THERMAL-ISOMERIZATION OF 4-AMINO-3-VINYLPYRIDINES - SYNTHESIS OF FUSED 1,6-NAPHTHYRIDINES AND UNEXPECTED NEW TERT-AMINO EFFECT CYCLIZATION TO AZEPINES

4-amino-3-(2,2-dicyanovinyl)pyridines react thermally in dimethylsulfo xide via [1.5] hydrogen transfer followed by carbon-carbon bond format ion to give hexahydro-1H-amino[1,2-a][1,6]naphthyridine derivatives. T he 4-piperazino, 4-morpholino- and 4-thiomorpholino-3-(2,2-dicyanoviny l)pyridines also lend themselves to the simultaneous formation of hexa hydro-1H-imidazolo[2,1-f]pyrido [4,3-b]azepine, hexahydro-1H-oxazolo[2 ,3-g] pyrido[4,3-b]azepine and hexahydro-1H-pyrido[3,4-f]thiazolo[3,2- a]azepine derivatives, respectively, by a new ''tert-amino effect'' ty pe of cyclization. A rational explanation for the new reactivity based on a neighboring-group mechanism is put forward.