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Pyrrole-Based Anion-Responsive π-Electronic Molecules as Hydrogen-Bonding Catalysts
Goki Hirata1, Hiromitsu Maeda1
1Department of Applied Chemistry, College of Life Sciences , Ritsumeikan University , Kusatsu 525-8577 , Japan.
Organic Letters
|May 9, 2018
Summary
Dipyrrolyldiketone boron complexes act as effective hydrogen-bonding catalysts. They activate N-acyl heteroarenium chlorides via anion binding, facilitating Mannich-type and N-alkylation reactions without bases.
Area of Science:
- Organic Chemistry
- Catalysis
- Supramolecular Chemistry
Background:
- Organocatalysis is a rapidly growing field in synthetic chemistry.
- Hydrogen-bonding catalysis offers a powerful strategy for activating substrates.
- Dipyrrolyldiketone boron complexes represent a novel class of potential organocatalysts.
Purpose of the Study:
- To investigate the catalytic potential of dipyrrolyldiketone boron complexes.
- To explore their efficacy as hydrogen-bonding donor organocatalysts.
- To elucidate the mechanism of activation for N-acyl heteroarenium chlorides.
Main Methods:
- Utilized Mannich-type reactions involving N-acyl heteroarenium chlorides and a silyl enol ether.
- Employed classical N-alkylation of amines with trityl chloride under base-free conditions.
- Conducted 1H NMR spectroscopy to examine catalyst-substrate interactions.
Main Results:
- Dipyrrolyldiketone boron complexes demonstrated catalytic activity in both reaction types.
- NMR studies indicated hydrogen-bonding interactions between the catalyst's pyrrole NH and the chloride anion.
- Evidence suggests catalyst activation occurs through specific anion binding.
Conclusions:
- Dipyrrolyldiketone boron complexes function as effective hydrogen-bonding donor organocatalysts.
- Anion binding is the key mechanism for activating N-acyl heteroarenium chlorides.
- These findings open new avenues for base-free catalytic transformations.
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