Hydrogen selenide reaction with nitriles

Thus a second method was envisaged, the reaction of a nitrile, hydrogen selenide, and an a-halogenated ketone in the presence of a condensation catalyst, which can be POCl, or POCI3 with a Lewis acid such as PCI3 or anhydrous ZnCl. The use of fresh AICI3 leads to the formation of tarry side-products. 

The comparatively ready accessibility of selenocarboxamides has encouraged the use of this procedure for the synthesis of selenazoles (1889LA(250)294). Reaction of the a-chloro-carbonyl compound (73) with the selenocarboxamide (74) provided a ready synthesis of a variety of substituted selenazoles (75). Useful variations of this general procedure are described in detail in Chapter 4.20, and particularly attractive is the reaction of hydrogen selenide with a mixture of a nitrile and the a-halogenoketone to afford the selenazole (48YZ191, 79S66). 

Primary selenoamides are prepared by reaction of nitriles with appropriate selenating reagent, such as phosphorus (V) selenide (P2Se5), hydrogen selenide (H2Se), Al2Se3, NaSeH, trw(trimethylsilyl)monoselenophosphate or potassium selenobenzoate (Scheme 81).248 252... 

In Older to avoid the handling of poisonous hydrogen selenide, two other useful syntheses have been devised. One method uses the reaction of aromatic nitriles with aluminum selenide in the presence of pyridine, triethylamine and water (Scheme 24), while the other is performed by the reaction of nitriles with selenium, carbon monoxide and water in the presence of triethylamine (Scheme 25). These methods are exceedingly convenient in terms of manipulation without the isolation of hydrogen selenide for the preparation of selenoamides. Using these methods, a variety of aromatic and heterocyclic selenoamides can be obtained from the corresponding nitriles in high yields. 

A seemingly straightforward method to prepare aromatic selenoamides (451) is to react the corresponding nitrile (450) with elemental selenium in aqueous THF containing Et N under 5 atm of carbon monoxide.Presumably the key reagent is hydrogen selenide formed in a water-gas shift reaction the method is unfortunately much less efficient when applied to aliphatic nitriles. 

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