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. NMR‐titration studies revealed significant differences in anion affinity between the halogen bonding receptor and its hydrogen bonding parent. Selective recognition of chiral dicarboxylates and asymmetric induction in a benchmark organocatalytic reaction were demonstrated using the halogen bond donor. Inversions in the absolute sense of chiral recognition, enantioselectivity, and chiroptical properties relative to the related hydrogen donor were observed. Computational modeling suggested that these effects were the result of distinct anion‐binding modes for the halogen‐ versus hydrogen‐bond donors.
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 2 as a versatile soft nucleophile to gain access to these valuable compounds in a simple and straightforward manner is presented.
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 0.5 mol %).
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