Nucleophilic substitutions such as S_N1 and S_N2 are fundamental textbook reactions. Their stereoselective versions have been shown to be versatile in the preparation of enantiopure compounds. In this review, we discuss challenges surrounding achieving stereoinvertive S_N2 and S_N1 reactions at tertiary carbon centers. This is followed by discussions on stereoconvergent substitutions at tertiary carbon centers using strategies such as chiral-catalyst-directed S_N1, radical-based nucleophilic substitution, and halogen-bonding-assisted S_N2X reactions. Mechanistic discussions provide insights on how these reactions can be differentiated.

中文翻译：

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三级碳中心的立体有择和立体会聚亲核取代反应

亲核取代如 S _N 1 和 S _N 2 是基本的教科书反应。它们的立体选择性形式已被证明可用于制备对映纯化合物。在这篇综述中，我们讨论了围绕在叔碳中心实现立体倒置 S _N 2 和 S _N 1 反应的挑战。随后讨论了使用手性催化剂导向的 S _N 1、基于自由基的亲核取代和卤素键辅助的 S _N 2X 反应等策略在三级碳中心进行立体会聚取代。机理讨论提供了有关如何区分这些反应的见解。