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Photoelectrocatalytic Cross-Dehydrogenative Coupling of Unactivated Aliphatic Hydrogen Donors with Benzothiazoles: Synthetic Applications and Mechanistic Insights

preprint
submitted on 24.11.2020, 17:14 and posted on 25.11.2020, 12:37 by Luca Capaldo, Lorenzo L. Quadri, Daniele Merli, Davide Ravelli
We report herein a photoelectrocatalytic strategy for the smooth preparation of 2-alkylbenzothiazoles via the cross-dehydrogenative coupling of unactivated aliphatic hydrogen donors (e.g. alkanes) with benzothiazoles. We used tetrabutylammonium decatungstate (TBADT) as the photocatalyst to cleave the strong C(sp3)-H bonds embedded in the chosen substrates via Hydrogen Atom Transfer (HAT), while electrochemistry ensured the success of this net-oxidative transformation by scavenging the extra electrons. The reaction progress was monitored through kinetic analysis, highlighting the transient formation of the redox-neutral adduct 2-alkylbenzothiazoline. Further cyclic voltammetry and laser flash photolysis experiments unveiled the chameleonic behavior of TBADT that features a three-fold role: HAT photocatalyst to activate alkanes, photoredox catalyst to activate the 2-alkylbenzothiazoline and electrocatalyst to promote the oxidation of short-lived radical intermediates. The adopted potentiostatic mode allowed to tame the multi-faceted reactivity of TBADT and to ensure its recovery after each catalytic cycle with a very high faradaic efficiency. We proved the versatility of the proposed approach by replacing the potentiostat with a couple of cheap batteries in the preparation of the desired products.

Funding

The authors acknowledge Fondazione CARIPLO (grant n. 2018‐2627) and the University of Pavia (InROAd project “ElectroLight”) for financial support.

History

Email Address of Submitting Author

davide.ravelli@unipv.it

Institution

Department of Chemistry, University of Pavia

Country

Italy

ORCID For Submitting Author

0000-0003-2201-4828

Declaration of Conflict of Interest

The authors declare no competing financial interest.

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