Syntheses Giving Quinolizones and Quinolizine Imines

Syntheses of 2-quinolizones are given first, then 4-quinolizones and 4-quinolizine imines, and finally hydroxyquinolizones. 

Pyridinium dicyanomethylide reacts with diphenylcyclopropenone to give the 2-quinolizone 33 (Eq. 15).23 Other syntheses of 2-quinolizones start from 2-cyanomethyl- or 2-alkoxycarbonylmethylpyridines, which react with diketene (Eq. 16),24,25 or acetylene dicarboxylate (Eq. 17).17,26 The reaction 

In all cases one of the groups R2 or R3 in Eq. (19) has been an ester, and in most cases the ester group cyclizes on to the pyridine nitrogen atom. However, cyclization of a nitrile can give a quinolizine imine (Eq. 20). In an example where ethyl ethoxymethylene cyanoacetate was used32 the formation of imine was favored at —10° but not at higher temperatures where 4-quinolizone becomes the major product. Examples of the reaction (Eq. 20) have been reported where R1 was a nitrile,32,35 ester,32,35,36 or ketone 

Maseda, Y. Tominaga, R. Natsuki, Y. Matsuda, and G. Kobayashi, Chem. Pharni. Bull. 22, 1424 (1974). 

Tanaka, Chem. Pharm. Bull. 22, 744 (1974). 

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