Organoselenium reagents

ORGANOLITHIUM COMPOUNDS, addition to allyl alcohols, 55,1 Organoselenium reagents, 59, 141 ORGANOTELLURIUM INTER-... 

Show how by using regioselective enolate chemistry and organoselenium reagents, you could convert 2-phenylcyclohexanone to either 2-phenyl-2-cyclohexen-l-one or 6-phenyl-2-cyclohexen-l-one. 

Similarly, electrophilic cyclizations of dienols and trienols, such as homogeraniol and homonerol, were carried out without addition of strong acid, using benzeneselenenyl triflate18,144 as the organoselenium reagent (equations 145 and 146). 

Show how, using enolate chemistry and organoselenium reagents, you could convert... 

A number of organoselenium reagents have been used as efficient initiators of ring closure, leading from unsaturated substrates to the lactones and cyclic ethers (81T4097). The reaction is termed phenylselenoetherification. The phenyl selenoethers obtained are subject to a selection of transformations, e.g. their conversion to allylic ethers (Scheme 50) and their... 

Scheme 11. Applications of organoselenium reagents covalently bound to polymers.

Scheme 12. Electrophilic addition of polymer-bound chiral organoselenium reagents to alkenes.

Paulsen and co-workers98 successfully employed a new organoselenium reagent namely, 2-methyl-2-selenoxo-l,3-benzothiazole for conversion of various anhydro sugars 230-232 and 236 into unsaturated derivatives 233-234 and 235. The conversion proceeds during 5 to 10 h at room temperature in generally high yields. 

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

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. 

In organoselenium reagent induced carbocyclization, the enolic C —C double bond of -di-carbonyl systems can also participate. Various reaction conditions can be used, including addition of A,-(phenylseleno)phthalimide (V-PSP) with zinc(II) iodide59 or tin(IV) chloride60 catalysis, e.g., to give 48 and 49. 

Organoselenium Reagents Prepared from Diphenyl Diselenide or Benzeneselenenyl Chloride... 

Bridged ethers can readily be prepared by the electrophilic attack of various organoselenium reagents on olefins. Nicolaou and his group " have given full details of the attack of selenohalides on unsaturated alcohols (Scheme 21), and oxyselenation of dienes is also effective (Scheme 22). If phenyl selenocyanate is used in the presence of cupric chloride, as the electrophile, the product ratio (123) (124) is strongly solvent-dependent. As the organoselenium substituent... 

Review. Recent applications of organoselenium reagents have been reviewed in detail. 

Enantioselective synthesis of heterocycles mediated by organoselenium reagents 06ARK(7)186. 

Caution Owing to the extreme toxicity of organoselenium reagents, appropriate care must be taken in the handling and disposal of these compounds. All work should be carried out in a well-ventilated hood. 

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