Oxyselenenylation Reactions

A limited number of new addition reactions has been described in recent years. These mainly concern reactions carried out in the presence of external oxygen (oxyselenenylation reactions) or nitrogen nucleophiles. On the other hand, oxyselenenylation reactions have been largely used as a probe to test the efficiency of the various chiral selenenylating agents. 

The oxyselenenylation reactions, i.e. the stereospecific anti addition of an organoseleno group and of an oxygen nucleophile, such as an OH, OR, OCOR 

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]. 

---

An interesting application of sequential oxyselenenylation reactions was reported recently by Kim for the synthesis of biologically important cyclitols [41,42]. Both, the stereochemistry and the regiochemistry of the sequential oxyselenenylation of cyclohexene, were controlled by the use of chiral diol hydrobenzoin as the nucleophile. Illustrated in Scheme 5 are the various steps employ-... 

Scheme 5. Serial Oxyselenenylation Reactions. Synthesis of Cyclitols...

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]. 

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

As an electrochemical reaction, Torii and co-workers demonstrated that the facile transformation of alkenes into allylic alcohols and ethers proceeded in the presence of a catalytic amount (10 mol%) of diphenyl diselenide (Scheme 15) [18]. Most of terminal co double bonds of isoprenoids undergo regioselective oxyselenenylation-deselenenylation to give frans-allylic alcohols in aqueous acetonitrile and methyl ethers in methanol. The addition of SOI salts improves chemical yields since SOI salts prevent the conversion of phenylselenenic acid (PhSeOH) into the inert phenylseleninic acid (PhSe02H) by both disproportionation and electro-oxidation. This method was also applied to intramolecular reaction to form -lactone in high yield. 

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. 

The first catalytic asymmetric oxyselenenylation-oxidative deselenenylation reaction was reported by Tomoda and co-workers in 1994 [26]. The treatment of... 

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]. 

---