Modulating the Acidity: Highly Acidic Brønsted Acids in Asymmetric Catalysis

Abstract

Recently, chiral highly acidic Brønsted acids have emerged as powerful catalysts for enantioselective C-C and C-X bond-forming reactions. Their strong acidity renders them valuable tools for the activation of imines, carbonyl compounds, and other weakly basic substrates. As a result, new perspectives are opened and highly stereoselective transformations based on the concept of chiral contact-ion-pair catalysis can be realized. This Minireview gives an overview of the design and application of these new organocatalysts and presents recent results in this rapidly growing field.

Development and Mechanism of an Enantioselective Bromocycloetherification Reaction via Lewis Base/Chiral Brønsted Acid Cooperative Catalysis

“…Related studies in these laboratories had demonstrated that Lewis base catalyzed seleno, thio and bromocycloetherification are greatly accelerated by the addition of a stoichiometric amount of an achiral Brønsted acid. The pK a and general applicability of chiral phosphoric acids made them attractive candidates for the development of an enantioselective bromocycloetherification process using a catalytic amount of a chiral Brønsted acid, potentially in conjunction with a Lewis base co‐catalyst . This line of research led to the development of an enantioselective bromocycloetherification reaction of 5‐arylpentenols ( 1a , 1d , 1e , 1f , 1g , 1h , 1i , 1j , 1k , 1l , 1m ) cooperatively catalyzed by the combination of the versatile chiral phosphoric acid TRIP ( 2a ) and the achiral Lewis base Ph 3 P=S, producing chiral tetrahydrofurans ( 3a , 3d , 3e , 3f , 3g , 3h , 3i , 3j , 3k , 3l , 3m ) and tetrahydropyrans ( 4a , 4d , 4e , 4f , 4g , 4h , 4i , 4j , 4k , 4l , 4m ) (Fig.…”

Asymmetrische Brønsted‐Säure‐katalysierte Synthese von Triarylmethanen – Aufbau von Communesin‐ und Spiroindolin‐Gerüsten

“…Zuschriften stoffbrücken-oder Ionenpaarbildung [13] führt und die Selektivität der Addition mit dem angreifenden Nukleophil kontrolliert.…”

Light‐Driven Single‐Electron Transfer Processes as an Enabling Principle in Sulfur and Selenium Multicatalysis

“…100 kcal mol −1 ) by means of multiple‐site PCET mechanisms. According to the authors’ design plan, the combination of Ir(dF(CF 3 )ppy) 2 (bpy)PF 6 ( E 1/2 red (Ir III*/II )=+1.68 V versus SCE in MeCN) and Bu 4 NPO 4 Bu 2 (p K a ≈12 in MeCN), which was reported to correspond to an effective BDFE of about 103 kcal mol −1 , was considered to be suitable for the formal N−H bond homolysis. The resulting amidyl radicals 40 were shown to engage in a set of intramolecular 5‐ exo ‐trig cyclizations to furnish the respective heterocycles 39 in yields ranging from 68 to 94 % upon polarity‐matched,– thiophenol‐catalyzed hydrogen atom transfer onto carbon‐centered radical 41 .…”