Syntheses Giving Di- or Tetrahydroquinolizinium Salts

In many syntheses the cyclization product is a di- or tetrahydroquinolizinium salt, usually with some group which can be subsequently eliminated to give the fully aromatic system. To this category belong the first reported synthesis of the parent quinolizinium salts13 and a more recent variant (Eq. 9).14 Both these routes, and the route to 1-substituted quinolizinium 

Carelli et al,15 have described a variant of the Westphal, Jann, and Heffe procedure8 using ketomalonate (Eq. 11), in which the intermediate alcohol 22 is isolated. Further treatment with stronger base causes hydrolysis and dehydration to give the quinolizinium betaine 23. 

A large number of cycloaddition reactions between pyridine or its derivatives and acetylenic esters have been reported, and in many cases these 

The other major route from hydroquinolizinium salts is the aromatization of l-keto-l,2,3,4-tetrahydroquinolizinium salts, discovered by Glover and 

Jones19,20 (Eq. 14). Miyadera and Iwai reported an alternative route to the cyclic ketones 28, which allows of the introduction of a substituent by alkylation of the keto lactone 2721 Hough and Jones22 subsequently showed that ketone 26 could be alkylated by reactive halides (for example, allyl bromide, giving eventually 2-n-propylquinolizinium bromide). 

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