Bases anhydro

The nucleophilic carbon of ketomethylene compounds can react with anhydrobases of different species in a basic medium. This reaction presents a narrow similitude with -CHj attack. The resulting dye, neut-rodimethine cyanine either mesomethyl-substituted or not. varies with the nature of the anhydro base (Scheme 30) (53. 54). 

The use of 2-substituted amino-3-aminopyridines (or corresponding 3-substituted amino-2-amino, 3-substituted amino-4-amino and 4-substituted amino-3-amino derivatives) gives the corresponding TV-substituted pyridopyrazinones with esters or alloxan, or with diketones gives quaternary salts such as (403) or their anhydro bases (404) e.g. 56CB2684, 78HCA2452). 

Anhydro bases can attack the a-position, e.g. of thiazolium cations, with the formation of adducts capable of oxidation to cyanine dyes, e.g. Scheme 18 (see Section 4.02.3.3.4). 

Proton loss from alkyl groups a or 7 to a cationic center in an azolium ring is often easy. The resulting neutral anhydro bases or methides (cf. 381) can sometimes be isolated they react readily with electrophilic reagents to give products which can often lose another proton to give new resonance-stabilized anhydro bases. Thus the trithione methides are anhydro bases derived from 3-alkyl-l,2-dithiolylium salts (382 383) (66AHC(7)39). These... 

Compounds which can formally be considered as anhydro bases can sometimes react with nucleophiles. Thus unsaturated azlactones with Grignard reagents give saturated azlactones (Scheme 50) (65AHC(4)75). 

With l,3-dimethyl-2,l-benzisoxazolium salts, however, considerable reactivity has been reported. Condensation occurs readily with aldehydes, ketones, orthoesters and diazonium salts to yield styryl, cyanine and azo compounds, respectively (78JOC1233). In the presence of triethylamine, dimerization was observed, and the reactions of the cation were considered to involve the intermediacy of the anhydro base (77JOC3929). 

Benzothiazolylium salts, 2-alkoxy-3-methyl-reactions, 6, 289 Benzothiazolylium salts, 3-alkyl-deprotonation, 6, 262 Benzothiazolylium salts, 2,3-dimethyl-anhydro base structure, 6, 238 reactions... 

Dithiolylium salts, 3-alkyl-anhydro bases, 5, 89 condensation reactions, 4, 799 deprotonation, 6, 793... 

The subject was then fully investigated by Pyman, who found that the products obtained depended partly on the material started with and partly on the conditions of the experiment. Thus under his conditions, Z-canadine methohydroxide when dried in vacuo gave rise to three anhydro-bases, a and b optically inactive, and c optically active whilst the methohydroxide of the dZ-base formed only two, a and Z , but the proportion of b formed in this instance was equal to the amount of b and c together in the case of the Z-base (canadine). For this and other reasons b was regarded as the racemic form of c and, like it, is represented by F (R = Me),... 

It is of interest in this connection to note that the conversion of tetrahydroberberine into an anhydro-base of type E (p. 337) represents transformation from the berberine to the cryptopine type (p. 295), and that a-canadine methochloride occurs in Zanthoxylum brachyacanihum with its cryptopine analogue, y-homochelidonine ( -aiiocryptopine, p. 301). 

From the same point of view, 4-pyrones (8a) or 2-pyrones are anhydro bases of 4-hydroxypyrylium (9) or 2-hydroxypyrylium salts. Vinylogs (10) and phenylogs (12) (violones, after Dilthey and Burger ) of these systems are known, whose conjugate acids are monocyclic pyrylium salts (11 and 13). 

Recent work has justified the suspicions that the methylated cinnolones had been allocated the incorrect structures. D. E. Ames and H. Z. Kucharska [J. Chem. Soc. 4924 (1963)] have shown that the compound previously believed to be l-methyl-4-cinnolone is the dipolar anhydro-base of 4-hydroxy-2-methyl-cinnolinium hydroxide. It is likely, therefore, that those cinnoline salts whose structures had been based upon the presumed l-methyl-4-cinnolones are, in fact, 2-salts of structure 56. (Cf. p. 28.)... 

The anhydro-bases (3) derived from quaternary salts of 4-carboline by treatment with alkali were designated as isocarbolines or j/>-carbo-lines. ... 

Anhydro-bases derived from quaternary )S-carbolinium salts are reduced to p /r-A-substituted-l,2,3,4-tetrahydro-j8-carboline derivatives on hydrogenation over Adams catalyst in methanol solution made alkaline to ensure the presence of anhydro-base. ... 

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