A simple and rapid synthesis of (S)-pyroglutamic acid was developed by the thermal cyclodehydration of (S)-glutamic acid under solvent-free conditions, with continuous swirling during heating (220°C) to ensure homogeneity of the melt. The reaction proceeds until the bubbles disappear, not exceeding 5 min. The heating immediately ceases, then cooling the reaction vessel to prevent degradation and racemization. (S)-pyroglutamic acid is obtained in 70% yield, and the enantiomeric ratio is 97:3. The same reaction under microwave heating in an aqueous solution afforded a low yield of racemic product.

中文翻译：

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(S)-焦谷氨酸的实际合成


通过在无溶剂条件下热环化（S）-谷氨酸，并在加热（220°C）期间连续旋转以确保熔体的均匀性，开发了一种简单快速的（S）-焦谷氨酸合成方法。反应进行至气泡消失，不超过5分钟。立即停止加热，然后冷却反应容器以防止降解和外消旋化。得到(S)-焦谷氨酸，收率70％，对映体比例为97:3。在微波加热下，在水溶液中进行相同的反应，得到低产率的外消旋产物。