Science of Synthesis

Braverman, S.; Cherkinsky, M.; Birsa, M. L., Science of Synthesis, (2005) 18, 254.

In some early work, it was proposed that the formation of selenoureas from carbon diselenide and primary amines proceeds through the intermediacy of the corresponding diselenocarbamates and isoselenocyanates.[‌1110‌] Later, this method was developed into a satisfactory preparative procedure. Alkylammonium N-alkyldiselenocarbamates ‌556‌, readily prepared from primary amines and carbon diselenide in petroleum ether, when treated with an electrophilic agent, followed by a weak base, undergo cleavage to the corresponding isoselenocyanates (‌Scheme 279‌).[‌1104‌] Lead(IV) nitrate–sodium bicarbonate, ethyl chloroformate–alumina, or tosyl chloride–sodium carbonate can be used as typical reagents. However, the application of the above two-step procedure is confined to amines that are more nucleophilic than the resultant diselenocarbamate ion. Otherwise, a side reaction between ‌556‌ and carbon diselenide becomes the main reaction path. A one-pot modification, free of these restrictions, involves the formation of a 1:1 adduct of a primary amine and mercury(II) chloride in an inert solvent and the reaction of this complex with carbon diselenide in the presence of triethylamine to give the isoselenocyanates ‌557‌ (‌Scheme 279‌).[‌1109‌] Mercury(II) chloride is an efficient trap for any diselenocarbamate formed and thus prevents further reaction of ‌557‌ with carbon diselenide. At the same time, it acts as an electrophilic catalyst, which is necessary for the cleavage step. The reaction is usually carried out in acetonitrile (Method A) for aryl isoselenocyanates and in dichloromethane in the case of low-boiling alkyl isoselenocyanates with C1–C4 groups (Method B).

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