"Chemical Reactivity of some substituted 6,8-dimethylchromones towards some nucleophilic reagents''

Abstract

In the present study, we aimed to synthesize a variety of 3-substituted-6,8-dimethylchromones, and study their chemical transformations towards a diversity of nucleophilic reagents. Vilsmier Haack formylation of 3,5-dimethyl-2-hydroxy- acetophenone using dimethylformamide and phosphoryl chloride, yielded 6,8-dimethylchromone-3-carboxaldehyde (1) as previously reported. Treatment of carboxaldehyde 1 with hydroxylamine hydrochloride in aqueous ethanol produced the corresponding oxime 2, which upon dehydration using acetic anhydride gave 6,8-dimethylchromone-3-carbonitrile (3) (Scheme 1). Herein, treating carboxaldehyde 1 with N-bromosuccinamide (NBS) in carbon tetrachloride under irradiation using 200-W Tungsten lamp followed by quenching with water afforded 6,8-dimethylchromone-3-carboxylic acid (4), via non isolable intermediate A. Quenching the reaction medium in the previous reaction with aqueous ammonia, instead of water, produced 6,8-dimethylchromone-3-carboxamide (5) in moderate yield (Scheme 1). Carboxamide 5 was also synthesized in good yield from acidic hydrolysis of carbonitrile 3 using concentrated sulfuric acid (Scheme 1).