No abstract

Chiral phosphoric acids and derivatives have attracted considerable attention as a powerful tool in asymmetric catalysis. Various enantioselective reactions have been developed by using these efficient Brønsted acid organocatalysts. Although initially the activation was restricted to reactive Brønsted basic substrates, recent reports are demonstrating the versatility of phosphoric acid catalysts in the activation of carbonyl compounds in a stereochemically controlled fashion. This tutorial review gives an overview of enantioselective Brønsted acid catalyzed transformations with the main focus on carbonyl activation. Different activation modes, key features of the catalysts and the applied substrates are presented and discussed with the goal to elucidate the origin of stereoselectivity in these Brønsted acid catalyzed transformations.

Asymmetric catalysis is a key feature of modern synthetic organic chemistry. Traditionally, different combinations of ligands and metals are used to perform highly enantioselective reactions. Since the renaissance of organocatalysis in the early 2000s, tremendous improvement in the field of metal‐free catalysis has been achieved. Recently, the combination of transition metals and organocatalysts has allowed the development of new protocols enabling transformations that could not previously be realized. This article aims to present the latest contributions in the field of combined chiral Brønsted acid and metal catalyzed reactions, highlighting the advantages of these catalytic systems as well as describing the uncertainties regarding the molecular structure of the catalytically active species and the reaction mechanisms.

Chiral contact ion-pair catalysis with particular focus on metal-free processes is gaining in interest. As a result, new perspectives are opened, and highly stereoselective transformations, traditionally performed under metal catalysis, can be realized. Herein, we report the development of an unprecedented asymmetric Brønsted acid-catalyzed allylic alkylation. The concept relies on chiral contact ion-pair catalysis, in which the chiral organic counteranion of an allylic carbocation induces high enantioselectivities and allows access to biologically relevant chromenes in good yields and with excellent enantioselection.

Unsaturated carbon-carbon bonds are one of the most common and important structural motifs in many organic molecules, stimulating the continuous development of general, efficient, and practical strategies for their functionalisation. Herein, we report a one-pot difunctionalisation of alkynes via a photoredox/nickel dual catalysed three-component cross coupling reaction under mild conditions, providing access to a series of highly important trisubstituted alkenes. Notably, in contrast to the traditional methods which are based on the steric hindrance of the substrates to control the reaction selectivity, both E-and Z-isomers of trisubstituted alkenes which are often energetically close, can be obtained via choosing an appropriate photocatalyst with a suitable triplet state energy. Beyond the immediate practicality of this transformation, this newly developed methodology might inspire the development of diverse and important one-pot functionalisations of carbon-carbon multiple bonds via photoredox and transition-metal dual catalysed multi-component reactions.Multi-component reactions are a class of useful transformations employed widely for the efficient synthesis of diverse compounds in organic synthesis 1-6 . In the past decades, significant progress has been achieved in the field of difunctionalisation of carbon-carbon multiple bonds via multi-component reactions. However, the employed methods rely largely on the use of organometallic species such as Grignard reagents 7 , organoboron 8 and organolithium 9 reagents and require high temperatures or multistep reactions. More recently, radical-mediated transformations have been developed, providing a good alternative for the one-pot difunctionalisation of these motifs. In this case, a radical is generally generated from a suitable precursor via a single electron transfer process by using O 2 10 , transition metal species 11-14 or photocatalysts [15][16][17] . The generated radical adds to the alkyne or alkene moiety to give a vinyl or alkyl radical intermediate. For transition metal catalysed transformations, various radical precursor including sulfonyl chlorides 11 , activated alkyl bromides 12 , and fluoroalkyl iodides 13 were used in the cross-coupling reactions with organoboron reagents. For