1-(3-Oxocyclobutyl) carboxylic acid (4a) was converted into N-Boc-protected 1-(3-oxocyclobutyl) urea (5a), a key intermediate for the preparation of agonists of metabotropic glutamate receptor 5, in one-step when treated with diphenyl phosphoryl azide and triethylamine in tert-butanol. The mechanism of the reaction involves a nucleophilic addition of the in situ generated tert-butyl carbamate to the isocyanate intermediate. This reaction is applicable to other 1-(3-oxocycloalkyl) carboxylic acids but not to linear γ-keto carboxylic acids.

中文翻译：

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Boc 保护的 1-（3-氧代环烷基）脲通过一步 Curtius 重排：机制和范围

1-(3-氧代环丁基) 羧酸 ( 4a )一步转化为N -Boc保护的 1-(3-氧代环丁基) 脲 ( 5a )，这是制备代谢型谷氨酸受体 5 激动剂的关键中间体用二苯基磷酰叠氮化物和三乙胺在叔丁醇中处理。该反应的机理涉及原位生成的氨基甲酸叔丁酯与异氰酸酯中间体的亲核加成。该反应适用于其他 1-(3-氧代环烷基)羧酸，但不适用于线性 γ-酮羧酸。