Stabilisation of condensed selenium heterocycles by a nitro group in the ortho-position to the chalcogen.

The synthesis of the 7-nitro-2-phenyl-1,2-benzisoselenazol-3(2H)-one 3a leads to an abnormal behavior due to a dipole stabilisation between the nitro group and the selenium atom. The first ever synthesis of a 2,1-benzoxasetenol-3-one 5is described. The unexpected insertion of a sulfur atom from thionyl chloride results in the formation of the 7-nitro-2,1-benzothiaselenol-3-one 6.