A one-step, Brønsted acid catalyzed tandem reaction for the synthesis of α-(4-oxazolyl)amino esters was developed. 4-Nitrobenzenesulfonic acid was found to be an efficient catalyst for the coupling of ethyl 2-oxobut-3-ynoates with amides to provide various α-(4-oxazolyl)amino esters. The experimental and X-ray crystallographic data suggest that a series of bond-forming reactions including imine formation, intermolecular Michael addition, and intramolecular Michael addition are involved to generate both the oxazole and amino acid functionalities.

中文翻译：

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布朗斯台德酸催化串联反应合成α-（4-恶唑基）氨基酯

开发了一步一步布朗斯台德酸催化串联反应合成α-（4-恶唑基）氨基酯的方法。发现4-硝基苯磺酸是使2-氧代丁-3-炔酸乙酯与酰胺偶联以提供各种α-（4-恶唑基）氨基酯的有效催化剂。实验和X射线晶体学数据表明，包括亚胺形成，分子间迈克尔加成和分子内迈克尔加成在内的一系列成键反应涉及生成恶唑和氨基酸官能团。