dc.description.abstract
Hydroacylation is a powerful and synthetically useful technique that enables the formation of carbon-carbon bonds functionalised with a carbonyl group. Recently, benzothiazolines have been used as hydroacylation reagents on electron-poor substrates.1,2 However, either additives or photosensitisers were needed.
Herein, we present an alternative photochemical hydroacylation strategy for electron-poor alkenes by the adaptation of Hantzsch esters as a reservoir for acyl radicals.3,4 Upon direct photoexcitation, Hantzsch esters can release an acyl radical without the need for any catalyst or additive to yield hydroacylation products with excellent yields of up to 96%. We also showed that this hydroacylation strategy can be expanded to other Michael acceptor-like substrates such as cyclic α,β-unsaturated enones. Furthermore, benzylidenemalononitrile-derived products could be easily oxidised to their fully conjugated alkenylation products by the addition of DDQ, resulting in yields of up to 85%.
References
[1] Acyl Radicals from Benzothiazolines: Synthons for Alkylation, Alkenylation, and Alkynylation Reactions: L. Li, S. Guo, Q. Wang, J. Zhu, Org. Lett., 2019, 21, 5462-5466.
[2] Benzothiazolines as radical transfer reagents: hydroalkylation and hydroacylation of alkenes by radical generation under photoirradiation conditions: T. Uchikura, K. Moriyama, M. Toda, T. Mouri, I. Ibáñez, T. Akiyama, Chem. Commun., 2019, 55, 11171-11174.
[3] Photocatalyst-free hydroacylations of electron-poor alkenes and enones under visible-light irradiation: A. M. Pálvölgyi, F. Ehrschwendtner, M. Schnürch, K. Bica-Schröder, Org. Biomol. Chem., 2022, 20, 7245-7249.
[4] Radical-Based C-C Bond-Forming Processes Enabled by the Photoexcitation of 4-Alkyl-1,4-dihydopyridines: L. Buzzetti, A. Prieto, S. R. Roy, P. Melchiorre, Angew. Chem. Int. Ed., 2017, 56, 15039-15043.
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