Substituted Catechols as H-Bonding Organocatalysts in Conjugated Addition Reactions of (Hetero-)Arenes to Nitroolefins
Abstract
Hydrogen-bond donor organocatalysts based on thioureas, silanols, amidines and diols have been studied in-depth. However, catechols – as prototypical diol catalysts – are comparatively underexplored despite their structural simplicity, straightforward accessibility, and tunability. Here, we systematically investigate substituted catechols as hydrogen-bond donor catalysts for the conjugate addition of indoles to nitroolefins. Screening of the catechol substitution pattern identified 4bromocatechol as the most active derivative. Comparison with related diols established the importance of the vicinal arrangement and phenolic nature of the hydroxy groups. The catechol catalyst exhibits broad functional group tolerance in diverse substrate combinations. Further, the reaction was performed on multigram scale under solvent-free conditions. Combined NMR spectroscopic studies, titrations, kinetic experiments, and DFT calculations suggest a concentration-dependent association of the catechol catalyst into dimers or higher aggregates. Remarkably, 4-bromocatechol outperformed established hydrogen-bond donor catalysts. These results establish catechol as a simple, readily tuneable, and highly effective hydrogen-bond donor motif and provide a fundamental understanding of their high activity.
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BibTeX
@misc{kuster2026substituted,
title = {{Substituted Catechols as H-Bonding Organocatalysts in Conjugated Addition Reactions of (Hetero-)Arenes to Nitroolefins}},
author = {Tom H.R. Kuster and Louis Blum and Tobias Schnitzer},
howpublished = {ChemRxiv},
year = {2026},
month = oct,
doi = {10.26434/chemrxiv.15010829/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010829/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Substituted Catechols as H-Bonding Organocatalysts in Conjugated Addition Reactions of (Hetero-)Arenes to Nitroolefins
AU - Tom H.R. Kuster
AU - Louis Blum
AU - Tobias Schnitzer
PY - 2026
DA - 2026/10/22
PB - ChemRxiv
DO - 10.26434/chemrxiv.15010829/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010829/v1
AB - Hydrogen-bond donor organocatalysts based on thioureas, silanols, amidines and diols have been studied in-depth. However, catechols – as prototypical diol catalysts – are comparatively underexplored despite their structural simplicity, straightforward accessibility, and tunability. Here, we systematically investigate substituted catechols as hydrogen-bond donor catalysts for the conjugate addition of indoles to nitroolefins. Screening of the catechol substitution pattern identified 4bromocatechol as the most active derivative. Comparison with related diols established the importance of the vicinal arrangement and phenolic nature of the hydroxy groups. The catechol catalyst exhibits broad functional group tolerance in diverse substrate combinations. Further, the reaction was performed on multigram scale under solvent-free conditions. Combined NMR spectroscopic studies, titrations, kinetic experiments, and DFT calculations suggest a concentration-dependent association of the catechol catalyst into dimers or higher aggregates. Remarkably, 4-bromocatechol outperformed established hydrogen-bond donor catalysts. These results establish catechol as a simple, readily tuneable, and highly effective hydrogen-bond donor motif and provide a fundamental understanding of their high activity.
ER -