The reaction of phenyl isoselenocyanate (1a) with malononitrile (= propanedinitrile) in DMF in the presence of Et3N leads to the intermediate ketene N,Se-hemiacetal 6a, which can be trapped with bromoacetonitrile or a-halogenated ketones 12a and 12b (Scheme 3). The products are [(alkylseleno)-(phenylamino)methylene]malononitriles 10 and 13, which are obtained in good yield. In the case of the (2-oxoalkyl)seleno derivatives 13, they are in equilibrium with the cyclic hemiacetals 14. Chemical and spectroscopic evidence for the structures of the new compounds are described. The structure of 14a was established by X-ray crystallography.