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

Lead tetraacetate oxidation of N‐aminophthalimide ( 11 ) in inert solvents gives as major products phthalimide ( 15 ) or trans‐1,4‐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): benzocyclobutenedione ( 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 2 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‐1,4‐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 2 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 2 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‐2‐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‐methylcarbamate ( 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 via a nitrene and a tetrazane, namely via 47 and 48 .