Selenium tetrachloride reactions with alkenes

The addition of selenium tetrachloride to two equivalents of a symmetrical alkene can theoretically result in the formation of ten stereoisomers of the bis-adduct two me so forms and four diastereomeric pairs. It was, however, found that the addition of selenium tetrachloride to two equivalents of (Z)-2-butene in dichloromethaiie at 25 °C gives only two products, bis(l R, 2R )-4 and [(12 , 2J XlS, 2S )]-4 in approximately 90% and 10% yields, respectively83. The reaction of selenium(IV) chloride with ( )-2-butene under the same conditions also affords two different products namely a mixture of bis(lS, 2/ )-4 and [(lS, 2/ )(l/ , ,2S )]-4in 90% and 10% yields, respectively83. 

Allylic animation. The reaction of selenium metal with 2 equiv. of anhydrous chloramine-T (TsNCINa) in CH2CI2 gives a solution of a reagent formulated as (1). A similar, but less reactive, reagent is formed by reaction of selenium tetrachloride with p-toluencsulfonamide. The reagent reacts with alkenes at 20°... 

Selenium and tellurium reagents have been used for stereoselective halogenations of alkenes. For example, trans addition of benzeneselenenyl chloride to alkenes followed by the displacement of the seleno moie with chloride can lead to dr-1,2-dichlorides (equation 25). The addition of 2-naph-thyltellurium trichloride proceeds in an anti stereospecific manner (equation 26), whereas tellurium tetra-diloride gives a mixture of syn and anti adducts. The reaction of allyl esters with tellurium tetrachloride accompanies acyl migration to give the l-(trichloiottlluro)-3-chk>io adduct (54 equation 27). ... 

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