Simple and cost effective acid catalysts for efficient synthesis of 9-aryl-1,8-dioxooctahydroxanthene

Organic synthesis by Twin Screw Extrusion (TSE): continuous, scalable and solvent-free

“…Milling of the starting materials at 25 Hz for 60 minutes resulted in a low conversion to product of only 7.5 %. Experiments employing Liquid Assisted Grinding (CHCl3 or H2O) and/or catalysts (CaCl2 and SmBr3.6H2O, reported to work in the solution reactions) 26,27 were also unsuccessful. In fact the use of CaCl2 was observed to hinder the ball mill reaction, resulting in a conversion to product of < 1.5 %.…”

“…The catalyst and the temperature determine the final product obtained from the reaction. 26,27 The dihydroxyl product (5) obtained in this work is typically formed at room temperature in solution. However, at reflux an alternative xanthene compound (5') is isolated instead (Figure 23).…”

Ultrasound-Promoted Synthesis of 9-Aryl-l,8-dioxo-octahydroxanthenes Using TiO2 as a Cheap and Reusable Catalyst

“…The products were obtained as colorless crystalline solids. All compounds were characterized by IR, 1 H, 13 C { 1 H} NMR and Mass Spectra. The reaction between aldehyde and dimedone under ultrasonic irradiation in acetonitrile without catalyst gave only chain compound 3b as the major product which was confirmed by the presence of singlet at δ 11.77, and 5.52 corresponding to -OH and methyne protons, respectively in the 1 H NMR spectrum.…”

“…Xanthene derivatives are parent compounds of a large number of naturally occurring as well as synthetic derivatives and occupy a prominent position in medicinal chemistry, such as antiviral, antibacterial, antiflammatory agents, novel CCR1 receptor antagonists, anticancer agents and antinociceptive 13 . Xanthene derivatives are also used as dyes, fluorescent materials and in laser technologies, due to their useful properties 14 .…”

Carbon Nanotube-Supported Butyl 1-Sulfonic Acid Groups as a Novel and Environmentally Compatible Catalyst for the Synthesis of 1,8-Dioxo-octahydroxanthenes

“…It is noteworthy that no competitive side reactions such as the formation of 2,2'-aryl-methylene bis(3-hydroxy-2-cyclohexene-1-one) derivatives were observed in these transformations. 10,17 To the best of our knowledge synthesis of 1,8-dioxooctahydroxanthenes from the reaction of aldehydes with dimedone at room temperature is rare. Most of the reported methods need high temperatures or the use of an additional energy (ultrasound or microwave).…”