51The following mechanism can be suggested, taking into account that 5-nitrocinnoline 2-oxide and 8-nitro-4-hydroxycinnoline are reported not to be intermediates'. As initial step the hydrogen peroxide adds to the azomethine bond in 1 yielding the hydroperoxide 12. A subsequent rearrangement involving ring opening gives the tautomer 13 of o-(formy1hydrazino)benzaldehyde which may undergo ring closure into N-formylindazole (14). Oxidation and decarboxylation yields 2. It cannot be excluded that initially oxidation of the N-formyl group occurs, then decarboxylation giving o-hydrazinobenzaldehyde, which cyclisizes into 2. Formation of indazoles by ring closure of o-substituted benzene derivatives, containing in one position an aldehyd-, acetal-or keto group and in the adjacent position a hydrazino 4roup is well established".
12Schetne 2
R'I ? '
14The mechanisms of the ring contraction of cinnoline -+ indazole and that of quinoline -+ i n d~l e~-~ have in common that it is the carbon atom adjacent to the nitrogen which is expelled.
Experimental partMelting points are uncorrected. Radioactivity measurements were carried out with a Mark I1 liquid scintillation counter (Nuclear -Chicago). The radioactivity of the nitroindazoles and nitrocinnolines was measured in 10 ml of a scintillation solution of 4 g PPO and 0.4 g of POPOP in 200 ml of ethanol and replenished to I 1 with toluene.
a. Oxidation of 5-nitro[4-'4C]cinnoline (8)The oxidation and the work-up procedure were carried out according to the prescription given for the unlabelled compound'. To a solution of 0.37 g (2.2 mmole) o f 8 in 4 ml of acetic acid 2.5 ml of 30':,, hydrogen peroxide were added. After heating for 8 h at 6&70° and addition of 4 ml of water the solution was evaporated to a volume of -2 ml. A further 4 ml of water were then added and this solution was evaporated to dryness. The residue was dissolved in chloroform and submitted to column chromatography (AI,O,) using chloroform as eluent. First both 5-nitr0[4-'~C]cinnoline 1and 2oxides were obtained; combined yield 190 mg (43 %). After changing the eluent to chloroform/ethanol (95 : 5 ) 4-nitr0[3-'~C]indazole (9) was isolated; yield 50 mg (14%). m.p. 202-204O (from water) (lit. 201-203O).
b. Oxidation of 8-nitro[4-'4C]cinnoline (10)The oxidation procedure was the same as described in section a., using 0.33 g of 10 (2.0 mmole), 3 ml of acetic acid and I .5 ml of 30 ' ' ,<, hydrogen peroxide. After addition of water, a precipitate was obtained, which was collected and extracted five times with benzene. The residue was recrystallized from ethanol, yielding 65 mg of 8-nitr0[4-'~C]cinnoline 2-oxide (17 %). The benzene extracts were evaporated to dryness and the residue was recrystallized from water; yield 90 mg of 7-nitro[3-'4C]indazole (11) (3373, m.p. 179-183" (lit. 181-183").
AcknowledgementWe wish to express our sincere thanks to Dr. D. A. de Bit, for his assistance with measurements of ''C-radioactivity.Abstract. The synthesis of various 2-(arylimino)imidazolidines is described. Most compounds wer...
