Benzo cinnolines nitration

Orientation in the nitration of the 5-oxide of benzo[c]cinnoline (11.20) depends upon conditions. With nitric acid alone it gives 69% of the 9-nitro 5-oxide and 13.5% of the 2-nitro 5,6-dioxide (62JCS2454). But with nitric acid/sulfuric acid, the products appear to be the 1- and 7-nitro 5-oxides in 43 and 26% yields, respectively. One group gives the yields as 43 and 26%, respectively (62JCS2454), whereas another finds the latter to be the major product (62JCS4384). 2,9-Dimethylbenzo[c]cinnoline 5-oxide and the 3,8-dimethyl isomer are nitrated at the 1- and 4-positions, respectively, as expected (62JCS4384). 

Two ring-contractions of dibenzo[c,/][l,2]diazepine derivatives to a benzo[c]cinnoline have been reported. Attempted nitration of3,8-dichloro-(llH)-dibenzo[c,/][l,2]diazepine (19) in sulfuric acid gave 3,8-dichloro-benzo[c]cinnoline (20), and the same compound was obtained when the corresponding diazepinone (21) was allowed to react with ethyl 4-(dietho-xyphosphinyl)crotonate. ... 

Benzo[c]cinnoline forms molecular complexes with halogens in organic solvents thus attempts to brominate it with molecular bromine have been unsuccessful. Using a source of positive bromine, bromine/silver sulfate in sulfuric acid, Corbett and Holt found that reaction occurred at room temperature to give 27% of a monobromo and 4% of a dibromo derivative. These compounds were at first identified as 1-bromo- and l,4-dibromo-(or l,7-dibromo-)benzo[c]cinnolines, but the former was subsequently shown to be the 4 isomer. A reinvestigation of the reaction has shown that both 1- and 4-bromobenzo[c]cinnolines are primary products, formed in the ratio of ca. 2.3 1 at room temperature. The lower isomer ratio as compared with nitration in sulfuric acid probably reflects the greater steric demand of the attacking species. The dibromo compound formed is the 1,4-isomer. The formation of the octachloro derivative by chlorination of benzo[c]cinnoline in the presence of aluminum chloride has been mentioned,but no details are available. 

Benzo[c]cinnoline-5-oxide is a colorless compound, m.p. 139°C, which is less basic than benzo[c]cinnoline, being precipitated on dilution of its solution in hydrochloric acid. Of its reactions, only nitration has received much attention. In sulfuric acid at 70°-80°C, l-nitrobenzo[c]cinnoline 6-oxide (43%) and 4-nitrobenzo[c]cinnoline 6-oxide (26%) are formed, ° ° whereas with nitric acid alone it is reported that the main product is 2-nitrobenzo[c]cinnoline-6-oxide (60-70%), ° ° with some disagreement... 

Like other cyclic compounds having a cis-azo linkage, benzo[c]cinnoline forms fairly stable complexes with many transition metal salts.These all have a 1 1 ligand metal ratio except in the case of palladium(II) chloride, where a 2 1 complex has been isolated.Benzo[c]cinnoline 5-oxide also gives 2 1 complexes with palladium(ll) chloride and with silver nitrate. " A nickel(O) complex, Ni(PEt3)2(benzo[c]cinnoline)2, has been obtained by reaction with biscyclooctadiene nickel and triethylphosphine in hexane. " ... 

Nitration of benzo[c]cinnoline (Section IV,B) gives the 1-nitro, 4-nitro, and 1,10-dinitro derivatives, the first being the most readily available. Others, such as 2- and 3-nitrobenzo[c]cinnolines, are obtainable by nonreductive ring synthesis methods. The 2-phenylazo compound has also been described. ... 

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