Cinnoline preparation

Little is known quantitatively about substituent effects in the nitration of derivatives of azanaphthalenes. In preparative experiments 4-hydroxy-quinoline, -cinnoline, and -quinazoline give the 6- and 8-nitro compounds, but with nitric acid alone 4-hydroxyquinoline and 2,4-di-hydroxyquinoline react at With nitric acid, 4-hydroxycinnoline... 

Since the pyridazine ring is generally more stable to oxidation than a benzene ring, oxidation of alkyl and aryl substituted cinnolines and phthalazines can be used for the preparation of pyridazinedicarboxylic acids. For example, oxidation of 4-phenylcinnoline with potassium permanganate yields 5-phenylpyridazine-3,4-dicarboxylic acid, while alkyl substituted phthalazines give pyridazine-4,5-dicarboxylic acids under essentially the same reaction conditions. 

A large number of pyridazines are synthetically available from [44-2] cycloaddition reactions. In one general method, azo or diazo compounds are used as dienophiles, and a second approach is based on the reaction between 1,2,4,5-tetrazines and various unsaturated compounds. The most useful azo dienophile is a dialkyl azodicarboxylate which reacts with appropriate dienes to give reduced pyridazines and cinnolines (Scheme 89). With highly substituted dienes the normal cycloaddition reaction is prevented, and, if the ethylenic group in styrenes is substituted with aryl groups, indoles are formed preferentially. The cycloadduct with 2,3-pentadienal acetal is a tetrahydropyridazine derivative which has been used for the preparation of 2,5-diamino-2,5-dideoxyribose (80LA1307). 

Surprisingly, no fully detailed syntheses of pyridopyridazines by joining of two heteroatoms have been recorded, although a recent patent claimed the preparation of pyrido-[2,3-c]-, -[3,2-c]-, -[3,4-c]- and -[4,3-c]cinnolines by reduction of 2,2 -dinitro substituted phenylpyridines with a variety of reagents (80GEP2939259). 

The first synthesis of cinnoline was reported by von Richter in 1883. The diazonium chloride 5 which was obtained from o-aminophenylpropiolic acid (4), was heated in water at 70°C to provide the 4-hydroxycinnoline-3-carboxylic acid (6). When this acid 6 was heated above its melting point, carbon dioxide was liberated and 4-hydroxycinnoline (7) was obtained. Distillation of 4-hydroxycinnoline (7) with zinc dust furnished a small amount of oil, which was assumed to be cinnoline (8). The preparation of 4-hydroxycinnoline (7) was repeated by Busch and Klett, although in lower yield when compared to the original report. Busch and Rast later converted the 4-hydroxycinnoline (7) successfully to cinnoline (8) via the 4-chlorocinnoline (9). ... 

Only a limited number of cinnoline derivatives have been prepared via the von Richter cinnoline synthesis. ... 

The von Richter cinnoline process was further extended to solid-phase synthesis. The route began from benzylaminomethyl polystyrene and the required diverse o-haloaryl resins represented by 21 were prepared from substituted o-haloanilines. A Pd-mediated cross-coupling reaction with 21 and the alkynes provided the alkynylaryl derivatives represented by alkyne 22. The von Richter cyclization reaction with hydrobromic or hydrochloric acid in acetone/HaO and cleavage from the resin occurred in the same step to furnish the cinnoline derivatives 23 in 47-95% yield and 60-90% purity (no yield reported for each entry). 

The o-aminophenylpropiolic acid 4 (20 g) in water (60 mL) and aqueous ammonia (9 mL, d = 0.88) was added with shaking during 15 minutes to a mixture prepared from ferrous sulfate (220 g), water (440 mL), and aqueous ammonia (110 mL, d = 0.88). After 45 minutes, with occasional shaking but no external cooling, the suspension was filtered. The residue was washed with water, and the combined filtrates were treated with ammonium acetate (60 g) and made weakly acidic with acetic acid. The solution was then cooled to 0°C by addition of crushed ice, and then made acidic to Congo-red with concentrated hydrochloric acid (70-80 mL). Additional hydrochloric acid (20 mL, 2 N) was immediately added, and the turbid solution which resulted was diazotized with 20% aqueous sodium nitrite, after which the mixture was kept at 70°C. The cinnoline acid 6 was separated over 45 minutes as a dark brown, granular solid (12.5 g), m.p. 260-265°C. ... 

The reaction conditions of this modified indazole synthesis can also be applied to the preparation of 1,2-diazanaphthalenes, the so-called cinnolines, although in such syntheses no deprotonation prior to cyclization is likely to occur. Ruchardt and Hassmann (1980) obtained 4-phenylcinnoline (6.85) in 53% yield from 2-(a-methyl-ene-benzyl)aniline (Scheme 6-53). 

Oxidative photocyclization of benzylideneaniline appears to proceed efficiently only in the presence of strong acid. The phenanthridine 31, however, has been prepared by irradiation of the imine 3228 few other examples of the photocyclization of arylimines have been reported.29 Strong acid is also required for successful photocyclization of azobenzenes to benzo-[c]cinnolines. Here, protonation is claimed to lower the reactive n, n excited state below the level of the unreactive n, it state. 2-Phenylazopyridine,... 

The [l,2,4]triazino[3, 4 2,3][l,3,4]thiadiazino[5,6-c]cinnolin-9-one551 was prepared (90JIC351) by cyclocondensation of 3,4-dichlorocinnoline with the triazine derivative. 

Various pyridazine-A-oxides (including cinnoline A-oxides) have been prepared as potential antitumour agents in Japan [276-278]. Among several 4-nitro-pyridazine 1-oxides tested for activity against rat ascites hepatoma AH-13, 3,6-dimethoxy-4-nitropyridazine 1-oxide (74) has been found to be the most potent compound a minimal effective dose of 5 mg/kg has been estimated [276], Also pyridazine A-oxides of type (75) bearing a bis(2-chloroethyl)ami-nomethyl side-chain at C-6 have been reported to be effective (0.5-5 mg/kg, i.p.) against AH-13 in rats [278]. Both types of compound (74), (75, R = H, Br), however, have been shown to be inactive against mouse lymphoid leukaemia L-1210. 

In the same way, cinnoline and 1,4-dihydrocinnoline were prepared from ortho-nitrophenyl ethylamine by a two-step electrolysis performed either in a batch cell [58] or in a flow cell [53] (Scheme 41). 

Unsubstituted 7-oxo-l,2,3,7-tetrahydropyrido[3,2,l-i ]cinnoline-8-carboxylates were A-alkylated with dialkyl sulfates, and they were also A-acylated with acetic anhydride in acetic acid to give the 1-substituted derivatives (92EUP470578). The 1-hydroxymethyl derivatives were prepared from the 1-unsubstituted compound with formalin in acetic acid. 

Benzimidazo[l,2- ]cinnolines 250 were prepared via pyrolysis of benzotriazoles 249 (Equation 62) <2003T9455>. 

In CHEC(1984) and CHEG-II(1996) the most important ways to prepare the commercially available parent compounds pyridazine, phthalazine, and cinnoline were described <1984CHEC(2)1, 1996CHEC-II(6)1>. Also functionalized derivatives that are useful in synthetic programs were nicely covered. The most important type of substrates for this purpose are the easily accessible, halogenated (commonly chlorinated) derivatives exemplified by 3,6-dichloropyrid-azine, 3,4,5- and 3,4,6-trichloropyridazine, 2-substituted 4,5-dichloropyridazin-3(2//)-ones, 1,4-dichlorophthalazine, and... 

In the first reported solid-phase Richter reaction, cinnolines 143 were prepared through a two step sequence of a Heck-type coupling to give intermediates 142 followed by intramolecular ring formation and release of ciimolines 143 <99TL6201>. 

There are a number of important reactions in this category and all of them involve at least one heteroatom functioning as a nucleophile and another as an electrophile. Diazo-tization of a variety of ortho-substituted anilines for instance, followed by intramolecular nucleophilic trapping of the corresponding diazonium salts by either nitrogen or carbon nucleophiles, is the basis of a series of very important syntheses of 1,2,3-benzotriazine and cinnoline derivatives, and this general approach has been widely exploited for the preparation of polycyclic systems. Representative examples are given in equations (51)—(54). 

A variation of this procedure is given in Preparation 3-3, in which a mixed solvent is used in the preparation of benzo[c]cinnoline by a lithium aluminum hydride reduction [67]. 

Preparation of Benzo[c]cinnoline by Lithium Aluminium Hydride Reduc-... 

See the Borsche Cinnoline Synthesis and the von Richter Cinnoline Synthesis for other preparations of cinnolines. 

It was previously mentioned1 that cinnoline and 3-substituted cinnolines (94) could be prepared from the condensation products (95) between an o-nitrobenzaldehyde and a nitroalkane by electrochemical reduction. The reaction has been further studied,138 and it was noticed that when the reduction was carried out stepwise, anthranils (96) were formed, especially at elevated temperatures. The final ring closure was catalyzed by traces of oxygen, whereas too much oxygen produced the cinnoline JV-oxide (97) the ring closure was believed to be a radical chain reaction where the formation of the aromatic cinnoline was part of the driving force [Eq. (76)]. 

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