Some new rearrangements in nitrogen heterocyclic chemistry.

The oxidation of 3-niono- and 3, 4-di-substituted 2-pyrazolin-5-ones was studied to determine whether the pyrazol-3-one intermediates generated would decompose with loss of nitrogen to give cyclopropenones. Cyclopropenones were not formed however; this parallels the behaviour of 3-indazolones which had been shown not to give benzocyclopropenone. 4, 5-Diphenylpyrazol-3-one lost nitrogen and carbon monoxide to give diphenylacetylene, and nitrogen to give 2, 3, 6, 7-tetraphenylpyrazolo-(l,2a)-pyrazol-l,5- dione. The unstable alpha-carbonyl-azo intermediates from 2-pyrazolin-5-ones were trapped with tetracyclone to give stable Diels Alder adducts in good yield. When heated these adducts partly undergo a retro-Diels Alder reaction and partly undergo a novel molecular rearrangement, paralleled in the mass spectrometer, to give carbon dioxide and 1, 7a-diazaindenes. (This is described in Section 1). Efforts towards the synthesis of 5, 6-diphenyl-l, 2, 3-triazin- 4-one are described since its 3-amino derivative should give diphenylcyclopropenone on oxidation. Amination of 3, 4-diphenyl-2-pyrazolin-5-one caused ring expansion to 5, 6-diphenyl-l, 2, 3, 4-tetrahydro-1, 2, 4-triazin-3-one, which on oxidation gave 5, 6-diphenyl-1, 2, 4-triazin-3-one. Amination of the latter caused ring contraction, however, to give 4, 5-diphenylimidazolin-2-one with hydroxylamine-0-sulphonic acid, and 4, 5-diphenyl-l, 2, 3-triazole with chloramine. (This is described in Section 2). l-Amino-3, 4, 5, 6-tetraphenyl-2-pyridone was prepared as a possible precursor to hexaphenyl-1, 7a-diazaindene (see above). When oxidised with lead tetra-acetate it underwent an unusual rearrangement to give 3, 4, 5, 6-tetraphenylpyridazine; evidence for a nitrene intermediate was provided by oxidation of the N-amino-pyridone in dimethyl sulphoxide when the nitrene was trapped as the sulphoximine. Pyrolysis of this gave the same products as the oxidation reaction. The nitrene formed by oxidation of the hydrazine, and by photolysis of the sulphoximine, was trapped with cyclohexene to give the same aziridine. By contrast, oxidation of N-aminophenanthridone gave 4, 5-benzocoumarin and l-amino-2, 3-diphenyl-4-quinolone gave a bis-quinolone. (This is described in Section 3). The preparation of 2, 3-bis-(m-methoxyphenyl)-cyclopropenone and the attempted oxidative coupling of this and the bis-phenol to give the phenanthracyclopropenone system are described in the Appendix. Mechanisms are proposed for all the new reactions described.