Acridizinium

Acridizinium salts, 8-diazo-7-oxo-in lithography, 2, 570 Acridizinium salts, 7,10-dihydroxy-oxidation, 2, 539... 

Acridizinium salts, lO-(phenylsuIfonyl)-synthesis, 2, 545 5-Acridone UV spectrum, 2, 156 9-Acridone acylation, 2, 352 alkylation, 2, 350 synthesis, 2, 422 Acridone alkaloids, 2, 513 9-Acridonequinones synthesis, 2, 348 Acridones fluorescence, 2, 20 mass spectrometry, 2, 134 synthesis, 2, 93, 401 from 3-arylanthranils, 2, 496 from benzotriazinones, 2, 506 tautomerism, 2, 347 Acridones, tetrahydro-synthesis... 

Although it is possible to have a polar cycloaddition with a cation containing only carbon and hydrogen, the majority of those which have been found to undergo 1,4-cycloaddition are aromatic quaternary salts. The acridizinium cation (1) used in the first polar cycloaddition reaction of a quaternary salt has been used in the largest number of polar cycloaddition studies to date. The acridizinium ion (1) is particularly suitable for such a study since it is easily prepared, is stable (permitting sealed... 

Table I records the results obtained in the preparation of 30 cycloaddition products from the acridizinium cation. As was demonstrated by Fields, Regan, and Dignan, even preparative experiments done at different temperatures and in different solvents are adequate to prove the inverse electron demand character of the reaction. Nucleophilic alkenes, like ketene diethyl acetal, reacted in minutes at room temperature while the strongly electrophilic alkene, tetracyanoethylene, failed to react under any conditions.

The yields of product isolated when para-substituted styrenes were allowed to react with the acridizinium ion (Table I) are not indicative of the rates of reaetion. In an experiment patterned after that used by Sauer and Wiest in the first demonstration of the existence of cycloaddition with inverse electron demand, it was shown that the relative rates of addition of para-substituted styrenes to the acridizinium nucleus were as follows CHgO, 4.3 CHg, 1.7 H, 1.0 NOg, 0.34 or in the order expected from the nucleophilicity of the styrenes. 

Fields et al. showed that a variety of unsymmetrical alkenes added regiospecifically to the acridizinium nucleus and pointed out that the great majority of cases could be rationalized by the assumption that the more negatively polarized end of the alkene was preferentially attracted toward position 6, the previously demonstrated center for nucleophilic attack on the acridizinium ring. At the same time they reported that the addition of acrylonitrile to yield a 12- rather than a 13-cyano adduct is the reverse of what would be expected from the polarization of the acrylonitrile molecule. Possible explanations for this exception are offered in Section V. 

In the first cycloaddition reaction of the acridizinium ion, that with maleic anhydride, it had been observed that addition had occurred with great stereoselectivity, although it iVas not ascertained whether the product (4) was syn or anti with respect to the benzenoid ring. It was later demonstrated by use of NMR and IR evidence (derived from the... 

Not shown in Table I are several adducts obtained by cycloaddition of the acridizinium ion with 5,6-endo-substituted norbomene derivatives. These adducts each have two (imequally shielded) methylene hydrogen atoms which make simple the NMR analysis of mixtures of syn (8) and anti (9). When the 5,6-endo chain (R) was of the type... 

A number of cycloadducts have been prepared from substituted acridizinium salts. Bradsher and Stone studied the rate of addition of st30-ene to acridizinium salts having methyl groups at the meso (6,11) positions. 

Significant synthetic application of the reaction products of the acridizinium ion with alkenes has been made by Fields et Although... 

Although dimethyl acetylenedicarboxylate was reported earlier not to undergo cycloaddition with the acridizinium ion, it was later... 

Another important observation by Fields et al ° was that the acridizinium ion (25) will undergo cycloaddition with benzyne, affording... 

Fields cf oZ. have pointed out that the differences observed between the rate of cycloaddition of ketene acetal with the acridizinium ion and that of various acridizinium benzologs qualitatively parallels those which are encountered when the rate of cycloaddition of maleic anhydride with... 

When ring A was replaced by an imidazo ring, it was found ° that the new system (39) was less reactive than acridizinium (probably due to... 

The most recent extension of the 4 + 2 cycloaddition to aromatic quaternary salts has been carried out with isoquinolinium salts (42), in effect, dispensing with ring A of the acridizinium ion. Although there was an earlier claim that the addition of an ynamine to 2-methyl-isoquinolinium iodide led to a 2 1 adduct, the assigned structure... 

After the acridizinium system (Section II, A), the most-studied electrophile in polar cycloaddition is the JV-raethylenium amide system (101). 

In cycloaddition reactions involving the acridizinium and isoquino-linium ions, the presence of a positive charge leads with great stereoselectivity to products which could not be predicted by the rule of Alder and Stein. A charge-transfer complex arising from the attraction... 

Dependence of the Rate of Addition of Styrene to Acridizinium Nucleus upon Electron Deficiency at Position 6... 

The rate of cycloaddition (see 134) of styrene with the acridizinium nucleus (133) varied directly with the electron-withdrawing capacity of a... 

In spite of the known tendency of norbornene and related systems to undergo rearrangements of the Wagner-Meerwein type during eleetro-philic addition, no such rearrangement was observed when norbornene underwent cycloaddition with the acridizinium or the. A/ -methylenium benzamide cation. As Schmidt correctly pointed out, this lack of rearrangement is an argument for a concerted reaction. Alternatively, if the cycloaddition is nonsynchronous, the time interval between step 1 and step 2 must be very short. 

Change in the Rate of Cycloaddition Produced by Substitution at the Meso Positions of the Acridizinium Ion... 

Fig. 1. Plot of log hjk vs. o-constants for reaction of styrene with the acridizinium ion. See Westerman and Bradsher t by permission of American Chemical Society.

The three possible benzo derivatives of the quinolizinium ion are each well known (69ACR181), the benzo[a]- (2), benzo[6]- (acridizinium) (3) and benzo[c]-quinolizinium (4) ions. 

Evaluation of the UV-visible spectra has been used to demonstrate the formation of charge transfer complexes between the acridizinium (benzo[6]quinolizinium) ion and polycyclic aromatic hydrocarbons (78ZC33). Similar measurements have been employed to demonstrate the existence of an interaction between DNA and coralyne, a dibenzo[a,g]-quinolizinium salt (76JMC1261). 

The acridizinium (benzo[6]quinolizinium) ion, being isoelectronic with anthracene, is fluorescent (55JA4812). The fluorescent quantum yield for acridizinium perchlorate in methanol was reported to be 0.52 (80MI21000). The rate of quenching of this fluorescence by alkyl halides was found to be related to the ionization potential of the halide (78MI21001). Quenching by anions was also measured (79JPR420). 

The conductivity of anhydrous acridizinium (benzo[ lquinolizinium) bromide in the form of void-free plates has been reported to be 1.2 fl-1 cm- at 90 °C (68JA3120). It was believed that most of the current was carried by bromide ion either interstitially or through anion... 

The C-hydroxylation of benzoquinolizinium ions is easier and, although the position of the attack on benzo[a]quinolizinium (2) salts is not known, it has been demonstrated (67JOC733) that hydroxylation of the acridizinium (benzo[6]quinolizinium, 3) ion must occur at position 6 (Scheme 8). It was not possible to obtain a pure sample of the pseudobase (17) or the 2-(2-formylbenzyl)pyridine (18) in equilibrium with it, but oxidation of the mixture with ferricyanide afforded a small amount of benzo[Z>]quinolizinone (19) (62CI(L)1292), while reaction with hydroxylamine afforded a good yield of 2-(2.-pyridyl-methyl)benzaldoxime (20) (67JOC733). 

The simplest quinolizinium derivative which reacts with cyanide ion is the acridizinium ion (3) (58JCS3067,59JA1938) it gives an unstable product (Scheme 11) which was not isolated, but was dehydrogenated by bromine to afford what was believed to be the 6-cyanoacridizinium ion (23). 

With the benzo[Z>]quinolizinium (acridizinium) ion, ring opening has not been observed instead an unstable substance believed to be a piperidinylbenzoquinolizine was obtained (Scheme 14). 

It has been demonstrated (59JA1938) that the attack of phenylmagnesium bromide on acridizinium bromide (3) is at position 6, for oxidation afforded 2-(2-benzoylben-zoyl)pyridine (Scheme 16). 

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