Benzo quinolizinium salts

Up to 1967 benzo[ ]quinolizinium salts could be made by the general methods shown in Eqs. (28-32). Two syntheses of benzo[a]quinolizinium... 

An example of this displacement between a pyridine nitrogen atom and an aryl halide is shown in Scheme 21. When 2-pyridyl acetates 138 were C-acylated with 2-halobenzoyl chlorides, the enolized products 139 resulting from the reaction suffered an intramolecular nucleophilic attack of the pyridine nitrogen atom onto the ipso-position to give benzo[c]quinolizinium salts 140 as intermediates. Loss of HC1 gas from 140 afforded benzo[c]quinolizine derivatives 141 <2002JOC2082>. 

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 reduction of a crude 4-chlorobenzo[a]quinolizinium salt by action of zinc and acetic acid made possible the transformation of benzo[a]quinolizin-4-one to benzo[a]quin-olizinium perchlorate (2) in an overall yield of 75.5% (Scheme 63) (77JOC1122). 

In a reinvestigation of earlier work (33LA(505)103) by Diels and Alder, Acheson et al. (60JCS1691) established that the stable isomer obtained by addition of two moles of dimethyl acetylenedicarboxylate to one of pyridine was the 4/7-quinolizine (96) and that this with bromine was oxidized to a quinolizinium salt (97 Scheme 65). 4iT-Quinolizines obtained from isoquinoline (62JCS748) and phenanthridine (63JCS3888) were similarly aromatized to afford benzo[a]quinolizinium (98) and dibenzo[a,c]quinolizinium ions (99) respectively. 

As part of a study of the properties of the easily prepared salts (154 Scheme 89) (61JOC4944), it was discovered that their exposure to hydrogen peroxide in acetic acid followed by warming led to ring contraction and loss of sulfur, with formation of benzo[a]quinolizinium salts. Present evidence (62JOC4475, 66JOC978) indicates that the extrusion of sulfur occurs after the salt has been oxidized to the sulfoxide level. Despite the modest yields (Table 5), this ring contraction has preparative potential as well as theoretical interest. The variety of arenethiols (150) and 2-bromopyridines (151) available makes a variety of substituted 2-phenylthiopyridines (152) accessible as intermediates. 

Table 6 Benzo[a]quinolizinium Salts by Irradiation of Styrylpyridinium Salts (Scheme...

Table 8 Synthesis of Benzo[a]quinolizinium Salts (178) by Cyclization of Quaternary Salts (177) Derived from 2-Phenylpyridine (176) and its Congeners (Scheme 97)...

The cycloaddition of ketene diethyl acetal to benzo[6]quinolizinium salt 247, followed by hydrolysis and thermolysis, gave over-crowded 1-pyridyl-8-rerf-butylnaphthalene 248. The naphthalene 248 was oxidized electro-chemically or with anhydrous CuCl2 to afford azoniafluoranthene salt 249,... 

Benzo[ ]quinolizinium 297 with a fused indole ring was synthesized (17%) by the cyclodehydration of the quaternary salt 296, obtained (95%) from 1-phenylpyridoindole 295 and bromoacetone (64JHC168). 

Substituent Effect on Absorption Spectra of Benzo[6]quinolizinium Salts... 

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