Aryl diselenides

Aryl diselenides can be prepared directly by treatment of aryl chlorides with NaSeCH, in refluxing HMPT. ... 

Diselenides are generally prepared by the aerial oxidation of selenols or selenolates (see Section 2) or by the reaction of Li2Sc2, Na2Se2, or other 802 species with alkyl or aryl halides. In the latter case, elevated temperatures and DMF as the solvent are recommended. Aryl diselenides may also be obtained from the reaction of 802 with diazonium salts (Scheme 6). Relatively few unsymmetrical diselenides have been reported. Triselenides are also known but have not been as widely studied. 

Aryl diselenides are similarly cleaved to selenols (ArSeH) with Cp2TiH followed by Ph2l+X . ... 

On the other hand, good yields of tetraselenated products have been obtained (87JOC3444) by treatment of 16 with four equivalents of dialkyl (aryl) diselenides. Analogous reactions with dialkyl(aryl) disulfides are also satisfactory, but it was reported in the same paper that the reaction... 

Finally, a,p-unsaturated aldehydes are converted into vinyl formates, when treated with hydroperoxides [186]. Catalytic quantities of aryl diselenides catalyze this oxidation [Eq. (10)]. 

Aryl diselenides (see Selenium, under Section 9.2.1.4) in combination with hydrogen peroxide are also attractive catalysts for Baeyer-Villiger reactions [333]. 

The analogous trifluoromethylseleno and pentafluorophenylseleno copper compounds are prepared via reaction of the corresponding diselenide with copper metal [265, 269] Coupling with aryl iodides gives the arylselenium denvative [265] (equation 185)... 

Aryl trimethylsilylmethyl selenides also yielded the diaryl diselenide as the major product, but possibly through a somewhat different mechanism, due to the increased stability of the initially formed radical cation (Fig. 31) ... 

Photolysis at room temperature of aryl telluroformates gives rise to oxoacyl radicals, which can be trapped with diphenyl diselenides giving the corresponding phenyl seleno-formates. ... 

Crich and Rumthao reported a new synthesis of carbazomycin B using a benzeneselenol-catalyzed, stannane-mediated addition of an aryl radical to the functionalized iodocarbamate 835, followed by cyclization and dehydrogenative aromatization (622). The iodocarbamate 835 required for the key radical reaction was obtained from the nitrophenol 784 (609) (see Scheme 5.85). lodination of 784, followed by acetylation, afforded 3,4-dimethyl-6-iodo-2-methoxy-5-nitrophenyl acetate 834. Reduction of 834 with iron and ferric chloride in acetic acid, followed by reaction with methyl chloroformate, led to the iodocarbamate 835. Reaction of 835 and diphenyl diselenide in refluxing benzene with tributyltin hydride and azobisisobutyronitrile (AIBN) gave the adduct 836 in 40% yield, along with 8% of the recovered substrate and 12% of the deiodinated carbamate 837. Treatment of 836 with phenylselenenyl bromide in dichloromethane afforded the phenylselenenyltetrahydrocarbazole 838. Oxidative... 

For the synthesis of selenocysteine derivatives that are suitable for peptide synthesis essentially two approaches have been used to date (1) conversion of p-chloroalanine 23 or serine-O-tosylate derivatives 24 into the desired selenocysteine derivatives by a nucleophilic displacement reaction with an areneselenol and (2) full reduction of selenocystine and in situ reaction with aryl halides to produce the aryl selenides. 7 25 In this context, reduction of selenocystine in 2 M NaOH with 2-methyl-2-propanethiol for concomitant formation of the mixed selenide/sulfide derivative 5e-(tert-butylsulfanyl)selenocysteine in analogy to the formation of 5-(fett-butylsulfanyl)cysteine 26 fails as a consequence of the difficult reduction of the diselenide with monothiols. 27 ... 

The aryl selenides are crystalline solids or liquids heavier than water. Oxidation by atmospheric oxygen or dilute alkali yields diaryl diselenides. 

The diselenides occur as by-products when aryl magnesium bromides react with selenium bromide in ether. 

In a rare example of the use of iodonium salts for heteroatom-heteroatom bond formation, diaryliodonium halides were employed with sodium 0,0-diethyl phosphoroselenolate for a one-pot synthesis of diaryl diselenides (Scheme 9) [27]. These transformations probably occur via arylation of the phosphoroselenolate salt with the diaryliodonium ions, hydrolysis of the resulting aryl phosphoroselenolates with sodium hydroxide, and air oxidation of the arene-selenide ions thus produced. 

NiBr2(2,2 -bipyridine) complex44. Aryl halides, such as 4-bromobenzophenone, or 2-bromoquinoline could be transformed into diaryl diselenides 20 or ditellurides 21 elec-trochemically using sacrificial selenium or tellurium cathodes as can be seen in equation 20. 

An improvement in this technique of sacrificial electrodes (Se and Mg) for the formation of the Z2-2 ions was achieved by using an undivided cell and by addition of fluoride ions to avoid the precipitation of the Se2Mg304. Thus, the reaction of 2-chloroquinoline with Se2-2 gave 79% yield of 248a. Following this methodology the diselenides 250 were prepared by reaction with aryl halides 249 (equation 162)303. 

Ansteigende Substitution des Phosphans mit Aryl-Resten verlangsamt die Umsetzung ebenso wie Phenyl-Substituenten am Diselenid. Zwischen tert. Phosphanen und tert. Phosphan-seleniden erfolgt ein rascher Selen-Austausch600a (s.Bd. E2/S. 86, 94). 

Arylpropanoic acids. The ethylene kctals (2) of aryl a-phenylselenoethyl ketones, prepared by reaction of aryl a-bromo ketals (1) with diphenyl diselenide and sodium wire, are converted into the hydroxycthyl esters (3) of 2-arylpropanoic acids (4) on oxidation with excess w-chloroperbenzoic acid. The reaction probably involves a selenone intermediate, in which the rearrangement of the aryl group occurs. The acetal group of 2 is essential for this rearrangement. 

---