Benzo quinolizinium salts synthesis

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)...

Only two syntheses of benzo[c]quinolizinium salts were available at the time of Bradsher s52 review. These are shown in Eqs. (36 and 37). A variation of the Fozard and Bradsher synthesis was provided by cyclization of the imine 68, or the ketone 69, to give, respectively, 6-amino- or 6-hydroxybenzo-[c]quinolizinium salts in good overall yield.82 Dimroth and Odenwaelder83 heated pyrylium salts with o-aminobenzaldehyde to give alkyl and arylbenzo-[c]quinolizinium salts (Eq. 38), probably via the pyridinium salts. This... 

The cyclodehydration method used for the synthesis of benzo[a jquinolizinium ion and its congeners (Scheme 97) requires that phenylpyridines (176) (including benzo analogs) be converted into quaternary salts (177) by the action of a -halo ketones or a -halo aldehyde derivatives. The acid-catalyzed cyclization of these salts (177) has provided access to a number of compounds containing the benzo[a]quinolizinium system (178) (Table 8). 

The first synthesis of the benzo[6]quinolizinium ion (Scheme 98, Table 9, example 1) was by hydrobromic acid-catalyzed cyclization of the quaternary salt formed between 2-pyridinecarbaldehyde and benzyl bromide. Aromatic cyclodehydration has continued to the present as almost the only method used for the preparation of the acridizinium ion, its derivatives and benzo analogs. Because of its instability, 2-pyridinecarboxaldehyde has been replaced by more efficient derivatives. The first of these was the oxime (example 2) which not only gave a better overall yield, but also made possible the isolation of a crystalline intermediate (181 Z = NOH). The disadvantages are that it is not suitable for high temperature cyclizations involving polyphosphoric acid, and some products (182) (e.g. example 10, Table 10) may tend to form double salts with hydroxylamine hydrobromide. 

Benzo[(i]quinolines, 1,2,3,4,4a,5,6,1 Ob-octahydro-, stereoisomers, 57, 57 Benzoquinolizinium (ions/salts) reactivity indexes, 55, 344 reactivity with nucleophiles, 55, 346 Benzo[a]quinolizinium (ions/salts) calculated electron densities, 55, 275 calculated electronic spectrum, 55, 324 nitration, 55, 342 synthesis, 55, 282 Benzo[a]quinolizinium (ions),... 

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