Racemic carboxylic acid, a Diels-Alder cycloadduct derived from 5-bromo-3-phenyl-α-pyrone and acrylate dienophile, was resolved into enantiomers by diastereomeric salt crystallization. Quinidine was used as a sole resolving base. The salt of (+)-acid crystallized from aqueous acetonitrile solution. Once this salt was separated by filtration, quinidine salt with (−)-acid crystallized from mother liquor. As a result, both enantiomers of Diels-Alder cycloadduct were isolated in high enantiomeric purity.

中文翻译：

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通过非对映体盐拆分：使用拆分碱的相同对映体获得外消旋酸的两种对映体

外消旋羧酸是由 5-溴-3-苯基-α-吡喃酮和丙烯酸酯亲二烯体衍生的狄尔斯-阿尔德环加合物，通过非对映体盐结晶拆分成对映体。奎尼丁用作唯一的拆分碱。(+)-酸的盐从乙腈水溶液中结晶。一旦通过过滤分离该盐，奎尼丁与(-)-酸的盐就从母液中结晶出来。结果，狄尔斯-阿尔德环加合物的两种对映体均以高对映体纯度分离出来。