Chiral diselenide

Figure 3 Selected chiral diselenides as precursors for the corresponding selenium electrophiles.

In the asymmetric selenomethoxylation of alkenes using the chiral, C2-symmetric electrophilic organoselenium reagent 13, prepared in situ from the corresponding chiral diselenide 12, a variety of optically active cwh-selenomethoxylatcd adducts 14 A and 14B are produced93. 

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. 

Chiral Diselenides and Selenides as Procatalysts for Diethylzinc Addition to Aldehydes... 

Asymmetric Catalytic Allylic Oxidation of Alkenes Using Chiral Diselenides... 

If the optically active organoselenium compounds can be used for Tomoda s or Tiecco s catalytic system using diselenide and persulfate (see Sect. 4.1), a catalytic asymmetric oxidation reaction should be possible. The enantioselectivity of the produced allylic compounds may depend on the stereoselectivity of the oxyselenenylation step of chiral selenium electrophiles with prochiral alkenes. Several groups have reported diastereoselective oxyselenenylation using a variety of chiral diselenides in moderate to high diastereoselectivity [5 f, g, i, 25]. The detailed results are reviewed in Chap. 2. 

Many chiral diselenides have been designed for the purpose of alkene functionalization. These reagents (e.g., 47, 48, 49 ) are usually activated with bromine and the reaction carried out by adding AgOTf. Properly constituted alkenylarenes are cyclized by using the last reagent. Camphor substituted with selenium at C-3 endo) forms another class of such... 

Another approach towards asymmetric Baeyer-VdUiger reactions involves the use of chiral diselenide 53 [351]. In combination with ytterbium triflate and hydrogen peroxide (30%) it forms a catalyst, which is able to produce lactone 46 from cyclobutanone 50 with 19% ee in up to 92% yield. 

Furthermore, the authors demonstrated that excellent enantiomeric excesses can be obtained with hydrogen peroxide at -10°C by employing the sulfur-containing chiral diselenide 499 (Scheme 7.80). Se NMR indicated that the diselenide 499 suffered oxidation to seleninic acid or peracid. H NMR and NMR signals of the aliphatic moiety suggested that the sulfur has been oxidized too, thus the corresponding sulfone may be involved. 

Scheme 7.80 Enantioselective dihydroxylation of olefins catalyzed by sulfur-containing chiral diselenide 499...

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