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首页> 外文期刊>The Journal of Organic Chemistry >Esters of pyromellitic acid. Part I. Esters of achiral alcohols: Regioselective synthesis of partial and mixed pyromellitate esters, mechanism of transesterification in the quantitative esterification of the pyromellitate system using orthoformate esters, and a facile synthesis of the ortho pyromellitate diester substitution pattern.
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Esters of pyromellitic acid. Part I. Esters of achiral alcohols: Regioselective synthesis of partial and mixed pyromellitate esters, mechanism of transesterification in the quantitative esterification of the pyromellitate system using orthoformate esters, and a facile synthesis of the ortho pyromellitate diester substitution pattern.

机译：均苯四酸的酯。第一部分：非手性醇的酯：部分和混合均苯四酸酯酯的区域选择性合成，使用原甲酸酯对均苯四酸酯体系进行定量酯化的酯交换反应机理，以及易合成的均苯四甲酸二酯取代模式。

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摘要

Mild conditions and reversible anhydride formation allow a relative differentiation to be made of the four equivalent carbonyl groups of pyromellitic dianhydride (PMDA, benzene-1,2,4,5-tetracarboxylic dianhydride) in esterification, leading to regioselective methods to generate a wide range of partially or totally esterified products or products bearing differing esterifying groups at the different positions. Pyromellitate monoester anhydrides form efficiently in dichloromethane/triethylamine from 1 equiv of the alcohol. Under the same conditions, two different alcohols can be made to react sequentially. With 2 equiv of an alcohol, the usual mixture of meta and para diesters is obtained, separated by crystallization from HOAc. Meta and para dibenzyl pyromellitates served as regiospecific sources of other diesters, by further esterification followed by hydrogenolysis. Refluxing orthoformate triesters were found to effect quantitative esterification of the pyromellitate system under autocatalytic conditions; minor ester exchange with pre-existing esters (0-5% of total product) was ascribed to reversible anhydride formation. For general esterification with alcohols, partial ester acid chlorides were obtained using oxalyl chloride. Pyromellitate triesters afforded the ortho diester anhydrides upon distillation, thereby providing facile entry into the mostly novel ortho substitution pattern in this system. The requisite triesters were prepared by selective saponification or by the prior incorporation of one benzyl ester substituent, which could be removed by catalytic hydrogenolysis. The various benzyl esters of pyromellitates hydrogenolyzed smoothly to release the carboxylic acid groups without disturbance of pyromellitate aromaticity.
机译：温和的条件和可逆酸酐的形成允许在酯化过程中对均苯四甲酸二酐（PMDA，苯-1,2,4,5-四羧酸二酐）的四个当量羰基进行相对区分，从而导致区域选择性方法产生大范围部分或全部酯化的产品或在不同位置带有不同酯化基团的产品。均苯四甲酸单酯酸酐在二氯甲烷/三乙胺中由1当量的醇有效形成。在相同条件下，可以使两种不同的醇顺序反应。用2当量的醇，获得通常的间和对二酯混合物，通过与HOAc结晶分离。间苯二甲酸和对二苄基均苯四酸酯通过进一步酯化然后氢解而充当其他二酯的区域特异性来源。发现回流的原甲酸三酯在自动催化条件下影响均苯四酸体系的定量酯化。与预先存在的酯（占总产物的0-5％）进行的少量酯交换归因于可逆酸酐的形成。为了用醇进行一般的酯化反应，使用草酰氯获得了部分酯酰氯。均苯四酸三酯在蒸馏时提供邻二酯，从而使该体系中大多数新颖邻位取代形式的进入变得容易。通过选择性皂化或通过预先结合一个苄基酯取代基来制备必需的三酯，该苄基酯取代基可通过催化氢解除去。均苯四甲酸酯的各种苄基酯可平滑地氢解以释放出羧酸基团，而不会影响均苯四甲酸酯的芳香性。

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