Preparation of the Carbaldehydes and Ketones

One or both of these carbonyl entities has (have) been made by primary synthesis (see Chapter 22), by oxidation of alkyl-1,8-naphthyridines (see Section 23.2.2), or by the procedures illustrated in the following examples. 

4-Hydroxy-l,8-naphthyridin-2( 1 //)-one (37, R = H) gave 4-hydroxy-2-oxo-l, 2-dihydro-l,8-naphthyridine-3-carbaldehyde (37, R = CHO) (POCI3, Me2NCHO %).1281 

7-Dimethyl-2,3-dihydro-1,8-naphthyiidin-4(l//)-one (38) gave its 3-hydroxy-methylene derivative (39) (Et02CH, NaOEt, PhH, 20°C 81%) that underwent oxidation in refluxing benzene to afford l,7-dimethyl-4-oxo-l,4-dihydro-l,8-naphthyridine-3-carbaldehyde (40) as the main product ( 45%).1394 

Ethyl 7-chloro-l-cyclopropyl-6-fluoro-4-oxo-5-trimethylsilyl- (41, R=SiMe3) gave ethyl 7-chloro-1 -cyclopropyl-6-fluoro-5-formyl-4-oxo-1,4-dihydro-1,8-naphthyridine-3-carboxylate (41, R=CHO) (POCl3, Me2NCHO, o-C 12C6H4, 90°C 24%).1172 

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