Dihydroacridine, from acridine

Attempts failed to prepare 9-azatriptycene (304) analogously from acridine or acridine A -oxide. However, the targeted compound can be readily obtained, in 54% yield, by treating 9-(2-chlorophenyl)-9,10-dihydroacridine with potassium amide for 90 min in refluxing liquid ammonia (Scheme 1-237). 9-Azatriptycene (304) shows all attributes of a basic amine. For example, it combines with acids and with methyl iodide, whereas the noncaged analogue triphenylamine even resists protonation by concentrated sulfuric acid. 

Acridine (9) combines readily with dimethyl acetylenedicarboxylate in methanol yielding the methoxide (11), which is in equilibrium with the corresponding 9-methoxy-9,10-dihydroacridine (12). Presumably the first formed zwitterion (10) abstracts a proton from the solvent,... 

Pyridine reacts with sodium hydrazide in the presence of hydrazine to yield 2-hydrazinopyridine in the absence of free hydrazine a hydrazo compound is formed (Scheme 88) (64AG(E)342). A difference between hydrazination and amination is the formation of 1,4-adducts which cannot be rearomatized even on heating. This is reflected in the behaviour of quinoline, which gives only a 0.5% yield of a -hydrazino product, whereas 4-methylquino-line is hydrazinated in 76% yield (64AG(E)342). Acridine behaves differently with sodium hydrazide/hydrazine, 9,10-dihydroacridine is formed almost quantitatively, but reaction in the absence of hydrazine yields 9-aminoacridine (65%). An even higher yield of 9-amino-acridine is obtained when sodium Af.AC-dimethylhydrazide is used (Scheme 89). Good evidence for intermediacy of (151) comes from the isolation of (152) on hydrolysis of (151). 

Protonated pyridines and derivatives readily undergo acylation at C-2 or C-4 (Table 28) (76MI20503). Acyl radicals are usually generated either by hydrogen abstraction from aldehydes (Scheme 210), or by oxidative decarboxylation of a-keto acids (Scheme 211). In the former case (Scheme 210) with acridine as the substrate, reduction can take place to give a dihydroacridine. 

Acridine (123) is polarographically reducible both in acid and alkaline solution.144 In strongly acid solution a single one-electron wave is found, and from a preparative reduction compounds dimerized at C-9 were isolated.54 In less acid and in alkaline solution 2 one-electron waves are found, the latter probably resulting in 9,10-dihydroacridine (124). 

Both a dihydroacridine and an acridine result from the thermolysis of 2-azidotriphenylmethanes (9) (R.N. Garde et al.t J. chem. Soc. Perkin I, 1978, 1211 1981, 1132). In an analogous manner. 2-(phenylamino)phei lcarbenes (10), generated in the vapour phase from the... 

Nitrogen analogues (5) of o-xylylenes are produced as transient intermediates in the flash pyrolysis of o-amino-benzyl alcohols (4). They do not undergo ring-closure to benzazetines but cyclize to acridines via dihydroacridines. Possibly the same type of imine methide is involved in the thermal and photochemical extrusion of sulphur dioxide from the cyclic sulphones (6), which in this case does give the benzazetine. ... 

For the formation of 7, a change from the conventional SNAr mechanism (cf. p. 353) to a radical SET process with successive dimerization is likely to be responsible [220], Organolithium compounds and CH-acidic compounds add to acridine at the 9-position to give 9,10-dihydroacridines. For instance, with nitromethane in basic medium, the adduct 8 is formed, whereas phenyhnethylsulfone yields 9-methylacridine, since the adduct 9 eliminates phenylsulfinic acid ... 

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