From a Pyridine Substrate with One Synthon

3-[(3-Hydroxy-2-methyl-3-phenylpropyl)amino]pyridine (24) underwent dehy-drative cyclization to give 3-methyl-4-phenyl-l,2,3,4-tetrahydro-l,5-naphthyridine (25) (70% H2S04, 0°C — 25°C, 15h 65%) that was easily dehydrogenated to give 3-methyl-4-phenyl-l,5-naphthyridine (26) (neat substrate, Pd/C, 200°C, 3 h 56%).879 Also other examples.48 485 865 967 1232 1245 

Most primary syntheses of 1,5-naphthyridines fall into this basket. Procedures are divided initially into categories in which the synthon provides one, two, or three atoms to the final 1,5-naphthyridine when necessary, such categories are further subdivided according to which specific atoms are provided by the synthon. 

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The primary synthesis of 1,6-naphthyridines has been accomplished by condensation of two or more aliphatic substrates by cycbzation of a single pyridine substrate by condensation of a pyridine substrate with an aliphatic synthon that provides one, two, three, or even four ring atoms by condensation of a pyridine substrate with two or more synthons or from other heterocyclic substrates by degradation, rearrangement, or other elaborative processes. 

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