Intramolecular Catalysis in Addition of Carboxyl to Carbon-Carbon Triple Bonds1
Intramolecular Catalysis in Addition of Carboxyl to Carbon-Carbon Triple Bonds1
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DOI：
10.1021/ja01082a012
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发表时间：
1965-02
影响因子：
15
通讯作者：
R. Letsinger;E. Oftedahl;J. Nazy
中科院分区：
文献类型：
--
作者：
R. Letsinger;E. Oftedahl;J. Nazy
研究了含羧基的Tolan化合物在碳-碳三键上加成羧酸的反应机理。结果表明，2，2‘-甲苯二酸(I)在乙醇溶液中于室温下容易异构化为3-(2-羧基亚甲基)苯基(IV)，在醋酸-硫酸溶液中升温后，再重排为3-(2-羧基苯基)异香豆素(VI)和二内酯。2-甲苯甲酸(II)和2，4‘-甲苯二酸(III)比2，2’-甲苯二酸更不容易异构化，前者生成3-亚苄基苯基(IX)和3-苯基异香豆素(XI)，后者生成3-(4-羧基亚苄基)苯酞(XI)。乙腈中的银离子催化II和III的异构化，而不催化I的异构化。在30℃时，I、II和III在乙醇中异构化的相对速率为22000：1：2.6。在水溶液中，I的异构化速率与I衍生的单阴离子的浓度成正比，I的单阴离子的反应速度比II的阴离子快6000倍。这些结果支持了I异构化的机理，在该机理中，羧基起分子内催化剂的作用，加速了羧酸盐阴离子对相邻碳-碳三键的攻击。
Aspects of the mechanism of addition of a carboxylic acid to a carbon-carbon triple bond were investigated with tolan compounds bearing carboxyl substituents. It was found that 2, 2'-tolandicarboxylic acid (I) isomerizes readily in alcohol solution at room temperature to 3-(2-carboxybenzylidene) phthalide (IV), which in turn rearranges to 3-(2-carboxyphenyl) isocoumarin (VI) and a dilactone when warmed in an acetic-sulfuric acid solution. 2-Tolancarboxylic acid (II) and 2, 4'-tolandicarboxylic acid (III) isomerize much less readily than 2, 2'-tolandicarboxylic acid, the former affording 3-benzylidenephthalide (IX) and 3-phenylisocoumarin () and the latter yielding 3-(4-carboxybenzylidene) phthalide (XI). Silver ion in acetonitrile catalyzes the isomerization of II and III but not that of I. The relative rates of isomerization of I, II, and III in ethanol at 30 are 22,000: 1: 2.6. In aqueous buffers the rate of isomerization of I is proportional to the concentration of the mono-anion derived from I, and the monoanion of I reacts 6000 times faster than the anion of II. These results support a mechanism for isomerization of I in which a carboxyl group functions as an intramolecular catalyst in accelerating attack of a carboxylate anion on the neighboring carbon-carbon triple bond.