N-Protected oxindole derivatives of unprecedented malleability bearing ester moieties at C-3 have been shown to participate in enantioselective phase-transfer-catalysed alkylations promoted by ad-hoc designed quaternary ammonium salts derived from quinine bearing hydrogen-bond donating substituents. For the first time in such phase-transfer-catalysed enolate alkylations, the reactions were carried out under base-free conditions. It was found that urea-based catalysts outperformed squaramide derivatives, and that the installation of a chlorine atom adjacent to the catalyst’s quinoline moiety aided in avoiding selectivity-reducing complications related to the production of HBr in these processes. The influence of steric and electronic factors from both the perspective of the nucleophile and electrophile were investigated and levels of enantiocontrol up to 90% ee obtained. The synthetic utility of the methodology was demonstrated via the concise enantioselective synthesis of a potent CRTH2 receptor antagonist.

中文翻译：

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通过双功能相转移催化对 2-羟吲哚进行无碱对映选择性 SN2 烷基化

N-在 C-3 上具有前所未有的可塑性的酯部分的受保护的羟吲哚衍生物已被证明参与了对映选择性相转移催化的烷基化反应，这种烷基化反应由来自带有氢键供体取代基的奎宁衍生的特别设计的季铵盐促进。在这种相转移催化的烯醇烷基化中，第一次在无碱条件下进行反应。发现脲基催化剂优于方酸酰胺衍生物，并且在催化剂的喹啉部分附近安装一个氯原子有助于避免与这些过程中产生 HBr 相关的选择性降低并发症。从亲核试剂和亲电子试剂的角度研究了空间和电子因素的影响，并获得了高达 90% ee 的对映控制水平。该方法的合成效用通过一种有效的 CRTH2 受体拮抗剂的简明对映选择性合成得到了证明。