Palladium‐Catalyzed Regioselective ortho‐Acylation of Azoxybenzenes with Aldehyde Derivatives

Abstract

An efficient strategy for the regioselective ortho-acylation of azoxybenzenes with various aldehydes in the presence of palladium catalysts has been developed and furnishes good to excellent yields. The reaction proceeds smoothly and can tolerate a variety of functional groups.

Palladium-Catalyzed Regioselective ortho-Acylation of Azoxybenzenes under Aqueous Conditions

“…Based on the results obtained and the literature, [15,17,18] a tentative reaction mechanism for the palladium-catalyzed ortho-C-H acylation of azoxybenzene (1a) was proposed Scheme 2 Control experiments and depicted in Scheme 3. The palladium catalyst reacted with azoxybenzene by chelation-directed C-H activation to generate complex A (Figure 1).…”

“…[13] In view of their importance, a number of methods have been established to build a structural skeleton. [14] Recently, Wang, Sun and Cui group [15] realized ortho-acylation of azoxybenzenes using aldehydes, α-oxocarboxylic acids and alcohols (Scheme 1). However, most of these processes are performed in organic solvents.…”

Aldehydes: magnificent acyl equivalents for direct acylation

“…49 The authors have prepared a library of derivatives using differently substituted azoxybenzenes and aryl/alkyl aldehydes. However, in comparison to Sun's protocol 46 , aliphatic aldehydes gave inferior yields and heterocyclic aldehydes could not be applied for this transformation, which shows the significance of the reaction temperature. The authors also performed some control experiments to investigate the reaction mechanism.…”

“…The reaction was found to progress following the reaction pathway as shown by Kuang et al The authors developed an interesting approach for the selective ortho-acylation of azoxybenzenes using various aromatic, heteroaromatic and aliphatic aldehydes in the presence of Pd(TFA) 2 as catalyst and TBHP as oxidant. 46 They prepared 19 different mono-acylated azoxybenzenes with 23-87% yield in 24 h at 60 o C. The presence of mild electronwithdrawing groups (F, Cl, Br) at the para-position of the benzaldehydes positively affected the reaction giving higher yields of the mono-acylated derivatives. However, strong electron-withdrawing groups (CN, NO 2 ) had a reverse effect resulting in very poor yields of the corresponding products.…”

Acylation of (Hetero)Arenes through CH Activation with Aroyl Surrogates

“…Additionally, ortho ‐acylated azoxybenzenes are important building blocks for preparing medicines, fragrances, and natural products. In 2014, Sun and co‐workers reported an interesting strategy for the regioselective ortho ‐acylation of azoxybenzenes 12a. Various aldehydes were applied as the coupling partner in the presence of palladium catalysts, and good to excellent yields of the desired products were formed with good functional group tolerance (Scheme ).…”