Visible-Light-Mediated Hydroacylation of Azobenzenes with α-Keto Acids

Abstract

A visible-light-mediated protocol for the hydroacylation of azobenzenes with α-keto acids has been developed. In the absence of any catalyst or additive, decarboxylative hydroacylation proceeded smoothly under visible-light irradiation at room temperature. A wide range of azobenzenes and α-keto acids were well-tolerated and afforded hydroacylation products in high to excellent yields. Preliminary investigations indicated that photoactive azobenzenes absorb visible light to enable the transformation.

Decarboxylation‐Initiated Intermolecular Carbon‐Heteroatom Bond Formation

“… [360] Both radicals are generated in the presence of 4CzlPN as the photocatalyst, thus leading to a cascade synthesis of 1,3,4‐oxadiazole skeletons through a decarboxylation/cyclization sequence. Huo and co‐workers showcased that acyl radicals undergo addition to the N=N bonds of azobenzenes [361] . Although it requires no external photocatalyst and additive, light is necessary to excite the photoactive azobenzene, thus enabling the hydroacylation reaction.…”

Catalyst-Free Organic Transformations under Visible-Light

“…In 2020, Huo et al introduced a visible-light-promoted process for the hydroacylation of azobenzenes using α-keto acids without photocatalyst or additives at room temperature (Scheme ). Using this protocol, a variety of azobenzenes 26 . 1 and α-keto acids 26 .…”

“…In 2020, Huo et al introduced a visible-light-promoted process for the hydroacylation of azobenzenes using α-keto acids without photocatalyst or additives at room temperature (Scheme 26). 88 Using this protocol, a variety of azobenzenes 26.1 and α-keto acids 26.2 were successfully transformed into the desired adducts 26.3 in high yields. Interestingly, aliphatic α-keto acids successfully participated in the reaction and furnished the corresponding products in 30%−90% yields.…”

Visible-Light-Promoted Diboron-Mediated Transfer Hydrogenation of Azobenzenes to Hydrazobenzenes

“…In addition, the latter also requires the use of some specific hydrogen donors, and the reaction time is long and the yield is not high (Scheme c). Therefore, combining our previous research foundation of visible-light-promoted reactions and the reductive performance of diboron reagents, we wish to develop a visible-light-promoted, diboron-mediated strategy to enable the transfer hydrogenation of azobenzenes facilely and efficiently under mild conditions (Scheme d).…”