Donor–Acceptor Complex Enables Alkoxyl Radical Generation for Metal‐Free C(sp³)–C(sp³) Cleavage and Allylation/Alkenylation

Abstract

The alkoxyl radical is an essential and prevalent reactive intermediate for chemical and biological studies.Here we report the first donor-acceptor complex-enabled alkoxyl radical generation under metal-free reaction conditions induced by visible light. Hantzsch ester forms the key donoracceptor complex with N-alkoxyl derivatives,w hich is elucidated by aseries of spectrometry and mechanistic experiments. Selective C(sp 3 )-C(sp 3 )b ond cleavage and allylation/alkenylation is demonstrated for the first time using this photocatalyst-free approachw ith linear primary,s econdary,a nd tertiary alkoxylr adicals.

3-Acetoxyquinuclidine as Catalyst in Electron Donor–Acceptor Complex-Mediated Reactions Triggered by Visible Light

“…Electron donor-acceptor (EDA) complexes, 12 on the other hand, emerged as an alternative to the use of photocatalysts in visible light-triggered reactions. [12][13][14][15][16] These complexes are formed by two species, an electron donor and an electron acceptor, which show a change transfer band only when combined. When this band occurs in the visible region of the spectra, visible light can be used to induce an electron transfer from the donor to the acceptor.…”

Catalyst‐free Hantzsch Ester‐mediated Organic Transformations Driven by Visible light

“…Also, the authors pointed out the redox potentials of N-alkoxyl derivatives were irrelevant to their reactivity, which further indicated the direct photoexcitation of HE to reduce the N-alkoxyl derivatives was unlikely. [35] All these studies suggested the formation of a donor-acceptor complex between N-alkoxyphthalimides and Hantzsch esters. Based on these mechanistic investigations they proposed that the reaction is initiated by the formation of the donor-acceptor complex between Hantzsch esters and N-alkoxyphthalimides (Scheme 21).…”

“…Further, NMR titration experiments revealed that 1 H NMR signal of 4‐isopropyl HE shifted downfield with the addition of tetrachloro‐substituted N ‐alkoxyphthalimide. Also, the authors pointed out the redox potentials of N ‐alkoxyl derivatives were irrelevant to their reactivity, which further indicated the direct photoexcitation of HE to reduce the N‐alkoxyl derivatives was unlikely [35] . All these studies suggested the formation of a donor‐acceptor complex between N ‐alkoxyphthalimides and Hantzsch esters.…”

Generation of Alkyl Radicals: From the Tyranny of Tin to the Photon Democracy

“…Loss of formaldehyde formed the desired alkyl radical which reacted with 26 – 2 , to obtain product 26 – 3 in 60% yield ( Scheme 26 ). 127 …”