Remarkable Alkene-to-Alkene and Alkene-to-Alkyne Transfer Reactions of Selenium Dibromide and PhSeBr. Stereoselective Addition of Selenium Dihalides to Cycloalkenes.

The original goal of this research was to study stereochemistry of selenium dihalides addition to cycloalkenes and properties of obtained products. Remarkable alkene-to-alkene and alkene-to-alkyne transfer reactions of selenium dibromide and PhSeBr were discovered during this research. The adducts of selenium dibromide with alkenes or cycloalkenes easily exchange SeBr with other unsaturated compounds, including acetylenes, at room temperature, in acetonitrile. Similar alkene-to-alkene and alkene-to-alkyne transfer reactions of the PhSeBr adducts with alkenes or cycloalkenes take place. The supposed reaction pathway includes the selenium group transfer from seleniranium species to alkenes or alkynes. It was found that the efficient SeBr and PhSeBr transfer reagents are Se(CHCHBr) and PhSeCHCHBr, which liberate ethylene, leading to a shift in equilibrium. The regioselective and stereoselective synthesis of bis(-2-bromovinyl) selenides and unsymmetrical 2-bromovinyl selenides was developed based on the SeBr and PhSeBr transfer reactions which proceeded with higher selectivity compared to analogous addition reactions of SeBr and PhSeBr to alkynes under the same conditions.