Novel heterocyclic systems. Part 28. Preparation and characterization of the 1,6-, 1,7-, 1,8-, and 1,9-diazaphenoxaselenines: an unexpected divergence between closely related sulphur and selenium systems

Abstract

Preparations are reported of the parent members of four new heterocyclic systems, the 1,6-, 1,7-, 1,8-, and 1,9-diazaphenoxaselenines. Whereas the reaction of the dianion of 3-hydroxypyridine-2(1H)thione with 2-chloro-3-nitropyridine gives only 1,9-diazaphenoxathiine, the corresponding reaction of the dianion of 3-hydroxypyridine-2(1H)-selone (4) gives a mixture of 1,6- and 1,9-diazaphenoxaselenines. Furthermore, the 1,6-isomer, presumably formed via a Smiles rearrangement which does not occur in the phenoxathiine series, predominates. Reaction of the dianion of (4) with 3-chloro-4-nitropyridine 1-oxide gives a mixture of the N-oxides of the 1,7- and 1,8-diazaphenoxaselenines, the 1,8-isomer predominating. This mixture is separated by flash-column chromatography and the individual isomers are reduced to their respective diazaphenoxaselenines with phosphorus trichloride.