Cinnolines ring opening

A mixture of finely powdered 2,3-dichloroquinoxaline and water heated on a steam bath, vigorously stirred and treated with not more than 5 parts KMn04, an amount predetermined spectrophotometrically 2,3-dihydroxypyrazine-5,6-dicarboxylic acid. Y 45%.—Direct oxidation of 2,3-dihydroxyquinoxaline was not successful. The above is the first hydroxylated pyrazine-2,3-dicarboxylic acid described in the literature. H. I. X. Mager and W. Berends, R. 77, 842 (1958) cinnoline ring opening s. G. M. Atkinson and R. E. Rodway, Soc. 1959, 1 isothiazoles from benz[d]isothiazoles s. A. Adams and R. Slack, Soc. 1959, 3061. 

Ring-opened products were obtained from pyrido[l,2-6]cinnolin-6-ium hydroxide inner salt (17, R = H) by oxidation with 3-chloroperoxybenzoic acid, or by reduction with Zn in acetic acid, and from the 5-methyl derivative 43 by reduction with Zn in acetic acid (74JHC125). 

Diazotization of 2-(di-2-furylmethyl)anilines 255 gave the corresponding diazonium salts. Intramolecular attack of the diazonium functionality on the 7t-system of one of the electron-rich furan rings yielded 256. Subsequent elimination results in ring opening which yielded cinnolines 257 (Scheme 64) <1997MOL62, 2000T8933>. 

Pyridazine can be obtained from its benzologs by oxidation. Thus, various cinnolines, phthalazines, or other polycycles afforded the corresponding pyridazinedicarboxylic or tetracarboxylic acids (see Section IV,E). Similarly, pyridazines with a fused three- or four-membered ring readily give substituted pyridazines upon ring opening. 

LAH converts l-alkylpyridazin-6-ones (60) into the corresponding 1,6-dihydropyridazines (57 R = Me, R = H), whereas excess reagent reduces 4,5-dihydropyridazin-6-ones (61) to a mixture of 1,4,5,6-tetrahydro- (62) and hexahydro-pyrazines (63).2 Cinnolines (64) and phthalazines (66) both undergo ring opening during cathodic reduction, giving diamines (65) and (67), respectively. ... 

Durr et al. have described some novel complex cinnoline derivatives which show photochromic properties. Albini et al. have provided some new evidence on the mechanism for the photoisomerization of heterocyclic N-oxides. Simple pyridine N-oxides are exceptional. Thus irradiation of pyridine N -oxide in aqueous base affords the ring-opened product (23). Aoyama et al. have described the unprecedented photocyclization of the amide (24) to the lactam (25). The first examples of C2a+2Tr] photoreactions of a three-membered ring and an azo-compound have been described by Hunig and Schmitt. Nicolaou et al. have prepared the first stable example of a 1,2-dithiethane the procedure involves (2i +2Tr) photodimerization of C=S groups. 

Recently it has been shown that benzo[c]cinnoline 5-oxide, together with its 3-methoxy and 3,8-dimethoxy derivatives, reacts with dimethyl acetylene-dicarboxylate under forcing conditions to give low yields of the ylides 65-67, formed by electrocyclic ring opening of the initial 1,3-dipolar cycloadducts. This parallels the process that takes place readily with benzo[c]cinnoline A -imides (Section IV,F). 

Reduction of the (benzo)pyridazine derivatives was not discussed in CHEC-I, but reduction of these systems is known to occur readily. Cleavage of the N—N bonds can occur, in addition to hydrogenation of the ring, to give open chain products (e.g., tetramethylenediamine from pyridazine) which may re-cyclize (e.g., to give indoles from cinnolines). Examples of work from the current review period are given below. 

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