Phthalimido‐nitren I. Bleitetraacetat‐Oxydation von N‐Aminophthalimid in inerten Lösungsmitteln. Bildung und Eigenschaften von trans‐1,4‐Bisphthaloyl‐2‐tetrazen

Abstract

Summary. Lead tetraacetate oxidation of N-aminophthalimide (11) in inert solvents gives as major products phthalimide (15) or truns-l.4-bisphthaloyl-2-tetrazene (12), the former (15) on slow, the latter (12) on fast addition of the oxidizing agent. As by-products are found: (a) in the presence of acetic acid : N-acetylamino-phthalimide (14). and (b) in its absence (especially at higher temperatures) : banzocyclobutenedione (13) along with N-phthalimido-phthalimide (16) as well as traces of phthalic anhydride (17).The tetrazene 12 and phthalimide (15) are considered to be formed by oxidation and fragmentation, respectively, of the intermediate 1,4-bisphthaloyl-tetrazane (18). Phthalimido-nitrene (22), or its conjugated acid 23, is postulated to be the species which initiates the major reactions, namely: (a) addition to the educt 11 to give the tetrazane 18 and (b) fragmentation with loss of N, to give the dione 13. The minor by-products 16 and 17 may be the result of cross-amidation of 11 with 15 and rearrangement-oxidation via phthalazine-1.4-dione (30), respectively.The structure of the tetraacyltetrazene 12 follows from its properties, among others a comparison of its UV. spectrum with that of the known 1,4-dimethoxycarbonyl-l,4-dimethyl-2-tetrazene (32). Methanolysis of 12 affords 1,4-di-(o-methoxycarbonyl-benzoyl)-2-tetrazene (33).The diacyltetrazene 33 is converted to methyl N-methoxycarbonyl-anthranilate (36), N, and phthalimide (15) on thermolysis, or to methyl N-acetylphthalamate (35), methyl N, N'-carbonyldianthranilate (37) and methyl N-acetyl-anthranilate (38) on acetylation in pyridine. The intermediate in these reactions, leading to 36, 37 and 38, probably is o-methoxycarbonyl-phenylisocyanate (34), itself the result of a Curtius-type rearrangement. Acetolysis of the tetrazene 12 gives phthalimide (15), N, and N-carboxyanthranilic anhydride (42) by a mechanism analogous to that of the methanolysis of 12.In the preparation of 1,4-dimethoxycarbonyl-1,4-dimethyl-Z-tetrazene (32), required for the above mentioned comparison, by zinc reduction of methyl N-methyl-N-nitro-carbamate (43), followed by bromine oxidation of methyl N-amino-N-methylcarbarnate (44), a deamination of 43 to methyl N-methyl-carbamate (45) was observed both in the reductive and in the oxidative step. Both formations of 45 can be formulated v i a a nitrene and a tetrazane, namely via 47 and 48.