Naphthyridine and Alkyl-2,6-Naphthyridines

6-Methyl-3,7-diphenyl-l//-pyrano[4,3-c]pyridine-l,5(6//)-dione (22) gave 2,6-dimethyl-3,7-diphenyl-2,6-naphthyridine-1,5(2//,6//)-dione (23) (Me NIL/ MeOH, 20°C 86%),914 analysis.788 

4- Dibenzoyl-1-methyl-2,4-diphenylpyrrole with benzylamine has been reported to afford a separable mixture of hexaphenyl-2,6- and hexaphenyl-2,7-naphthyridine (KOH, EtOH, reflux 29% and 41%, respectively) by an obscure pathway. The original paper should be consulted for details of this 

Ethyl l,2,4-triazine-3-carboxylate (25) underwent a Diels-Alder reaction with ferf-butyl 4-(pyrrolidin-1 -yl)-1,2,3,4-tetrahydropyridine-1 -carboxylate (24) to give ethyl 6-ferf-butoxycarbonyl-5,6,7,8-tetrahydro-2,6-naphthyridine-l-carboxylate (26) as a minor product (CHC13, 20°C 8%).941 

Despite a general paucity of information on 2,6-naphthyridines, the system has been included in several reviews 50-52 57 58 61,265,436,1357 1430 1432 4-methyl-2,6-naphthyridine has been found to occur naturally in several Antirrhina species,226 241 267 and physical properties of the parent heterocycle (1) have been quite extensively studied, usually for comparison with those of the other unsubstituted naphthyridines (see Section 29.2.2). 

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