Studies on ketene and its derivative. LXXV. Reaction of diketene with N-benzylacetimidate and lactim ethers to give 1,6-naphthyridine derivatives

Reaction of diketene with ethyl N-benzylacetimidate (Ia) in acetic acid gave 3-acetyl-1, 6-dibenzyl-4, 7-dimethyl-1H, 6H-1, 6-naphthyridine-2, 5-dione (IIa) in 51% yield. Similarly lactim ethers such as 2-methoxy-1-pyrroline (Ib), 2-methoxy-3, 4, 5, 6-tetrahydropyridine (Ic), and 2-methoxy-3, 4, 5, 6-tetrahydro-7H-azepine (Id) gave the corresponding 5-acetyl-6-methyl-4, 7-dioxo-1, 2, 10, 11-tetrahydro-4H, 7H, 9H-dipyrrolo[1, 2-g : 3', 2', 1'-tj]-1, 6-naphthyridine (IIb) (35%), 6-acetyl-7-methyl-5, 8-dioxo-2, 3, 10, 11, 12, 13-hexahydro-1H, 5H, 8H-quinolizino[1, 9-ab]quinolizine (IIc) (66%), and 7-acetyl-8-methyl-6, 9-dioxo-1, 2, 3, 4, 12, 13, 14, 15-octahydro-6H, 9H, 11H-bisazepino[1, 2-g : 3', 2', 1'-tj]-1, 6-naphthyridine (IId) (40%). Treatment of IIa-d with KOH in EtOH resulted in the formation of the deacetylated derivatives IIIa-d.