Synthesis of (E)-2-Styrylchromones and Flavones by Base-Catalyzed Cyclodehydration of the Appropriate β-Diketones Using Water as Solvent.

Joana Pinto,Artur Silva,Vera Silva,Ana Silva

doi:10.3390/molecules200611418

Abstract

A low cost, safe, clean and environmentally benign base-catalyzed cyclodehydration of appropriate β-diketones affording (E)-2-styrylchromones and flavones in good yields is disclosed. Water was used as solvent and the reactions were heated using classical and microwave heating methods, under open and closed vessel conditions. β-Diketones having electron-donating and withdrawing substituents were used to evaluate the reaction scope. The reaction products were isolated in high purity by simple filtration and recrystallization from ethanol, when using 800 mg of the starting diketone under classical reflux heating conditions.

Highlights

Flavones (I), the most prominent group of naturally occurring chromones, are present in a wide variety of plants [1] and are well-known by their broad range of biological properties, such as Molecules 2015, 20 antibacterial, antifungal [2,3], antiviral [4], antiinflammatory [5], antioxidant [6], antiallergic [7], hepatoprotective [8], antithrombotic and antitumoral [9,10] activities (Figure 1)
The typical established methods for the cyclodehydration reaction of 5-aryl-1-(2hydroxyphenyl)pent-4-ene-1,3-diones 4 involve the use of strong acidic conditions, p-toluenesulfonic acid, or a catalytic amount of iodine in DMSO at 90–100 °C [16,17,18,25]
Our results indicate that 0.5 molar equiv of base are enough to perform the expected cyclodehydration reaction under classical reflux heating (Table 1, Entries 1 and 2)

Summary

Introduction

Flavones (I), the most prominent group of naturally occurring chromones, are present in a wide variety of plants [1] and are well-known by their broad range of biological properties, such as Molecules 2015, 20 antibacterial, antifungal [2,3], antiviral [4], antiinflammatory [5], antioxidant [6], antiallergic [7], hepatoprotective [8], antithrombotic and antitumoral [9,10] activities (Figure 1). Some reaction conditions employed an excess of sulfuric acid in glacial acetic acid [30], cationic exchange resins in isopropyl alcohol [31], CuCl2 in ethanol [32], ionic liquids under microwave irradiation [33], heteropolyacids, carbon supported triflic acid [34,35,36,37] and grinding techniques in the presence of phosphorus pentoxide [38] Some of these methods require high temperatures or long times to complete the reactions [30,31,37], other require the preparation of the catalysts, involving non-green and time consuming procedures [34,35,36,37], and almost all of them were used to prepare flavones or simple chromones, but were not used in the synthesis of 2-styrylchromones [30,31,32,33,34,35,36,37].

Results and Discussion

General Information

Conclusions