Oxyselenenylation elimination

Scheme 45. Asymmetric Oxyselenenylation-Elimination Reactions of )8,y-Unsaturated Esters and Nitriles...

Wirth and co-workers used various chiral nitrogen-containing diselenides 20 - 24, which worked effectively as procatalysts for diethylzinc addition to aldehydes (see Sect. 3.1) [13] and for the catalytic oxyselenenylation-elimination reaction of frans- -methylstyrene (Scheme 26) [30]. Under the reaction conditions reported by Iwaoka and Tomoda [19], the diselenide 20 yields the product with highest enantioselectivity (up to 56% ee). Potassium peroxodisulfate seems to be superior to sodium and ammonium analogues. Effect of metal salts on stereoselectivity in the catalytic reaction using the diselenide 20 was investigated since it is known that metal ions can accelerate the decomposition of peroxo-... 

Wirth et al. reported a catalytic asymmetric oxyselenenylation-elimination reaction using 10 mol% of chiral nitrogen-containing selenide 475. Trans-P-methylstyrene (469) gives the allyhc ether 471 with 75% ee but in only 23% yield (Scheme 7.75) [317]. 

Scheme 7.75 Oxyselenenylation-elimination using chiral nitrogen-containing selenide 475 as...

The reaction of cyclohexene with AT-(phenylseleno)phthalimide in the presence of (S,S)-hydrobenzoin in methylene chloride afforded two diastereomeric oxyselenides (38 and the (li , 2R) diastereomer) in a 1 1 ratio. Compound 38 was separated and converted into the olefin 39 via selenoxide elimination. The second PhSeOTf promoted oxyselenenylation reaction gave only the cis fused bicyclic dioxane 40. Oxidation and subsequent elimination provided the olefin 41. This is the key intermediate for the syntheses of the cyclitols 42 and 43, that were obtained from a series of classical reactions as indicated in the Scheme. Oxyselenenylation reactions have also been employed to promote glycosylation reactions [43]. 

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. 

Oxyselenenylation-oxidative deselenenylation (oxyselenenylation-selenoxide elimination) sequence provides the double-bond transpositioned allylic alcohols and ethers from alkenes. Oxyselenenylation of alkenes and its asymmetric... 

Allylic anda-Allenic Alcohols. The electrochemical generation of a selenenylat-ing reagent, presumably PhSeOR, from a catalytic amount of diphenyl diselenide in the presence of water or an alcohol (ROH) is the basis of a new method for direct conversion of alkenes to allylic alcohols or ethers (Scheme 13). Regio-specific Markovnikov oxyselenenylation followed by electrochemical oxidation and selenoxide elimination, regenerating a selenenylating species, accounts for a sequence that is obviously closely related to the bromide-mediated method reported last year (5,158). 

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