10-Cyanotetrahydrobenzo[ b][1,6]naphthyridines 3 , 4 undergo addition of DMAD, followed by a Stevens rearrangement of the intermediate ylide to yield methyl dioates 8 and 9 . An alternative transformation sequence starts with migration of the dimethyl butenedioate anion to the carbon of the CN group, followed by the addition of 1 mol of water, to provide succinates 10 and 11 . In contrast, tetrahydropyrido[4,3- b]pyrimidines 5– 7 undergo a tandem cleavage process, involving one molecule of solvent. The resulting enamines are easily cleaved by strong acids, to give dihydropyrymidinylethylamines, which are scarcely available by other synthetic means.