Acetals of lactams and acid amides. 39. Synthesis of three-ring derivatives of pyrido [l,2-a] pyrimidines on the basis of the reaction of dimethylformamide acetal with dicyanomethylenecycloalkanes

New synthesis of benzo[b][1,6]naphthyridines and pyrido[4,3-b]benz[f]azepines from lactim ethers of 3,4-dihydrocarbostyril and 1H-2,3,4,5-tetrahydrobenz[b]azepin-2-one

“…Indeed, compound 1 does not react with dimethylformamide diethyl acetal (2) either in boiling ethanol, benzene, or toluene (oxindole reacts with ac etal 2 at room temperature) or with AlCl 3 as a catalyst. 2 Only when refluxing lactam 1 in excess acetal 2 for 5 h in the presence of catalytic amounts of piperidine, we obtained 3 dimethylaminomethylidene derivative 3 in low yield (22%) (Scheme 1). The catalytic effect of pi peridine is associated with the formation of intermediate N,O acetal 4.…”