37542-10-2Relevant academic research and scientific papers
Preparative and Regiochemical Aspects of the Palladium-Catalyzed Carbonylative Coupling of 2-Hydroxyaryl Iodides with Ethynylarenes
Ciattini, Pier Giuseppe,Morera, Enrico,Ortar, Giorgio,Rossi, Sabina Strano
, p. 6449 - 6456 (2007/10/02)
The title reaction has been conveniently carried out in DMF at 60 deg C under 1 atm CO pressure using DBU as the base and Pd(OAc)2(DPPF)2 as the catalyst to afford generally mixtures of flavones 4 and aurones 5 in varying yields, depending on the substituents in the both reactants.Factors controlling the regioselectivity for 4 or 5 formation in this and in similar, previously reported, coupling procedures have been examined.
FLAVONE FORMATION IN THE WHEELER AURONE SYNTHESIS
Donnelly, John A.,Higginbotham, Clement L.
, p. 7219 - 7226 (2007/10/02)
Dihydrochalcones, formed by bromomethylation of the side-chain of 2'-acetoxychalcones, were found to produce minor quantities of flavones as well as the major product, aurones, when cyclized by aqueous ethanolic sodium hydroxide.The yields of flavone increased with increasing base concentration.The optimum concentration of hydroxide for aurone formation was below 1percent.Greatly diminished yields of O-heterocycles were obtained when a nitro substituent was introduced para to the cyclizing 2'-oxy function.
6-Endo-Dig vs. 5-Exo-Dig Ring Closure in o-Hydroxyaryl Phenylethynyl Ketones. A New Approach to the Synthesis of Flavones and Aurones
Garcia, Hermenegildo,Iborra, Sara,Primo, Jaime,Miranda, Miguel A.
, p. 4432 - 4436 (2007/10/02)
The aryl phenylpropynoates 3a-c, prepared by esterification of phenylpropynoic acid with the corresponding phenols, by means of N,N'-dicyclohexylcarbodiimide, give upon irradiation the o-hydroxyaryl phenylethynyl ketones 4a-c.The cyclization of these compounds in basic media follows two alternative pathways: 6-endo-dig ring closure, to give the flavones 8a-c, and /or 5-exo-dig ring closure , to give the aurones 9a-c.The predominance of one or the other cyclization mode is strongly influenced by the reaction conditions.Thus, the use of potassium carbonate in acetoneas cyclizing reagent favors the 6-endo-dig process, while the 5-exo-dig process becomes clearly enhanced when using sodium ethoxide or potassium carbonate in ethanol.The mechanistic implications of these facts are discussed within the framework of Baldwin's rules.From the preparative point of view, the above results disclose the synthetic possibilities of the key ketones 4 as precursors of flavones and aurones.
