[1,4]Benzodioxinopyridazines

3-Chloro[1,4]benzodioxino[2,3-c]pyridazine was prepared from 3,4,6-trichloropyridazine and catechol and was catalytically reduced to [1,4]benzodioxino[2,3-c]pyridazine. Attempted nucleophilic displacement reactions of the chloro-compound with alkoxide ions or with amines generally cleaved the dioxin ring preferentially, though with some amines the chloro-substituent was replaced without ring cleavage. [1,4]Benzodioxino[2,3-c]pyridazine and [1,4]benzodioxino[2,3-b]quinoxaline were less reactive; the dioxin ring was not attacked on heating with morpholine but ring cleavage was effected by boiling methanolic sodium methoxide. The preparation of [1,4]benzodioxino[2,3-d]pyridazine by way of the 1-chloro-derivative is described.