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

Treatment of dibromides of 3-arylidenechromanones and -1-thiochromanones wi th sodium azide resulted in the formation of 3-(alpha -azidobenzyl)chromone s and -1-thiochromones whereas dibromides having no antiperiplanar vicinal hydrogen in the ring such as flavanone, 1-thioflavanone and benzosuberone d erivatives afforded only the parent enones by bromine elimination. Evidence supported the intermediacy of 3-(cr-bromobenzyl)chromones and -1-thiochrom ones in this reaction. These postulated intermediates were prepared in an i ndependent way and transformed into azides in high yield. (C) 2001 Elsevier Science Ltd. All rights reserved.