3-Cyanochromones constitute an important class of intermediates because of their use in the synthesis of anti-allergic substances.The cyano group enhances the dienophilic nature of the carbon-carbon double bond of the cyclic enone system and thus 3-cyanochromones have been extensively used as dienophiles in the synthesis of compounds with selective acetyl-cholinesterase inhibiting activity.Several methods have been reported for the synthesis of 3-cyanochromones(3)by dehydration of the corresponding aldoximes(2).These include refluxing for 12 hrs in alcohol in the presence of hydrochloric acid,sodium formate in acetic acid and acetic anhydride.Sulfuric acid promoted elimination of methanol from O-methyloximes has also been reported for the synthesis of 3-cyanochromones.Most of these methods involve i)prior preparation of oximes and ii)dehydration,with the disadvantages of strongly acidic conditions,expensive reagents,long reaction times,tedious isolation of products and low overall yields.The synthetic potential and medicinal interest of 3-cyanochromones and the difficulties encountered in the synthesis of 3-cyanochromones prompted a search of a convenient method.
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