Cinnolines, rearrangement

There are some recent examples of this type of synthesis of pyridazines, but this approach is more valuable for cinnolines. Alkyl and aryl ketazines can be transformed with lithium diisopropylamide into their dianions, which rearrange to tetrahydropyridazines, pyrroles or pyrazoles, depending on the nature of the ketazlne. It is postulated that the reaction course is mainly dependent on the electron density on the carbon termini bearing anionic charges (Scheme 65) (78JOC3370). 

Quinoline 1-oxides can be rearranged photochemically into indoles (103 — 104 — 105) or N-hydroxyindoles (106 — 107). Cinnolines are reductively ring-contracted into indoles (Section 3.2.1.6.9.ii). 

It has been known for some time that irradiation of azobenzene (324) in either 22 N sulfuric acid350 351 or acetic acid with added ferric chloride 352 yields benzo[c]cinnoline (325). This is accompanied by the formation of an almost equal quantity of benzidine (326), undoubtedly arising by rearrangement of hydrazobenzene (327). The mechanism of this reaction differs, therefore, from that of the stilbene cyclodehydrogenation, and azobenzene itself functions as the hydrogen acceptor. Yields of not more than 50% of benzo[c]cinnoline are generally observed. 

Similarly, the base-catalyzed rearrangement of 3 -hydroxy-2-nitrobenzene-sulfonanilide (8) leads to 2-amino-4-hydroxy-2 -nitrobiphenyl, which cyclizes to 3-hydroxybenzo[c]cinnoline 6-oxide under the reaction conditions [Eq. (4)]. When the rearrangement is carried out in aqueous solution at 250°C, the sulfite produced reduces the IV-oxide to 3-hydroxybenzo[c]cinnoline. 

When 2,2 -dianiinobiphenyl is bis-diazotized at 0°C (see also Section II,A,2) and the solution is neutralized with ammonia at that temperature, dibenzo[rf,/][l,2,3]triazepine (22) precipitates as a yellow solid (Scheme 4). Although moderately stable, 22 rearranges quantitatively to benzo[c]-cinnoline-5-imide (23) on heating in benzene. The imide (23) is also the... 

The reaction of benzo[c]cinnoline with aminating agents such as 0-mesitylsulfonylhydroxylamine gives the dipolar benzo[c]cinnoline 5-imide (23). ° The same compound is formed by thermal rearrangement of... 

Apart from esterification reactions and thermal decarboxylation of the 2-carboxylic acid, the only other reaction to be reported is the Beckmann rearrangement of the oxime of 3-acetylbenzo[c]cinnoline, which proceeds normally to give the 3-amino compound.63... 

Reduction of 5- and 8-nitrocinnolines with zinc amalgam in aqueous acetic acid gives the corresponding 4- and 7-amino-indoles these conditions have previously been used to effect ring-contraction of 4-alkyl- and 4-aryl-cinnolines. Treatment of the perhydropyridazine (95) with hot concentrated sulphuric acid results in nearly quantitative rearrangement to the pyrazole (96). ... 

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