Reactions of 4-(Diethylamino)selenet-2(2H)-imine with Nucleophiles - Synthesis of 2-Methylen-3-oxobutane Selenoamides

3-Acetyl-N-(4-bromophenyl)-4-(diethylamino)selenet-2(2H)-imine (5a), which is conveniently obtained from the formal [2+2] cycloaddition of 4-bromophenyl isoselenocyanate and 4-(diethylamino)-3-butyn-2-one, reacts with amines, alcohols, water, and thiophenol to give the corresponding 2-methylen-3-oxobutane selenoamides 7 in good yields via ring opening to the ketenimine 6 and subsequent addition of the nucleophile.