Syntheses of Benzoquinolizones and Imines

In principle, most of the syntheses of quinolizones could be applied to the synthesis of benzoquinolizones by starting with the quinoline or isoquinoline equivalent of the pyridine component. Thus Kappe84 has obtained the hydroxybenzo[ ]quinolizin-4-ones 70, and the hydroxybenzo[c]quino-lizin-l-ones 71 from methylquinolines, quinolyl- or isoquinolylacetates, and malonic esters or carbon suboxide. Kato and co-workers37-38 have used the Vilsmeier derivatives of 2-quinolylacetate with diketene (Eq. 39)37 or with anhydrides (Eq. 40)38 to give benzo[e]quinolizin-l-ones. 

A photochemical route to benzo[u]quinolizin-4-ones (73) from 1-styryl-2-pyridones has been reported by Mariano et al.8S Acid was found to be essential and the cyclization was thought to proceed through the excited enol 72, with eventual oxidation by air or by added iodine. Benzo[b]-quinolizin-6-one (74)76 and the corresponding imine (75)86 have been prepared by cyclization of 2-(2-carboxybenzyl)pyridine and 2-cyanobenzyl-pyridine, respectively. Eicher and Hansen87 have reported two routes to a benzo[c]quinolizin-l-one (76) (Eqs. 41 and 42) and one to the 1-thione 77 (Eq. 41). Treatment of quinoline N-oxide with 1,1-dicyanoalkenes also led to benzo[c]quinolizin-l-ones (Eq. 43),88 while the same A-oxide with the sulfur ylid 78 gave a benzo[c]quinolizin-3-one.89 

Watanabe, M. Kodera, T. Kinoshita, and S. Furukawa, Chem. Pharm. Bull. 23, 2598 (1975). 

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