Diselenides, catalytic

Scheme 15.1 Catalytic cycle for the conversion of a diselenide to a selenenic acid...

Diorgano diselenides have been used extensively as precursors to seleninic acids in the presence of hydrogen peroxide.The catalytic activity of preformed seleninic acids and seleninic acids generated in situ are identical. Diorgano ditellurides have also been used as catalysts in thiolperoxidase-like reactions for the oxidation of thiols with various peroxides. However, tellurinic acids are not thought to be involved even though RTe(=0)SPh types of structures are proposed as intermediates. 

Electrochemical catalytic cycles allow the efficient use of diphenyl diselenide in the oxyselenation of alkenes. In the presence of bromide ions, the electrochemi-cally generated bromine foims phenylselenium bromide which reacts with the alkene regenerating bromide ion [68]. In the absence of bromide ions and at more... 

Sctiem 2.3. Catalytic cycle for the allylic hydroxytation of alkenes by anodic oxidation in the presence of diphenyl diselenide. 

A formal [4-1-3] cycloaddition leading to products with a core structure similar to that of 220 was found when 2-iodophenols and furan are treated with a mixture of BusSnH, 2,2 -azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70), and a catalytic amount of diphenyl diselenide, albeit moderate yields have been achieved (Equation 86) <2005OL3625>. 

Dehydrogenation of 3-ketosteroids.2 By use of this method for generation of the reagent, dehydrogenation of 3-keto-steroids to A1,4-diene-3-ones can be a catalytic process with respect to the diselenide. Use of m-iodosylbenzoic acid is experimentally convenient, since the m-IC6H4COOH formed is easily separated from the ketonic product. 

Dehydrogenation of 3-kelo steroids. The dehydrogenation of 3-keto steroids to l,4-diene-3-ones with benzeneseleninic anhydride (8, 31) can be carried out in comparable yield by use of a process in which the benzeneseleninic anhydride is used in catalytic amounts and is continuously regenerated from diphenyl diselenide by oxidation with iodylbenzene. In practice, m-iodylbenzoic acid is a more convenient reagent, since m-iodobenzoic acid is easily recovered. 12-Keto and 12-hydroxy steroids arc oxidized by the catalytic system to A9(1 - -keto steroids in high yield. In fact, methyl desoxycholate (1) can be oxidized in this way directly to the trienedione 2 in 64% yield.1... 

The chlorine atom in r/-butyl-2-chloronicotinatc can be displaced with a diselenide group in moderate yield using dilithium diselenide in THF <2003SC3805>. The resulting diselenide is hydrolyzed and cleaved to the chlorose-lenide on treatment with thionyl chloride and catalytic amounts of DMF (Scheme 29). 

Iodylbenzene with catalytic amounts of 2,2-dipyridyl diselenide converted alkenes into allylic ketones directly the actual oxygenating agent was 2-pyridineseleninic anhydride, formed in situ. 

Alkenylfurans were synthesized from a Pd-catalyzed cyclization reaction of an a-propargyl (5-keto ester. High /Z-selectivity was realized when the Me3Si- group was introduced at the a -position of the triple bond. The geometry of the double bond was almost completely inverted by reaction with a catalytic amount of diphenyl diselenide <02OL1787>. 

It is possible to perform selenenylation-deselenenylation sequences with only catalytic amounts of selenium species. This reaction sequence provides double bond transpositioned allylic ethers, allylic esters, or allylic alcohols 240 from the corresponding alkenes (Scheme 71). This sequence can be performed electrochemically, and the selenium electrophile is generated from catalytic amounts of diphenyl diselenide.467,468 It has been shown that the electrophilic selenium species can also be generated using diselenides and peroxosulfates together with copper (ii)... 

Using Pd-catalysts and incorporating a TMS group in the a -propargyl position, 2-alkenylfurans can be obtained with high ( /Z)-selectivities (Scheme 5). The geometry of the double bond can be inverted with catalytic amounts of diphenyl diselenide <20020L1787>. 

Oganoselenium reagents have been observed to exhibit selectivity for the oxidation of allylic alcohols, for example a catalytic amount of dimesilyl diselenide with r-butyl hydroperoxide as cooxidant will oxidize benzyUc and allylic alctdiols in the presence of saturated alcohols, as in the case of the diol (7 equation 4). 

Torii has reported the electrochemical oxyselenation-deselenation of alkenes to give allylically rearranged allyloxy products. A typical example is given below (equation 23).Benzyl- or acetyl-(S)-citronellol was mixed in acetonitrile/water solution with diphenyl diselenide (0.5 mol equiv.) and a catalytic amount of tetraethylammonium bromide, and was electrolyzed at room temperature in an undivided cell using platinum electrodes and a constant current density of 10 mA cm. The corresponding allylic alcohols were isolated in excellent yields. In methanolic solution, using a reduced amount of diphenyl diselenide (20 mol %), the methoxy compounds were obtained in slightly reduced yields. 

Acetoxyselenation. Diphenyl diselenide in combination with either Cu(OAc)2 or Pb(OAc)4 effects trans-acetoxyselenation of alkenes in about 70% yield. Cupric acetate can be used in catalytic amounts when oxygen is introduced into the... 

Adamantane 205 reacts with oxaziridine 206 at 22°C to give 1-adamantanol 207 in 73% yield <2005JA15391>. A catalytic version of this oxidation has been developed using catalytic amounts of the imine 208 and diselenide 209 with excess urea-H202 (UHP) as the oxidant. 

Engman reported that the acetoxyselenenylation of alkenes could be better carried out with PhSeBr in acetic acid in the presence of acetic anhydride and KNO3 [40]. In the case of terminal olefins the addition proceeds with poor regio-control. However, when the chloroform solution of the two products was treated with catalytic amounts of boron trifluoride etherate, isomerization takes place and the anti-Markovnikov adduct was transformed into the Markovnikov product. The acetoxyselenenylation of alkenes can be cleanly effected also by oxidation of diphenyl diselenide with iodobenzene diacetate in acetonitrile [22]. 

The first example of a catalytic approach to the selenium promoted conversion was reported by Torii, who described an oxyselenenylation-deselenenylation process using catalytic amounts of diphenyl diselenide [115]. The electrophilic species was produced from the diselenide by electrochemical oxidation in the presence of the alkene 233 in methanol or in water. As indicated in Scheme 36, the addition product is electrochemically oxidized to afford the selenoxide which by elimination gives the allylic ether or alcohol 234 and the phenylselene-nic acid which continues the cycle by adding again to the alkene 233. 

As previously observed for the diphenyl diselenide (Scheme 2) [24], Pandey has found that the phenyl alkyl selenides also can be transformed into the corresponding radical cations by photostimulated single electron transfer to 1,4-dicyanonaphthalene (DCN). These intermediates, as proposed above, suffer fragmentation to afford diphenyl diselenide and a carbocation, which can be trapped by a nucleophile. On the basis of these observations Pandey [121] described a sequential one-pot selenenylation-deselenenylation of alkenes in methanol using only catalytic amounts of diphenyl diselenide. An example is reported in Scheme 41 which illustrates the single steps of this process... 

The first example of this type of a catalytic conversion is indicated in Scheme 42 [123]. This refers to, y-unsaturated esters and amides 261, which, on treatment with an excess of ammonium persulfate and a catalytic amount of diphenyl diselenide, in methanol, ethylene glycol or in water, gave the addition products 262. These, by reaction with persulfate, afforded the y-alkoxy or the y-hydroxy-a, -unsaturated derivatives 263, respectively. 

Several research groups have recently investigated the asymmetric version of the catalytic one-pot selenenylation-deselenenylation sequence described above. In particular, attention was devoted to the process in which the deselenenylation occurs with elimination. These experiments are simply carried out by replacing the diphenyl diselenide with a chiral diselenide and are suggested to proceed through a sequence of reaction steps similar to those proposed for the diphenyl diselenide by Tomoda [122] or by Tiecco [116] and indicated in the Schemes 36 and 37. 

Recent advances of the preparation of novel optically active organoselenimn compounds, mainly organic diselenides, and their application as chiral ligands to some transition metal-catalyzed reactions and also as procatalysts for asymmetric diethylzinc addition to aldehydes are reviewed. Recent results of catalytic reactions using some organoselenimn compounds such as aUylic oxidation of alkenes and its asymmetric version as well as epoxidation of alkenes are also summarized. 

Catalytic AUylic Oxidation of Alkenes Using Diselenides.245... 

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