2- selenoamide, reaction with

Furyl)selenoamide, reaction with o-chioro-o-ethoxalyl acetate, 237... 

Selenienvl) selenoamide reaction with u-chloro-o-ethoxalyl acetate,... 

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. 

Reaction of aryl selenoamides 274 with a-arylsulfonyl-a-bromoacetophenone 276 gave compound 79 in 44 47% yield (Equation 35) <1999JHC901>. 

The most common reaction of selenolates is the nucleophilic substitution of halide compounds. For the synthesis of selenides 82 the selenolates 80 can be reacted with halides. Nucleophilic selenium species can also be reacted with a variety of other electrophilic compounds. The reaction with acid chlorides, chloroformates, or carbamoyl chlorides leads to the corresponding selenoesters 83 (R" = R ), selenocarbonates 83 (R" = OR ), or selenoamides 83 (R" = NR 2), respectively (Scheme 17).166... 

The reaction of aryl selenoketones [72], selenothioacetic acid S-esters [73], and iV -alkylidene selenoamides [74] with TONE and acetylenes having electron-withdrawing groups have been carried out to afford cyclic selenides 40-42 and acyclic selenides 43. 

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. 

Reactions of primary selenoamides with dimethyl acetylenedicarboxylate afford 5-methoxycarbonylmethylene-4,5-dihydro-l,3-selenazol-4-ones 75 (Equation 17). Reactions with acetylenedicarboxylic acid in ethanol give 4-ethoxy-4-hydroxy-5-carboxymethylene, 5 dihydro-l,3-selenazoles 76 (Equation 18) <2006JHC79>. 

Isoselenocyanates and selenoamides. Formamides are converted to isoseleno-cyanates by reaction with Se, EtjN, and phosgene in toluene. Selenoamides are obtained" from secondary amines, Se, and 1,1-dihaloalkanes in the presence of NaH in HMPA. An oxidation is involved. 

Retrocyclization of the 4/7-1,3-selenazine 145 can be carried out in refluxing dichloromethane to afford the vinylogous selenoamide 146 (Scheme 37) <1995TL237, 1998T2545>. Further reaction with dimethyl acetylene-dicarboxylate (DMAD) affords the 4/7-selenin 147. 

Selenazolone derivatives 126 have been prepared by the reaction of primary aromatic selenoamides 124 with haloacyl halides 125. 1,3-Selenazol-4-ones were the only products obtained, the isomeric 1,3-scleno-5-oncs were not observed as determined by Se- C coupling constants. The formation of 126 is explained by initial amide bond formation followed by ring closure. When aliphatic selenoamides were used as substrates only decomposition products were obtained <01S731>. 

Displacement of Sulphur. The Wittig reaction of resonance-stabilized phosphorus ylides with thioacyl-urethanes gives acylated enamines, e.g. (84), from which )ff-keto-esters are obtained by hydrolysis. Hydrazine displaces sulphur in thioanilides, giving amidrazones, but with two equivalents of arylselenoamides it gives 2,5-diaryl-1,3,4-selenadiazoles. Selenoamides react with an excess of hydrazine to give 1,2,4,5-tetrazines (see also Chap. 6, p. 294). l,2-Bis(thio-benzamido)ethane, when treated with NEt, and HgO, cyclizes to 2-phenyl-... 

In two patents,the preparation of thioether-substituted selena-zoles of the general formula (6) have been described. These are stated to be formed by reaction of halogenoketothioethers with selenoamide components selenoacetamide, selenobenzamide, and A -ethylseleno-urea are given as examples. The resulting selenazoles were not further characterized. They are stated to be starting materials for the preparation of cyanine dyestuffs which are useful photographically. 

Pyrryl)selenazole is protected for the same purpose, by another patent. This is stated to be prepared from 2-chloroacetyl-pyrrole with selenoamides by analogy with the corresponding thiazole. No concrete example of the reaction is given. 

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... 

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