9- acridine, tautomerism

Acridine-9-thione alkylation, 2, 357 oxidation, 2, 357 tautomerism, 2, 356 9-Acridinium bromide reactions... 

Thiol-thione tautomerism is similar to that exhibited by the oxygen analogues but with the a- and y-thiones, e.g. (129), slightly more favoured than the corresponding a- and y-oxo compounds. UV and other data have indicated the predominance of the thione forms of quinoline-2- and -4-thione, e.g. (130), isoquinoline-1- and -3-thione, e.g. (131), and acridine-9-thione (132) (76AHC(S1)144>. 

A number of studies have been directed specifically at the acridine nucleus. The effect of substituents in the 9-position in acridine (V-oxides on Rf values for thin-layer chromatography (TLC) is measured by ap,198 and there is also a relation between this parameter and the N—O stretching frequencies. The effect of substituents on the basicity of acridine and the possibility of amine-ketimine tautomerism in 9-aminoacridines have been evaluated, taking quinoline as a model... 

For some time Tanasescu held the view that a group of compounds obtained by reaction of o-nitrobenzaldehydes with aromatic compounds in concentrated sulfuric acid, containing one oxygen atom more than the arylanthranils formed concurrently, were anthranil-A-oxides (e.g., 172).2QQ 201,206 Lehmstedt opposed this, and put forward the A-hydroxyacridone structure (173),213 312 which Tanasescu himself later adopted, although he preferred the tautomeric hydroxy-acridine- A-oxide structure (174).195 198 199 313... 

FIGURE 11.20. Tautomerism of l-nitro-9-(alkylamino)acridines, revealed by X-ra studies (Ref. 87). Shown are chemical formulae for both amino and imino tautomers of the nonprotonated and protonated forms. Crystal structures of all but salts of th imono tautomer have been reported (see Ref. 87). 

Tetraphosphorus decasulphide in hexamethylphosphoric triamide converts 9-acridones into the corresponding thiones, complementing the established routes from acridine and sulphur and from a 9-haloacridine and various sulphur reagents. The method is an improvement on the previous techniques for 0-S exchange in acridones (R.R. Smolders et al,. Synthesis, 1982, 493). Various thioacridones have beer. S-alkylated and S-acylated under mild phase transfer conditions, utilising the tautomeric nature of the thione (M. Vlassa, M. Kezdi and I. Goia, Synthesis, 1980, 850). 

Another structural requirement considered for antimalarial activity of acridines and quinolines was the planarity of the heterocycles. Simulation of all these facts led Curd and Rose to synthesize 2-(4-chlorophenylamino)pyrimidines of the type 26 and 27 [37,39,40]. Since both these structure contained a guanidino function, though in a cyclic structure, the characteristic tautomeric structures were possible. In a further effort to modify the structure of the pyrimidines, the synthesis of the biguanide... 

B. Thiono-Mercapto Tautomerism 1. Pyridines, Quinolines, and Acridines... 

On the other hand, when o -adducts of arylacetonitrile carbanions to para-substituted nitroarenes are converted into substituted nitrosoarenes in aprotic media via silylation in the presence of trialkylamines, the produced o-nitrosoaryl acetonitriles can undergo further hetero-cyclization on alternative pathway to produce substituted acridines [28]. Reactions of arylacetonitriles with nitroarenes unsubstituted in the para position under identical protic conditions result in the formation of p-nitrosoaryl arylacetonitriles that can be isolated in the tautomeric form of p-arylcyanomethylene quinone oximes (Scheme 11.13) [27b]. 

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