A Green Nanopalladium-Supported Catalyst for the Microwave-Assisted Direct Synthesis of Xanthones

Abstract

We report an efficient, selective, rapid and eco-friendly protocol for the one-step synthesis of a small xanthone library via an intermolecular catalytic coupling from readily available salicylaldehydes and 1,2-dihaloarenes under ligand-free conditions. To achieve this advantageous direct annulation, we used a novel recoverable palladium nanocatalyst supported on a green biochar under microwave irradiation. Unlike other existing palladium-based approaches, our synthetic strategy showed a greater operational simplicity, drastic reduction in reaction times, and an excellent tolerance to diverse functional groups. The reaction proceeds in very good yields and with high regioselectivity. The novel heterogeneous catalyst can be recycled and reused up to four times without significant loss of activity.

An Update on the Anticancer Activity of Xanthone Derivatives: A Review

“…Another recent approach to synthesize xanthone derivatives was reported by Steingruber et al, employing salicylaldehyde and dibromobenzene derivatives using palladium nanoparticles. High yield (up to 88% yield), as well as high regioselectivity reaction, were achieved within 30 min reaction time in which the nanopalladium catalyst can be used up to four consecutive cycles without losing its activity [84]. Figure 7 shows the recent examples of the synthesis of xanthone derivatives using MAOS technique.…”

Recent advances in the synthesis of xanthones and azaxanthones

“…A rapid and con- venient ligand-free alternative was later reported for this direct annulation using a recoverable palladium nanocatalyst supported on a green biochar under microwave irradiation, with a drastic reduction in reaction times. 127 This eco-friendly strategy proceeded in very good yields (54-88%) and with high regioselectivity for a scope of 20 xanthone derivatives.…”

“…Aside the o-acylation of phenols with 2-substituted aldehydes, the xanthone core can also be constructed through a selective palladium-catalysed acylation/nucleophilic aromatic substitution (S N Ar) approach of salicylaldehyde derivatives with aryl halides (Scheme 3). 127,128 The first methodology reported consisted of the use of a bulky electron-rich trialkylphosphine ligand, n-BuPAd 2 , which prevents the decomposition of the palladium catalyst, observed with the use of other ligands. 128 The scope of the reaction was extended to 22 different xanthones (41-81% yield); however, only activated salicylaldehydes were tolerated, long reaction times (12 h) were needed, and it was impractical to recover and reuse the catalyst.…”

A decennary update on applications of metal nanoparticles (MNPs) in the synthesis of nitrogen- and oxygen-containing heterocyclic scaffolds

“…Gerbino and co-workers reported the synthesis and characterization of efficient, novel and recyclable PdNPs anchored on green biochar (PdNPs/BC) through a precipitation-reduction method employing the use of PdCl 2 as the precursor, biochar as the support, and the pyrolytic product of lignocellulosic biomass. 306 The were employed in the microwave-mediated, ligand-and additive-free, regioselective synthesis of xanthones (136b) from substituted salicylaldehydes (21f) and o-bromo haloarenes (82l) (Scheme 168). The PdNPs/BC NCs were separated by ltration and reused for up to four cycles in 88-82% yield, where they maintained their initial activity, as conrmed by AAS and XRD.…”

“…Kaushik et al reported that commercially available zinc oxide nanoparticles (ZnO NPs) as a Lewis acid catalyzed the synthesis of 1,2-dihydro-1-arylnaphtho[1,2-e][1,3]oxazine-3-ones (305) and 14-substituted-14H-dibenzo [a,j]xanthenes (306,Scheme 195) under solvent-free conditions. 357 The synthesis of 305 was achieved from substituted benzaldehyde (21a) and urea (22b) following the sequential addition of b-naphthol (111d) in 76-94% yield, whereas 306 was synthesized from substituted benzaldehyde (21a) and b-naphthol (111d) at 120 C via random addition in 80-92% yield (Scheme 196).…”