Beilstein Arch. 2022, 202243. https://doi.org/10.3762/bxiv.2022.43.v1
Published 03 Jun 2022
It is well known that the electrochemical reduction of 1-butyl-3-methylimidazolium tetrafluoroborate (BMImBF4) yields the corresponding N-heterocyclic carbene (NHC). This carbene is quite unstable and its main use is as an organocatalyst in umpolung reactions of aldehydes. Due to its instability, NHC quantification can be indirectly carried out through its transformation into the corresponding thione, by reaction with elemental sulfur. The cathodic generation is carried out in a divided cell, as NHCs readily oxidise at the anode. The need for high amounts of supporting electrolyte is one of the major drawbacks of batch electrochemistry, which can be addressed by using flow electrolysis cells with small interelectrode gaps. In flow cells the distance between the two electrodes can decrease to such an extent that sometimes no supporting electrolyte is needed, offering additional benefits such as simplification of product isolation. Moreover, flow electrochemistry can provide higher rates of conversion compared to batch. Only one paper in the literature reports NHC generation by cathodic reduction of an imidazolium salt, in a undivided cell, in which the NHC oxidation problem is overcome by the use of a sacrificial anode (Cu), which releases Cu+ ions to form NHC-Cu complexes. In this paper we present the first electrochemical generation of NHC carried in a divided flow cell with NHC accumulation and subsequent use as organocatalyst. We demonstrated not only the NHC accumulation (indirectly by reaction with elemental sulfur), but also the possibility to use this NHC in two classical umpolung reactions of cinnamaldehyde: its cyclodimerization and its oxidative esterification.
Keywords: Flow Electrochemistry; N-heterocyclic carbene; Breslow intermediate; oxidative esterification; cathodic reduction
When a peer-reviewed version of this preprint is available, this information will be updated in the information box above. If no peer-reviewed version is available, please cite this preprint using the following information:
Rocco, D.; Folgueiras-Amador, A. A.; Brown, R. C. D.; Feroci, M. Beilstein Arch. 2022, 202243. doi:10.3762/bxiv.2022.43.v1
Citation data can be downloaded as file using the "Download" button or used for copy/paste from the text window below.
Citation data in RIS format can be imported by all major citation management software, including EndNote, ProCite, RefWorks, and Zotero.
© 2022 Rocco et al.; licensee Beilstein-Institut.
This is an open access work licensed under the terms of the Beilstein-Institut Open Access License Agreement (https://www.beilstein-archives.org/xiv/terms), which is identical to the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0). The reuse of material under this license requires that the author(s), source and license are credited. Third-party material in this work could be subject to other licenses (typically indicated in the credit line), and in this case, users are required to obtain permission from the license holder to reuse the material.