One pot synthesis of aryl substituted aurones
Graphical abstract
Highlights
► One pot synthesis of aurones. ► Thermal synthesis of aryl substituted aurones. ► Fast and easy synthesis of aurone dyes.
Introduction
Aurones (2-benzylidenebenzofuran-3(2H)-ones) are natural occurring yellow dyes found especially in plants and in some marine organisms, usually in a hydroxylated form. Both E and Z isomers can be found in nature, although the latter is thermodynamically more stable and thus much more abundant. Besides their contribution to the pigmentation of flowers and fruits [1] aurones exhibit a wide variety of biological activities: they have been described as antifungal agents [2], [3], [4], antibacterial agents [5], [6], [7], [8], [9], insect antifeedant agents [10], antioxidants [11], [12], [13], [14], as inhibitors of tyrosinase [15], iodothyronine-deiodinase [16], acetylcholinesterase [17], anticancer [18], [19], [20], [20][a] and as possessing anti-inflammatory properties [10]. These compounds are usually prepared by three main methods: condensation between benzofuranones and benzaldehydes [10], [15], [17], [18], [21], [22], oxidative cyclisation of 2′-hydroxychalcones [11] or by catalysed cyclisation of ortho-(1-hydroxyprop-2-ynyl)phenols or ortho-hydroxyaryl arylethynyl ketones [23], [24], [25]. In this paper we describe a fast and easy one-pot synthesis of new aryl substituted aurones starting from commercially available materials under thermal conditions.
Section snippets
Results and discussion
2′-Hydroxychalcones can be easily prepared, under mild conditions, by aldol condensation between 2′-hydroxyacetophenone and different benzaldehydes in the presence of base. This reaction is very general and these compounds are valuable intermediates in the synthesis of flavones [26], [27], [28] and aurones [11] (Scheme 1).
The reaction of 2′-hydroxyacetophenone with benzophenone in the presence of t-BuOK in toluene at reflux, gives the expected aryl substituted 2′-hydroxychalcone an useful
Experimental
The reactions were monitored by thin-layer chromatography on aluminum plates precoated with Merck silica gel 60 F254 (0.25 mm). Melting point were determined in capillary tubes and are uncorrected. The new compounds were determined to be >95% pure by 1H NMR spectroscopy. UV–Vis spectra were recorded on a CARY 50 Varian spectrophotometer. IR spectra were obtained on a Perkin–Elmer FTIR 1600 spectrometer using KBr disks (wavenumbers in cm−1). Electronic impact mass spectra were measured on a
Acknowledgements
To FCT (Portugal’s Foundation for Science and Technology) and FEDER for financial support through the research unit Centro de Química-Vila Real (POCTI-SFA-3-616) and project PTDC/QUI/66012/2006. The 500 MHz NMR facilities were funded by the Région Nord-Pas de Calais (France), the Ministère de la Jeunesse de l’Education Nationale et de la Recherche (MJENR) and the Fonds Européens de Développement Régional (FEDER).
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2015, Tetrahedron LettersCitation Excerpt :Silver(I) ion-catalyzed cyclization of o-alkynoylphenols results predominantly in the 5-exo cyclized aurone product, however, trace amounts of the 6-endo product are also formed.19 A similar outcome has been observed when tributylphosphine was employed as a catalyst.20 Product mixtures are problematic since separation of structurally similar aurone and flavone products is not trivial.
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