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Dynamic Kinetic Sensitization of β‐Dicarbonyl Compounds—Access to Medium‐Sized Rings by De Mayo‐Type Ring Expansion
Ist Teil von
Angewandte Chemie (International ed.), 2022-01, Vol.61 (5), p.e202112695-n/a
Auflage
International ed. in English
Ort / Verlag
Germany: Wiley Subscription Services, Inc
Erscheinungsjahr
2022
Link zum Volltext
Quelle
Alma/SFX Local Collection
Beschreibungen/Notizen
Herein, we present a photocatalyzed two‐carbon ring expansion of β‐dicarbonyl compounds with unactivated olefins that provides facile access to medium‐sized rings. Selective sensitization of the substoichiometric enol tautomer enables reactivity of substrates incompatible with the classical De Mayo reaction conditions. Key to success is the identification of the metal‐based sensitizer fac‐[Ir(CF3‐pmb)3], which can be excited using common near‐visible LEDs, and possesses a high triplet excited state energy of 73.3 kcal mol−1. This exactly falls in the range between the triplet energies of the enol and keto tautomer, thereby enabling a dynamic kinetic sensitization. Demonstrating the applicability of fac‐[Ir(CF3‐pmb)3] as a photocatalyst in organic synthesis for the first time, we describe a two‐step photocycloaddition‐ring‐opening cascade with β‐ketoesters, ‐diketones, and ‐ketoamides. The mechanism has been corroborated by time‐resolved spectroscopy, as well as further experimental and computational studies.
A photocatalyzed ring expansion procedure for a two‐carbon homologation of cyclic carbonyl compounds, towards medium‐sized ring systems, is introduced. Key to success is the catalyst fac‐[Ir(CF3‐pmb)3] (ET=73.3 kcal mol−1), which allows for selective activation of the substoichiometric enol species. The mechanism has been corroborated by time‐resolved spectroscopy and enabled a full kinetic analysis of the dynamic kinetic sensitization scenario.