这些甲基化反应中观察到邻近效应并有充分的证据。
Abstract The reactions of isosorbide and its epimers, isomannide and isoidide, with dimethyl carbonate have been herein investigated as easy access to bio-based products by a free-halogen chemistry approach. Isosorbide and its epimers show a different reactivity in bimolecular nucleophilic substitution with dimethyl carbonate (DMC). Carboxymethylation reaction was carried out in the presence of DMC and a weak base resulting in the high-yielding synthesis of dicarboxymethyl derivatives. Isomannide was the most reactive anhydro sugar due to the less sterically hindered exo position of the OH groups. On the other hand, methylation of isosorbide and its epimers, conducted in the presence of a strong base and DMC, showed the higher reactivity of the endo hydroxyl group, isoidide being the most reactive epimer. This result has been ascribed to the neighboring effect due to the combination of the oxygen in β-position and the intramolecular hydrogen bond within the anhydro sugar structure. Methylation reactions were also conducted in autoclave at high temperature with the amphoteric catalyst hydrotalcite using DMC as reagent and solvent. In this case, the reactivity of the epimers resulted quite differently with isosorbide being the most reactive reagent possibly as a result of the structure of hydrotalcite comprising of both acidic and basic sites. The neighboring effect was observed with good evidence in these methylation reactions.