Palladium(ii) oxide impregnated on magnetite as a catalyst for the synthesis of 4-arylcoumarins via a Heck-arylation/cyclization process

Abstract

Heck-arylation/cyclization has been achieved using the heterogeneous palladium(II) oxide impregnated on magnetite catalyst (2.5 mol%), using a lower catalyst loading than that reported for similar processes. Ethanol was used as nontoxic and bio-renewable solvent. Good yields are afforded using a broad range of substrates (40-98 %). The catalyst could be partially recycled and analyses confirmed the almost total reduction of palladium(II) oxide to palladium(0) as well as iodine poissoning effect as the main barrier to complete recyclability.

Cascade Synthesis of 4‐Arylcoumarins: Pd‐Catalyzed Arylations and Cyclizations with (E)‐Ethyl 3‐(2‐Hydroxyaryl)acrylates and Triarylantimony Difluorides

“…At the present, reaction mechanism operating in this cascade reaction process remains unclear. We consider that the mechanism would be similar to that of the cascade reaction for the synthesis of 4‐arylcoumarins from 3‐(2‐hydroxyaryl)acrylates and diaryliodonium salts by Ramón et al, the Heck‐type reaction of cinnamate derivatives with aryldiazonium salts by Correia et al, and the reaction of alkenes with arylsulfonyl hydrazines by Kwong et al The initial step in the reaction presumably involves the transmetalation between Pd II catalyst and Ar 3 SbF 2 to form ArPd II X A with the liberation of Ar 2 SbF 2 X. The coordination of A to the alkene produces π complex B , followed by insertion to form the σ complex C ; subsequent β‐hydride elimination forms complex D , which undergoes reductive elimination and cyclization to produce 4‐arylcoumarin, Pd 0 , and HX.…”

“…as a base . Wang and Ramón independently developed similar reactions using diaryliodonium tetrafluoroborates and triflates as aryl sources in the presence of Pd(OAc) 2 (10 mol‐%) and PdO‐Fe 3 O 4 (2.5 mol‐%) , . In 2018, Chen et al reported an improved method using aryl iodides in the presence of 10 mol‐% PdCl 2 (CH 3 CN) 2 and 2 equiv.…”

Design, Synthesis and Characterization of Aurone Based α,β‐unsaturated Carbonyl‐Amino Ligands and their Application in Microwave Assisted Suzuki, Heck and Buchwald Reactions

“…4‐phenyl‐2H − Chromen‐2‐one (5 n) : [47] White solid; Yield 86%; m. p 99–100 °C; 1 H NMR (400 MHz, CDCl 3 ) δ 8.58 (d, J =2.5 Hz, 1H), 7.85–7.82 (m, 2H), 7.64–7.53 (m, 4H), 7.49–7.40 (m, 1H), 7.13 (t, J =8.84 Hz, 1H), 5.28 (s, 1H).…”

Deep eutectic solvents: cutting-edge applications in cross-coupling reactions

“…Mizoroki and Heck independently reported the Pd-catalyzed reaction of alkene derivatives and aryl or alkenyl halides in the presence of a base 129,130 and soon thereafter, this practical cross-coupling reaction was exponentially explored by Heck and other scientific groups, as a versatile and useful class of Pd-catalyzed C-C bond formations. [131][132][133] For the first time, König research group examined this reaction in two types of DES revealing that ᴅ-mannose:DMU (3:7) is a better medium than one obtained from Lcarnitine:urea (2:3); aryl iodides and n-butyl acrylate with different Pd sources, such as Pd(OAc) 2 or PdCl 2 (PPh 3 ) 2 led to the desired coupling products in good yields. Nonetheless, this green catalytic report suffered from a lack of diversity 134 and the protocol could not be improved using ultrasound as an alternative energy input source.…”