Reactions of Electrophilic Selenium Reagents with Hydroxyalkynes. The Regio- and Stereoselectivity of Addition of Benzenselenenyl Chloride to the Triple Bond.

Yulia Kalendar, Chemistry, Bar Ilan University, Ramat Gan, Israel 
Samuel Braverman*, Chemistry, Bar Ilan University, Ramat Gan, Israel
Marina Cherkinsky, Chemistry, Bar Ilan University, Ramat Gan, Israel

Since selenium is an essential trace element for animals and its biochemical role in mammals has been established, the design and synthesis of novel organoselenium compounds with useful biological activity continue to attract attention.

During our work on the reactivity of various electrophilic selenium reagents with hydroxyalkynes we have found that the regio- and stereochemistry of the reaction are affected by the nature of the electrophilic reagent. Thus, selenium dihalides react with differently substituted propargyl alcohols in completely regio- and stereospecific manner, affording the product of syn addition and anti-Markovnikov orientation. To test the generality of these surprising results, the reaction with benzenselenenyl chloride has been investigated.

In this case, the regiochemistry of the electrophilic addition depends on the substitution on the parent propargyl alcohols. Thus, for α-substituted alcohols only adducts with anti-Markovnikov orientation were observed, whereas in the case of γ-substituted propargyl alcohols, a mixture of regioisomers was obtained. The observed stereochemistry of addition was anti as expected, except for propargylic diols (e.g. 1,4- butyne-diol). In this case the stereochemistry of addition for both selenium dichloride and benzenselenenyl chloride are reversed.

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