A base-promoted condensation between 2-hydroxyacetophenones and aliphatic aldehydes has been studied. The reaction has been optimized to afford 2-alkyl-substituted 4-chromanones in an efficient manner using microwave heating. Performing the reaction using diisopropylamine in EtOH at 170 degrees C for 1 h gave moderate to high yields (43-88%). The 4-chromanones could be further converted into highly functionalized 2,3,6,8-tetrasubstituted chromones in which a 3-substituent (acetate, amine, or bromine) was introduced via straightforward chemical transformations.

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Benzopyran derivatives R 0350Synthesis of 2-Alkyl-Substituted Chromone Derivatives Using Microwave Irradiation. -Treatment of 2-hydroxyacetophenones with aliphatic aldehydes under microwave conditions allows fast and efficient access to 2-substituted chromanones which can smoothly be converted into various derivatives. The reaction with aromatic aldehydes gives no or only low yields. -(FRIDEN-SAXIN, M.; PEMBERTON, N.; DA SILVA ANDERSSON, K.; DYRAGER, C.; FRIBERG, A.; GROETLI, M.; LUTHMAN*, K.; J. Org. Chem. 74 (2009) 7, 2755-2759; Dep. Chem., Univ. Goeteborg, S-412 96 Goeteborg, Swed.; Eng.) -Jannicke 33-147