4- Substituted benzo naphthyridines

Dehydrogenation of 5,6-dihydro derivatives of 2,7-naphthyridines 339, prepared by the addition of organolithium compounds to 4-substituted benzo[c][2,7]nap-hthyridines 340, afforded naphthyridines 341 (1995JCS(P1)979). 

Thermal isomerization of l//-pyrimido[l,2-a]quinolin-l-ones (185) into benzo(6)-l,8-napthyridin-4(li/)-ones (186) (94AJC1263), did not occur whereas 6-substituted 4//-pyrido[l,2-a]pyrimidin-4-ones gave 1,8-naphthyridin-4( l//)-ones [77JCS(P1)789]. 

The UV spectral parameters of six isomeric formyl-substituted 4,6-benzo-l,5-and -1,6-naphthyridines were calculated (1998MI5). 

The treatment of 2,5-dichloro-3,6-dihydroxycyclohexa-2,5-diene-l,4-dione 269 with 2-substituted-l,8-naphthyr-idine-3-carboxylic acid hydrazides 270 in ethanol under reflux resulted in the formation of 3,8-di(2-substituted-l,8-naphthyridin-3-yl)benzo(l,2-r 4,5- )bis[l,3,4]oxadiazine-5,10[l//,6//]diones 271 <2000IJH311> (Equation 42). 

Oxazoles readily participate in cycloaddition reactions as dienophiles and as dienes in Diels-Alder reactions, and suitably substituted oxazoles participate in sigmatropic rearrangements (e.g., aza-Claisen rearrangements). In particular, the Diels-Alder reaction of oxazoles is one of the most widely explored and synthetically useful reactions, and as such, it has been used extensively both in natural product syntheses and to convert oxazoles to other heterocyclic ring systems. For example, a partial list of heterocyclic systems readily accessible from oxazoles via Diels-Alder reactions or other cycloadditions include pyridines hydroxy-pyridines isoindoles pyridazines tetrahydronaphthyridines benzo[h]-l,6-naphthyridines benzopyrano[3,4-b]pyridines 2-substituted, 2,4-disubstituted,... 

Later, Tu and coworkers [57] reported domino synthesis of furo[3,4-h][l, Sjnaphthyridines 93 through three-component reactions of aldehydes 69, 2-aminoprop-l-ene-l,l,3-tricarbonitrile 29, and N-substituted 4-aminofuran-2(5H)-ones 57 in EtOH using EtONa as a base (Scheme 12.36). N-substituted 3-aminocyclohex-2-enones were also suitable for this domino reaction, affording 21 examples of benzo[h][l,8]naphthyridines in 69-84% chemical yield, with the concomitant formation of two new pyridine rings. 

SCHEME 4 Regioselective homolytic substitution of benzo[c][2,7]naphthyridines. 

A. Plodek, S. Raeder, F. Bracher, Regioselective homolytic substitution of benzo[c][2,7]naphthyridines. Tetrahedron 68 (2012) 4693-4700. 

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