P-Hydroxychalcones

Various m- and p-hydroxychalcones were anchored to a Wang resin through their phenolic groups. Stetter reactions were performed with various aliphatic, aromatic, and heteroaromatic aldehydes, affording 1,4-diketones. m-Chalcones, as well as aliphatic and aromatic aldehydes, gave superior results. 

Kobayashi, A., S. Yata, and K. Kawazu A P-Hydroxychalcone and Flavonoids from Alfalfa Callus Stimulated by a Fungal Naphthoquinone, PO-1. Agric. Biol. Chem., 52, 3223 (1988). 

A more detailed study [6] showed the P-amination of an unsaturated ketone and the formation of adduct 2 (Scheme 4.1) to be the first stage of this reaction. Later the general character of the interaction between 0-PDA and substituted ketones or their vinylogs was established [7, 8]. Unsuccessful attempts [7] to synthesize aromatic dihydrobenzodiazepine derivatives from 1,2-diaminoan-thraquinone, 4-nitro-, 4-nitrile-4,6-dichlor- and TV-phenyl-substituted 0-PDAs were also reported. Condensation of 0-PDA with 0r /z0-hydroxychalcone 5... 

Substrates with electron acceptors are given in Scheme 4. For these rather unreactive n-systems, besides longer reaction times and excess dioxirane, elevated temperature (ca. 25 °C) was essential for complete conversion into their corresponding epoxides. Fortunately, these epoxides, which were all obtained quantitatively, were sufficiently stable for rigorous characterization. The specific substrate types include oc,P-unsaturated acids [20] 21 and esters [20] 22 hydroxychalcones [21] 23 a,P-enones [20] 24 2-cyclohexenones [20] 25 methylene-P-lactones [22] 26 tetracyclone [20] 27 and naphthaquinone [16] 28. The particular advantage of the dioxirane methodology is that labile functional groups, e.g. the phenolic moiety in the chalcones, do not require protection. 

The condensation of substituted benzaldehydes with 2-hydroxyacetophenones to give a,P unsaturated ketones (hydroxychalcones) of industrial interest has been reported by Climent et al. [29] to reach a yield of 85 % at a temperature of 443 K on hydrotalcite. The rate went through a maximum for a Al/(Mg Al) ratio close to 0.3. The presence of electron-acceptor groups in the aromatic ring of benzaldehyde increased the reaction rate in proportion to the value of the Hammett constant, although bulky substituents such as NO2, Cl, or OCH3 resulted in geometrical effects as a result of diffusional problems or steric restrictions. 

Pears (Pyrus communis) were cultivated by the Phoenicians and later by the Romans. There are now in excess of 500 named varieties worldwide. The total phenolic content of some cultivars of pears has been shown to be between 1235 and 2500 mg/kg in the peel and 28-81 mg/kg in the flesh (Galvis-Sdnchez etal. 2003). The phenolic composition of pears is very similar to that of apples containing 5-0-caffeoylquinic acid, 4-O-p-coumaroylquinic acid, procyanidins and quercetin glycosides. The main difference in the phenolic content of apples and pears is the presence of hydroquinone glucoside (arbutin) (Figure 7.24) in pears and the hydroxychalcones in apples (Spanos and Wrolstad 1992). The average... 

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