Ketone Synthesis via Irradiation-Induced Generation of a Persistent Ketyl Radical from Acyl Azolium Salts

Abstract

A novel three-component α-acylated difunctionalization of alkenes strategy has been developed on the basis of a direct hydrogen atom transfer (HAT) process of photoinduced acyl azolium salts. With simple irradiation without the catalyst, a variety of olefins can be directly converted into ketone derivatives, including 1,4-dione, β-silyl ketone, 1,5-dione, etc. Mechanistic investigations indicated that the unique reactivity of the acyl azonium triplet excited state is crucial to the strategy’s success.

Radical Reactions with N-Heterocyclic Carbene (NHC)-Derived Acyl Azoliums for Access to Multifunctionalized Ketones

“…In 2023, Feng, Fan, Zhang, and their co-workers extended this intermolecular hydrogen atom transfer process to abstract hydrogen atoms from aldehydes 36 and silianes 38 for generating acyl radicals 42 and silyl radicals 45 (Scheme ). Further trapping of these radicals by terminal alkenes 35 and subsequent radical cross-coupling with the resultant NHC-bound ketyl radical eventually afford 1,4-diketones 37 and β-silyl ketones 39 . These transformations provide convenient methods for producing a variety of 1,4-diketones and β-silyl ketones under mild conditions without the presence of any photo or nonphoto catalysts.…”

“…In 2023, Feng, Fan, Zhang, and their co-workers extended this intermolecular hydrogen atom transfer process to abstract hydrogen atoms from aldehydes 36 and silianes 38 for generating acyl radicals 42 and silyl radicals 45 (Scheme 7). 21 Further trapping of these radicals by terminal alkenes 35 Halogen atom abstraction (XAT, X = Cl, Br, or I) is one of the most frequently used strategies to form carbon radicals from activated or nonactivated haloalkanes. In 2023, Feng and co-workers combined this process with the NHC-bound acyl azolium-based radical acylation reactions in difunctionalization of alkenes 35 for construction of structurally diverse ketones 49 (Scheme 8).…”

“…In 2023, Feng and co-workers combined this process with the NHC-bound acyl azolium-based radical acylation reactions in difunctionalization of alkenes 35 for construction of structurally diverse ketones 49 (Scheme 8). 21 In these reactions, the α-aminoalkyl radical intermediates 51 generated from photoexcitated acyl azolium and amine were used as a halogen atom abstracting reagent. A variety of haloalkenes including α-bromo ethyl difluoroacetate (e.g., 49a) and α-halogenated ketones (e.g., 49c) are all competent carbon radical procursors.…”