Selenoamides and Selenoureas

Reports regarding selenoamides and selenoureas are less than the corresponding thioamides, thioureas, amides and ureas because of instability of compounds including selenium atom and their difficulty in the preparation. Recently, preparation methods to overcome some difficulties have been developed. Their reactions, preparation, application to heterocycles or biological assay systems have been actively investigated. 

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Selenoureas are prepared by reaction of isoselenocyanates with amines, or by reaction of carbodiimides with a mixture of LiAlH4/Se and by reaction of cyanamides with LiAlH4/Se.267 272 The tyrosinase inhibitory activity and superoxide radical scavenger effect of selenoamides and selenoureas have been investigated (Scheme 84).273 275... 

Reactions of selenoamides and selenoureas with aldehydes or ketones proceed via a nucleophilic attack of the selenium atom and lead to the formation of selenium- and nitrogen-containing heterocycles.419-424 The reaction of selenourea with 1,3-dicarbonyl compounds in the presence of potassium hydroxide leads to the formation of selenouracil 212 425 its biological activity has also been tested (Scheme 65).426... 

The reaction of selenoamides and selenourea with aldehydes and ketones has been known to take place via the nucleophilic attack of the selenium atom and end up in the formation of a variety of selenium- and nitrogen-containing heterocycles [99]. For example, selenourea was treated with j0-keto ester in the presence of KOH to give selenouracil (Eq. 27) [100], and its biological activity has been tested [100b]. Very recently, Lewis acid mediated addition of primary selenoamides to a, -unsaturated ketones has been reported to give 1,3-selena-zines (Eq. 28) [99 f]. 

S-Butyl selenothioacetate serves as a 1,3-dipolarophile [23]. Therefore, the azo-methine ylide 78, generated by the thermolysis of oxazolidinone 79, was trapped with the selenothioacetate to give the cycloadduct 80 as a 1 1 mixture of stereoisomers with a 45% yield (Scheme 9). Similar reactions took place when se-lenoketones and 0-methyl selenobenzoate were used as 1,3-dipolarophiles. However, S -methyl diselenobenzoate, selenoamides, and selenourea failed to give the corresponding cycloadducts. 

Selenazole and selenazine derivatives are obtained by reaction of selenoamide or selenourea with nucleophiles.276... 

The alkylation and acylation of the selenium atom of selenoamides [89], selenourea [90], l,3-dithia-2-selones, or l,3-diselena-2-selones [91] with alky-... 

The condensation of two molecules of primary selenoamides proceeds with bromine under extrusion of selenium to give selenadiazoles [93]. The reaction of selenocarbonates, selenothiocarbonates [94], and selenourea [95] with bromine and iodine has been widely tested. The products depend on the amount of halogen used. For example, in the reaction of N-methylthiazoline-2(3H)-selone, the use of one equivalent of bromine gives hypervalent lO-Se-3 complexes 44, whereas two equivalents of bromine cleave the carbon selenium double bond to give product 45. A similar hypervalent compound is formed from 4-imidazolin-2-selone,but the iodination of bis(imidazolin-2-selone)methane gives iodinated product 46. The availability of some of halogen adducts has been tested as a conducting material. 

Amides such as DMF or ureas such as N,N-tetramethylurea react with bis(trimethylsilyl)selenide 604 in the presence of BF3-OEt2 to give selenoamides, for example 617, or selenoureas whereas esters such as n-butyl benzoate react with 604 in the presence of Bp3-Et20 and 2,3-dimethylbutadiene to give 619 via 618 [157]. On heating with P4Sio/sulfur and hexamethyldisiloxane 7 y9-ketoesters such as ethyl acetoacetate are converted to 3H-l,2-dithiole-3-thiones such as 620 in high yields [158] (Scheme 5.51 cf. also Section 8.6). 

In the presence of Et20-B] 3. (Me3Si)2Se reacts with nitriles to give selenoamides while cyanates give the selenourea. Amides and tetramethylurea behave similarly, but the reaction with benzoates gives benzoin and 2,3,5,6-tetraphenyl-l,4-diselenin via selenoesters. These selenoesters can be trapped as conjugated diene cycloadducts (Scheme 5)78. 

Various other complexes have been formed by reacting selenourea or selenoamides with the corresponding metal halides or metal carbonyl compounds, such as Cu,432 Ag, Au,433,434 Zn, Cd,435,436 Co,437 and Cr, Mo, W.438 Metal complexes of type 214 are also quite well known and such complexes have been characterized by various analytical techniques.439,440 The electric conductivity of complexes 215 is especially interesting and many of these compounds have been prepared and their properties studied.441,442... 

Alternatively, the reaction of isolated selenocarbonyl compounds with transition metal complexes has been applied to the synthesis of metal complexes of type 53. The complexation of furanselenoamides and thiopheneselenoamides to Pd, Rh, and Ru halides is accompanied with cyclometallization (Eq. 30) [111]. The formation of Cu [112a], Ag, Au [112b,c], Zn, Cd [113], Co [114], Cr, Mo, and W [115] complexes has been attained by reacting selenourea or selenoamides with the corresponding metal halides or metal carbonyls. 

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