Substituent Effects on Dissociation Constants of trans-3-Hydroxy-6-styryl-4-pyrones

Abstract

The dissociation constants of 6-substituted 3-hydroxy-4-pyrones and trans-6-(substituted styryl)-3-hydroxy-4-pyrones were measured spectrophotometrically in 50% aqueous methanol at 25 °C. The results are correlated to the substituent constants σ, the following equations being obtained: pKa=8.57–1.53 σ and pKa=8.54–0.23 σ. The transmission coefficient through the styryl group was found to be 0.150 for the 3-hydroxy-6-styryl-4-pyrone system.

New Route Synthesis of Styryl Pyrones: High Yield Synthesis, Reactions and Spectral Properties of 2-Phenyl-6-Styryl-4-Pyrones

“…1 H NMR spectra, showed beside other characteristics two doublets at δ 6.49-6.92 and δ 6.84-7.62 with the coupling constants 16.2-16.7 Hz proving the trans-configuration for the ethylenic double bonds of the styryl moiety at position 2. 8 Treatment of 4a with phosphorus pentasulfide afforded 2-phenyl-6-styryl-4H-pyran-4-thione 5 which on treatment with hydroxylamine hydrochloride and aqueous methylamine afforded the oxime 6 and 1-methyl-2-phenyl-6-styrylpyridine-4(1H)-thione 7, respectively (Scheme 2). While the treatment of thione 5 with malononitrile in the presence of triethylamine gave (2-phenyl-6-styryl-4H-pyran-4-ylidene)malononitrile 8 in moderate yield (Scheme 2).…”

“…4,5 Also, 2-hydroxy-5-styryl-4-pyrone has been used in the formulation of skin-lightening cosmetic 6 as well as in the synthesis of polycondensed heterocyclic compounds. 7 Several 2-hydroxy-5-arylethenyl-4pyrones as well as 5-methoxy analogues have been prepared by condensation of benzaldehyde with allomaltol monomethyl ether 8 or by Wittig reaction of 2-chloromethyl-5-methoxy-4-pyrone with triphenylphosphine 9 followed by the reaction with aryl aldehydes, respectively. The yields of these reactions did not exceed 36%.…”