Fine-Tuning Substrate-Catalyst Halogen-Halogen Interactions for Boosting Enantioselectivity in Halogen-Bonding Catalysis.

A new approach towards highly enantioselective halogen-bonding catalysis has been developed. To circumvent the intrinsic issues of the nature of the halogen-bond (XB) and the resultant unresolved limitations in asymmetric catalysis, fine-tuned halogen-halogen interactions between the substrate and XB-donor were designed to preorganize the substrate in the catalyst's cavity and boost enantiocontrol. The present strategy exploits both the electron cloud (Lewis base site) and the sigma (σ)-hole site of the halogen substituent of the substrates to form a tight catalyst-substrate-counteranion chiral complex, thus enabling a controlled induction of high levels of chirality transfer.

Benzotriazolium Salts: Emergent Readily Accessible Bench-Stable Lewis Acid Catalysts.

In this work, benzotriazolium salts have been introduced as efficient, readily accessible, bench-stable Lewis acid catalysts. Though these sorts of N-heterocyclic compounds have found wide applications as ionic liquids or electrolytes, their Lewis acid catalytic activity remained unexplored. Herein, their potential as Lewis acid catalysts was demonstrated in two prototypical allylic and Nazarov cyclization reactions, showing a matching reactivity and allowing low catalytic loadings (down to 0.

Neutral Chiral Tetrakis-Iodo-Triazole Halogen-Bond Donor for Chiral Recognition and Enantioselective Catalysis.

Halogen bonding represents a powerful tool in the field of noncovalent interactions. However, applications in enantioselective recognition and catalysis remain almost nonexistent, due in part to the distinct features of halogen bonds, including long covalent and noncovalent bond distances and high directionality. Herein, this work presents a novel chiral tetrakis-iodo-triazole structure as a neutral halogen bond donor for both chiral anion-recognition and enantioinduction in ion-pair organocatalysis.

Mild, Metal-Free Oxidative Ring-Expansion Approach for the Synthesis of Benzo[ b]azepines.

Benzo[ b]azepines are important structural motifs for the pharmaceutical industry. However, their syntheses are usually lengthy, involving several steps, transition-metal catalysts, and/or harsh conditions. A novel, general, mild, and metal-free oxidative ring expansion tandem reaction of hydroquinolines with TMSCHN as a versatile soft nucleophile to gain access to these valuable compounds in a simple and straightforward manner is presented.

Metal-free desilylative C-C bond formation by visible-light photoredox catalysis.

A newly developed methodology for the use of organosilanes as radical precursors under metal-free and visible-light conditions is presented. The strong oxidant character of the 9-mesityl-10-methylacridinium salt in its excited state enables the transformation of simple silanes to the corresponding carbon-centered radicals, which were trapped by various acceptor molecules.