Carbamoyl diselenides

An isocyanate intermediate may also be involved in the selenium-catalyzed process, which starts with the formation of carbonyl selenide from the reaction between selenium and CO, followed by nucleophilic attack by NuH (Scheme 28). When NuH = primary amine, the resulting RNH(CO)SeH intermediate may eliminate H2Se to give the isocyanate, which then reacts with Nu H to give the final product (Scheme 28, path a). Alternatively, oxidation of Nu(CO)SeH by 02 may lead to a bis(carbamoyl)diselenide species, which is attacked by NuH (Scheme 28, path b). 

When 59 or 60 are treated with a reducing agent such as hydrazine or triphenyl-phosphine, the Se-N bond is cleaved to give 2-(carbamoyl)phenyl diselenides [92], The ring cleavage with thiols leads to the selenosulfides [10, 97],... 

Another preparative route for synthesis of benzisoselenazol-3(27/)-ones is based on the lithiation of the benzamides, followed by the conversion of dilithium derivatives by direct treatment with selenium, or via 2-[(carbamoyl)phenyl]methyl selenides or 2,2 -bis[(carbamoyl)phenyl] diselenides [167-172], These diselenides are oxidatively cyclized and, depending on the oxidant used, benzisoselenazol-3 (2H)-ones or their 1-oxides are produced in high yields [92, 173],... 

Oxidation catalyst. These compounds (1), as well as bis(2-carbamoyl)phenyl diselenides, are very effective catalysts for the oxidation of sulfides, dimethylhydrazones (to nitriles), and azines (to carbonyl comjwunds). 

In 1994, successful isolations of various alkyl and aryl selenocarboxylic acids [14] enabled them to undergo exact reactions. Reactions of selenocarboxylic acids with dicyclohexylcarbodiimide (DCC) yield the corresponding diacyl selenides 25 and selenourea 26 quantitatively (Scheme 15) [14], as in reactions of thio- [44] and dithiocarboxylic acids [45,46]. In air,selenocarboxylic acids are immediately oxidized to afford the corresponding diacyl diselenides [13, 14]. Also, thio- and dithio-carboxylic acids readily react with aryl isocyanates to give acyl carbamoyl [47,48] and thioacyl carbamoyl sulfides [49, 50], respectively. 

---