Molecular iodine-catalyzed C3-alkylation of 4-hydroxycoumarins with secondary benzyl alcohols

A highly efficient method for the C-C bond formation via molecular iodine-catalyzed C3-alkylation reaction of 4-hydroxycoumarins with benzylic, benzhydrylic, allylic, and propargyl alcohols at 50 degrees C in MeNO2 is described. The 3-alkylated-4-hydroxycoumarins were obtained in good yields (up to 97%). By applying this reaction as the key step, a multi-substituted pyranocoumarin can easily be synthesized in a one-pot procedure. The advantages of this method are broad scope, mild conditions, and easy handling since water is the only side product. (C) 2009 Elsevier Ltd. All rights reserved.