A number of 2,1-benzisoxazole and 2,1-benzisothiazole compounds containing alkoxy or amino substituents in the 3-position and carboxy substituents in the 7-position, and potentially capable of valency tautomerism have been synthesized by reduction or oxidation, respectively, of suitable 2-nitro- or 2-aminoisophthalic acid derivatives. Thionation of 2-aminoisophthalic esters gave benzothiazaphosphorine derivatives. A temperature dependent n.m.r. study of the benzisoxazole and benzisothiazole derivatives indicates that in only one case, for methyl 3-methoxy-2,1-benzisothiazole-7-thionocarboxylate is there evidence for tautomerism at 200°.
7-Acetyl-3-methyl-2,1-benzisoxazole has been synthesized by reduction of 2,6-diacetylnitrobenzene. While the chemical properties of the compound indicate that it undergoes valency-tautomerism, spectroscopic studies indicate that this is a relatively slow process. Comparisons with other heterocyclic systems having similar properties are noted.