Naphthyridines from Other Heterocyclic Substrates

Several heterocyclic systems other than pyridine have been used as substrates for the primary synthesis of 2,6-naphthyridines. The procedures are illustrated in the following examples. 

6- Diisopropyl-l,6-diazacyclodeca-3,8-diyne (20) gave 2,6-diisopropyl-4-methoxy-l,2,3,5,6,7-hexahydro-2,6-naphthyridine (21) (MeOH, 140°C, sealed 45%) also related syntheses.684,cf 580 

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The primary synthesis of 1,5-naphthyridines may be accomplished by double cyclization of appropriate aliphatic substrates by cyclization of appropriately substituted pyridines by cyclocondensation of pyridine substrates with one or more aliphatic synthons or from other heterocyclic substrates by degradation, rearrangement, or the like. Partially or fully reduced 1,5-naphthyridines are often made by somewhat similar procedures such cases are usually illustrated toward the end of each subsection. Some reviews of naphthyridine chemistry contain material on the primary synthesis of 1,5-naphthyridines49 52 61 231 265 670 1260 1273 1430 1432... 

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. 

Like the primary syntheses of other naphthyridines, the primary synthesis of 1,8-naphthyridines may be done by cyclization of appropriate aliphatic substrates, with or without auxiliary synthons, by cyclization of appropriately substituted pyridines with or without synthons, or from other heterocyclic substrates by several processes. 

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