Chiral Brønsted acids have found widespread applications as organocatalysts. Weakly acidic species such as diols and (thio)ureas, typically classified as hydrogen bonding catalysts, as well as stronger phosphoric acids, have proven to be highly effective in catalyzing a wide range of asymmetric transformations. In contrast, the use of chiral carboxylic acids as Brønsted acid catalysts is much less developed but has recently garnered increased attention. Given that their pK_a's generally lie between those of typical hydrogen bond donors and chiral phosphoric acids, chiral carboxylic acids provide the opportunity to activate a different set of substrates requiring intermediate catalyst acidity. In addition, by taking advantage of judicious catalyst design, the acidity of carboxylic acids can be modulated, for instance by stabilizing the corresponding carboxylate counterion. This review provides an overview of this field, with the aim of highlighting both catalyst design and synthetic applications.

中文翻译：

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手性羧酸的不对称布朗斯台德酸催化

已发现手性布朗斯台德酸作为有机催化剂得到了广泛的应用。弱酸性物质，例如通常被归类为氢键催化剂的二醇和（硫）脲，以及更强的磷酸，已被证明在催化广泛的不对称转化方面非常有效。相比之下，使用手性羧酸作为布朗斯台德酸催化剂的开发尚不多，但最近引起了越来越多的关注。鉴于他们的p K _a通常在典型的氢键供体和手性磷酸之间，手性羧酸提供了活化另一组需要中间催化剂酸度的底物的机会。另外，通过利用明智的催化剂设计，可以例如通过稳定相应的羧酸根抗衡离子来调节羧酸的酸度。这篇综述提供了该领域的概述，旨在突出催化剂设计和合成应用。