Acridine N-oxides

The nitrations of a wide range of substituted quinoline N-oxides under various conditions [82HC(382)447] show the usual pattern of substituent effects superimposed upon the pattern resulting from the use of nitric acid/sulfuric acid at low temperature (5,8-positions), weaker mixtures of these acids at high temperature (4-position), or acyl nitrates (3-position). Nitration of acridine N-oxide by nitric acid/sulfuric acid occurs in the 5-position (60JCS3367). 

Cyano- and 10-chloro-acridine N-oxides yield 1,2-oxazepines on photolysis in benzene (Scheme 237). When the 10-substituent is methyl the unstable 1,2-oxazepine undergoes electrocyclization to a benzisoxazoline (320). Secondary photoproducts may be formed by direct irradiation of N- oxides or by rearrangement of the primary photoproduct. 

Irradiation of acridine N-oxide takes a different course depending on the solvent system, as shown in Scheme 121 (69LA(723)95, 68TL4519). 

Anthranil (119) and benzyne (from oxidation of 9 with lead tetraacetate) afford acridine (5%)81 depending on the sequence of bond forming and breaking, an oxygen-bridged cycloadduct and/or acridine N-oxide (120) may be intermediates in this reaction (Scheme 15), although 120 is known to react with benzyne in a different sense (Section IX). The addition of benzyne to oxazoles leads, ultimately, to anthracene derivatives in high overall yield.82b... 

However, 3,5-dimethylpyridine 1-oxide (244) and benzyne (from decomposition of 4 below 45°C) afforded 250 (24%) and isomeric adducts 247 and 248 (25 and 23%, respectively) via 1,3- and 1,5-sigmatropic rearrangement of the primary 1,3-cycloadduct (Scheme 23).121 Both 247 and 248 also rearranged at 100°C to form 250. The rearranged adduct corresponding to 248 from 3,5-dichloropyridine 1-oxide spontaneously lost hydrogen chloride at 0°C to give 3-chloropyrido[3,2-b]benzofuran (251).121 Acridine N-oxide (120)... 

The reaction of 2-fluoro-5-nitrobenzaldehyde with a wide variety of aryl-amines gives mixtures of the corresponding 2-arylamino-5-nitrobenzaldehydes and the related anils. Both aldehydes and anils underwent acid-catalysed cyclization to the corresponding 2-nitroacridines (80). The acridine N-oxide (81) was obtained as the major product by the reaction of < -fluorobenzyl cyanide with p-chloronitrobenzene in methanolic potassium hydroxide. ... 

Oxazepines have previously been suggested as unstable intermediates in the photolysis of acridine N-oxide and related N-oxides now two examples, (175 R = CN) and (175 R = Cl), have been isolated for the first time. " As predicted, they are unstable and undergo a variety of isomerization reactions in the dark and under mild conditions. The novel cyclic sulphilimine (176) ring-expands when boiled in xylene to give the dibenzothiazepine (177) in moderate (26%) yield." ... 

Skeletal rearrangement. A soln. of acridine N-oxide in methylene chloride irradiated 3.5 hrs. with a 100 w. high-pressure Hg-lamp and Pyrex filter -> cyclohept[b]indol-10(5H)-one. Y 70-80%. M. Ishikawa, C. Kaneko, and S. Yamada, Tetrah. Let. 1968, 4519 pyrazoles from pyridazine N-oxides s. P. L. Kumler and O. Buchardt, Am. Soc. 90, 5640 (1968). 

With acridine N-oxide and terpyridine trioxide [Ni(C,3H,N0)4(H20)](C104)2 4H2O room 3.57 Farad tetragonally distorted 70P18... 

Yamada, S., Ishikawa, M., and Kaneko, C, Photochemistry of acridine N-oxides, Chem. Pharm. Bull, 23, 2818, 1973. 

A similar mechanism applies to the acridine phenyl esters and acridine N-oxide phenyl esters [21]. Quantum yields are not quite so high, and in the former case, dipolar aprotic solvents are required, presumably to enhance nucleophilic attack at the now less activated 9-position. Quinolinium (10) and phenanthridinium (11) esters are also chemiluminescent but with a lower efficiency [21] ... 

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