Synthesis of 7a-phenyl-1a,7a-dihydro-benzopyrano[2,3-b]azirin-7-ones via photoisomerization reaction

A novel protocol has been developed for the synthesis of 7 a -phenyl-1 a ,7 a -dihydro-benzopyrano[2,3- b ]azirin-7-ones via the photoisomerization of 4-phenyl-5-(2-hydroxyphenyl)isoxazoles. This procedure involves a photo-catalyzed ring opening of isoxazole and subsequent intramolecular nucleophilic addition between a 2 H -azirine intermediate and a phenolic hydroxyl group. The synthetic method offers several notable advantages including operational simplicity, mild reaction conditions, moderate to high yields and environmental friendliness.