Reactivity of α-arylidene benzoheteracyclanone dibromides toward azide ion: an effective approach to 3-(α-substituted-benzyl)chromones and -1-thiochromones

Treatment of dibromides of 3-arylidenechromanones and -1-thiochromanones with sodium azide resulted in the formation of 3-(α-azidobenzyl)chromones and -1-thiochromones whereas dibromides having no antiperiplanar vicinal hydrogen in the ring such as flavanone, 1-thioflavanone and benzosuberone derivatives afforded only the parent enones by bromine elimination. Evidence supported the intermediacy of 3-(α-bromobenzyl)chromones and -1-thiochromones in this reaction. These postulated intermediates were prepared in an independent way and transformed into azides in high yield.