Photochemical Hydroacylation of Michael Acceptors Utilizing an Aldehyde as Photoinitiator

Abstract

The hydroacylation of Michael acceptors constitutes a useful tool for the formation of new C−C bonds. In this work, an environmentally friendly procedure was developed, utilizing 4cyanobenzaldehyde as the photoinitiator and household bulbs as the irradiation source. A great variety of substrates was well‐tolerated, leading to good yields, and mechanistic experiments were performed to elucidate the catalyst's possible mechanistic pathway. Moreover, the inherent selectivity challenge regarding α,α‐disubstituted aldehydes (decarbonylation problem) was studied and addressed.

Aldehydes as powerful initiators for photochemical transformations

“…In 2019, Kokotos and co-workers employed 4-cyanobenzaldehyde (53) as the photoinitiator for the hydroacylation of Michael acceptors under irradiation with 80 W household bulbs [59]. 4-Cyanobenzaldehyde (53) exhibited the highest yield tion was placed in the dark at 60 °C, the reaction did not proceed.…”

A General Approach to Intermolecular Olefin Hydroacylation through Light‐Induced HAT Initiation: An Efficient Synthesis of Long‐Chain Aliphatic Ketones and Functionalized Fatty Acids

“…Importantly, the products 21 – 23 were isolated when α‐branched aldehydes were allowed to react with dec‐1‐ene under this protocol in only moderate yields. High propensity for decarbonylation of the secondary acyl radical is likely the responsible for such observation [7a, d] . A sharp improvement in the reactivity of α‐branched aldehydes was observed with electron‐deficient olefin.…”

Photochemical Reaction of N,N‐Dimethylanilines with N‐Substituted Maleimides Utilizing Benzaldehyde as the Photoinitiator

“…Thioxanthen‐9‐one ( 4 a ) [10k,l] and phenylglyoxylic acid ( 4 c ), [10a–i] afforded mediocre yields (Table 1, entries 1–3). Aromatic aldehydes, as aromatic ketones, have shown catalytic activity upon irradiation in organic synthetic reactions or in polymerization reactions [3f,10j] . As shown in Table 1, 4‐cyanobenzaldehyde ( 4 e ), 4‐methoxybenzaldehyde ( 4 f ) and benzophenone ( 4 g ) were tested, but benzaldehyde ( 4 d ) proved to be the best photoinitiator for this specific reaction (Table 1, entries 1–11).…”

“…Having studied the substrate scope of both maleimides and anilines and the mechanistic experiments, a plausible reaction mechanism for this reaction can be suggested (Scheme 4). Initially, benzaldehyde (PC), upon excitation is advancing to its triplet state and then a radical pair is formed between an excited molecule of benzaldehyde and a ground state molecule of benzaldehyde [3f,10j] . This a well‐established process in literature.…”