Simple swaps of CO2 The loss of carbon dioxide (CO2) from carboxylic acids is a common reaction in both biochemical and synthetic contexts, but it has generally involved catalysis or prolonged heating. Kong et al. now report that certain polar solvents, such as dimethylformamide, promote reversible CO2 loss all by themselves from carboxylates bridged by one carbon to aromatic rings. With electron-withdrawing substituents on the ring, isotopically labeled CO2 can be efficiently swapped in even at room temperature. Alternatively, reaction with aldehydes leads to alcohol formation. Science, this issue p. 557 Certain polar solvents labilize CO2 bound at benzylic sites under surprisingly mild conditions. Many classical and emerging methodologies in organic chemistry rely on carbon dioxide (CO2) extrusion to generate reactive intermediates for bond-forming events. Synthetic reactions that involve the microscopic reverse—the carboxylation of reactive intermediates—have conventionally been undertaken using very different conditions. We report that chemically stable C(sp3) carboxylates, such as arylacetic acids and malonate half-esters, undergo uncatalyzed reversible decarboxylation in dimethylformamide solution. Decarboxylation-carboxylation occurs with substrates resistant to protodecarboxylation by Brønsted acids under otherwise identical conditions. Isotopically labeled carboxylic acids can be prepared in high chemical and isotopic yield by simply supplying an atmosphere of 13CO2 to carboxylate salts in polar aprotic solvents. An understanding of carboxylate reactivity in solution enables conditions for the trapping of aldehydes, ketones, and α,β-unsaturated esters.

中文翻译：

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二甲基甲酰胺溶液中稳定有机酸的直接可逆脱羧反应

CO2 的简单交换 羧酸中的二氧化碳 (CO2) 损失是生化和合成环境中的常见反应，但它通常涉及催化或长时间加热。孔等人。现在报告某些极性溶剂，如二甲基甲酰胺，它们本身会促进可逆的 CO2 损失，这些都是由一个碳桥接到芳环的羧酸盐。由于环上有吸电子取代基，即使在室温下，同位素标记的 CO2 也可以有效交换。或者，与醛的反应导致醇的形成。科学，这个问题 p。557 某些极性溶剂在令人惊讶的温和条件下使结合在苄基位点的 CO2 变得不稳定。有机化学中的许多经典和新兴方法依赖于二氧化碳 (CO2) 挤出来生成用于成键事件的反应中间体。涉及微观逆向的合成反应 - 反应中间体的羧化 - 通常使用非常不同的条件进行。我们报告化学稳定的 C(sp3) 羧酸盐，如芳基乙酸和丙二酸半酯，在二甲基甲酰胺溶液中经历未催化的可逆脱羧。脱羧 - 羧化发生在底物上，在其他条件相同的情况下，对布朗斯台德酸的原脱羧作用有抵抗力。通过简单地向极性非质子溶剂中的羧酸盐提供 13CO2 气氛，可以以高化学和同位素产率制备同位素标记的羧酸。