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