Reaction in Dry Media: Silica Gel Supported Ferric Chloride Catalyzed Synthesis of 1,8-Dioxo-octahydroxanthene Derivatives

Catalyst Development for the Synthesis of Ozonides and Tetraoxanes Under Heterogeneous Conditions: Disclosure of an Unprecedented Class of Fungicides for Agricultural Application

The catalyst H_3+x PMo_12-x ⁺⁶ Mo_x ⁺⁵ O₄₀ supported on SiO₂ was developed for peroxidation of 1,3- and 1,5-diketones with hydrogen peroxide with the formation of bridged 1,2,4,5-tetraoxanes and bridged 1,2,4-trioxolanes (ozonides) with high yield based on isolated products (up to 86 and 90 %, respectively) under heterogeneous conditions. Synthesis of peroxides under heterogeneous conditions is a rare process and represents a challenge for this field of chemistry, because peroxides tend to decompose on the surface of a catalyst . A new class of antifungal agents for crop protection, that is, cyclic peroxides: bridged 1,2,4,5-tetraoxanes and bridged ozonides, was discovered. Some ozonides and tetraoxanes exhibit a very high antifungal activity and are superior to commercial fungicides, such as Triadimefon and Kresoxim-methyl. It is important to note that none of the fungicides used in agricultural chemistry contains a peroxide fragment.

Immobilized copper-layered nickel ferrite on acid-activated montmorillonite, [(NiFe2O4@Cu)(H+-Mont)], as a superior magnetic nanocatalyst for the green synthesis of xanthene derivatives

In this study, the immobilization of copper-layered nickel ferrite on the surface and in the cavities of acid-activated montmorillonite (H⁺-Mont) was investigated. In this context, magnetic nanoparticles (MNPs) of NiFe₂O₄ as the prime magnetic cores were prepared. Next, through the reduction of Cu²⁺ ions with sodium borohydride, the nanoparticles of Cu⁰ were immobilized on the nanocore-surface of NiFe₂O₄, and the constituent NiFe₂O₄@Cu MNPs were obtained. Moreover, through the activation of montmorillonite K10 (Mont K10) with HCl (4 M) under controlled conditions, the H⁺-Mont constituent was prepared. The nanostructured NiFe₂O₄@Cu was then intercalated within the interlayers and on the external surface of the H⁺-Mont constituent to afford the novel magnetic nanocomposite (NiFe₂O₄@Cu)(H⁺-Mont). The prepared clay nanocomposite was characterized using FTIR spectroscopy, SEM, EDX, XRD, VSM and BET analyses. The obtained results showed that through acid-activation, the stacked-sheet structure of Mont K10 was exfoliated to tiny segments, leading to a significant increase in the surface area and total pore volume of the H⁺-Mont constituent as compared to those of montmorillonite alone. SEM analysis also exhibited that the dispersion of NiFe₂O₄@Cu MNPs in the interlayers and on the external surface of acid-activated montmorillonite was carried out successfully, and the nanoparticle sizes were distributed in the range of 15–25 nm. The BET surface analysis also indicated that through the immobilization of NiFe₂O₄@Cu MNPs, the surface area and total pore volume of the H⁺-Mont system were decreased. The catalytic activity of (NiFe₂O₄@Cu)(H⁺-Mont) was further studied towards the synthesis of substituted 13-aryl-5H-dibenzo[b,i]xanthene-5,7,12,14(13H) tetraones 3(a–k) and 3,3,6,6-tetramethyl-9-aryl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H) diones 5(a–k)via the pseudo-one-pot three-component cyclocondensation of 2-hydroxy-1,4-naphthoquinone (Lawsone)/dimedone and aromatic aldehydes in a mixture of H₂O–EtOH (1 : 1 mL) as a green solvent at 80–90 °C. The (NiFe₂O₄@Cu)(H⁺-Mont) MNPs can be easily separated from the reaction mixture by an external magnetic field and reused for seven consecutive cycles without significant loss of catalytic activity.

In this study, the catalytic activity of the prepared (NiFe₂O₄@Cu)(H⁺-Mont) MNPs was studied towards the synthesis of dibenzo[b,i]xanthene tetraones 3(a–k) and hexahydroxanthene diones 5(a–k).

Direct Synthesis of Xanthenes from Benzyl Alcohols using Choline Peroxydisulfate Ionic Liquid as a Reagent under Otherwise Solvent-Free Conditions

14-Aryl-14 H-dibenzo[ a,j]xanthenes and 1,8-dioxo-octahydroxanthenes were synthesised directly from benzyl alcohols by a tandem catalytic process using choline peroxydisulfate (ChPS). The synthesis proceeds through two steps: an oxidation of the benzyl alcohol to the corresponding benzaldehyde followed by condensation with 2-naphthol (or dimedone) to form the products. Choline bisulfate, generated in situ from ChPS, catalyses the product formation.

Silica gel mediated oxidative C–O coupling of β-dicarbonyl compounds with malonyl peroxides in solvent-free conditions

For the first time silica gel was observed to activate peroxides in oxidative coupling reactions. Here we report silica gel mediated oxidative C–O coupling of β-dicarbonyl compounds with cyclic diacyl peroxides affording α-acyloxy derivatives with 100% atom efficiency. The highest yields of coupling products were achieved in solvent free conditions. C–O coupling products were prepared in yields up to 86%.