By the photolysis of the ozonide derived from 1, 4-benzodioxins, o-benzoquinones were obtained in moderate yields independent of the stability of o-benzoquinone@ and of the substituent groups, except the nitro group. Through the mechanistic studiea, it was indicated that 0-benzoquinonea were formed through a radical decomposition pathway, while catechols were formed through an ionic decomposition pathway induced by acidic ...