The thermocyclisation of phenylenediamine-bis (methylene Meldrum's acid) derivatives has been investigated. Those of o-phenylenediamines give 1, 10-phenanthroline derivatives, while those of m-and p-phenylenediamines lead to the preferential formation of angular diazatricycles. Thus, for example, the di-Meldrum's acid derivative of 2, 5-dichloro-1, 4- phenylenediamine gives, via ipso-substitution, the unexpected angular product 19.
![5-[[2-[(2,2-dimethyl-4,6-dioxo-1,3-dioxan-5-ylidene)methylamino]anilino]methylidene]-2,2-dimethyl-1,3-dioxane-4,6-dione Structure](https://image.chemsrc.com/caspic/471/503863-91-0.png)